BIW2012 - List of Authors (Loos, H.)

Paper	Title	Page
TUPG035	Evaluation of New, Fast Wire Scanner Designs for the LCLS	210
	P. Krejcik, M.L. Campell, N.W. Fong, J.C. Frisch, H. Loos SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DE-AC0276SF00515. Transverse beam size measurement for emittance tuning of the LCLS electron beam relies on wire scanners strategically placed on the beam line. It was originally intended to use Optical Transition Radiation (OTR) screens to obtain single shot measurements of the transverse beam size but it was soon discovered that the Coherent OTR that is a feature of ultra-short bunch length operation in linac FELs swamped the signal and rendered this diagnostic unusable. The original SLAC wire scanners that have been in operation for about 20 years are fairly slow and not optimized for the rapid measurements needed to monitor and fine tune the very small LCLS beam emittances, taking over a minute to complete a measurement in both planes. Two new wire scanner designs are being tested at LCLS that make use of state-of-the-art mechanical slides and position read-back systems to make fast, vibration-free measurements of the beam size. One uses an in-vacuum piezo-controlled linear slide and the other uses a dc linear servo motor coupled through a pair of vacuum bellows. The merits of the two designs are compared to the original SLAC design that relies on a ball screw driven by a stepping motor.

THBP01	Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflecting Cavity	264
	P. Krejcik, Y.T. Ding, J.C. Frisch, Z. Huang, H. Loos, J.W. Wang, M.-H. Wang SLAC, Menlo Park, California, USA C. Behrens DESY, Hamburg, Germany P. Emma LBNL, Berkeley, California, USA
	Funding: This work was supported by Department of Energy Contract No. DE-AC0276SF00515. The technique of streaking an electron bunch with a RF deflecting cavity to measure its bunch length is being applied in a new way at the Linac Coherent Light Source with the goal of measuring the femtosecond temporal profile of the FEL photon beam. A powerful X-band deflecting cavity is being installed downstream of the FEL undulator and the streaked electron beam will be observed at an energy spectrometer screen at the beam dump. The single-shot measurements will reveal which time slices of the streaked beam have contributed to the FEL process by virtue of their greater energy loss and energy spread relative to the non-lasing portions of the electron bunch. Since the diagnostic is located downstream of the undulator it can be operated continuously without interrupting the beam to the users. The resolution of the new X-band system will be compared to the existing S-band RF deflecting diagnostic systems at SLAC and consideration is given to the required RF phase stability tolerances required for acceptable beam jitter on the monitor. Simulation studies show that about 1 fs (rms) time resolution is achievable in the LCLS over a wide range of FEL wavelengths and pulse lengths.

Paper

Title

Page

Evaluation of New, Fast Wire Scanner Designs for the LCLS

210

P. Krejcik, M.L. Campell, N.W. Fong, J.C. Frisch, H. Loos
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy Contract No. DE-AC0276SF00515.
Transverse beam size measurement for emittance tuning of the LCLS electron beam relies on wire scanners strategically placed on the beam line. It was originally intended to use Optical Transition Radiation (OTR) screens to obtain single shot measurements of the transverse beam size but it was soon discovered that the Coherent OTR that is a feature of ultra-short bunch length operation in linac FELs swamped the signal and rendered this diagnostic unusable. The original SLAC wire scanners that have been in operation for about 20 years are fairly slow and not optimized for the rapid measurements needed to monitor and fine tune the very small LCLS beam emittances, taking over a minute to complete a measurement in both planes. Two new wire scanner designs are being tested at LCLS that make use of state-of-the-art mechanical slides and position read-back systems to make fast, vibration-free measurements of the beam size. One uses an in-vacuum piezo-controlled linear slide and the other uses a dc linear servo motor coupled through a pair of vacuum bellows. The merits of the two designs are compared to the original SLAC design that relies on a ball screw driven by a stepping motor.

THBP01

Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflecting Cavity

264

P. Krejcik, Y.T. Ding, J.C. Frisch, Z. Huang, H. Loos, J.W. Wang, M.-H. Wang
SLAC, Menlo Park, California, USA
C. Behrens
DESY, Hamburg, Germany
P. Emma
LBNL, Berkeley, California, USA

Funding: This work was supported by Department of Energy Contract No. DE-AC0276SF00515.
The technique of streaking an electron bunch with a RF deflecting cavity to measure its bunch length is being applied in a new way at the Linac Coherent Light Source with the goal of measuring the femtosecond temporal profile of the FEL photon beam. A powerful X-band deflecting cavity is being installed downstream of the FEL undulator and the streaked electron beam will be observed at an energy spectrometer screen at the beam dump. The single-shot measurements will reveal which time slices of the streaked beam have contributed to the FEL process by virtue of their greater energy loss and energy spread relative to the non-lasing portions of the electron bunch. Since the diagnostic is located downstream of the undulator it can be operated continuously without interrupting the beam to the users. The resolution of the new X-band system will be compared to the existing S-band RF deflecting diagnostic systems at SLAC and consideration is given to the required RF phase stability tolerances required for acceptable beam jitter on the monitor. Simulation studies show that about 1 fs (rms) time resolution is achievable in the LCLS over a wide range of FEL wavelengths and pulse lengths.