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| MO3001 | Intense Heavy-Ion Beam Production with ECR Sources | ion, electron, ion-source, coupling | 18 | ||
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An average increase of about one order of magnitude per decade in the performance of ECR ion sources was obtained up to now since the time of pioneering experiment of R. Geller at CEA Grenoble and this trend is not deemed to get the saturation at least in the next decade, according to the increased availability of powerful magnets and microwave generators. Electron density above 1013 cm-3 can be obtained by 28 GHz microwave heating, but only an adequate plasma trap may allow to exploit that plasma for heavy elements ionization. A study about the optimization of the magnetic field and of the other different parameters affecting the ECRIS plasma is presented, with a special emphasis on the coupling of microwaves to plasma. Long-term perspectives are presented finally, with an analysis of the possibilities opened by higher frequency generators, as 60 GHz gyro-TWTs, with the use of moderate confinement trap, by combining the large plasma density with larger escape rates in order to get larger ion beam currents.
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| MOP026 | Positron Source from X-rays Emitted by Plasma Betatron Motion | positron, electron, photon, ion | 94 | ||
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A new method for generating positrons has been proposed that uses betatron X-rays emitted by an electron beam in a high-K plasma wiggler. The plasma wiggler is an ion column produced by the head of the beam when the peak beam density exceeds the plasma density. The radial electric field of the beam blows out the plasma electrons transversely, creating an ion column. The focusing electric field of the ion column causes the beam electrons to execute betatron oscillations about the ion column axis. At the proper plasma density, this leads to synchrotron radiation in the 1-50 MeV range. These photons strike a thin (.5Xo), high-Z target and create electron-positron pairs. A computational model was written and matched with experimental results taken at the Stanford Linear Accelerator Center. This model was then used to design a more efficient positron source, giving positron yields of 0.44 positrons/electron, a number that is close to the target goal of 1-2 positrons/electron for future positron sources.
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| MOP029 | Laser Beat-Wave Microbunching of Relativistic Electron Beam in the THz Range | electron, laser, undulator, radiation | 100 | ||
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Laser-driven plasma accelerators have recently demonstrated a ~1GeV energy gain of self-trapped electrons in a several-centimeter-long plasma channel. Potential staging of such devices will require external injection of an electron beam prebunched on the scale of 1-10 THz into a plasma accelerating structure or plasma LINAC. Seeded FEL/IFEL techniques can be used for modulation of the electron beam longitudinally on the radiation wavelength. However a seed source in this spectral range is not available. At the UCLA Neptune Laboratory a Laser Beat-Wave (LBW) microbunching experiment has begun. Interaction of the electron beam and the LBW results in ponderomotive acceleration and energy modulation on the THz scale. This stage is followed by a ballistic drift of the electrons, where the gained energy modulation transfers to the beam current modulation. Then the beam is sent into a 33-cm long undulator, where a coherent start-up of THz radiation takes place providing efficient bunching of the whole beam. The performance of LBW bunching is simulated and analyzed using 3D FEL code for the parameters of an existing photoinjector and two-wavelength TW CO2 laser system.
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| TU1004 | Development of High-Current, High-Duty-Factor H- Injectors | emittance, SNS, ion, electron | 213 | ||
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SNS, FNAL, and CERN have projects that require the production of H- beams with increased intensity and increased duty factors. The most demanding requirements are set by SNS, which plans to upgrade its power to 3 MW. This power level requires a LINAC peak current of 59 mA, which results from an RFQ input current between 67 and 95mA when injecting with rms-emittances between 0.20 and 0.35 Pi-mm-mrad, respectively. Predicted downstream losses exclude the use of higher emittance beams. Ion source lifetime and reliability requirements are also stringent to meet the 99.5% availability goal for the injector of a user facility with 95% availability. LEBT options are currently being studied to optimally match the ion source output into the RFQ with a minimal distortion of the beam emittance. Several ion source and LEBT options under consideration will be discussed.
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| TU2002 | Laser-Based Heavy Ion Production | ion, laser, rfq, target | 219 | ||
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We have focused on high brightness of induced plasma in Laser Ion Source (LIS) to provide intense highly charged ions efficiently. To take the advantage of the intrinsic density of the laser plasma, Direct Plasma Injection Scheme (DPIS) has been developed. The induced laser plasma has initial expanding velocity and can be delivered directly to the RFQ. Extraction electrodes and focusing devices in LEBT are not needed. Since 2004, a newly designed RFQ has been used to verify the capability of the new ion production scheme. We succeeded to accelerate 60 m A of Carbon beam and 60 mA of Aluminium beam. We have also tried to understand plasma properties of various species by measuring charge states distributions and time structures, and are now ready to accelerate heavier species. Currently Silver 15+ beam is planned to be accelerated. In the conference, design strategies and detailed techniques for the DPIS will be described based on the measured plasma properties of various elements and new findings obtained from recent acceleration experiments. The durability and the reproducibility will be also explained.
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| TUP053 | Initial Tests of an Elemental Cs-System for the SNS Ion Source | ion, SNS, ion-source, injection | 364 | ||
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The ion source employed in the Spallation Neutron Source* (SNS) is an RF-driven, Cs-enhanced, multi-cusp H- source. To date, the source has been successfully utilized in the commissioning of the SNS accelerator producing 10–40 mA. Presently, Cs is dispensed within the source using Cs2CrO4 cartridges located in an air heated/cooled cylindrical collar surrounding the outlet aperture. The temperature of the collar is elevated to release Cs into the source. Typically, this process can only be repeated 2-3 times before the Cs is depleted and the source needs to be replaced. In addition, the dispensers are subject to poisoning by the residual gases in the source leading to beam decay. This is especially problematic at high duty-factor. This report describes the design of an elemental Cs system incorporating an external reservoir based on the proven Fermilab system. Source performance is characterized and compared for both the original and the elemental Cs systems.
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| TUP054 | A Proposed Helicon Driver for the SNS Ion Source | SNS, ion, ion-source, extraction | 367 | ||
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The H- ion source employed in the Spallation Neutron Source* (SNS) is an RF-driven, multi-cusp source, which utilizes a helical antenna to inductively couple power into the source plasma. To date, the source has been successfully utilized in the commissioning of the SNS accelerator producing 10–40 mA of H- with duty-factors of ~0.1%. Ultimately, the SNS facility will require beam duty-factors of 6% and ~60 mA of H- injecting the linac. This may require currents of up to ~100 mA from the source depending on the ion source emittance. To date, the SNS source has only delivered sustained currents of ~33 mA at full duty factor. Therefore, we are developing plasma generators capable of achieving much higher plasma densities. Plasmas generated through helicon-wave coupling can develop densities up to 100 times greater than those produced by conventional inductive coupling. This report presents an initial design and discusses considerations for a source which combines the forward portion of the SNS source with a helicon system. The helicon system consists largely of components retrofitted from the proven hydrogen VASIMR system employed in space propulsion.
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| TUP055 | A Plasma Gun Driver for the SNS Ion Source | ion, gun, ion-source, SNS | 370 | ||
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The ion source developed for the Spallation Neutron Source (SNS) is an RF-driven, multi-cusp source designed to produce ~ 40 mA of H- with a normalized rms emittance of less than 0.2 π mm mrad. To date, the source has been successfully utilized in the commissioning of the SNS accelerator producing 10–40 mA of H- with duty-factors of ~0.1%. Recently, we found the H- yield from the source could be increased dramatically with the introduction of streaming plasma particles injected into the primary RF plasma from a hemispherical glow discharge chamber located in the rear of the source. In some cases, a 50% increase in the H- beam current was observed. The system also eliminated the need for other plasma ignition systems like a secondary low-power RF generator. This report details the design of the plasma gun as well as the parametric dependence of H- current on source operating conditions. Comparisons are made with and without the gun energized. Finally, an off-line test stand was employed to characterize the plasma current emitted directly from the gun as well as perform lifetime characterization.
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SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy. |
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| TUP056 | The Development of a High-Power, H- Ion Source for the SNS-Based on an External Antenna | SNS, ion, ion-source, gun | 373 | ||
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The ion source developed for the Spallation Neutron Source* (SNS) is a radio frequency, multi-cusp H- source, which utilizes an internal antenna immersed within the source plasma. To date, the source has been utilized successfully in commissioning of the SNS accelerator delivering 10 - 40 mA with duty-factors of ~0.1% for periods of several weeks. Ultimately, the SNS facility will require beam currents of ~60 mA at 6% duty-factor. Tests have shown that the internal antenna is susceptible to failure at this duty-factor. Currently, two ion sources are being developed which feature ceramic plasma chambers surrounded by an external antenna. The first is a low-power, test version which employs a high-inductance external antenna and produces considerably higher H- beam currents than the original SNS source when both are operated without Cs. The second is a high-power version which features a Faraday shield with an integrated magnetic confinement structure and is designed to operate at full duty factor. The performance of this source should also greatly exceed that of the present SNS source. Details of the design and the measured performance of each source are discussed.
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| TUP061 | The HERA RF-Driven Multicusp H- Ion Source | electron, vacuum, coupling, SNS | 388 | ||
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The HERA RF-Volume Source is the only source that delivered routinely a H- current of 40 mA without Cs. This current has been improved to 60 mA. For HERA a pulse length of less than 200 μsec is necessary. It was possible to demonstrate a pulse length of 3 msec with the HERA source at DESY in a cooperation with SNS, FNAL and CERN. RF H- sources are now in permanent use for accelerators like HERA or SNS. The reliability of these sources becomes very important. Special techniques for a reliable external RF coupling to the plasma, ignition, filter field, collar transition for extraction and electron dumping have been developed at DESY. The physics of the extraction plasma region was the subject of very detailed investigations with special sets of collars, cones and Langmuir probes.
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| WE2001 | Neutralized Drift Compression Experiments (NDCX) | ion, simulation, vacuum, acceleration | 492 | ||
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Intense ion beams offer an attractive approach to heating dense matter uniformly to extreme conditions, because their energy deposition is nearly classical and volumetric. Simultaneous transverse and longitudinal beam compression, in a neutralizing plasma medium, along with rapid beam acceleration, are being studied as a means of generating such beams, which will be used for warm dense matter (WDM), high energy density physics (HEDP), and fusion studies. Recently completed experiments on radial and longitudinal compression demonstrated significant enhancements in beam intensity. In parallel with beam compression studies, a new accelerator concept, the Pulse Line Ion Accelerator (PLIA), potentially offers cost-effective high-gradient ion beam acceleration at high line charge density. We report experimental results on beam neutralization, neutralized focusing, neutralized drift compression from a series of experiments. We also report energy gain and beam bunching in the first beam dynamics validation experiments exploring the PLIA.
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| THP021 | Study of Vacuum Insulator Flashover for Pulse Lengths of Multi-Microseconds | cathode, vacuum, electron, diagnostics | 610 | ||
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We have studied the flashover of vacuum insulators for applications where high voltage conditioning of the insulator and electrodes is not practical and for pulse lengths on the order of several microseconds. The study was centered about experiments performed with a 100-kV, 10-μs pulsed power system and supported by a combination of theoretical and computational modeling. The base line geometry for the experiments was a cylindrically symmetric, +45° insulator between flat electrodes. In the experiments, flashovers or breakdowns were localized by operating at field stresses slightly below the level needed for explosive emissions with the base line geometry. The electrodes and/or insulator were then seeded with an emission source, e.g. a tuff of velvet, or a known mechanical defect. Our study differs from most vacuum insulator studies in that our emphasis was on flashovers originating at the anode triple junction as well as bulk breakdowns within the insulator. Various standard techniques were employed to suppress cathode-originating flashovers/breakdowns. We present the results of our experiments and discuss the capabilities of modeling insulator flashover.
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| THP024 | Development of Ultra-fast Silicon Switches and their Applications on Active X-Band, High-Power RF Compression Systems | simulation, coupling, laser, resonance | 619 | ||
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In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer inserted into a cylindrical waveguide operating in the TE 01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. A switch module is composed of the silicon switch, a circular waveguide T with the silicon switch at the center port and a movable short at the other end of silicon switch. The module can tune the S-matrix of on and off states to desired value. Our current design uses a CMOS compatible process and the fabrication is accomplished at SNF (Stanford Nanofabrication Facility). The switch has achieved <300ns on time with ~3% loss on the wafer. The RF energy is stored in a room-temperature, high-Q 400 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has a achieved a gain of 7, which is the ratio between output and input power. Power handling capability of the switch is estimated at the level of 10MW.
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| THP094 | GeV Laser Wakefield Acceleration and Injection Control at LOASIS | laser, electron, simulation, injection | 806 | ||
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Experiments at the LOASIS laboratory of LBNL have demonstrated production of GeV electron beams with low energy spread and divergence from laser wakefield acceleration. The pondermotive force of a 40 TW laser pulse guided by a 3 cm capillary discharge plasma density channel drove an intense plasma wave (wakefield), producing acceleration gradients on the order of 50 GV/m. Electrons were trapped from the background plasma and accelerated. Beam energy was increased from 100 to 1000 MeV*, compared to earlier experiments**, by using a longer guiding channel at low density, demonstrating the anticipated scaling to higher beam energies. Particle simulations are used to understand the trapping and acceleration mechanisms. Other experiments and simulations are also underway to control injection of particles into the wake, and hence improve beam quality and stability further. Recent experimental and simulation results from channel guided laser acceleration, and initial injection results, will be presented.
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*W. P. Leemans et al, submitted. |
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