Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session Q14: Beam Physics |
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Sponsoring Units: DNP Chair: Larry Cardman, Jefferson Lab Room: Plaza Court 4 |
Monday, May 4, 2009 10:45AM - 10:57AM |
Q14.00001: Benchmarking a 3D Map-Based Approach to Modeling Beam Transport in RF Cavities Ilya Pogorelov, Dan Abell, Peter Stoltz, Jim Amundson We present results of benchmarking our recently developed capability for generating High-Order Mode (HOM) maps of RF cavity fields for use in particle tracking code-based simulations. We use VORPAL field data as a starting point, and follow the approach of Abell to produce transfer maps that are subsequently incorporated into the MaryLie/IMPACT (ML/I) and Synergia frameworks. For the m = 0 mode, we conducted detailed comparisons between map-based ML/I simulations of on- and off-axis beam transport through a realistic RF cavity on one hand, and the results of a direct 3D EM VORPAL simulation on the other. We present and discuss these benchmarking results. [Preview Abstract] |
Monday, May 4, 2009 10:57AM - 11:09AM |
Q14.00002: BTF simulations for Tevatron and RHIC with resistive wall wake field Vahid Ranjbar, Andrey Sobol, Tanaji Sen, Hyung Jin Kim, Cheng-Yang Tan Recent improvements to BBSIM permit detailed simulations of collective effects due to resistive wall wake fields. We compare results of beam transfer measurements (BTF) in the Tevatron and RHIC with and without the effects of resistive wall wake fields. These are then compared to actual BTF measurements made in both machines and the impact of intensity on our measurements. We also investigate the impact of resistive wall wake fields on various chromaticity measurement approaches. [Preview Abstract] |
Monday, May 4, 2009 11:09AM - 11:21AM |
Q14.00003: Reduction of the friction force in electron cooling systems due to magnetic field errors Andrey Sobol, George Bell, David Bruhwiler, Alexei Fedotov, Vladimir Litvinenko Magnetic field errors can limit the dynamical friction force on co-propagating ions and, hence, increase the cooling time. We present theoretical and numerical results for reduction of the friction force due to bounded transverse magnetic field errors, as a function of wavelength. VORPAL [1] simulations using a binary collision algorithm [2] show that small-wavelength field errors affect the friction logarithmically, via the Coulomb log, while long-wavelength errors reduce the friction by effectively increasing the transverse electron temperature. A complete understanding of finite-time effects and the role of small impact parameter collisions is required to correctly interpret the simulation results. We show that the distribution of electron-ion impact parameters is similar to a Pareto distribution, for which the central limit theorem does not apply. A new code has been developed to calculate the cumulative distribution function of electron-ion impact parameters and thus correctly estimate the expectation value and uncertainty of the friction force. [1] C. Nieter and J. Cary, J. Comp. Phys. 196 (2004), p. 448. [2] G. Bell et al., J. Comp. Phys. 227 (2008), p. 8714. [Preview Abstract] |
Monday, May 4, 2009 11:21AM - 11:33AM |
Q14.00004: On kinetic instabilities in collisionless ultra-relativistic streaming cold electron-proton plasma Gregory Vereshchagin, V.M. Chechetkin, V.F. Dyachenko, S.L. Ginzburg, N.N. Fimin, Remo Ruffini, Ivan Siutsou We consider cold collisionless electron-proton plasma, moving in the vacuum with large bulk Lorentz factor. In order to describe such a system numerical integration of Vlasov-Maxwell equations is performed by a 3-dimensional Eulerian code. The plasma is shown to experience kinetic instabilities, leading to generation of stochastic electro-magnetic fields. The motion of electrons and protons randomizes in these stochastic fields, leading to a thermal-like spread in the distribution function of electrons and protons. Both electrons and protons, and the electromagnetic field reach equipartition on a timescale L/c, where L is the characteristic size in the problem, c is the speed of light. We discuss particle distributions in coordinate and momentum space, as well as the structure of electromagnetic fields. Consequences of the considered phenomenon for astrophysical sources are quite general and include, in particular, gamma-ray bursts. [Preview Abstract] |
Monday, May 4, 2009 11:33AM - 11:45AM |
Q14.00005: Influence of Ion Effects on a Space Charge Limited Field Emission Flow: From Classical to ultrarelativistic regimes M.C. Lin, P.C. Chang, J.P. Verboncoeur The effects of ions in space charge limited field emission flow is studied using a self-consistent model, and confirmed by particle-in-cell (PIC) simulations. The field emission of electrons is described quantum mechanically by the Fowler--Nordheim equation. The cathode plasma and surface properties are considered within the framework of the effective work function approximation. Ionization effects at the anode as well as electron space-charge effects are described by Poisson's equation coupled with the energy conservation equation including relativistic effects. The closed form of formulas has been derived and the numerical calculations are carried out self-consistently to yield the steady state of the bipolar flow from classical to ultrarelativistic regimes. The upstream ion current included in Poisson's equation has been treated as a tuning parameter. The field-emission currents in the presence of saturated ion currents are enhanced by 1.8, 1.5, and 1.4 times of the case with no ion current in the classical, intermediate, and ultrarelativistic regimes, respectively. The solutions have also been verified using 1D PIC simulations as implemented in the OOPD1 code developed by the PTSG of UC Berkeley. [Preview Abstract] |
Monday, May 4, 2009 11:45AM - 11:57AM |
Q14.00006: Assessments of Sequential Intensity Modulated Radiation Therapy Boost (SqIB) Treatments Using HART Anil Pyakuryal A retrospective study was pursued to evaluate the SqIB treatments performed on ten head and neck cancer patients(n=10).Average prescription doses (PDs) of 39 Gy,15Gy and 17.8Gy were delivered consecutively from larger to smaller planning target volumes(ptvs) in three different treatment plans using 6 MV X-ray photon beams from a Linear accelerator (SLA Linac, Elekta) on BID weak on-weak off schedules. These plans were statistically evaluated on basis of plan indices (PIs),dose response of targets and critical structures, and dose tolerance(DT) of various organs utilizing the DVH analysis automated software known as Histogram Analysis in Radiation Therapy-HART(S.Jang et al., 2008, Med Phys 35, p.2812). Mean SqIB PIs were found consistent with the reported values for varying radio-surgical systems.The 95.5{\%}(n=10)of each ptvs and the gross tumor volume also received 95{\%} (n=10)of PDs in treatments. The average volume of ten organs (N=10) affected by each PDs shrank with decreasing size of ptvs in above plans.A largest volume of Oropharynx (79{\%},n=10,N=10) irradiated at PD, but the largest volume of Larynx (98{\%}, n=10, N=10) was vulnerable to DT of structure (TD50).Thus, we have demonstrated the efficiency and accuracy of HART in the assessment of Linac based plans in radiation therapy treatments of cancer. [Preview Abstract] |
Monday, May 4, 2009 11:57AM - 12:09PM |
Q14.00007: The New Heavy Element Program at Texas A{\&}M University C.M. Folden III, M.C. Alfonso, A.A. Al-Harbi A new program to study the heaviest elements has begun at the Texas A{\&}M University Cyclotron Institute. As part of a DOE-sponsored upgrade, the existing 88-Inch K150 Cyclotron is being recommissioned and will provide the intense, stable beams at Coulomb barrier energies that are necessary for the production of actinide and transactinide elements. The ECR2 ion source will be moved to the 88-Inch Cyclotron to provide the necessary ion beams. Additional work has focused on modifying the Momentum Achromat Recoil Separator for heavy element studies, and an experiment to study the production of neutron-deficient At isotopes in the $^{40}$Ar + $^{165}$Ho reaction will be conducted in Spring 2009. Excitation functions will be measured and compared with existing data; the measured separator transmission will be compared with the results of simulations. This talk will discuss the suitability of available facilities and first experimental results. [Preview Abstract] |
Monday, May 4, 2009 12:09PM - 12:21PM |
Q14.00008: The T2K Neutrino Beamline Alysia Marino The T2K long-baseline neutrino oscillation experiment will search for evidence of neutrino flavor change over a distance of 295 km in a beam composed primarily of muon neutrinos. This high-intensity beam is being constructed at the new J-PARC facility in Tokai-mura, Japan, and is scheduled to begin operation in the spring of 2009. The talk will describe the design of the neutrino beamline and report on the current status. [Preview Abstract] |
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