13 research outputs found
Homdyn Study for the Lcls RF Photo-Injector
The authors report the results of a recent beam dynamics study, motivated by the need to redesign the LCLS photoinjector, that led to the discovery of a new effective working point for a split RF photoinjector. The HOMDYN code, the main simulation tool adopted in this work, is described together with its recent improvements. The new working point and its LCLS application is discussed. Validation tests of the HOMDYN model and low emittance predictions, 0.3 mm-mrad for a 1 nC flat top bunch, are performed with respect to the multi-particle tracking codes ITACA and PARMELA
Transverse emittance measurements on an S-band photoinjector rf electron gun
Proposed fourth generation light sources using SASE FELs to generate short
pulse, coherent, X-rays require demonstration of high brightness electron
sources. The Gun Test Facility (GTF) at SLAC was built to test high brightness
sources for the proposed Linac Coherent Light Source at SLAC. The transverse
emittance measurements are made at nearly 30 MeV by measuring the spot size on
a YAG screen using the quadrupole scan technique. The emittance was measured to
vary from 1 to 3.5 mm-mrad as the charge is increased from 50 to 350 pC using a
laser pulse width of 2 ps FWHM. The measurements are in good agreement with
simulation results using the LANL version of PARMELA.Comment: 12 pages, 4 figures, contributed to The 23rd Int. FEL Conf.,
Darmstadt, 20-24 Aug. 200
Recent Progress at SLAC Extracting High Charge from Highly-Polarized Photocathodes for Future-Collider Applications
Future colliders such as NLC and JLC will require a highly-polarized
macropulse with charge that is more than an order of magnitude beyond that
which could be produced for the SLC. The maximum charge from the SLC
uniformly-doped GaAs photocathode was limited by the surface charge limit
(SCL). The SCL effect can be overcome by using an extremely high (>1019 cm-3)
surface dopant concentration. When combined with a medium dopant concentration
in the majority of the active layer (to avoid depolarization), the surface
concentration has been found to degrade during normal heat cleaning (1 hour at
600 C). The Be dopant as typically used in an MBE-grown superlattice cathode is
especially susceptible to this effect compared to Zn or C dopant. Some relief
can be found by lowering the cleaning temperature, but the long-term general
solution appears to be atomic hydrogen cleaning.Comment: 11 pages, 3 figures, 1 table, contributed to 10th Workshop on
Polarized Sources and Targets, Novosibirsk, Sept. 22-26, 2003, to be
submitted to Nucl. Instrum. and Meth.
Photoinjector design for the LCLS
The design of the Linac Coherent Light Source assumes that a low-emittance,
1-nC, 10-ps beam will be available for injection into the 15-GeV linac. The
proposed rf photocathode injector that will provide a 150-MeV beam with rms
normalized emittances of 1 mm in both the transverse and longitudinal
dimensions is based on a 1.6-cell S-band rf gun that is equipped with an
emittance compensating solenoid. The booster accelerator is positioned at the
beam waist coinciding with the first emittance maximum and is provided with an
accelerating gradient of ~25 MeV/m, i.e., the "new working point." The uv
pulses required for cathode excitation will be generated by tripling the output
of a Ti:sapphire laser system consisting of a highly stable cw mode-locked
oscillator and two bow-tie amplifiers pumped by a pair of Q-switched Nd:YAG
lasers. The large bandwidth of the Ti:sapphire system accommodates the desired
temporal pulse shaping. Details of the design and the supporting simulations
are presented.Comment: 13 pages (double spaced), 4 figures, contributed to The 23rd
International Free Electron Laser Conference, Darmstadt, Germany, 20-24
August 200
A source of highly polarized electrons at the Stanford Linear Accelerator Center
Alguard MJ, Clendenin JE, Ehrlich RD, et al. A source of highly polarized electrons at the Stanford Linear Accelerator Center. Nucl.Instrum.Methods. 1979;163(1):29-59
Homdyn study for the LCLS RF photo-injector
Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Istituto Nazionale di Fisica Nucleare, Via E. Fermi, 40 -Frascati - Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
COMPARISON OF ALINGAAS/GAAS SUPERLATTICE PHOTOCATHODES HAVING LOW CONDUCTION BAND OFFSET *
The main advantage of superlattice (SL) structures as spin polarized electron emitters is the ability to provide a large splitting between the heavy hole (HH) and light hole (LH) valence bands (VB) over a large active thickness compared to single strained layers. Two important depolarization mechanisms in these structures are the scattering effects during the transit of the electrons in the active region and the depolarization that takes place in the band bending region (BBR) near the surface. In this paper, we systematically study the effects of the electron mobility and transit time by using an InAlGaAs/GaAs SL with a flat conduction band (CB). Initial results by the SPTU-SLAC collaboration using such structures grown by the Ioffe Institute showed polarization and quantum yield (QE) of 92 % and 0.2 % respectively. We report measurements using similar structures grown by SVT Associates. The results (polarization up to 90%) are also compared with simulations. 1