Paper 
Title 
Page 
MOPPH023 
Enhancing FEL Power with Phase Shifters

69 

 A. Chao, Z. Huang
SLAC, Menlo Park, California
 D. F. Ratner
Stanford University, Stanford, Califormia



Undulator taper is a wellknown technique to increase the FEL efficiency past saturation by maintaining the resonant condition. In this paper, we demonstrate that shifting the electron bunch phase relative to the radiation is equivalent to tapering the undulator parameter. Using discrete phase changes derived from optimized undulator tapers for the LCLS xray FEL, we show that placing appropriate phase shifters between undulator sections can reproduce the power enhancement of these undulator tapers. The phase shifters are relatively easy to implement and operate, and hence can be used to aid or replace the undulator taper for optimizing the FEL performance.


MOCAU05 
Space Charge Effect in an Accelerated Beam

200 

 Z. Huang, G. V. Stupakov
SLAC, Menlo Park, California



It is usually assumed that the space charge effects in relativistic beams scale with the energy of the beam as the inverse relativistic factor gamma factor squared. We show that for a beam accelerated in the longitudinal direction there is an additional space charge effect in free space that scales as the ratio of the accelerating field to the gamma factor. This space charge field has the same origin as the "electromagnetic mass of the electron" discussed in textbooks on electrodynamics. It keeps the balance between the kinetic energy of the beam and the energy of the electromagnetic field of the beam. We then consider the effect of this field on a beam generated in an RF gun and calculate the energy spread produced by this field in the beam.



Slides


TUPPH019 
Simulations for the LCLS Injector

260 

 Y. T. Ding, D. Dowell, P. Emma, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, P. Krejcik, H. Loos, A. Miahnahri, J. F. Schmerge, J. L. Turner, W. E. White, J. Wu, C. LimborgDeprey
SLAC, Menlo Park, California



The commissioning of the LCLS Injector has started this year. The electron beam quality for producing high power SASE Xrays is very challenging to reach. In this paper, we will describe comparisons between simulations made with multiparticle tracking code and electron beam measurements performed on the LCLS injector.

