137 research outputs found
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Input to NAS Plasma 2010 panel
A number of areas of plasma physics have had outstanding success over the last decade. The author comments on progress in understanding and manipulating particle beams, a variety of non-neutral plasmas. Some of the key manipulations were made possible by immersing a particle beam in neutral plasma in order to greatly reduce space-charge forces on the beam
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Planning Electron cloud/Gas desorption activities in the HIF-VNL during FY06
The Heavy-Ion Fusion (HIF) group, under the DOE Office of Fusion Energy Science (OFES) funding, has been carrying out studies of e-cloud and gas primarily for our own needs. During this effort we have developed unique experimental and simulation tools that we believe have broader applications. To a limited degree, as part of OFES' charter, we can pursue basic science for plasma and accelerator research and can also pursue issues of interest in high energy physics and other areas of accelerator research. We would appreciate your suggestions on specific needs that you have for which we might be able to make contributions towards understanding and mitigation. The following list of potential tasks provides a guide to our capabilities, plus some directions that we are considering; they are designed around our facilities, but we are open to collaborating at other sites. We will be firming up our plans after funding is set for the year--we currently expect that to happen in late October. The following list of tasks for FY06 assumes significant restoration of funds by Congress to a similar level as in FY05. Each area would be studied with coordinated experimental and simulation efforts. Most of these tasks deal with electron or gas issues, the last few are more general high-brightness beam issues
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Ion cyclotron resonant heating 2 x 170/sup 0/ loop antenna for the Tandem Mirror Experiment-Upgrade
This paper reviews the mechanical design and improvements that have taken place on the loop type ion cyclotron resonance heating (ICRH) antennas that are located in the center cell region of the Tandem Mirror Experiment-Upgrade (TMX-U)
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Electron Cloud Effects in Intense, Ion Beam Linacs: Theory and Experimental Planning for Heavy-Ion Fusion
Heavy-ion accelerators for HIF will operate at high aperture-fill factors with high beam current and long pulses. This will lead to beam ions impacting walls: liberating gas molecules and secondary electrons. Without special preparation a large fractional electron population ({approx}>1%) is predicted in the High-Current Experiment (HCX), but wall conditioning and other mitigation techniques should result in substantial reduction. Theory and particle-in-cell simulations suggest that electrons, from ionization of residual and desorbed gas and secondary electrons from vacuum walls, will be radially trapped in the {approx}4 kV ion beam potential. Trapped electrons can modify the beam space charge, vacuum pressure, ion transport dynamics, and halo generation, and can potentially cause ion-electron instabilities. Within quadrupole (and dipole) magnets, the longitudinal electron flow is limited to drift velocities (E x B and {del}B) and the electron density can vary azimuthally, radially, and longitudinally. These variations can cause centroid misalignment, emittance growth and halo growth. Diagnostics are being developed to measure the energy and flux of electrons and gas evolved from walls, and the net charge and gas density within magnetic quadrupoles, as well as the their effect on the ion beam
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Energy Loss, Range, and Electron Yield Comparisons of the CRANGE Ion-Material Interaction Code
We present comparisons of the CRANGE code to other well-known codes, SRIM and ASTAR, and to experimental results for ion-material interactions such as energy loss per unit length, ion range, and ion induced electron yield. These ion-material interaction simulations are relevant to the electron cloud effect in heavy ions accelerators for fusion energy and high energy density physics. Presently, the CRANGE algorithms are most accurate at energies above 1.0 MeV/amu. For calculations of energy loss per unit length of a potassium ion in stainless steel, results of CRANGE and SRIM agree to within ten percent above 1.0 MeV/amu. For calculations of the range of a helium ion in aluminum, results of CRANGE and ASTAR agree to within two percent above 1.0 MeV/amu. Finally, for calculations of ion induced electron yield for hydrogen ions striking gold, results of CRANGE agree to within ten percent with measured electron yields above 1.0 MeV/amu
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Electron Production and Collective Field Generation in Intense Particle Beams
Electron cloud effects (ECEs) are increasingly recognized as important, but incompletely understood, dynamical phenomena, which can severely limit the performance of present electron colliders, the next generation of high-intensity rings, such as PEP-II upgrade, LHC, and the SNS, the SIS 100/200, or future high-intensity heavy ion accelerators such as envisioned in Heavy Ion Inertial Fusion (HIF). Deleterious effects include ion-electron instabilities, emittance growth, particle loss, increase in vacuum pressure, added heat load at the vacuum chamber walls, and interference with certain beam diagnostics. Extrapolation of present experience to significantly higher beam intensities is uncertain given the present level of understanding. With coordinated LDRD projects at LLNL and LBNL, we undertook a comprehensive R&D program including experiments, theory and simulations to better understand the phenomena, establish the essential parameters, and develop mitigating mechanisms. This LDRD project laid the essential groundwork for such a program. We developed insights into the essential processes, modeled the relevant physics, and implemented these models in computational production tools that can be used for self-consistent study of the effect on ion beams. We validated the models and tools through comparison with experimental data, including data from new diagnostics that we developed as part of this work and validated on the High-Current Experiment (HCX) at LBNL. We applied these models to High-Energy Physics (HEP) and other advanced accelerators. This project was highly successful, as evidenced by the two paragraphs above, and six paragraphs following that are taken from our 2003 proposal with minor editing that mostly consisted of changing the tense. Further benchmarks of outstanding performance are: we had 13 publications with 8 of them in refereed journals, our work was recognized by the accelerator and plasma physics communities by 8 invited papers and we have 5 additional invitations for invited papers at upcoming conferences, we attracted collaborators who had SBIR funding, we are collaborating with scientists at CERN and GSI Darmstadt on gas desorption physics for submission to Physical Review Letters, and another PRL on absolute measurements of electron cloud density and Phys. Rev. ST-AB on electron emission physics are also being readied for submission
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Heavy-Ion-Induced Electronic Desorption of Gas from Metals
During heavy-ion operation in several particle accelerators worldwide, dynamic pressure rises of orders of magnitude were triggered by lost beam ions that bombarded the vacuum chamber walls. This ion-induced molecular desorption, observed at CERN, GSI, and BNL, can seriously limit the ion beam lifetime and intensity of the accelerator. From dedicated test stand experiments we have discovered that heavy-ion-induced gas desorption scales with the electronic energy loss (dEe/dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering
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New experimental measurements of electron clouds in ion beams with large tune depression
We study electron clouds in high perveance beams (K = 8E-4) with a large tune depression of 0.2 (defined as the ratio of a single particle oscillation response to the applied focusing fields, with and without space charge). These 1 MeV, 180 mA, K+ beams have a beam potential of +2 kV when electron clouds are minimized. Simulation results are discussed in a companion paper [J-L. Vay, this Conference]. We have developed the first diagnostics that quantitatively measure the accumulation of electrons in a beam [1]. This, together with measurements of electron sources, will enable the electron particle balance to be measured, and electron-trapping efficiencies determined. We, along with colleagues from GSI and CERN, have also measured the scaling of gas desorption with beam energy and dE/dx [2]. Experiments where the heavy-ion beam is transported with solenoid magnetic fields, rather than with quadrupole magnetic or electrostatic fields, are being initiated. We will discuss initial results from experiments using electrode sets (in the middle and at the ends of magnets) to either expel or to trap electrons within the magnets. We observe electron oscillations in the last quadrupole magnet when we flood the beam with electrons from an end wall. These oscillations, of order 10 MHz, are observed to grow from the center of the magnet while drifting upstream against the beam, in good agreement with simulations
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