A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago Argonne National Laboratory Office of Science U.S. Department of Energy I. Vasserman Break Length Tuning and Phase Adjustment LCLS UNDULATOR SYSTEM MEETING June 29, 2004

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Outline Break length correction at regular part: Phase shims, pole gap change, trajectory shims, K eff Phase correction at saturation Complex amplitude vs. distortions One device removed Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Breake length change vs. phase shim number 0.2 mm thick phase shims at one end (magnets from 7 to 2)

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Phase Shims Signature Phase shims 0.2 mm thick applied to 12 magnets at U/S end

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Complex amplitude and phase Complex amplitude of radiation and phase slippage are defined below Phase slippage over the length of one section Complex amplitude of radiation Intensity of radiation is defined by |A| 2

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Break length definition L f = n u (1+K 2 eff /2) -> required length in free space: Tolerance for phase error between sections ~10  Supposed tapering required after saturation at last 30 m of undulator to compensate for particle energy loss 0.4%: corresponds to 2.5° of phase error for break section with n=1, or 7.5° with n=3

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 |A| vs. arg(A) for two devices in row n=3 LCLS prototype. Close to 100% performance. |A| is equal to length of the vector at plot

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Energy changed by 0.4% Performance is close to zero, very sensitive to the energy change. Worst case with biggest energy loss and long break is chosen

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, % Energy change. Keff corrected Performance is 97.5%. Close to requirements with no break length correction

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Full correction of Keff to compensate for phase Performance is 99.2%, close to perfect. No break length correction

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Discussion Recent 3 mrad cant requires ~8mm shift in X to obtain change in K eff for compensation of 0.4% change in energy. A possible option is to shift devices at saturation area in X to –4 mm in advance to allow then going full way up to 4 mm to cover all range of energy change. Additional tuning for such devices could be necessary to provide proper performance in wide X- range Possibility to remove one device during commissioning was investigated. For recent design with K eff =3.63 L d /L f =16.08 Such distorrtion could be corrected by changing the K eff ; for K eff =3.44 (gap 6.9 mm) L d /L f = It means that this option requires a phase shifter to adjust the phase after removing the device

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 One device removed, K eff corrected (k=3.636*0.9996) 0.08 phase distortion compensated by change of  K/K (0.8mm shift in X), 99.3% performance

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Same as before for K= phase distortion compensated by change of  K/K (3.2 mm shift in X), 81.6% performance

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Summary If phase between devices too big: Phase shims must be applied to correct the break length; If phase between devices too small: gap for end poles must be decreased. This option is undesirable, and initial break length should be defined with part of phase shims already in place to allow tuning of the break length in both directions without affecting the gap; Other possibilities could be chosen as well if necessary (K eff correction, trajectory shims) Initial tuning

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Summary (Cont) Main reason for K eff variation desirability is particle energy change at saturation stage; By adjusting the K eff proper performance could be easily restored. Performance is extremely sensitive to K eff. Even in case of tuning in advance the devices to the proper K eff, remote control of it is absolutely necessary during commissioning, taking into account uncertainty in beam energy loss at saturation; Another source of concern for K eff stability is temperature variation. Two possible solutions are: remote X-position control to compensate for temperature change and/or temperature stabilization of the whole tunnel. Each section must have at least 2 temperature sensors at U/S and D/S end of the device and this temperature must be stable within ±0.2°C. Could it be achieved by tunnel temperature control only remains doubtful.

Pioneering Science and Technology Office of Science U.S. Department of Energy Isaac Vasserman Argonne June 29, 2004 Summary (Cont) Main conclusion from here: no active correction of phase between devices is necessary K eff tuning is crucial and remote control of X-position is necessary option with K eff =3.44 requires phase shifter to work with one device removed