| Paper |
Title |
Page |
| TUP044 |
Shunt Impedance Measurement of the APS BBC Gun
|
346 |
| |
- Y.-E. S. Sun, J. W. Lewellen
ANL, Argonne, Illinois
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The Advanced Photon Source (APS) ballistic bunch compression (BBC) injector is presently in use as a beam source for a number of experiments, including THz generation, beam position monitor testing for the Linac Coherent Light Source (LCLS), novel cathode testing, and radiation therapy source development. The APS BBC gun uses three independently powered and phased rf cavities, one cathode cell and two full cells, to provide beam energies from 2 – 10 MeV with variable energy spread, energy chirp, and, to an extent, bunch duration. The shunt impedance of an rf accelerator determines how effectively the accelerator can convert supplied rf power to accelerating gradient. The calculation of the shunt impedance can be complicated if the beam energy changes substantially during its transit through a cavity, such as in a cathode cell. We present the results of direct measurements of the shunt impedance of the APS BBC gun on an individual cavity basis, including the cathode cell, as well as report on achieved gradients. We also present a comparison of the measured shunt impedance with theoretical values calculated from the rf models of the cavities.
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| TUP045 |
Photothermal Cathode Measurements at the Advanced Photon Source
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349 |
| |
- Y.-E. S. Sun, J. W. Lewellen
ANL, Argonne, Illinois
- D. W. Feldman
IREAP, College Park, Maryland
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| |
The Advanced Photon Source (APS) ballistic bunch compression (BBC) injector presently uses an M-type thermionic dispenser cathode as a photocathode. This “photothermal” cathode offers substantial advantages over conventional metal photocathodes, including easy replacement and easy cleaning via the cathode’s built-in heater. We present the results of quantum efficiency measurements as a function of cathode heater power, laser pulse energy, and applied rf field strength.
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| TUP058 |
The RF Design of a HOM Polarized RF Gun for the ILC
|
379 |
| |
- J. W. Wang, J. E. Clendenin, E. R. Colby, R. H. Miller
SLAC, Menlo Park, California
- J. W. Lewellen
ANL, Argonne, Illinois
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| |
The ILC requires a polarized electron beam. While a highly polarized beam can be produced by a GaAs-type cathode in a DC gun of the type currently in use at SLAC, JLAB and elsewhere, the ILC injector system can be simplified and made more efficient if a GaAs-type cathode can be combined with a low emittance RF gun. Since this type of cathode is known to be extremely sensitive to contamination including back bombardment by ions, any successful polarized RF gun must have a significantly improved operating vacuum compared to existing RF guns. We present a new RF design for an L-Band NC RF gun for the ILC polarized electron source. This design incorporates a higher order mode (HOM) structure, whose chief virtue in this application is an improved conductance for vacuum pumping on the cathode. Both 2-D and 3-D models have been used to optimize the RF parameters with two principal goals: first to minimize the required RF power; second to reduce the peak surface field relative to the field at the cathode in order to suppress field emitted electron bombardment. The beam properties have been simulated initially using PARMELA. Vacuum and cooling considerations for this design are discussed.
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| THP083 |
Generation of Ellipsoidal Beam Through 3-D Pulse Shaping of a Photoinjector Drive Laser
|
776 |
| |
- YL. Li, J. W. Lewellen
ANL, Argonne, Illinois
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| |
Due to the linear space-charge force, an ellipsoidal beam is expected to have much smaller emittance in comparison with beams of other geometries, which is critical for many accelerator applications. Up to now, no practical way of generating such beams is available. In this paper we present a few schemes for 3-D laser pulse shaping that can be used to generate ellipsoidal laser pulses that in turn can be applied for generating ellipsoidal electron bunches from a photoinjector. Our simulations show that 3D laser pulse shaping can be realized through laser phase tailoring in combination with properly designed refractive and diffractive optics. Performance of an electron beam generated from such shaped laser pulses is compared with that of the ideal flat-topped and Gaussian electron bunches by numerical simulation, showing improvement in both beam dynamics and performance.
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