| Paper | Title | Page |
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| MPPT068 | A Compact High Gradient Pulsed Magnetic Quadrupole | 3771 |
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Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. A design for a high gradient, low inductance pulsed quadrupole magnet is presented. The magnet is a circular current dominated design with a circular iron return yoke. Features include a five turn eddy current compensated solid conductor coil design which theoretically eliminates the first four higher order multipole field components, a single layer "non-spiral bedstead" coil design which both minimizes utilization of radial space and maximizes utilization of axial space, and allows incorporation of steering and correction coils within existing radial space. The coils are wound and stretched straight in a special winder, then bent in simple fixtures to form the upturned ends, simplifying fabrication and assembly. |
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| TOAA005 | Field Quality Optimization of Superconducting Quadrupoles for the HCX Experiment | |
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Funding: Supported by the Office of Energy Research, US DOE, at LBNL and LLNL under contract numbers DE-AC03-76SF00098, W-7405-Eng-48, and at MIT under contract number DE-FC02-93-ER54186. The High Current Experiment (HCX) is exploring the physics of intense beams with high line-charge density. Superconducting focusing quadrupoles are being developed for future magnetic transport studies at the HCX. A baseline design was selected following the testing of several pre-series models. Optimization of the baseline design led to the development of a first prototype in 2003. This magnet achieved a conductor-limited gradient of 132 T/m in a 70 mm bore without training, with measured field errors at the 0.1% level. Based on these results, both the magnet geometry and the fabrications procedures were modified to further improve the field quality. These modifications were implemented in a second prototype. In this paper, comparisons between the design harmonics and magnetic measurements performed on the new prototype will be presented and discussed. |
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| ROPB002 | Experiments Studying Desorbed Gas and Electron Clouds in Ion Accelerators | 194 |
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Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL under contract No. W-7405-Eng-48, and by LBNL under Contract DE-AC03-76F00098. Electron clouds and gas pressure rise limit the performance of many major accelerator rings. We are studying these issues experimentally with ~1 MeV heavy-ion beams, coordinated with significant efforts in self-consistent simulation and theory.* The experiments use multiple diagnostics, within and between quadrupole magnets, to measure the sources and accumulation of electrons and gas. In support of these studies, we have measured gas desorption and electron emission coefficients for potassium ions impinging on stainless steel targets at angles near grazing incidence.** Our goal is to measure the electron particle balance for each source – ionization of gas, emission from beam tubes, and emission from an end wall – determine the electron effects on the ion beam and apply the increased understanding to mitigation. *J-L. Vay, Invited paper, session TICP; R. H. Cohen et al., PRST-AB 7, 124201 (2004). **M. Kireeff Covo, this conference; A. W. Molvik et al., PRST-AB 7, 093202 (2004). |
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| ROPB006 | Filling in the Roadmap for Self-Consistent Electron Cloud and Gas Modeling | 525 |
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Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL and LBNL under contracts W-7405-Eng-48, and DE-AC03-76F00098. Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment,* theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell accelerator code WARP and the electron cloud code POSINST, with additional functionalities.** The development of the new capability follows a "roadmap" describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electrons and ions motion.*** Samples of applications of the new capability to the modeling of intense charge dominated beams**** and LHC beams***** will be shown as available. *A.W. Molvik, these proceedings. **J.-L. Vay, Proc. "ECLOUD04," Napa (California), 2004. ***R.H. Cohen, these proceedings. ****P.A. Seidl, these proceedings. *****M.A. Furman, these proceedings. |
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| FPAP015 | Electron and Gas Effects on Intense, Space-Charge Dominated Ion Beams in Magnetic Quadrupoles: Comparison of Experiments and Simulations | |
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Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL and LBNL under contracts W-7405-Eng-48, and DE-AC03-76F00098. Accelerators for inertial fusion energy, high-energy density physics and other high intensity applications have an economic incentive to minimize the clearance between the beam edge and the aperture wall. This increases the risk from electron clouds and gas desorbed from walls. Using the High Current Experiment at LBNL, we have measured the beam (0.18 A, 1 MeV K+ ) distribution upstream and downstream of a short lattice of magnetic quadrupoles where the 2·rms beam size is =50% of the quadrupole aperture, and the generalized perveance is ˜10-3. Between magnets, the transverse beam distribution is also imaged. The beam potential is 1-2 kV, large enough to trap electrons produced by, for example, K+ - gas collisions. Gas and electron effects are intentionally induced by varying gas pressure and the bias of e- controlling electrodes.* The measurements are compared to WARP PIC simulations that include the self-consistent tracking of electrons and ions.** *A. W. Molvik et al., this conference. **J-L Vay et al., this conference. |
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| FPAT026 | The Dynamic Aperture of an Electrostatic Quadrupole Lattice | 1946 |
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Funding: Work supported by the U.S. DOE, under contract numbers DE-AC03-76SF00098 and W-7405-Eng-48. In heavy-ion-driven inertial fusion accelerator concepts, dynamic aperture is important to the cost of the accelerator, most especially for designs which envision multibeam linacs, where extra clearance for each beam greatly enlarges the transverse scale of the machine. In many designs the low-energy end of such an accelerator uses electrostatic quadrupole focusing. The dynamic aperture of such a lattice has been investigated for intense, space-charge-dominated ion beams using the 2-D transverse slice version of the 3-D particle-in-cell simulation code WARP. The representation of the focusing field used is a 3-D solution of the Laplace equation for the biased focusing elements, as opposed to previous calculations which used a less-accurate multipole approximation. 80% radial filling of the aperture is found to be possible. Results from the simulations, as well as corroborating data from the High Current Experiment at LBNL, will be presented. |
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| FPAP033 | Beam Energy Scaling of Ion-Induced Electron Yield from K+ Ions Impact on Stainless Steel Surfaces | 2287 |
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Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, LLNL under contract No. W-7405-Eng-48, and by LBNL under Contract DE-AC03-76F00098. The cost of accelerators for heavy-ion inertial fusion energy (HIF) can be reduced by using the smallest possible clearance between the beam and the wall from the beamline. This increases beam loss to the walls, generating ion-induced electrons that could be trapped by beam space charge potential into an "electron cloud," which can cause degradation or loss of the ion beam. In order to understand the physical mechanism of production of ion-induced electrons we have measured impact of K+ ions with energies up to 400 KeV on stainless steel surfaces near grazing incidence, using the ion source test stand (STS-500) at LLNL. The electron yield will be discussed and compared with experimental measurements from 1 MeV K+ ions in the High-Current Experiment at LBNL.* *A.W. Molvik et al., PRST-AB 7, 093202 (2004). |