SLAC Magnetic Measurements Date: 07-18-1995 Time: 06:18:47 Magnet Name (Serial #): 053 Bar Code Number: 025 Project: PEP II High Energy Ring Sextupoles Test Stand: IR8, S1, N Measurement Coil: # 1 Operator: bmd Run Number: 1 Comment: Standardization Currents (A): 250.0 10.0 200.0 10.0 200.0 10.0 200.0 10.0 Test Currents (A): 25.0 50.0 100.0 125.0 150.0 175.0 200.0 150.0 100.0 50.0 25.0 Harmonics Measurements Date: 07-18-1995 Time: 06:49:05 Magnet Name: 053 Run Number: 1 FIELD HARMONICS Magnet Current, Imag = 25.61969 +- 3.197585E-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 0.00006 0.00000 -105.67 1.01 1.1369 0.0108 2 0.00006 0.00000 -84.48 0.37 1.2136 0.0064 3 0.00526 0.00000 30.11 0.00 100.0000 0.0673 4 0.00001 0.00000 -7.59 2.58 0.1349 0.0248 5 0.00001 0.00000 -14.18 3.01 0.1290 0.0120 6 0.00000 0.00000 6.22 9.02 0.0291 0.0270 7 0.00000 0.00000 -7.96 4.21 0.0792 0.0136 8 0.00000 0.00000 -4.74 9.05 0.0343 0.0115 9 0.00002 0.00000 -9.38 0.47 0.3689 0.0492 10 0.00000 0.00000 -4.05 9.99 0.0401 0.0189 11 0.00000 0.00000 0.65 5.49 0.0407 0.0357 12 0.00000 0.00000 -4.29 7.87 0.0269 0.0076 13 0.00000 0.00000 -2.14 5.89 0.0246 0.0141 14 0.00000 0.00000 4.31 4.26 0.0271 0.0149 15 0.00000 0.00000 -5.50 1.18 0.0884 0.0195 16 0.00000 0.00000 3.80 3.23 0.0381 0.0242 The magnetic center is at X = 52.2 +- 3.4 microns Y = 267.3 +- 1.6 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: 07-18-1995 Time: 06:52:30 Magnet Name: 053 Run Number: 1 FIELD HARMONICS Magnet Current, Imag = 50.60001 +- 1.507188E-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 -102.03 0.40 0.7142 0.0024 2 0.00012 0.00000 -85.00 0.24 1.2137 0.0021 3 0.01027 0.00000 30.11 0.00 100.0000 0.0401 4 0.00001 0.00000 -8.39 1.80 0.1056 0.0057 5 0.00001 0.00000 -16.65 1.72 0.1358 0.0381 6 0.00000 0.00000 7.01 13.72 0.0097 0.0046 7 0.00001 0.00000 -11.96 2.07 0.0499 0.0268 8 0.00000 0.00000 -0.83 6.92 0.0144 0.0055 9 0.00003 0.00000 -10.00 0.05 0.3349 0.0082 10 0.00000 0.00000 -1.22 13.24 0.0228 0.0110 11 0.00000 0.00000 3.80 12.11 0.0124 0.0045 12 0.00000 0.00000 3.08 10.92 0.0140 0.0047 13 0.00000 0.00000 -0.44 8.49 0.0144 0.0053 14 0.00000 0.00000 5.10 2.20 0.0116 0.0050 15 0.00001 0.00000 -5.76 0.17 0.0677 0.0021 16 0.00000 0.00000 4.13 6.07 0.0131 0.0032 The magnetic center is at X = 47.3 +- 2.3 microns Y = 268.2 +- 0.6 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: 07-18-1995 Time: 06:55:59 Magnet Name: 053 Run Number: 1 FIELD HARMONICS Magnet Current, Imag = 100.5946 +- 1.413287E-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 0.00010 0.00000 -98.99 0.26 0.5008 0.0010 2 0.00024 0.00000 -85.22 0.04 1.1990 0.0055 3 0.02039 0.00001 30.10 0.00 100.0000 0.0683 4 0.00002 0.00000 -7.71 0.44 0.1135 0.0038 5 0.00002 0.00000 -16.88 1.83 0.0998 0.0241 6 0.00000 0.00000 18.73 11.38 0.0097 0.0039 7 0.00001 0.00000 0.89 12.67 0.0259 0.0047 8 0.00000 0.00000 -0.78 1.73 0.0145 0.0056 9 0.00007 0.00000 -9.80 0.09 0.3225 0.0053 10 0.00000 0.00000 -6.95 11.83 0.0073 0.0033 11 0.00000 0.00000 0.62 10.93 0.0078 0.0014 12 0.00000 0.00000 -0.39 1.67 0.0067 0.0031 13 0.00000 0.00000 -7.79 3.39 0.0072 0.0055 14 0.00000 0.00000 -1.78 0.54 0.0124 0.0045 15 0.00002 0.00000 -6.09 0.09 0.0785 0.0036 16 0.00000 0.00000 -2.63 5.71 0.0063 0.0030 The magnetic center is at X = 44.7 +- 0.4 microns Y = 265.3 +- 1.2 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: 07-18-1995 Time: 07:02:42 Magnet Name: 053 Run Number: 1 FIELD HARMONICS Magnet Current, Imag = 150.5742 +- 4.334154E-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 -96.51 0.34 0.4449 0.0019 2 0.00036 0.00000 -85.24 0.04 1.1965 0.0019 3 0.03045 0.00001 30.11 0.00 100.0000 0.0496 4 0.00004 0.00000 -7.41 0.39 0.1169 0.0049 5 0.00004 0.00001 -16.14 1.15 0.1334 0.0259 6 0.00000 0.00000 3.78 0.46 0.0099 0.0031 7 0.00001 0.00001 -10.09 2.59 0.0374 0.0176 8 0.00001 0.00000 -0.24 0.45 0.0186 0.0019 9 0.00010 0.00000 -9.82 0.05 0.3316 0.0033 10 0.00000 0.00000 4.03 12.59 0.0024 0.0006 11 0.00000 0.00000 -3.39 5.18 0.0021 0.0009 12 0.00000 0.00000 1.55 13.43 0.0052 0.0013 13 0.00000 0.00000 -6.22 2.92 0.0020 0.0002 14 0.00000 0.00000 -2.09 1.82 0.0072 0.0011 15 0.00002 0.00000 -5.86 0.11 0.0690 0.0026 16 0.00000 0.00000 -3.31 2.78 0.0052 0.0012 The magnetic center is at X = 44.4 +- 0.4 microns Y = 264.8 +- 0.4 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: 07-18-1995 Time: 07:09:25 Magnet Name: 053 Run Number: 1 FIELD HARMONICS Magnet Current, Imag = 200.5696 +- 2.484045E-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 0.00016 0.00000 -95.79 0.29 0.3948 0.0023 2 0.00048 0.00000 -85.33 0.03 1.1978 0.0009 3 0.04045 0.00001 30.11 0.00 100.0000 0.0219 4 0.00005 0.00000 -7.59 0.44 0.1174 0.0031 5 0.00005 0.00000 -16.90 1.22 0.1235 0.0101 6 0.00000 0.00000 2.57 2.30 0.0073 0.0018 7 0.00001 0.00000 -12.18 3.46 0.0273 0.0106 8 0.00001 0.00000 -0.72 2.32 0.0159 0.0035 9 0.00013 0.00000 -9.82 0.02 0.3321 0.0016 10 0.00000 0.00000 -2.30 13.02 0.0060 0.0024 11 0.00000 0.00000 0.01 4.21 0.0055 0.0021 12 0.00000 0.00000 2.67 7.43 0.0023 0.0011 13 0.00000 0.00000 -1.11 4.75 0.0039 0.0020 14 0.00000 0.00000 -4.16 4.06 0.0058 0.0021 15 0.00003 0.00000 -5.82 0.10 0.0720 0.0018 16 0.00000 0.00000 0.23 9.84 0.0039 0.0028 The magnetic center is at X = 43.6 +- 0.3 microns Y = 265.2 +- 0.2 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)