SLAC Magnetic Measurements Date: 07-06-1995 Time: 09:45:39 Magnet Name (Serial #): 000 Bar Code Number: 001 Project: PEP II High Energy Ring Sextupoles Test Stand: IR8, S1 Measurement Coil: # 1 Operator: pdr Run Number: 14 Comment: Measuring to higher currents Standardization Currents (A): 350.0 10.0 200.0 10.0 200.0 10.0 200.0 10.0 Test Currents (A): 25.0 50.0 100.0 150.0 200.0 250.0 300.0 250.0 200.0 150.0 100.0 50.0 25.0 Harmonics Measurements Date: 07-06-1995 Time: 10:07:43 Magnet Name: 000 Run Number: 14 FIELD HARMONICS Magnet Current, Imag = 50.59154 +- 4.36695E-03 A Coil Radius, Rcoil = .044882 m Coil # Turns, Nturns = 20 Average, # Rotations/Measurement = 10 , # Measurements = 4 Nmain = 3 N BLn sigBLn THspole sigTH BLn/BLN sBLn/BLN (Tm) (Tm) (deg) (deg) (%) (%) --- --------+-------- --------+-------- --------+-------- 1 0.00007 0.00000 -105.23 0.47 0.7201 0.0077 2 0.00012 0.00000 -52.24 0.30 1.1724 0.0038 3 0.01027 0.00000 30.11 0.00 100.0000 0.0447 4 0.00001 0.00000 -5.41 0.34 0.1344 0.0111 5 0.00002 0.00000 -17.68 0.40 0.1579 0.0031 6 0.00000 0.00000 1.18 5.60 0.0203 0.0088 7 0.00000 0.00000 -15.16 1.11 0.0376 0.0072 8 0.00000 0.00000 4.10 6.44 0.0223 0.0110 9 0.00003 0.00000 -9.93 0.17 0.3293 0.0029 10 0.00000 0.00000 -6.89 2.96 0.0155 0.0114 11 0.00000 0.00000 -1.78 7.26 0.0130 0.0064 12 0.00000 0.00000 -1.91 2.66 0.0115 0.0035 13 0.00000 0.00000 2.48 8.73 0.0113 0.0055 14 0.00000 0.00000 0.14 1.33 0.0102 0.0030 15 0.00001 0.00000 -6.29 0.44 0.0715 0.0068 16 0.00000 0.00000 -1.85 3.29 0.0042 0.0025 The magnetic center is at X = 254.7 +- 1.1 microns Y = 65.8 +- 2.7 microns The magnetic center is measured relative to the coil axis effectively at the longitudinal center of the magnet. Pitch and yaw are not seen by the coil. View from the non-lead end of the magnet: y ^ | N S S --> x N N S Date: 07-06-1995 Time: 10:12:08 Magnet Name: 000 Run Number: 14 FIELD HARMONICS Magnet Current, Imag = 100.5857 +- 4.372994E-03 A Coil Radius, Rcoil = .044882 m Coil # Turns, Nturns = 20 Average, # Rotations/Measurement = 10 , # Measurements = 4 Nmain = 3 N BLn sigBLn THspole sigTH BLn/BLN sBLn/BLN (Tm) (Tm) (deg) (deg) (%) (%) --- --------+-------- --------+-------- --------+-------- 1 0.00011 0.00000 -101.24 0.33 0.5257 0.0021 2 0.00024 0.00000 -51.75 0.26 1.1612 0.0035 3 0.02038 0.00000 30.10 0.00 100.0000 0.0134 4 0.00002 0.00000 -5.69 0.29 0.1215 0.0057 5 0.00003 0.00000 -17.22 0.16 0.1683 0.0026 6 0.00000 0.00000 20.19 4.09 0.0070 0.0031 7 0.00001 0.00000 -12.39 1.13 0.0379 0.0052 8 0.00000 0.00000 9.91 2.41 0.0174 0.0055 9 0.00007 0.00000 -9.90 0.05 0.3312 0.0050 10 0.00000 0.00000 -0.69 7.63 0.0075 0.0024 11 0.00000 0.00000 -0.14 5.21 0.0071 0.0044 12 0.00000 0.00000 -0.20 1.27 0.0108 0.0056 13 0.00000 0.00000 -5.55 4.86 0.0068 0.0022 14 0.00000 0.00000 4.90 1.99 0.0103 0.0033 15 0.00002 0.00000 -6.15 0.23 0.0744 0.0011 16 0.00000 0.00000 -0.12 4.31 0.0079 0.0028 The magnetic center is at X = 253.4 +- 0.9 microns Y = 60.8 +- 2.3 microns The magnetic center is measured relative to the coil axis effectively at the longitudinal center of the magnet. Pitch and yaw are not seen by the coil. View from the non-lead end of the magnet: y ^ | N S S --> x N N S Date: 07-06-1995 Time: 10:16:37 Magnet Name: 000 Run Number: 14 FIELD HARMONICS Magnet Current, Imag = 150.5672 +- 5.477522E-03 A Coil Radius, Rcoil = .044882 m Coil # Turns, Nturns = 20 Average, # Rotations/Measurement = 10 , # Measurements = 4 Nmain = 3 N BLn sigBLn THspole sigTH BLn/BLN sBLn/BLN (Tm) (Tm) (deg) (deg) (%) (%) --- --------+-------- --------+-------- --------+-------- 1 0.00014 0.00000 -99.44 0.52 0.4638 0.0014 2 0.00035 0.00000 -51.28 0.12 1.1497 0.0005 3 0.03046 0.00001 30.10 0.00 100.0000 0.0277 4 0.00004 0.00000 -5.28 0.53 0.1261 0.0010 5 0.00005 0.00000 -16.94 0.05 0.1696 0.0042 6 0.00000 0.00000 2.50 2.12 0.0123 0.0015 7 0.00001 0.00000 -12.63 0.42 0.0395 0.0027 8 0.00000 0.00000 9.54 2.14 0.0134 0.0023 9 0.00010 0.00000 -9.90 0.06 0.3328 0.0041 10 0.00000 0.00000 -0.88 10.21 0.0084 0.0030 11 0.00000 0.00000 -3.11 5.83 0.0060 0.0032 12 0.00000 0.00000 -2.56 9.00 0.0071 0.0036 13 0.00000 0.00000 2.69 7.81 0.0076 0.0036 14 0.00000 0.00000 3.07 4.80 0.0044 0.0033 15 0.00002 0.00000 -5.65 0.36 0.0667 0.0056 16 0.00000 0.00000 -4.33 2.93 0.0084 0.0019 The magnetic center is at X = 251.8 +- 0.3 microns Y = 56.1 +- 1.1 microns The magnetic center is measured relative to the coil axis effectively at the longitudinal center of the magnet. Pitch and yaw are not seen by the coil. View from the non-lead end of the magnet: y ^ | N S S --> x N N S Date: 07-06-1995 Time: 10:21:00 Magnet Name: 000 Run Number: 14 FIELD HARMONICS Magnet Current, Imag = 200.5701 +- 1.199294E-02 A Coil Radius, Rcoil = .044882 m Coil # Turns, Nturns = 20 Average, # Rotations/Measurement = 10 , # Measurements = 4 Nmain = 3 N BLn sigBLn THspole sigTH BLn/BLN sBLn/BLN (Tm) (Tm) (deg) (deg) (%) (%) --- --------+-------- --------+-------- --------+-------- 1 0.00017 0.00000 -98.90 0.34 0.4108 0.0012 2 0.00046 0.00000 -51.13 0.09 1.1458 0.0037 3 0.04044 0.00001 30.10 0.00 100.0000 0.0306 4 0.00005 0.00000 -5.03 0.62 0.1253 0.0062 5 0.00007 0.00000 -17.30 0.27 0.1641 0.0046 6 0.00001 0.00000 3.95 2.03 0.0130 0.0040 7 0.00001 0.00000 -13.23 0.37 0.0356 0.0021 8 0.00001 0.00000 9.15 1.48 0.0155 0.0022 9 0.00014 0.00000 -10.01 0.04 0.3344 0.0027 10 0.00000 0.00000 -1.86 9.20 0.0038 0.0022 11 0.00000 0.00000 -2.13 9.02 0.0035 0.0010 12 0.00000 0.00000 1.73 9.20 0.0031 0.0019 13 0.00000 0.00000 -1.88 6.97 0.0040 0.0010 14 0.00000 0.00000 1.44 7.15 0.0069 0.0044 15 0.00003 0.00000 -5.76 0.27 0.0722 0.0028 16 0.00000 0.00000 2.42 5.50 0.0052 0.0029 The magnetic center is at X = 251.3 +- 0.8 microns Y = 54.6 +- 0.8 microns The magnetic center is measured relative to the coil axis effectively at the longitudinal center of the magnet. Pitch and yaw are not seen by the coil. View from the non-lead end of the magnet: y ^ | N S S --> x N N S Date: 07-06-1995 Time: 10:25:48 Magnet Name: 000 Run Number: 14 FIELD HARMONICS Magnet Current, Imag = 250.5285 +- 7.138656E-03 A Coil Radius, Rcoil = .044882 m Coil # Turns, Nturns = 20 Average, # Rotations/Measurement = 10 , # Measurements = 4 Nmain = 3 N BLn sigBLn THspole sigTH BLn/BLN sBLn/BLN (Tm) (Tm) (deg) (deg) (%) (%) --- --------+-------- --------+-------- --------+-------- 1 0.00017 0.00000 -99.35 0.17 0.3300 0.0005 2 0.00057 0.00000 -50.97 0.09 1.1409 0.0041 3 0.05011 0.00001 30.10 0.00 100.0000 0.0314 4 0.00006 0.00000 -5.65 0.72 0.1167 0.0011 5 0.00008 0.00000 -17.22 0.17 0.1515 0.0004 6 0.00001 0.00000 2.95 0.20 0.0116 0.0024 7 0.00002 0.00000 -13.00 0.32 0.0361 0.0031 8 0.00001 0.00000 9.53 0.59 0.0145 0.0014 9 0.00017 0.00000 -9.96 0.04 0.3308 0.0020 10 0.00000 0.00000 -4.33 8.59 0.0047 0.0036 11 0.00000 0.00000 4.81 6.18 0.0049 0.0031 12 0.00000 0.00000 -4.96 8.41 0.0054 0.0016 13 0.00000 0.00000 0.02 9.89 0.0055 0.0027 14 0.00000 0.00000 2.01 4.29 0.0048 0.0021 15 0.00004 0.00000 -5.97 0.05 0.0703 0.0039 16 0.00000 0.00000 -2.90 4.04 0.0047 0.0008 The magnetic center is at X = 250.5 +- 0.9 microns Y = 52.9 +- 0.8 microns The magnetic center is measured relative to the coil axis effectively at the longitudinal center of the magnet. Pitch and yaw are not seen by the coil. View from the non-lead end of the magnet: y ^ | N S S --> x N N S SUMMARY OF THE CALCULATIONS AND CONVENTIONS USED Field Expansion: The expansion of the radial and azimuthal field in polar coordinates is Br(r,th) = Sum Bn (r/rref)^(n-1) cos(n(th-thspole)) Bth(r,th) = -Sum Bn (r/rref)^(n-1) sin(n(th-thspole)) Our convention is to set rref = Rcoil. Thspole is the angle of the first magnetic south pole with respect to the horizontal, measured ccw by a shaft encoder in the system. Coil Voltage: The coil voltage from each field harmonic is Vn(th) = Nturns * velocity * Brn(Rcoil,th) * L L is the magnet effective length, or BLn is the integrated field strength of the n'th harmonic. At the coil radius, the radial field as a function of angle is, Brn(Rcoil,th) * L = BLn * cos(n*(th - thspole)) The coil voltage is Vn(th) = Nturns * velocity * BLn * cos(n*(th - thspole)) = Nturns * Rcoil * ang_freq * BLn * cos(n*(th - THspole)) An FFT of the coil voltage gives Vn and PhiVn according to the formula Vn(i) = Vn * cos(n*2pi*i/N + PhiVn) Multipole Field Calculations: To find the multipole field magnitudes and phases, the measured voltage harmonics are related to their values calculated from the field harmonics: Nturns * Rcoil * ang_freq * BLn = Vn -n * thspole = PhiVn Or, BLn = Vn / (Nturns * Rcoil * ang_freq) thspole = -PhiVn / n Harmonic Strength Ratios: The main field, denoted by capital N, is the field harmonic with the largest strength at the coil radius. The field strength ratio is defined by Rn = BLn / BLN It gives the ratio of each harmonic field strength to the main field strength at the coil radius. Calculation Of SL: The sextupole strength S is defined by the vertical field on the x-axis (median plane). It is the quadratic term in the Taylor expansion. By(x) = 1/2 S x^2 On the x-axis, By(x) = Bth(r=x,th=0) From the expression for Bth above, By(x) = - B3 (x/rref)^2 sin(-3 thspole) Take rref = Rcoil, thspole = pi/6, then at x=Rcoil, By(Rcoil) = B3 = 1/2 S Rcoil^2 So, S = 2 B3 / Rcoil^2 The integrated sextupole strength is SL = 2 BL3 / Rcoil^2 Calculation Of The Sextupole Center: In the sextupole's frame, Bx' = S * x' * y' By' = 1/2 * S * (x'^2 - y'^2). In the coil's frame (unprimed frame) the magnetic center is at (x0, y0). In the coil's frame, Bx = S * (x - x0) * (y - y0) By = 1/2 * S * [(x - x0)^2 - (y - y0)^2]. The magnetic center can be found in terms of the measured quadrupole field. Compare Br and Btheta on the x-axis to Bxquad = -S * (x0 * y + y0 * x) Byquad = -S * (x0 * x - y0 * y). Evaluate at x = Rcoil, y = 0 and compare to Br(theta = 0) = Bx, Btheta(theta = 0) = By. In terms of the measured integrated strengths, this gives Xcenter = x0 = - (1/(SL * Rcoil)) * BL2 * sin(2 * THspole2) Ycenter = y0 = - (1/(SL * Rcoil)) * BL2 * cos(2 * THspole2)