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ABSTRACT: The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center. Comparisons between measurements and the predictions of design codes are made.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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ABSTRACT: ORION will be a user-oriented research facility for understanding the physics and developing the technology for future high-energy particle accelerators, as well as for research in related fields. The facility has as its centerpiece the Next Linear Collider Test Accelerator (NLCTA) at the Stanford Linear Accelerator Center (SLAC). The NLCTA will be modified with the addition of a new, high-brightness photoinjector, its drive laser, an S-band rf power system, a user laser room, a low-energy experimental hall supplied with electron beams up to 60 MeV in energy, and a high-energy hall supplied with beams up to 350 MeV. The facility design and parameters are described here along with highlights from the 2nd ORION Workshop held in February 2003.
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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P. R. Bolton,
J. E. Clendenin,
D. H. Dowell,
M. Ferrario,
A. S. Fisher,
S. M. Gierman,
R. E. Kirby,
P. Krejcik,
C. G. Limborg,
G. A. Mulhollan,
D Nguyen, D.T. Palmer,
J.B. Rosenzweig,
J. F. Schmerge,
L. Serafini,
X.J. Wang
[show abstract]
[hide abstract]
ABSTRACT: 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 2001
08/2001;
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D.T. Palmer,
E. Colby,
M. Hogan,
R. Noble,
R.H. Siemann,
J. Spencer,
D. Walz,
C. Joshi,
W. Mori,
J.B. Rosenzweig,
T. Katsouleas,
P. Muggli,
R. Byer
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ABSTRACT: Extending the center-of-mass energy frontier for high-energy
physics depends on the research and development that is conducted now in
the area of advanced accelerator physics and technology. In this
article, we present the design and beam dynamics simulations for the
emittance-compensated, RF photoinjector of the ORION Facility
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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M. Ferrario,
P. R. Bolton,
J. E. Clendenin,
D. H. Dowell,
S. M. Gierman,
M. E. Hernandez,
D Nguyen, D.T. Palmer,
J.B. Rosenzweig,
J. F. Schmerge,
L. Serafini
[show abstract]
[hide abstract]
ABSTRACT: We report the results of a recent beam dynamics study, motivated by the need to redesign the LCLS photoinjector, that lead to the discovery of a new effective working point for a split RF photoinjector. We consider the emittance compensation regime of a space charge beam: by increasing the solenoid strength, the emittance evolution shows a double minimum behavior in the drifting region. If the booster is located where the relative emittance maximum and the envelope waist occur, the second emittance minimum can be shifted to the booster exit and frozen at a very low level (0.3 mm-mrad for a 1 nC flat top bunch), to the extent that the invariant envelope matching conditions are satisfied. Standing Wave Structures or alternatively Traveling Wave Structures embedded in a Long Solenoid are both candidates as booster linac. A careful measurement of the emittance evolution as a function of position in the drifting region is necessary to verify the computation and to determine experimentally the proper position of the booster cavities. The new design study and supporting experimental program under way at the SLAC Gun Test Facility are discussed.
08/2000;
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R. Alley,
V. Bharadwaj,
J. Clendenin,
P. Emma,
A Fisher,
J Frisch,
T. Kotseroglou, D.T. Palmer,
J. Schmerge,
M. Woodley,
A D Yeremian,
J. Rosenzweig,
D. D. Meyerhofer,
L. Serafini
[show abstract]
[hide abstract]
ABSTRACT: We report on the design of the rf photoinjector of the Linac Coherent Light Source (LCLS). The rf photoinjector is required to produce a single 150 MeV bunch of ~1 nC and ~100 A peak current at a repetition rate of 120 Hz with a normalized rms transverse emittance of ~1 p mm-mrad. The design employs a 1.6-cell S-band rf gun with an optical spot size at the cathode of a radius of ~1 mm and a pulse duration with an rms sigma of ~3 ps. The peak rf field at the cathode is 150 MV/m with extraction 57 o ahead of the rf peak. A solenoidal field near the cathode allows the compensation of the initial emittance growth by the end of the injection linac. Spatial and temporal shaping of the laser pulse striking the cathode will reduce the compensated emittance even further. Also, to minimize the contribution of the thermal emittance from the cathode surface, while at the same time optimizing the quantum efficiency (QE), the laser wavelength for a Cu cathode should be tunable around 260 nm. Follo...
03/1999;
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[hide abstract]
ABSTRACT: Low power RF measurements, S11, of electro-discharge machined
(EDM) diffusion bonded mm-wave traveling wave RF cavities were not in
satisfactory agreement with electromagnetic simulations. During
subsequent mechanical inspection, the cell-to-cell iris were found to be
distorted. This led to a series of systematic experiments to study the
mechanical properties of oxygen free high conductivity copper and
Glidcop AL-15. Results of these studies which include cell-to-cell iris
distortion, EDM machining accuracies, surface quality, and the results
of different bonding techniques are presented. The results of our
mechanical studies are used to develop a set of mechanical design
constraints for a second series of constant impedance W-band structures
that also used wire EDM and high temperature bonding for their
manufacture
Particle Accelerator Conference, 1999. Proceedings of the 1999; 02/1999
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ABSTRACT: Photocathode RF guns depend on mode locked laser systems to
produce an electron beam at a given phase of the RF. In general, the
laser pulse is less than σ<sub>2</sub>=10° of the RF phase in
length and the required stability is of the order of
Δφ=1°. At 90 GHz (W-band), these requirements correspond
to σ<sub>z</sub>=333 fsec and Δφ=33 fsec. A laser system
with pulse lengths in the fsec regime is commercially available, the
timing stability is a major concern. We propose a multi-cell W-band
photoinjector that does not require a mode locked laser system, thereby
eliminating the stability requirements at W-band
Particle Accelerator Conference, 1999. Proceedings of the 1999; 02/1999
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[hide abstract]
ABSTRACT: The beam dynamics of an integrated S-band RF photoinjector based
on the plane wave transformer (PWT) concept, proposed as part of an SBIR
collaboration between UCLA and DULY Research, are studied. The design,
which calls for an 11.5 cell structure run at a peak accelerating field
of 60 MV/m and uses a compact solenoid around the initial 2.5 cells, is
based on a recently developed theory of emittance compensation. It calls
for matching the beam onto a generalized equilibrium envelope, which
produces a beam which diminishes in transverse size monotonically with
acceleration. This condition minimizes the emittance, which is 1 mm-rad
at Q=1 nC. This design is also scaled to produce nearly identical
performance at X-band, giving an injector appropriate to running an FEL
at the SLAC NLCTA. These designs are insensitive to RF emittance
increase, allowing a wide choice of injection phase, and the option to
compress the emitted pulse
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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[show abstract]
[hide abstract]
ABSTRACT: The Linac Coherent Light Source (LCLS) will use the last portion
of the SLAC accelerator as a driver for a short wavelength FEL. The
injector must produce 1-nC, 3-ps rms electron bunches at a repetition
rate of up to 120 Hz with a normalized rms emittance of about 1 mm-mrad.
The injector design takes advantage of the photocathode RF gun
technology developed since its conception in the mid 1980's, in
particular the S-band RF gun developed by the SLAC/BNL/UCLA
collaboration, and emittance compensation techniques developed in the
last decade. The injector beamline has been designed using the
SUPERFISH, POISSON, PARMELA, and TRANSPORT codes in a consistent way to
simulate the beam from the gun up to the entrance of the main
accelerator linac where the beam energy is 150 MeV. PARMELA simulations
indicate that at 150 MeV, space charge effects are negligible
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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[show abstract]
[hide abstract]
ABSTRACT: Polarized electron beams will play a crucial role in maximizing
the physics potential for future e<sup>+</sup>/e<sup>-</sup> linear
colliders. We review the SLC polarized electron source (PES), present a
design for a conventional PES for the Next Linear Collider (NLC), and
discuss the physics issues of a polarized RF gun
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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[show abstract]
[hide abstract]
ABSTRACT: A new iron dominated single emittance compensation solenoidal
magnet was designed to be integrated with the BNL/SLAC/UCLA 1.6 cell
S-Band photocathode RF gun. This emittance compensated photoinjector is
now in operation at the Brookhaven Accelerator Test Facility. It has
produced a 0.329±0.012 pC, τ<sub>95%</sub>=10.9 psec electron
bunches with a normalized RMS transverse emittance of ε<sub>n,rms
</sub>=1.17±0.16 π mm mrad. POISSON field maps were used with
PARMELA to optimize the emittance compensation solenoidal magnet design.
Magnetic field measurements show that at the cathode plane
B<sub>z</sub>⩽10 G for a peak magnetic field of B<sub>z,max</sub>=3
kG. Which is in agreement with POISSON simulation. A single emittance
compensation solenoidal magnet will produce a initial angular momentum
of the electron bunch that manifests itself in a initial magnetic
emittance term that cannot be eliminated. This magnetic emittance
ε<sub>n,rms</sub><sup>mag</sup> scales as 0.010 (π mm mrad)/G
at the cathode, which is in agreement with PARMELA simulations.
Experimental beam dynamics results are presented that shows relative
angular rotation and spot size as a function of cathode magnetic field.
These results are compared to theory
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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D.T. Palmer,
X.J. Wang,
R.H. Miller,
M. Babzien,
I. Ben-Zvi,
C. Pellegrini,
J. Sheehan,
J. Skaritka,
H. Winick,
M. Woodle,
V. Yakimenko
[show abstract]
[hide abstract]
ABSTRACT: The symmetrized 1.6 cell S-band photocathode gun developed by the
BNL/SLAC/UCLA collaboration is in operation at the Brookhaven
Accelerator Test Facility (ATF). A novel emittance compensation solenoid
magnet has also been designed, built and is in operation at the ATF.
These two subsystems form an emittance compensated photoinjector used
for beam dynamics, advanced acceleration and free electron laser
experiments at the ATF. The highest acceleration field achieved on the
copper cathode is 150 MV/m, and the guns normal operating field is 130
MV/m. The maximum rf pulse length is 3 μs. The transverse emittance
of the photoelectron beam were measured for various injection
parameters. The 1 nC emittance results are presented along with electron
bunch length measurements that indicated that at above the 400 pC, space
charge bunch lengthening is occurring. The thermal emittance, ε
<sub>0</sub>, of the copper cathode has been measured
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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[show abstract]
[hide abstract]
ABSTRACT: In this paper, we present the preliminary results of the
performance of the magnesium cathode in a high frequency RF gun. The
quantum efficiency of Mg showed a dramatic improvement upon laser
cleaning, increasing from 10<sup>-5</sup> to 4×10<sup>-4</sup>
after two hours of cleaning, and to 2×10<sup>-3</sup> after
systematic cleaning. The cleaning procedure for this increase is
described in detail. Charge measured as a function of the laser
injection phase relative to the RF phase indicates that the temporal
variation of the field on the cathode both due to the RF and the
shielding effect of the emitted electrons play a critical role in the
emission and extraction of electrons. A model that includes this
variation is numerically fitted to the measured charge and the results
are presented. The unexpected outcome of the fit was the low field
enhancement factor (0.1) predicted by the model for the photoemission.
The physical origin of this is still under investigation
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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[show abstract]
[hide abstract]
ABSTRACT: A 1.6 cell photocathode S-Band gun developed by the BNL/SLAC/UCLA
collaboration is now in operation at the Brookhaven Accelerator Test
Facility (ATF). One of the main features of this RF gun is the
symmetrization of the RF coupling iris with a identical vacuum pumping
port located in the full cell. The effects of the asymmetry caused by
the RF coupling iris were experimentally investigated by positioning a
metallic plunger at the back wall of the vacuum port iris. The higher
order modes produced were studied using electron beamlets with 8-fold
symmetry. The 8-fold beamlets were produced by masking the laser beam.
These experimental results indicate that the integrated electrical
center and the geometrical center of the gun are within 175 μm,.
which is within the laser alignment tolerance of 250 μm
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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M. Hernandez,
A. Fisher,
D. Meyerhofer,
R. Miller, D.T. Palmer,
S. Park,
D. Reis,
J. Schmerge,
J. Weaver,
H. Wiedermann,
H. Winick,
D. Yeremian
[show abstract]
[hide abstract]
ABSTRACT: The requirement of a high brightness electron source for the
proposed Linac Coherent Light Source (LCLS) project at SLAC has led to
the development of the Gun Test Facility (GTF). The facility consists of
a photocathode RF gun, emittance compensation solenoid, a single 3-meter
SLAC S-band linac section, a single XK-5 klystron, low and high energy
diagnostic sections and a cathode drive laser. In this paper, the
specifications of the desired electron beam are discussed along with
results of PARMELA simulations to determine the optimum laser pulse
shape for minimum beam emittance. The diagnostics of the GTF are
discussed and measurements are presented which were made at the SUNSHINE
Facility at Stanford to develop the instrumentation to be used at the
Gun Test Facility once it is operational. Future beam diagnostics are
also discussed
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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D.T. Palmer,
R.H. Miller,
C. Pellegrini,
H. Winick,
X.J. Wang,
M. Babzien,
I. Ben-Zvi,
J. Sheehna,
J. Skaritka,
M. Woodle,
V. Yakimenko
[show abstract]
[hide abstract]
ABSTRACT: The Next Generation Photoinjector (NGP) developed by the BNL SLAC / UCLA collaboration was installed at the Brookhaven National Laboratories Accelerator Test Facility (ATF). The commissioning results and performance of the photocathode injector are present. The Next Generation Photoinjector consists of the symmetrized BNL/SLAC/UCLA 1.6 cell S-band Photocathode RF gun and a single solenoidal magnet for transverse emittance compensation. The highest acceleration field achieved on the cathode is 150 m V, and the RF guns normal operating field is 130 MV/m. The quantum efficiency of the copper cathode was measured to be 4.5 x 10{sup -5}`. The transverse emittance and bunch length of the photoelectron beam were measured. The optimized rms normalized emittance for a charge of 300 pC is 0.77 {pi} mm mrad. The bunch length dependency of photoelectron beam on the RF gun phase and acceleration fields were experimentally investigated.
11/1996
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[show abstract]
[hide abstract]
ABSTRACT: A dedicated low energy (2 to 10 MeV) experimental beam line is now
under construction at Brookhaven National Laboratories Accelerator Test
Facility (BNL/ATF) for photocathode RF gun testing and photoemission
experiments. The design of the experimental line, using the 1.6 cell
photocathode RF gun developed by the BNL/SLAC/UCLA RF gun collaboration
is presented. Detailed beam dynamics simulations were performed for the
1.6 cell RF gun injector using a solenoidal emittance compensation
technique. An experimental program for testing the 1.6 cell RF gun is
presented. This program includes beam loading caused by dark current,
higher order mode field measurements, integrated and slice emittance
measurements using a pepper-pot and RF kicker cavity
Particle Accelerator Conference, 1995., Proceedings of the 1995; 06/1995
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[show abstract]
[hide abstract]
ABSTRACT: The longitudinal accelerating field E<sub>z</sub> has been
measured as a function of azimuthal angle in the full cell of the cold
test model for the 1.6 cell BNL/SLAC/UCLA 3 S-band RF gun using a needle
rotation/frequency perturbation technique. These measurements were
conducted before and after symmetrizing the full cell with a vacuum pump
out port and an adjustable short. Two different waveguide to full cell
coupling schemes were studied. The dipole mode of the full cell is an
order of magnitude less severe before symmetrization for the
θ-coupling scheme. The multi-pole contribution to the
longitudinal field asymmetry are calculated using standard Fourier
series techniques. The Panofsky-Wenzel theorem is used in estimating the
transverse emittance due to the multipole components of E<sub>z</sub>
Particle Accelerator Conference, 1995., Proceedings of the 1995; 06/1995
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P.R. Bolton,
J.E. Clendenin,
D.H. Dowell,
M. Ferrario,
A.S. Fisher,
S.M. Gierman,
R.E. Kirby,
P. Krejcik,
C.G. Limborg,
G.A. Mulhollan,
D. Nguyen, D.T. Palmer,
J.B. Rosenzweig,
J.F. Schmerge,
L. Serafini,
X.-J. Wang
[show abstract]
[hide abstract]
ABSTRACT: 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 meet this requirement is based on a 1.6-cell S-band rf gun equipped with an emittance-compensating solenoid. The booster accelerator with a gradient of 25 MV/m is positioned at the beam waist coinciding with the first emittance maximum, 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. Details of the design and the supporting simulations are presented.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
