Krejcik, P.

Paper	Title	Page
WG502	Feedback Concepts: Experience at SPPS, LCLS Plans
	P. Krejcik, S. Allison, P. Emma, D. Fairley, J. Wu SLAC, Menlo Park, California
	The LCLS will operate with single bunches at a repetition rate of 120 Hz. The control system is designed to measure and respond to beam errors within the 8.3 ms between pulses. Single-shot, high-resolution measurements of the beam position are required for trajectory feedback control as well as beam energy control in the bunch compressor chicanes and dog-leg beam lines. A single-shot measurement of the bunch length at the exit of bunch compressor chicanes is also required to provide full feedback control of the longitudinal phase space. The amplitude and phases of linac klystrons are controlled pulse-by-pulse within one global feedback loop to maintain the correct energy and bunch length of the beam. The bunch length is determined from measurements of the coherent radiation of the beam, but the type of detector employed varies with bunch length at each location and hence wavelength of the coherent radiation. Experience has been gained with single-shot pyroelectric detectors at the SLAC Sub-Picosecond Pulsed Source (SPPS) and simple feedback control was implemented to stabilize the bunch length. The plans for implementing a full feedback system at LCLS will also be presented.
	Slides
WG517	X-ray Pulse Length Characterization Using the Surface Magneto Optic Kerr Effect	51
	P. Krejcik SLAC, Menlo Park, California
	It will be challenging to measure the temporal profile of the hard X-ray SASE beam independently from the electron beam in the LCLS and other 4th generation light sources. A fast interaction mechanism is needed that can be probed by an ultra-fast laser pulse in a pump-probe experiment. It is proposed to exploit the rotation in polarization of light reflected from a thin magnetized film, known as the surface magneto optic Kerr effect (SMOKE), to witness the absorption of the X-ray pulse in the thin film. The change in spin orbit coupling induced by the X-ray pulse occurs on the sub-femtosecond time scale and changes the polarization of the probe beam. The limitation to the technique lies with the bandwidth of the probe laser pulse and how short the optical pulse can be made. The SMOKE mechanism will be described and the choices of materials for use with 1.5 Å X-rays. A schematic description of the pump-probe geometry for X-ray diagnosis is also described.
	Slides
WG524	Cavity BPMs for LCLS
	P. Krejcik, Z. Li, S. Smith, T. Straumann SLAC, Menlo Park, California R. M. Lill ANL, Argonne, Illinois
	Stabilization and alignment of the beam trajectory in the LCLS undulator requires single-shot measurement of the beam position with a resolution of 1 micron or better at a charge per bunch of 200 pC. A stripline beam position monitor is limited by signal to noise at this resolution since it relies on determining the precise difference between the signals from two opposite strips. In our high Q cavity beam position monitor we selectively look at the signal from a transverse mode excited by an off-axis beam, which grows in amplitude proportionally with beam offset. The LCLS undulator and launch region will be equipped with 40 X-band cavity BPMS. A mixer is located beside each BPM and the IF is transmitted via cable to surface buildings housing the digitizer electronics. The design choices effecting the construction and layout of the system will be discussed along with prototype tests and installation plans for the LCLS.
	Slides