| Paper | Title | Page |
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| MOPAC12 | Analysis of High Repetition Rate Effects in Dielectric Wakefield Accelerators | 93 |
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| Recently the question has arisen of whether dielectric charging might become a significant limiting effect on the performance of the dielectric wakefield undulator, leading either to deflection of the beam by the static electric field generated, or to catastrophic breakdown of the structure. In experiments to date this has not been problematic with appropriate choice of dielectric material. However, given the high repetition rate that would be required, the device would be subjected to essentially a dc bombardment from the beam halo and thus be vulnerable to these effects because there is no time between machine pulses for discharge of the dielectric. We have begun reexamining this problem, emphasizing the expected charging rate and charge distribution in a thin walled dielectric device and the physics of conductivity and discharge phenomena in a dielectric medium. Simulations of the charging process and halo formation will be presented. We will review early work on beam-induced charging of dielectric structures and also results from deep charging of satellite components by cosmic rays. Ageing and induced conductivity under large radiation doses are also investigated. | ||
| TUPSM05 | Studies of Field and Photo-Emission in a New Short-Pulse, High-Charge Cs2Te RF Photocathode Gun | 637 |
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Funding: This work was funded by the U.S. Dept. of Energy Office of Science under contract number Agency DE-AC02-06CH11357. A new high-charge RF gun is now operating at the Argonne Wakefield Accelerator (AWA) facility at Argonne National Laboratory (ANL). The 1.5 cell 1.3 GHz gun uses a Cesium telluride photocathode driven with a 248 nm laser to provide short-pulse, high charge electron beams for the new 75 MeV drive beamline. The high-gradient RF gun (peak field on the cathode > 80MV/m) is a key piece of the facility upgrade (see M. E. Conde, this proceedings). The large Cs2Te photocathode (diameter > 30 mm) is fabricated in-house. The photo-injector generates high-charge, short pulse, single bunches (Q > 100 nC) or bunch-trains (Q > 1000 nC) for wakefield experiments, typically involving dielectric-loaded accelerating structures. Field-emitted dark current from the Cs2Te cathode was measured during RF conditioning. Fowler-Nordheim plots of the data are presented and compared to similar measurements made using a copper cathode in the initial phase of conditioning. Results of quantum efficiency (QE) studies are presented with the cathode operating in both single and bunch-train modes. |
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| WEPMA08 | Tuning, Conditioning, and Dark Current Measurements of the 1300 MHz NCRF Cavities at Argonne Wakefield Accelerator (AWA) Facility | 996 |
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Six normal-conducting, L-band rf cavities have recently been commissioned as part of the upgrade to the AWA facility *. The cavity design is a seven-cell, standing-wave, 1300 MHz cavity made with OFE copper and was reported on earlier **. In this paper, we present data on: (i) tuning and balancing; (ii) high-power rf conditioning; and (iii) dark current measurements; of the cavities. All six cavities were tuned to 1300 MHz and were balanced to >96% in all cells. They are designed to operate with 10 MW of rf input power but were conditioned beyond this operating point to insure low dark current during operation. During rf conditioning, we recorded the arcing history to better understand the overall conditioning time and the final breakdown rate. Finally, dark current measurements were used to measure the cavity’s surface field enhancement factor, “beta” throughout rf conditioning to record how the condition of the surface evolved during rf conditioning.
* M.E. Conde et al., see these proceedings. ** J.G. Power et al., in proceedings of IPAC 2010 |
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