Transverse emittance measurements from a photocathode RF gun with variable laser pulse length

The gun test facility (GTF) at SSRL was started in 1996 to develop an appropriate injector for the proposed linac coherent light source (LCLS) at SLAC. The LCLS design requires the injector to produce a beam with at least 1 nC of charge in a 10 ps or shorter pulse with no greater than 1π mm mrad normalized rms emittance. The photoinjector at the GTF is 1.6 cell S-band symmetrized gun and emittance compensation solenoid. Emittance measurements, reported here, were made as function of laser pulse width using Gaussian longitudinal pulses. The lowest achieved emittance to date with 1 nC of charge is 5.6π mm mrad and was obtained with a pulse width of 5 ps (FWHM) and is in agreement with simulation. There are indications that the accelerator settings for these results may not have been optimal. Simulations also indicate that a normalized emittance meeting the LCLS requirement can be obtained using appropriately shaped transverse and temporal laser/electron beam pulses. Work has begun on producing temporal flat top laser pulses which combined with transverse clipping of the laser is expected to lower the emittance to approximately 1π mm mrad for 1 nC with optimal accelerator settings.

GTF
Photocathode
RF gun
LCLS
talk: Williamsburg 1998/08/16
electron: particle source
photoelectron
radiation: laser
beam emittance: transverse
beam monitoring: beam emittance

References(13)

Figures(0)

[1]

Performance and design concepts of a free electron laser operating in the X-ray region. In SPIE, Free-Electron Laser Challenges, volume 2988, pages 90 96, San Jose

M. Cornacchia

[2]

RF photocathode gun test facililty. In SPIE, Free-Electron Laser Challenges, volume 2988, pages 2 14, San Jose

J.F. Schmerge

[3]

Emittance Studies of the BNL UCLA 1.6 cell Photocathode rf Gun. In Particle Accelerator Conf

D.T. Palmer

[4]

Time-Bandwidth Products, model GLX-200, Zurich

[5]

Hamamatsu, model FESCA-500, streak camera

[6]

Intense electron emission due to picosecond laser-produced plasmas in high gradient electric fields

et al.

- J.Appl.Phys. 72 (1992) 888-894
•
DOI:
- 10.1063/1.351763

[7]

High quantum yield, low emittance electron sources. In 15th ICFA Advanced Beam Dynamics Workshop

J.E. Clendenin
,
G.A. Mulhollan

[8]

Therory and Design of Charged Particle Beams New York

M. Reiser

[9]

A high resolution Phosphor screen beam pro le monitor Trans., 32:2011, 1985

S. Yencho
,
D.R. Walz

[10]

New Photoelectric Injector Design For The Los Alamos National Laboratory XUV FEL Accelerator

B.E. Carlsten
(
- Los Alamos
)

- Nucl.Instrum.Meth.A 285 (1989) 313-319
•
DOI:
- 10.1016/0168-9002(89)90472-5

[11]

Emittance measurements for the gun test facility. In Particle Accelerator Conf

M. Hernandez

[12]

PARMELA, Lloyd Young, Los Alamos National Lab

[13]

High-energy pulse train and shaped pulse generator using a 100" throughput 2n-pulse Michelson interferometer. In Ultrafast Opt. Conf., Monterey, CA

C.W. Siders
,
A.J. Taylor