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| MOPPD046 | Lifetime of the Highly Efficient H− Ion Sources | 466 |
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Funding: Work supported by grant DE-SC0006267, and STFC JAI grant ST/G008531 Factors limiting operating lifetime of Compact Surface Plasma Sources (CSPS) are analyzed and possible treatments for lifetime enhancement are considered. CSPSs have high plasma density (up to 1014 cm-3), high emission current density of negative ions (up to 8 A/cm2), small (1–5 mm) gap between cathode emitter, and a small extraction aperture in the anode. They are very simple, have high energy efficiency up to 100 mA/kW of discharge (~100 times higher then modern large Volume RF SPS) and have a high gas efficiency (up to 30%) using pulsed valves. CSPSs are very good for pulsed operation but electrode power density is often too high for dc operation. However, CSPSs were successfully adopted for DC operation with emission current density ~300 mA/cm2 in Hollow cathode Penning Discharge and up to 1 A/cm2 in Spherical focusing semiplanotron. Flakes from electrodes sputtering and blistering induced by back accelerated positive ions are the main reasons of ion source failure. Suppression of back accelerated positive ions, flakes explosion by pulsed discharges, and flakes gasification by discharge in NF3 (or XeF2) can be used for significant increase of operating lifetime of CSPSs. |
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| MOPPD047 | Progress of Surface Plasma H− Ion Source with Saddle RF Antenna Plasma Generator | 469 |
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Funding: Supported in part by SBIR Grant 4729 · 09SC02690. Progress in development of RF H− surface plasma source (SPS) with saddle (SA) RF antenna which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability will be considered. Several versions of new plasma generators with a small Al2O3chamber and different antennas and magnetic field configurations were tested in the SNS small Test Stand. A prototype SA SPS was installed in the Test Stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency of 1.6 mA/kW. Control experiments with H− beam produced by SNS SPS with internal and external antennas in the similar conditions were conducted. A new version of the RF triggering plasma source (TPS) has been designed and fabricated. A Saddle antenna SPS with water cooling is being fabricated for high duty factor testing |
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| MOPPD048 | Ribbon Electron Beam Profile Monitor for Bunched Beam Tomography | 472 |
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Funding: Work supported by Contract DE-AC05-00OR22725 and by STTR grant DE-SC0007559 Advanced beam diagnostics are essential for high performance accelerator beam production and for reliable accelerator operation. It is important to have noninvasive diagnostics which can be used continuously with intense beams of accelerated particles. Recently, an electron probe was successfully used to determine accelerated particle density distributions. However, the apparatus used for this diagnostic is large and complex which restricts its wider use for tomography of accelerated bunches. We propose to use a strip cathode is for ribbon electron beam formation instead of a scanning of pencil beam used in the previous electron probe bunch profile monitors. The apparatus with the strip cathode is smaller, has simpler design and less expensive manufacturing, can have better magnetic shielding, higher sensitivity, higher resolution, can have better measurement accuracy and better time resolution. With this device it is possible to develop almost ideal tomography diagnostics of bunches in linear accelerators and in circular accelerators and storage rings. |
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| TUPPD043 | Resonant Reaction with a Superintense Circulating Beam | 1497 |
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| A system for efficient generation of resonance reaction in the interaction of the circulating ion beam with a thin internal target is considered. Features of this system are high intense space charge compensated circulating ion beam with an intensity greater then a space charge limit in a near integrable nonlinear focusing system. Ionization energy loss is compensated by inductive electric field. Multiple scattering and energy straggling are compensated by electron cooling with a tabular electron beam. In this method it is possible to compensate an energy loss of circulating particles after crossing the target and have a crossing of resonant energy in every passing of target. For sharp resonance reactions and monoenergetic beams a thin target method can increase greatly the energy efficiency. | ||
| TUPPD044 | Conceptual Gas Jet as a Stripping Target for Charge Exchange Injection | 1500 |
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| Stripping targets for charge exchange injection now uses thin carbon or Al2O3 foils. During long time injection for high intense beam accumulation by low current injection a foil life time can be compromised by overheating and alternative stripping targets need be developed. A pulsed supersonic gas jet was used as a stripping target in first realization of charge exchange injection with H− ion energy 1.5 MeV and stationary gas jets are used as internal targets in experiments with super high vacuum. A stripper target thickness is proportional to the injection energy and for energy 1GeV should be ~0.3 mg/cm2 of carbon. The pulsed gas target with such thickness acceptable for long time charge exchange injection can be produced with using of heavy hydrocarbon molecules used in the diffusion or booster vacuum pumps. Formation of the pulsed gas jet stripping targets will be considered. | ||
| TUPPD045 | Efficient Plasma Generation by Positive Circulating Beams | 1503 |
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| Performances of high brightness circulating beams are affected by development of strong “electron-proton” (e-p) instabilities connected with generation of an electron cloud (EC). For suppression of the EC generation it is proposed a coating of vacuum chambers by compounds with low secondary electron emission, which is very complex and expensive for large systems like LHC or RHIC. Threshold beam intensity for EC generation can be increased during the vacuum chamber bombarding by plasma particles generating by EC. Vacuum chamber processing (scrubbing) by EC is conducted by bunched beam with a highest possible intensity and with shortest gaps between bunches. Highly efficient plasma generation can be produced in the coasting circulating beam of positive particles with relative low intensity and energy. With the coasting positive beam the plasma particles are generating by low energy electrons trapped by a positive beam space charge. Dynamics of electrons and ions generation will be estimated and simulated. The rate of plasma generation and surface scrubbing can be increase by decrease of pumping and injection of selected gases. | ||
| TUPPD083 | Raising Photoemission Efficiency with Surface Acoustic Waves | 1596 |
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Funding: Supported in part by DOE STTR Grant DE-SC0006256. Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 We are developing a novel technique that may help increase the efficiency and reduce costs of photoelectron sources used at electron accelerators. The technique is based on the use of Surface Acoustic Waves (SAW) in piezoelectric materials, such as GaAs, that are commonly used as photocathodes. Piezoelectric fields produced by the traveling SAW spatially separate electrons and holes, reducing their probability of recombination, thereby enhancing the photoemission quantum efficiency of the photocathode. Additional advantages could be increased polarization provided by the enhanced mobility of charge carriers that can be controlled by the SAW and the ionization of optically-generated excitons resulting in the creation of additional electron-hole pairs. It is expected that these novel features will reduce the cost of accelerator operation. A theoretical model for photoemission in the presence of SAW has been developed, and experimental tests of the technique are underway. |
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