4. FY2006 SELF-APPRAISAL FOR DOE: ILC DEPARTMENT AND
NLCTA
by Nan Phinney and ILC Staff
Appendix B Self-Evaluation FY2006
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Contents
4.1 The ILC Department at SLAC
The SLAC ILC group is internationally recognized for its
expertise. SLAC has been a leader in linear collider
development for over 25 years. SLAC built and operated
the first linear collider, the SLC, and used that
experience to produce an integrated, comprehensive
design for a linear collider based on warm rf technology
for the accelerating structures. SLAC has accelerator
physics expertise in all
subsystems of the collider from the sources to the
Interaction Regions (IR). With the adoption of the
superconducting rf technology for the ILC in 2004, this
expertise has been refocused on developing a design
based on cold rf technology.
SLAC continues to be a major contributor to linear
collider development through its broad expertise and
unique test facilities. Over the years, significant R&D
has been performed on all of the subsystems of the
‘warm’ X-band design and both the ‘warm’ design and ILC
design share many common features. Less than 25% of the
cost of the superconducting design is in the
superconducting cavities or cryomodules – the rest of
the collider is based on normal-conducting technology
similar to that which SLAC has studied extensively. SLAC
is applying the major advances that were made for the
X-band design to the ILC. The activities in or supported
by the SLAC ILC program address 14 of the 15 critical R2
items identified in the ILC Technical Review Committee
(TRC) report from 2003 – many of these issues are
important to resolve as part of an international
Reference Design Report (RDR).
In addition, the SLAC accelerator complex provides
facilities capable of supporting a wide range of ILC
R&D. An L-band rf test facility is being developed in
End Station B, which benefits from the existing
infrastructure of the NLC Test Accelerator (NLCTA). This
facility will provide long-term testing of klystrons and
modulators, and rf power for coupler and
normal-conducting structure testing. The NLCTA beam and
beam-line support full power structure testing with
beam. Modifications are being made to produce an
ILC-type bunch for instrumentation development.
End Station A has been reconfigured as a test beam
facility for experiments with collimators, IR
instrumentation, and detector components. Two successful
runs were completed in FY06. This is the only
experimental area with access to multi-GeV high quality
electron beams. Prototype vacuum chambers utilizing
various electron cloud suppression techniques are being
installed for testing in PEP-II.
The rest of this section will describe the ILC
Department participation in the ILC GDE, participation
in Reviews and Conferences, and Department safety
issues. In the following sections, the close-out of the
X-band R&D program, the L-band R&D program, and the
Accelerator Design programs will be described. Following
this will be short sections describing the operation of
the NLC Test Accelerator (NLCTA) which the ILC
Department operates to support advanced accelerator R&D
as well as ILC R&D and participation in the LHC
Accelerator Research Program (LARP) in the form of
advanced beam collimators which were spun off from the
NLC R&D program.
4.1. a. ILC GDE Activities
The ILC Global Design Effort (GDE), which reports to the
International Linear Collider Steering Committee of the
International Committee for Future Accelerators, was
formed in 2004. Barry Barish was appointed director in
March 2005, and shortly thereafter he formed an
Executive Committee with three regional directors and
three accelerator physicists, Tor Raubenheimer (SLAC)
for the Americas, Nick Walker (DESY) for Europe, and
Kaoru Yokoya (KEK) for Asia. Three regional cost
engineers and three conventional facilities engineers
were also selected.
The rest of the GDE members were appointed and met for
the first time at the Snowmass 2005 workshop, and
several more have been added later to fill gaps in
expertise. In addition to Raubenheimer, SLAC has 9
members of the GDE including Chris Adolphsen, Tom Himel,
Tom Markiewicz, Ewan Paterson, Nan Phinney, Marc Ross,
Andrei Seryi and John Sheppard. The GDE director also
formed three boards, all of which have SLAC
participation: the Change Control Board with Tom
Markiewicz, the R&D Board with Tom Himel and Marc Ross,
and the Design Cost Board with Ewan Paterson and Nan
Phinney. Tom Markiewicz also chaired a committee to
select EDMS tools.
The major GDE task for 2005 was to develop the Baseline
Configuration Document for the ILC. Key decisions were
taken at the Snowmass workshop and these were further
developed and finalized for a GDE meeting in Frascati in
December, 2004. The SLAC ILC group played a major role
in formulating the shape and content of both the
Snowmass and Frascati meetings. In both cases, SLAC ILC
Department members made significant contributions to the
overall meeting structure, with many SLAC ILC members as
conveners of global or working groups..
The major task for 2006 is to develop a complete design
for the ILC with a preliminary cost estimate, documented
in a Reference Design Report (RDR) by the end of
calendar 2006. Again SLAC ILC physicists are playing a
major role in this effort. For the RDR, a matrix of
Area, Global and Technical System groups was formed,
with leaders from all 3 regions. SLAC physicists are
system leaders for 5 of the 6 Area Systems (Axel
Brachmann-Electron Source, John Sheppard-Positron
Source, Peter Tenenbaum-Ring to Main Linac, Chris
Adolphsen-Main Linac, Andrei Seryi-Beam Delivery). They
are also leaders of several Technical or Global groups
(Tom Himel-Operations & Availability, Fred
Asiri-Installation, Ray Larsen-RF Sources, Marc
RossInstrumentation, Tom Markiewicz-Dumps &
Collimators). In addition, Ewan Paterson is the Systems
Integration Engineer. Tor Raubenheimer and Ewan Paterson
are members of the RDR Management team and Nan Phinney
is chief editor for the RDR Report.
There have been three full GDE meetings in FY06. The
first was in Frascati, Italy, December 7-9, 2005, just
after a Tesla Technology Collaboration meeting. The 2nd
was in Bangalore, India Mar 911 2006 together with the
international LCWS. The third was in Vancouver, Canada
July 19-22, 2006 together with the ALCPG workshop. SLAC
ILC physicists played a major role in formulating the
shape and content of these GDE meetings. In addition,
there were meetings of the RDR Area leaders in January
at KEK and in February at FNAL and of the RDR Management
in August at KEK. Most of the Area, Technical and Global
groups have regular three-region teleconferences, often
augmented by a face-to-face meeting between full GDE
meetings. The three Boards, the RDR Management and the
Executive Committee also have weekly teleconferences.
4.1. b. Reviews and Meetings
The ILC group has participated actively in the national
and international community through reviews and meeting
participation.
From October 17-21, 2005, the Nanobeams Workshop was
held in Kyoto, Japan. SLAC ILC members served on the
program committee and as working group convenors.
In December 2005, an Availability Mini-Workshop was held
Dec 1-2 at Groemitz, Germany where SLAC ILC staff made
presentations. This was followed by the Tesla Technology
Collaboration and 2nd
GDE meetings in Frascati.
In February, SLAC hosted an ATF-2 collaboration meeting
on Feb 3-4.
In March, many SLAC ILC members attended the 3rd
GDE meeting Mar 9-13 in Bangalore, India, along with
satellite GDE Executive Committee, Change Control Board,
R&D Board and Design Cost Board meetings.
In April, SLAC ILC physicists made presentations on
several key areas of the ILC program at the Apr 4-6 DOE
Review and Apr 7-9 MAC meeting, both held at FNAL.
In May, SLAC hosted the second meeting of the Linear
Collider Forum of the Americas on May 1-2.
EPAC 2006, the biennial international particle
accelerator conference, was held in Edinburgh, Scotland
in June 2006. ILC staff submitted more than a dozen
papers and gave two invited talks.. In addition, ILC
staff members were active in the program committee for
the conference.
The SLAC ILC group also played a major role in
formulating the shape and content of the three ILC GDE
Meetings at Frascati in December 2005, at Bangalore,
India in March 2005 and at Vancouver in July 2006. SLAC
ILC Department members made significant contributions to
the overall meeting structure and to leadership of area,
technical and global groups.
In August, SLAC ILC engineers also attended Linac’06
where they made presentations on the modulator systems
that we are developing.
In September, SLAC ILC Physicists made presentations at
the second ILC MAC Meeting Sep 2022 at KEK. They
participated in meetings Sep 23-24 of the Executive
Committee, RDR Management, R&D Board, Design Cost Board,
and Linac working groups. On Sep 25-28, SLAC physicists
joined the Tesla Technology Collaboration meeting also
at KEK. SLAC also hosted the 9th
International Workshop on Accelerator Alignment Sept
25-29.
SLAC ILC members also participated in many other
conferences and workshops where they presented papers
and shared plans with colleagues without actual linear
collider experience and without the depth and breadth of
research that backs the SLAC ILC team. Other workshops
held at SLAC include an ongoing series on ATCA
technology as a possible basis for standardization of
ILC electronics.
4.1. c. Collaborations
The ILC Department has a long history of collaboration
with KEK and within the US with LLNL, LBNL, FNAL and
BNL. Additional collaborations are ongoing with Queen
Mary University of London, Oxford University, the
Rutherford Appleton Laboratory, the Daresbury Laboratory
and DES, and with the French laboratories CEA Saclay and
CEA Orsay.
Collaboration at DESY includes work on benchmarking
reliability and availability codes and working on the
Tesla Test Facility (TTF). Members of the ILC Department
also used concepts and technology developed for the
X-band program to measure the higher-order mode (HOM)
signals from the TESLA cavities. Such HOM detectors may
prove important to align the cavities in the ILC. At
DESY’s request, the ILC group built a set of 40 of these
detectors which were installed at the TTF. Ongoing R&D
is using these detectors to understand the internal
deformation of the 9cell cavities. Finally, SLAC has
formally joined the TTC and MOUs have been exchanged.
The ILC Department has a long-standing collaboration
with KEK on ATF and on rf technology. During FY2006, the
SLAC group has worked on three main projects with KEK
and has received roughly 400k$ of US-Japan funding. Much
of the effort focused on the development of the ATF-2
which would prototype the ILC beam delivery system
utilizing the extremely low emittance beam from the ATF
damping ring. Specifically, activities in FY2006 include
development of an ultrafast kicker for testing at ATF,
testing of a new technology for the ATF ring BPMs,
design of the ATF2 beamline, and the development of an
rf BPM system for the ATF-2. The ILC Department has had
a physical presence at KEK working on the ATF damping
ring that averaged roughly one FTE. An MOU with KEK on
the ATF which covers operation of the ATF and the
international construction of the ATF-2 has been
finalized. Ewan Paterson of SLAC chairs the ATF-2
International Collaboration Board and Tor Raubenheimer
and Andrei Seryi of SLAC are members of the ATF-2
Technical Board.
The End Station A Test Facility, which has been
developed to test prototypes of IR beam diagnostics and
IR design concepts using the high energy SLAC beam, is a
collaboration between SLAC and US and UK universities.
Most of the specific experimental proposals have at
least one spokesperson from a university in either the
UK or the US.
4.1.d. Safety
At SLAC and in the ILC Department, concern for safety is
an integral part of our culture. All personnel review
and update their JHAMs annually or when work activities
change, and they complete all other safety courses
recommended by their supervisors. Work authorization
procedures at the NLCTA, a major test facility operated
under the ILC Program, have been used as a model for
other facilities at SLAC. The ILC Conventional
Facilities engineers continue to contribute to the
lab-wide effort implementing risk mitigation measures.
ILC engineers and physicists participate in the various
Citizens’ Committees such as Radiation Safety and
Earthquake Safety.
4.2. X-band rf R&D
With the ITRP decision of the superconducting technology
for the ILC in August, 2004, the SLAC X-band program was
put on hold. In FY2005, the ILC group chose to continue
some of the X-band (11.4 GHz) structure testing in a
program to wrap-up the 15-year-long structure
development effort, and to provide useful information
for future high gradient applications. In FY2006, the
research using existing high gradient X-band structures
continued at a low level, and was funded by SLAC as part
of the newly created US Collaboration on High Gradient
Research program.
The program at NLCTA included the operation of an X-band
structure at a lower water cooling temperature to
determine whether this would reduce the breakdown rate,
as might be expected if breakdowns are related to
migration of surface contaminants. However, no
significant difference in breakdown rate was seen when
operating at the normal structure cooling water
temperature of 110 F and the reduced temperature of 60
F. Various vacuum venting experiments were also
performed on another structure and showed that purging
with nitrogen or venting to either filtered or
unfiltered tunnel air had minimal impact on high
gradient operation. However when the structure was
heated to ~ 160 °C and vented to filtered air, the
breakdown rate increased substantially and never fully
recovered after a week of rf processing. Presumably,
this slow recovery was the result of an oxide layer that
formed on the inner surfaces (such layers have been
observed in some structures, and are likely the result
of small vacuum leaks during brazing or baking).
The accelerator structure used in the water temperature
test was longer (75 cm) than the standard NLC high
gradient designs (60 cm) that were developed, and
performed as well as the best of them (about 25 had been
tested). It achieved a breakdown rate of 0.2 per hour
during 75 MV/m, 60 Hz operation with 400 ns NLC-like
pulses. Its performance would allow for a higher
gradient operation than the 65 MV/m unloaded value that
had been adopted for the NLC.
4.3. L-band rf
The ILC superconducting linacs require low cost, high
efficiency and high reliability rf sources that generate
10 MW, 1.6 ms, 5 Hz pulses of L-band (1.3 GHz) rf power
and distribute it to 24 accelerator cavities. Six ILC rf
system related programs based at SLAC are described
below. SLAC is the center for the ILC Americas rf system
development, which includes all elements in the main
linacs between the ‘wall plug’ and the cavity couplers,
and the normal-conducting injector accelerators.
4.3.a. Modulator
The ILC baseline modulator is a pulse transformer type
with an LC ‘bouncer’ circuit for droop compensation.
Although several of the baseline pulse transformer
modulators have been built and operated without major
reliability problems, they have very large and heavy
oil-filled transformers, and the switching is done at
the low voltage (10 kV), high current (1.6 kA) end,
which increases the losses. The goal of the SLAC
modulator program is to evaluate alternative designs
that could reduce the modulator size, weight and cost
while increasing reliability and energy efficiency.
The ILC alternate modulator choice is a Marx Generator
design, and a prototype is being developed at SLAC. For
this approach, a series of capacitors are slowly charged
in parallel, and discharged in series to form the pulse.
No transformer is used and all switching is done at the
lower load current (130 A). The modulator consists of a
series of 12 kV main cells (large circuits boards
mounted on a common backplane) and 900 V vernier cells
for regulation and droop compensation. These circuits
are summed to produce the required 120 kV, 1.6 ms flat
pulses at 5 Hz. Its modular design lends itself to high
reliability (extra cells are included to automatically
replace ones that fail), and to mass production assembly
techniques, which should provide significant cost
savings (~ 40%) over the baseline design. The
fabrication of a full-scale prototype is nearly complete
and initial testing is expected in the next month. One
of the cells has been operated at full specification and
shown to survive a shorted load.
Another design being evaluated at SLAC is the SNS High
Voltage Converter Modulator, which employs a high
efficiency, 20 kHz switching circuit in a compact
layout. A production unit on loan from SNS has been
installed and brought into operation at the SLAC L-band
Test Stand (see Section 3.f.). Its main drawback is that
droop compensation has yet to be successfully
implemented. The unit at SLAC may eventually be modified
to produce flat pulses for 10 MW klystron testing. Yet
another modulator being considered is a direct switch
unit being developed by Diversified Technologies through
SBIR funds. It uses a multiplier circuit to produce the
full voltage, which is then applied by a direct
solid-state switching element to the klystron. As in the
Marx approach, the pulse transformer is avoided, and as
in the baseline design, droop is compensated with a
bouncer circuit. The first unit is due to be delivered
to SLAC at the end of 2006 for evaluation.
4.3.b. Klystrons
The existing ILC high power rf source prototypes consist
of three vendor-produced 10 MW Multiple Beam Klystrons
(MBKs) that were built in a collaboration with DESY.
These designs achieve high efficiency (~ 65%) by using
six or seven beams to reduce the space charge forces
that limit rf bunching (single beam tubes typically have
40% - 45% efficiencies). However, these prototypes have
not yet proven robust or have not been tested long
enough to fully qualify them. The SLAC Klystron Group is
instead investigating the merits of a new class of
sources known as Sheet Beam Klystrons (SBKs). In these
tubes, a flat beam is used to reduce the space charge
forces, which should produce an efficiency similar to
that of the MBKs.
In FY2006, SLAC funded the design effort for the SBK,
and the ILC group has proposed for FY2007 that two
prototype SBKs be built at SLAC in the next two years.
This effort has benefited from the Klystron Group’s
recent design and fabrication efforts that led to
successful beam transport in a 91 GHz SBK (no commercial
SBKs exist at any frequency). The ILC prototypes, which
will be ‘plug compatible’ with the MBKs, will have a
40:1 beam aspect ratio and will utilize permanent
magnets for focusing (reducing the ILC power consumption
by about 4 MW).
Much work has been done over the past year in perfecting
3-D klystron simulations using recently developed
software modeling packages for the gun, beam transport
and rf power formation and extraction. The basic SBK rf
design is complete and the first prototype could be
fabricated by the fall of 2007. Future plans also call
for acquiring and long-term testing second generation,
10 MW MBKs.
4.3.c. Rf Distribution
To distribute the rf power from a klystron to the
cavities in the ILC linacs, the baseline design is to
have a series of tap-offs along a waveguide that runs
parallel to the beam line. There would be a circulator
in each cavity feed line followed by a three-stub tuner
to allow control of the cavity phase and Qext. Currently
the DESY rf distribution systems use off-the-shelf
components that are not necessarily optimized for this
application. Also, delivering the same power to each
cavity is inefficient with the ~ 5 % rms spread in
cavity operating gradients that is expected (i.e., the
worst cavity limits the gradients of the others).
At SLAC, four changes to the rf distribution design are
being considered. The circulators would be eliminated as
they are a big cost item, and the cavities would instead
be powered in pairs using 3dB hybrids. This would still
isolate the cavities, but would allow some power (< 1%)
to return to the klystron in the event of an rf fault in
a single cavity or coupler, which should be benign. A
second change would be to use a variable tap-off system
to feed the cavity pairs. One proposal is to have
rotatable, polarized TE11 circular waveguide sections
between the cavities whose orientation would be adjusted
(one time only) after the relative cavity performance
was measured. Another cost cutting measure is to replace
the 3-stub tuner with a simpler phase shifter that would
be adjusted once the system is set up, and would not
require further changes. Finally, with the large number
of waveguide flanges, a means of welding the waveguides
together is being sought to reduce cost and improve
reliability. At present, an rf design for a variable
tap-off system has been completed and some initial
waveguide welding tests have been done. The plan next
year is to assemble an eight cavity feed system for the
first FNAL cryomodule. It would incorporate these
proposed changes if they prove practical to implement
and robust in high power tests at SLAC (circulators
would be supplied for the initial cryomodule operation
to ensure full cavity isolation).
4.3.d. Coupler
The power coupler designs for the ILC superconducting
cavities are complex devices due to the required
cleanliness, high power rf operation, temperature
gradients (300 K to 2 K), vacuum isolation (with two rf
windows) and tunability requirements. The current ILC
baseline design (TTF3) works reasonably well, but the
couplers can take up to a few days to rf process.
To understand what limits the processing, Brian Rusnak
from LLNL, in collaboration with SLAC, has been
examining the coupler design and its performance. From
this study, a series of tests has been planned to power
various coupler parts including sections with and
without bellows, and sections with and without windows.
In FY06, significant progress was made in developing
components for the coupler test stand. An overall design
concept was configured and an L-band
waveguide-to-coaxial transition was designed that would
accommodate the SLAC L-band window and the installation
of components needed for the tests. The test stand
imposed significant constraints on the rf components and
how they interconnect. Since the goal of the experiment
is to measure gas loads during rf conditioning from
individual coupler components, it is important that all
rf electrical connections be robust and repeatable to
avoid anomalous arcing and heating. A further
complication comes from the need to reconfigure the
experiment multiple times, and requires that both the
inner and outer conductor connections to be easily
separable, robust, and repeatable. Finally, the design
of the inner conductor connections must ensure that
adequate thermal conductivity is maintained.
Currently all of the coupler test stand parts are being
fabricated in the SLAC shops. Commissioning the test
stand using a straight, stainless-steel coaxial line
should take place early in FY2007 using the L-band
source that was constructed in the End Station B (see
Section 3.f.). Afterwards, additional components will be
fabricated at SLAC and purchased from CPI, and processed
in the same way as DESY TTF-3 coupler components. They
will be used in a series of tests to identify those
features (e.g., bellows or widows) contributing to the
long coupler conditioning times. The results will also
be compared with multipactoring simulations by the SLAC
ACD group to see how well this phenomenon can be
predicted (see Section 4.d.).
4.3.e. L-Band Normal Conducting Accelerator Structures
After the ILC linac technology recommendation was made,
the NLC structure group turned its attention from X-band
structures to the normal-conducting cavities that are
required for the ILC position source. They have
developed an improved version from the DESY approach for
the positron accelerator that will be located just after
the target. A five cell prototype was designed in FY2005
and fabrication of the cells began last November. Since
then, a full set of drawings (over 100) was generated
for the five-cell cavity, surrounding solenoid magnet,
high power rf vacuum windows, supports and cooling
system. The solenoid was acquired from Boeing this
summer as a gift to Stanford. The magnet was made by
Thales for L-band klystrons, and could be used with our
klystrons if needed. The fabrication of the cavity has
been very slow due to the low priority of ILC work in
the Klystron Shop relative to work on klystrons for PEP
II and an rf gun for LCLS. So far, the inner half cells
have been machined, brazed in pairs and re-machined:
they still require tuning before they are assembled with
the end cells, which are still being machined.
In the next month, the rf vacuum windows should be
completed and at least two of them high power tested
(four are being built: one for the structure, one spare
and two for the coupler test stand). The cooling system
should be also assembled and tested at the required 100
gpm flow rate with 45 °C temperature-regulated water (a
preliminary test was done at 50 gpm earlier in the
year). The 5 MW rf power source (all components from the
LLRF system to the connecting waveguide) should also be
in place and ready for operation (see Section 3.f.).
Unfortunately, the structure itself will probably not be
available for test until at least December. After it is
installed, it will be processed to 15 MV/m with 1 ms
pulses at 5 Hz, and the absolute gradient and its
uniformity during the pulse measured by accelerating a
single bunch from the NLCTA injector at different times
relative to the rf pulse. The cavity will also be
operated in a 0.5 T solenoidal magnetic field, as
required in the ILC, to see if its performance is
affected
4.3.f. L-band Test Station
To gain experience with L-band sources and rf components
at SLAC, construction of an L-band test stand was
started in FY2005 at the Next Linear Collider Test
Accelerator (NLCTA). For this facility, a 140 kV
converter-style modulator was borrowed from SNS, and an
SDI-legacy, 10 MW, 160 kV, short-pulse klystron was
purchased from Titan. Also, a 500 W drive amplifier,
WR650 waveguide, loads, directional couplers and
high-power circulators were acquired, and an EPICS-based
low-level rf system configured.
The modulator was first tested using a resistor load,
and then used to power the klystron at 120 kV. In March,
this source produced 3.3 MW, 1 ms rf pulses at 5 Hz,
which is the peak power expected at this voltage. The
power was used to test a high power circulator and
waveguides that were pressurized (3 bar) with nitrogen
(instead of SF6) to suppress rf breakdown. Arcing at the
waveguide flanges was observed and has since been
eliminated by machining the flange mating surfaces
flatter (to < 1 mil) to reduce any gaps.
The step-up transformers and resonant circuit capacitors
in the modulator were then modified to allow higher
current (90 A) operation with a newly acquired 5 MW, 128
kV Thales 2104C klystron (this tube has been the
‘workhorse’ for testing at DESY and FNAL). This
modification was contracted to the group at LANL that
designed the modulator, and it took longer to implement
and was more difficult to make work than had been
anticipated (for a given configuration, modulator only
works reliably within a narrow range of load
impedances). Nonetheless, the upgraded modulator with
the new klystron has recently produced 4.9 MW, 1 ms
pulses at 5 Hz, limited only by modulator charging
supply voltage (a parallel HV water load is used to fine
tune the modulator load impedance). One shortcoming of
the SNS modulator is that the HV droop compensation
system was never made to work reliably and so is
disabled. In our case, the rf power droops by 10% during
a 1 ms pulse. However, when operating below saturation,
the rf drive system can be used to compensate for this
decrease, as is done at SNS.
As configured, the L-band Test Stand will provide power
to two experimental test areas. One will be used to rf
process coupler sections (see Section 4.3.d.) and other
rf components, and the other will be located in the
NLCTA beam enclosure to test prototype positron
accelerator cavities (see Section 3.e.). During the next
month, the waveguide transport system to these test
areas should be completed and the full control system
for rf processing should be commissioned. In FY2007, if
the new modulators that are being developed do not
perform well, the SNS modulator may again be modified to
allow operation of ILC prototype 10 MW klystrons (at 120
kV, 130 A).
4.4. ILC Accelerator Design and R&D
SLAC has more than 20 years of experience with the
design of a linear collider and has quickly moved to
play a leading role in the design of essentially all
components of the machine except the cryomodules and
cryogenics. The ILC group is actively developing designs
for the electron and positron sources, the damping
rings, the bunch compressors, the beam delivery and
machine-detector interface. In the main linacs, in
addition to work on the L-band rf power sources
described elsewhere, the effort includes optics and
simulations and superconducting quadrupole measurements.
The availability simulation developed for the US
Technology Options study has been expanded and used as a
tool to study various configuration options. SLAC is
also involved in developing diagnostics, controls and
high-availability hardware. The conventional facilities
group is actively collaborating with FNAL to develop
site criteria and US candidate sites.
4.4.a. Electron Source
SLAC now has more than 25 years developing and operating
polarized electron sources and 15 years experience with
the polarized electron source developed for the SLC. The
present polarized source program includes R&D on the
photo-injector source laser system and DC polarized
electron gun, photocathode development and design of the
injector beam lines up to 5 GeV, which is the beam
energy required for injection into the ILC damping ring.
The baseline design for the ILC adopted at Snowmass 2005
was based on the SLC source. Such an electron source
will fulfill the ILC requirements in terms of bunch
charge, but a laser system with the required wavelength
of 780 nm +/- 20 nm that can generate the required pulse
train is challenging and a feasibility demonstration is
needed.
During FY 06, a facility for the laser development
program was established. This facility will to combine
the laser system and electron gun to facilitate a ‘proof
of principle’ of the source. A conceptual design of the
laser system is complete that consists of a mode-locked
oscillator, electro-optical bunch train generation and
amplification. The laser system will be based on
Ti:Sapphire technology. Amplification of the pulse train
will be achieved by using Diode Pumped Solid State
(DPSS) pump lasers.
SLAC continues to have an active program on polarized
photocathode research. This program resulted in cathodes
capable of routinely delivering polarization well over
90% for the E158 experiment. The present program at the
Cathode Test Laboratory is focused on reoptimizing the
cathode parameters for the ILC bunch train format and on
further improvements in available quantum efficiency and
polarization. Work in FY06 investigated de-polarization
processes, such as internal charge scattering, that
prevent P>90% in GaAs-type cathodes. An SBIR
collaboration with Saxet, Inc. aimed at forward-biasing
the emitting layer to reduce the electron drift time.
GaAs/InGaP strained-superlattice structures have been
investigated to explore superlattice materials with a
lower spin relaxation rate. An SBIR collaboration with
SVT Associates was started to develop robust
photocathodes based on GaN for polarized gun
applications.
Beam line simulations have been completed starting from
the electron gun through the trans-relativistic region
of the bunching system up to the damping ring injection
point. The simulations established a physical beam line
layout and the required magnet system. These simulations
provide the basis for developing a model for cost
analysis of the polarized electron injector in
interaction with other area, technical and global
systems groups. First results were discussed at the GDE
meeting at the Vancouver Linear Collider Workshop in
July 2006.
4.4.b. Positron Source
SLAC has had a long-standing program of R&D on the
design of a conventional positron source and, in FY2005,
this was expanded to include design of an
undulator-based source. The SLAC positron source program
in FY06 included accelerator design as well as R&D
activities. The ILC positron source includes the
undulator based production source, a conventional 10%
intensity “keep alive” backup source, and the associated
5 GeV booster linac and requisite transport lines.
SLAC has taken the leadership role in coordinating the
world wide activities for the BCD and RDR design efforts
in FY06. In FY07, this will evolve into the design and
R&D in support of the Technical Design Report (TDR).
SLAC has been co-leader of the ILC GDE RDR effort and is
the US ILC wbs level 2 manager for positron work. To
accomplish these tasks (BCD, RDR, and TDR), SLAC is
defining the goals and working closely with US and
international collaborators, notably from ANL, LBNL,
LLNL, UCB, and Cornell. as well as from KEK,
DESY-Hamburg, DESY-Zeuthen, Liverpool U., Durham U.,
CCLRC Daresbury and CCLRC RAL.
The bulk of the design effort was spent in refining the
Baseline Configuration Document (BCD) by the end of
calendar 2005 and then was spent developing the
Reference Design Report (RDR) configuration, inventory,
and cost model. Significant ongoing effort is directed
towards cost and design optimization for the RDR. The
goal of present ILC positron RDR activities are directed
towards writing the text and cost estimate by the end of
calendar 2007.
To accomplish the RDR tasks, a full design model for the
ILC positron source has been developed with all major
components identified, specified, and costed. This work
is based on positron production, capture, transport, and
acceleration modeling developed at SLAC. The costing
effort was accomplished by coordinating, collecting, and
collating the efforts of the various ILC GDE Technical
and Global groups. The initial results of the costing
efforts were presented and discussed at the GDE meeting
in Vancouver in July 2006. Coordination of the TDR work
has begun and a first international meeting for this
effort has been organized by SLAC to be held at RAL
Oxford during the last week of FY06.
The R&D activities included ongoing data analysis and
post experiment component calibration for the E166
experiment. Initial studies have begun on the
determining the feasibility of utilizing a strong (~7 T)
dc solenoid in conjunction with a spinning target for
efficient positron collection. An R&D program for
FY07-09 has been developed in support of the TDR
requirements. This program will be overseen by SLAC and
carried out in collaboration with both US and
international partners.
4.4.c. Damping Rings
Large acceptance is an important requirement for the
position damping ring. Significant progress has been
made in improving and understanding the dynamic aperture
of the damping rings. First, by carefully studying the
nonlinearity in wigglers, we have found that well
designed wigglers, such as the superconducting wigglers
used in CESR, were not a limiting factor for the machine
acceptance. Second, we concluded that rings with a large
degree of symmetry have better dynamic aperture. As a
result, 6-km rings with a twelve-fold symmetry were
chosen to replace the 17-km TESLA dog-bone damping
rings. Finally, a baseline lattice with adequate
acceptance was established. Although this work was
carried out by an international collaboration including
ANL, LBNL, KEKB and Cornell, SLAC has provided a leading
and vital role.
From the experience in the existing B-Factories: PEP-II
and KEKB, collective instabilities due to electron cloud
are likely to become a severe performance limitation in
the positron damping ring. Based on the simulation, two
positron rings are required to separate adjacent bunches
enough to avoid the head-tail instability. SLAC has
continued a large R&D effort to find a way to mitigate
effects of electron cloud. A grooved vacuum chamber with
diagnostics has been designed and manufactured. The
chamber is scheduled to be installed in PEP-II before
the end of this year. Measurements with position beam
are expected in the next year. The success of this R&D
is crucial since the decision was recently taken to
eliminate one of the positron rings as a cost reduction
measure.
SLAC continues to play an important role in the design
of the ILC damping rings and development of the related
technical subsystems. We continue to collaborate with
our colleagues worldwide to complete the design. Urgent
tasks include developing a realistic impedance model,
evaluating classical instabilities, and developing a
fast injection and extraction kicker.
The SLAC-LLNL Kicker development continued with
investigation of fast switches to improve rise and fall
times of the kicker. In addition the prototype kicker
tested at ATF was modified with additional driver cards
to increase output voltage and provide a short flat top.
This unit can now achieve over +/-9 kV bipolar pulses
and is being returned to ATF for further tests.
Meanwhile after trying tests of a new MOSFET with
integrated driver that offered no improvement, a new
circuit was developed with a push-pull circuit to
achieve less than 2 ns rise and fall times, for a total
base pulse width of 4.1 ns. This is acceptable for the 6
km ring if after-pulse ripple can be sufficiently clean.
Some newer devices with inherently faster speed are also
being tested.
SLAC is also collaborating on testing a new device, a
Drift Snap Recovery Diode, DSRD, that showed almost 1 ns
rise and fall for a multi kV pulse, with some pre-and
after-baseline effects. This is under an SBIR program. A
workshop has been organized by the Damping Ring group to
discuss all these developments. FY07 plans include
construction of a new prototype that meets all
specifications including full power operation at
+/-10kV, 3 MHz CW.
4.4.d. Ring to Main Linac
The SLAC ILC group has taken the lead in the design and
cost estimation of the Ring to Main Linac (RTML)
transfer line. In collaboration with physicists from
DESY and Cornell University, a complete optics design
for the RTML, including all necessary pulsed extraction
systems, instrumentation, and other beamline elements
was completed. The RTML includes the SLAC/LBNL/LEPP
design for a two-stage bunch compressor which was
developed in 2005, but with a number of improvements to
reduce its total length and cost. A cost estimate for
the “as designed” RTML was developed by the worldwide
ILC GDE in the spring and early summer of 2006. Since
that time the SLAC group has developed and proposed a
number of design changes which could potentially reduce
the system cost, and has participated in developing a
“Central Damping Ring” design for the ILC which would
require significant changes in the RTML.
Additionally, a collaboration between SLAC, FNAL, and
Cornell University has been exploring the beam dynamics
issues of the RTML. These studies have so far
concentrated on the static tuning of the beamline (i.e.,
using the beam instrumentation to eliminate emittance
growth induced by static misalignments and errors of the
beamline components), with additional studies on the
longitudinal stability requirements of the bunch
compressors. Several members of this collaboration
attended the Low Emittance Transport (LET) workshop at
CERN in February of 2006. In the last few weeks, studies
have begun to explore whether the RTML is subject to
instabilities which have historically been regarded as
relevant only to storage rings (for example, the Fast
Beam-Ion Instability).
Future work on the RTML will focus on further
improvements and refinements in the design, with a goal
of completing a fully optimized design by the end of
FY07; completion of the static emittance preservation
and instability studies; and work on dynamic and
multi-system studies of beam dynamics, in collaboration
with the worldwide LET team.
4.4.e. Main linacs
A number of key linac design decisions were made in
FY2006, most notably, the overall linac configuration
has been chosen: 1 quad per rf station, which has 3
cryomodules, a vertically curved linac to allow the
entire linac to lie roughly on a gravitational
equipotential, with 1.2 km insertions for the positron
undulator on the electron side and for the timing
adjustment system on the positron side. High priority
activities for FY2007 are to: wrap up the last few
decisions required for the production linac lattices
(mainly related to dispersion matching and other
details); produce final production versions of the
electron and positron linac lattices; and transition the
simulation work to the production lattices.
A workshop on Low Emittance Transport (LET) was held
early in FY2006. At that time, the aforementioned
vertically curved lattice was adopted for main linac
studies, and agreement was reached on a set of
simulation tests which would be used to "certify" the
basic beam dynamics properties of a code before it was
accepted for use in linac studies. All of the codes
currently in use have been certified in this manner.
Since the LET workshop, studies of the main linac have
demonstrated that there is an incremental penalty in
emittance dilution for the use of a vertically-curved
linac as compared to a laser-straight version. This
penalty is sufficiently small that the vertically-curved
version has been accepted as the baseline configuration.
For the first time, a simulation result produced by one
group was reproduced, in full detail, by a separate
group with a completely independent simulation code
base.
In FY2007 work will continue in all these areas, both
area-by-area and in an integrated approach. The goals of
the effort will be: to demonstrate with 90% confidence
that the emittance budget of the ILC can be achieved; to
demonstrate multiple steering and alignment algorithms
which can be used in each area; and to have at least 1
independent verification of each simulation result
before it is accepted as a valid demonstration for these
purposes.
In addition to the LET studies, physicists from the
Advanced Computing Department (ACD) and Beam Physics
Group at SLAC made a good start in FY2006 at
understanding a number of issues related to wakefields
in the ILC linac cavities, and multipactoring in the
high power cavity couplers. They used both analytical
models and computer simulations to study the
characteristics of the cavity dipole modes (e.g. their
external Q values, polarization, frequency spread and
mode splitting), and the severity of multipacting in the
TTF3 coupler bellows. The cavity simulations show that
elliptical dipole modes will be generated with purely
symmetrical cavity cells, although they are unlikely to
be present in the ILC linacs due to the azimuthal
asymmetries introduced during the cavity manufacturing
process.
The main goals for this group in the FY2007 are to (1)
develop a model of the cavity shape distortions that
will explain the variations observed in the lowest-band
dipole mode properties, (2) use this model to verify
that the spectrum of (R/Q)*Qext for lowest band modes
will not produce significant beam breakup in the ILC
Linacs, (3) extend this analysis to trapped modes over
multiple cavities for frequencies up to ~8 GHz, which
will require massively parallel computer processing and
(4) complete the multipacting evaluation of the TTF-3
coupler and suggest design changes to reduce this
phenomenon.
The main focus of linac design R&D in FY2006 was on
proving beam-based quad alignment techniques that are
required to preserve the small emittances in the ILC
linacs. The simplest technique proposed requires that
the alignment of the magnetic center of each quad be
first measured relative to the electrical center of the
nearby BPM. This involves changing the quad strength and
recording the resulting beam kick. To achieve the
desired accuracy, the quad magnetic center cannot move
by more than a few microns when the field strength is
changed by 20%. The large aperture of ILC Linac quads
(78 mm) may make achieving this stability difficult,
especially if high gradient magnets with coil-defined
fields are used. The beam-based alignment procedures
also require large aperture beam position monitors
(BPMs) with micron-level resolution.
The goal at SLAC is to develop a SC quad and BPM that
meet these requirements. To this end, a TELSA SC linac
quad prototype was obtained (on loan) from DESY this
year along with gas-filled-type leads to power it (100 A
produces 60 T/m in the 0.66 m long magnet). The quad was
built by the CIEMAT group in Spain and tested initially
in a vertical Dewar at DESY. At SLAC, the design of a
warm-bore cryostat for this quad was started in FY2005
and finished this spring (keeping the magnet stable
vibrationally at the submicron level while allowing
contraction of the support system during cool-down is
not trivial). The cryostat is now under construction and
is about 80% complete (the quad was recently inserted in
the He vessel). The power supply and quench protection
circuit for the magnet was assembled and the gas-filled
lead assembly tested in a dewar at full current. The
magnet will be tested at the SLAC Magnetic Measurement
Lab using liquid He and N2 supplied by 2000 liter
portable dewars. The parts for the cryogenic supply
system have been purchased and are being assembled.
Also, a rotating coil system was built that will allow
the position of the quad magnetic center to be monitored
at the sub-micron level as the magnetic field is varied
(the design of this system is based on that developed
for the normal-conducting NLC quads). Finally,
accelerometers were purchased that will be used to
monitor the vibration of the quad relative to base on
which the cryostat will be supported (the measurements
will be done in collaboration with FNAL).
In a parallel program, a slotted-waveguide-style, S-band
(2.9 GHz), cavity BPM was designed, and three prototypes
constructed and tested at End Station A at SLAC. These
BPMs have a 36 mm aperture, which is about half of the
nominal ILC size. This choice makes testing this design
concept simpler, and it would be advantageous to adopt
this aperture size for the ILC. The BPM geometry
naturally suppresses monopole mode signals, and it was
carefully designed so the neighboring modes are well
separated in frequency. A low cavity Qext was chosen (~
500) to allow clean bunch-to-bunch signal separation in
the ILC (the signal drops to 0.2% of its initial level
after 337 ns, the nominal ILC bunch separation). The
prototype BPMs preformed well in beam tests with 29 GeV,
300 micron-long single bunches of 1.5e10 electrons.
Resolutions of 400800 nm were achieved when down-mixing
the signals to 73 MHz and digitizing them at 100 MHz.
These resolutions are better than that required in the
ILC linacs.
4.4.f. Beam Delivery System
SLAC is playing a leading role in the international
collaboration on the design of the Beam Delivery System
(BDS), including development of required hardware,
instrumentation and test facilities. SLAC played a key
role in the technical evaluation of the baseline
configuration and in the cost estimation of the beam
delivery. As a result, it was suggested that the BDS
would have improved performance and 15% lower cost if
the baseline configuration were changed to 14mrad
crossing angle in both IRs. This configuration was
analyzed from both the physics and technical perspective
and was adopted as a new baseline. SLAC continues to
play a key role in all accelerator physics aspects of
the BDS design.
SLAC is further enhancing its role in coordination of
the worldwide BDS development activities, providing
feedback and guidance for technical specifications and
design as well as in developing a coordinated plan for
the R&D and design work distribution between global
partners. The global plans for the next three years of
BDS R&D leading to an Engineering/Technical Design
Report will attempt to utilize the expertise in the
Americas as well as in worldwide collaborating labs and
universities.
The experimental studies to support a reliable BDS
design are being conducted at End Station A at SLAC
(described below) and will later be conducted at ATF-2
at KEK. The ATF-2 is being constructed by an
international collaboration. It will use the uniquely
small emittance ATF beam to achieve a beam size of about
35 nm, develop methods of tuning and maintaining a small
beam size for an extended duration, and eventually
stabilize the beam with nanometer precision. In FY2006,
SLAC built a prototype High Availability power supply
which was adopted for the ATF-2. SLAC also contributed
to the development of BPM electronics and the magnet
system for the ATF-2 proposal. In FY07 and beyond, SLAC
will continue contributing in-kind hardware for
construction and will be involved in the
pre-commissioning evaluation of ATF-2 hardware.
4.4.g End Station A Test Facility for Prototypes of Beam
Diagnostics and IR Design
The SLAC Linac can deliver to End Station A (ESA) a
high-energy test beam with similar beam parameters as
for the International Linear Collider (ILC) for bunch
charge, bunch length and bunch energy spread. ESA beam
tests run parasitically with PEP-II with single damped
bunches at 10Hz, beam energy of 28.5 GeV and bunch
charge of (1.5-2.0)·1010 electrons. Four experiments
were approved and took data in FY06. A 5-day
commissioning run was performed in January 2006,
followed by a 2-week run in April and a 2nd 2-week run
in July. These tests included measurements of collimator
wakefield kicks from 8 sets of collimators (T-480);
measurements of the electronic and mechanical stability
of bpms for a bpm energy spectrometer (T-474);
commissioning of a quartz fiber detector for a
synchrotron stripe energy spectrometer (T-475);
characterizing the performance of prototype beam
position monitors (BPMs) for the ILC Linac (part of
T-474), and a study of background effects for the IP
feedback BPMs (T-488). Beam tests were also performed to
characterize beam-induced electro-magnetic interference
(EMI) along the ESA beamline and to study an EMI failure
mode in the electronics for the SLD vertex detector; and
bunch length diagnostics were tested that have
applicability for ILC and LCLS.
The ILC test beam program in ESA is described in
SLAC-PUB-11988 (also available as
EUROTeV-Report-2006-060), which was prepared for a paper
and poster contribution at EPAC06. Two other papers and
posters were also contributed to EPAC06 for T-480 and
T-488. There are 22 institutions collaborating on the
ILC test beam program in ESA. More details of the ILC
test beam program in ESA in FY06 can be found in this
DOE self-assessment document in the section on Test
Beams. Analysis of the data taken in FY06 is ongoing.
The program will continue in FY07 with the addition of a
magnetic chicane, undulator magnet and new BPMs for the
energy spectrometer tests (T-474 and T-475), new
collimators for wakefield measurements (T480) and a new
bunch length measurement experiment using Smith-Purcell
radiation (T-487).
4.4.h Diagnostics and Controls
The most important ILC beam diagnostics are for
precision, ultra-high-resolution measurements of
position, transverse profile and longitudinal profile.
Development of these devices has long been recognized as
a high priority for linear collider R&D and SLAC has
maintained a leading role in this effort. The most
useful test facility for the development of precision
position and (transverse) profile monitors is the KEK
ATF which routinely produces the lowest emittance beam
available worldwide. During the last year the SLAC
group, supported by groups from LLNL, LBNL, Cornell
University and a group of UK universities, have
installed hardware and instrumentation that allows the
position of the precision beam monitors to be linked to
other beamline components. The 'optical anchor' hardware
will be used for ILC energy spectrometry. The SLAC group
at ATF also supports the effort, lead by the UK, to
deploy a laser-based beam profile monitor with
resolution better than 1 micron. In the last year, the
system was successfully used for initial precision scans
of the damped ATF beam.
For longitudinal profile measurements, the SLAC group
has developed a world record precision longitudinal
monitor based on a high-power S-band deflecting
structure. The device was tested in FY2005 at the DESY
Tesla Test Facility and showed resolution of 10 microns.
In 2006, this monitor was used to provide a basic
understanding of the transport of extremely short
bunches and for the first time provided 'slice
emittance' and longitudinal correlated energy spread
measurements. Finally, in support of the superconducting
rf cavity development at DESY, the SLAC group has
developed a signal-processing system that allows the
interpretation of the higher order mode signals
generated in the cavity for beam position monitoring.
The system was used in 2006 to provide critical offset
information with 30 micron indicating the placement of
the niobium cavities inside the cryostat. The system was
adapted to provide accurate beam to RF phase
measurements with a resolution of 0.1 degrees.
In 2006 controls efforts continued with the GDE Controls
Collaboration to refine all Baseline Conceptual Design
(BCD) models begun at Snowmass, defining system
architectures for both hardware and software, and
developing first order cost models for all components
down to the interfaces of controls with front end
instrumentation and major technical subsystems.
Integrated with this effort was an evaluation of a
commercial modular computing standard called ATCA which
features the critical High Availability features that
ILC requires to be a successful machine. This system
also provided the cost model for the core control
system, multiprocessing farm and Low Level RF
instrumentation for the Main Linac.
4.4.i. Operations and Availability
The availability simulation developed at SLAC and
reported in 2005 has continued to play an invaluable
role in guiding the overall machine design. As options
continue to be proposed, such as going to a 1 tunnel
design from the present 2 tunnel plan or putting both
damping rings in the same tunnel, the performance
implications are evaluated with the simulation.
Simulation results also have determined where High
Availability R&D programs are needed.
With the basis of performance now understood, major
progress was made in 2006 in advancing designs for
controls, power supply systems, diagnostics processors,
controls and Marx modulators. The latter is a lower cost
more reliable alternate to the baseline design that is
being developed. Evaluation of the ATCA core processor
and gigabit switching fabric network system has begun in
collaboration with the University of Illinois (Urbana).
HA power supplies consisting of n+1 redundant DC-DC
converters in current-shared operation, such that a
module can fail with no interruption to the machine,
were demonstrated. A bulk supply redundant system was
also demonstrated, and conceptual design of the critical
diagnostic controller was started. For the Marx,
redundant IGBT charging and switching on the base 12kV
cells became operational, and a special diagnostic
controller that could float at high voltage was
developed and is operational. Commercial contacts are
continuing to grow including vendor seminars,
presentations to subgroups of the Linear Collider Forum
of America, seminars, product evaluations of ATCA, and
evaluation of redundant highly reliable DC-DC converter
power system components built for the computer server
industry.
Within the ILC the high availability program has taken
firm root among the collaborating laboratories. The
proposal to interest other mega-projects in high
availability modular standards is ongoing. Formal papers
on the subject were given at the Nuclear Science
Symposium in 2004 and a seminar in 2005, Real Time
Conference in 2005 (Plenary talk)
4.4.j. Conventional Facilities Design and Installation
The SLAC Conventional Facilities (CF), partnering with
the FNAL-CF engineers, identified several potential
locations for the ILC alignment in northeast Illinois.
They assessed each location considering not only cost of
the construction and installation phase of the project,
but the environmental impacts as well as eventual impact
on the long term operations of the ILC. Results were
analyzed, reviewed, and amended into the global site
assessment matrix. As results of this effort, a Sample
Site for the Americas region was identified.
The baseline configuration layout as well as a complete
description for the CF portion of the ILC was developed
by a collaboration of SLAC, Fermilab, Japanese and
European engineers working closely with the Area System
leaders. In addition to baseline choices, alternate
configurations were also established that may have cost
benefits. These efforts were complete in time for
inclusion into the Baseline Configuration Document (BCD)
in December, 2004.
Subsequent to the adoption of the BCD, a concept design
and associated cost estimate for the ILC Conventional
Construction was developed. This effort included many
3-D visualization drawings which facilitated a top-level
assessment of the major choices, as well as a set of
concept designs that could provide cost effective, safe
underground and surface facilities. This initial design
and cost estimate was completed in FY06 and will form
the basis for the Reference Design Report expected by
the end of 2006.
In addition, SLAC has devoted a major effort in
initiating, organizing and setting-up a complete and
comprehensive cost model plan for the ILC Installation
Global System in collaboration with the Asian and
European engineers. The SLAC Installation group being
also partner in the Conventional Facilities Group has
tried to coordinate and to integrate the installation
effort with the CF work as well as with the other
Regional Technical and Area Teams. A first cut
installation cost estimate for ILC was completed in
FY06.
4.5. NLCTA Operations
During FY2006, the focus of the ILC effort at NLCTA was
on the development of L-band rf power systems. The
primary effort was to develop a 5 MW rf source as
described in ILC Section 4.3.f above. Planning work also
began for removing a large shielding wall in End Station
B to provide space for two new rf stations that will be
used to do long-term testing of the Marx and DTI
modulators using either a water load or 10 MW klystrons
as they become available.
The ILC group also worked to maintain the NLCTA as an
operating linac to be used for advanced accelerator R&D.
To this end, the 8-pack modulator, which was
contaminated with beryllium, was decommissioned and was
replaced with a newer 2-pack modulator, which was tested
initially in the Power Conversion Department Building in
FY2004. The 2-pack modulator will not deliver as much
power as the 8-pack but it will still accelerate the
beams to roughly 300 MeV. This modulator will be
recommissioned at NLCTA within the next month, and the
8-pack rf source used to test advanced SLED pulse
compression techniques (SLC operating budget funds).
As discussed in Section 4.2, high gradient R&D using
existing X-band accelerator structures continued in
FY2006, funded by SLAC as part of the US Collaboration
on High Gradient Research program. For this work, the
Station 2 X-band rf source was mainly used. Also,
members of the Accelerator Technology Research Group at
SLAC used the Station 1 rf source to study rf breakdown
in a molybdenum waveguide for the high gradient program.
In FY2005, the NLCTA was modified to provide beam for
the SLAC E-163, a 'Laser Acceleration at NLCTA'
experiment. See Section 6.1 for further detail
4.6. LHC Accelerator Research Program (LARP) Collimators
The LHC collimator R&D program developed out of a
request from CERN to study the applicability to the LHC
of the ‘consumable’ collimator technology that was
developed for the NLC. As the project became better
defined, it was added to the US LHC Accelerator Research
Proposal. All funding for this program flows through
LARP, although the program is administered out of the
ILC Department, where the technological concepts
originated and the people driving the effort are
located.
The LHC collimation system will be installed in two
phases. The first phase devices are carbon-jaw
collimators that can survive the direct impact of up to
8 nominal-intensity bunches, a rare but regularly
foreseen accident condition. The system will have
adequate efficiency and low enough impedance for
start-up luminosity of 10% nominal design or 1x1033
cm-2s-1. A system based on metal collimators with
improved efficiency and lower impedance must be devised
and installed before the LHC can reach the full design
luminosity of 1x1034
cm-2s-1.
The ILC Department has proposed to design and prototype
these so-called LHC Phase II collimators as an
extrapolation of the design that was developed and
prototyped for the NLC. The basic concept is one that
replaces classic rectangular jaws with cylindrical jaws
that can rotate to present a fresh surface to the beam
if the surface is damaged in an accidental beam abort.
Relative to the NLC design, the LHC jaws must be longer,
of a smaller diameter and each provided with ~12 kW of
water cooling.
In FY2005, tracking studies, energy deposition studies,
and finite element analyses were used to determine the
optimal design of the collimators. This information,
together with relevant 3-D CAD design drawings, was
assembled into a conceptual design report for a first
collimator prototype.
In FY2006 the conceptual design was independently
reviewed. It was recommended that before proceeding with
construction we increase our engineering manpower and
further develop the design of the mechanisms to a)
support the collimator jaws, b) prevent them from
intruding into the beam if thermally distorted, and c)
rotate the jaws after damaging asynchronous beam aborts.
In response, two FTEs were added to the engineering team
and the design developed that elegantly addressed all
the concerns of the reviewers.
In late FY2006 two rounds of short test jaws were
constructed to verify machining, brazing and assembly
procedures and drawings made for the first full size
collimator jaw. Additionally a clean room was prepared
and equipped with resistive heaters, thermocouples,
capacitive monitors and a data acquisition system. In
FY2007 it is planned to build and test the
thermo-mechanical properties of this full length jaw and
to build a full two-jaw vacuum compatible mechanical
prototype with all the mechanisms required for jaw
support and adjustment.
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Accelerator Laboratory, Menlo Park, CA