Daniela Leitner

Comparison of particle-in-cell simulation with experiment for the transport system of the superconducting electron cyclotron resonance ion source VENUS

The three-dimensional, particle-in-cell code WARP has been enhanced to allow end-to-end beam dynamics simulations of the VENUS beam transport system from the extraction region, through a mass-analyzing magnet, and up to a two-axis emittance scanner. This article presents the first results of comparisons between the simulation and experimental data. A helium beam (He+ and He2+) is chosen as an initial comparison beam due to its simple mass spectrum. Although a number of simplifications are made for the initial extracted beam, aberration characteristics appear in simulations that are also present in experimental phase-space current-density measurements. Further, measurements of phase-space tilt indicate that simulations must have little or no space-charge neutralization along the transport system to best agree with experiment. In addition, recent measurements of triangular beam structure immediately after the source are presented. This beam structure is related to the source magnetic confinement fields and ...

Space-charge compensation measurements in electron cyclotron resonance ion source low energy beam transport lines with a retarding field analyzer.

In this paper we describe the first systematic measurement of beam neutralization (space charge compensation) in the ECR low energy transport line with a retarding field analyzer, which can be used to measure the potential of the beam. Expected trends for the space charge compensation levels such as increase with residual gas pressure, beam current, and beam density could be observed. However, the overall levels of neutralization are consistently low (<60%). The results and the processes involved for neutralizing ion beams are discussed for conditions typical for ECR injector beam lines. The results are compared to a simple theoretical beam plasma model as well as simulations.

Design of a high temperature oven for an ECR source for the production of uranium ion beams

VENUS is the superconducting electron cyclotron resonance (ECR) ion source at the Lawrence Berkeley National Labs 88-Inch Cyclotron. To generate neutral atoms for ionization, the source utilizes a resistively- heated high temperature oven that is located in a magnetic field of up to 4 Tesla and operates at temperatures up to about 2000degC. However, temperatures between 2100- 2300degC are required to produce the desired 280 emuA of high charge state uranium ion beams, and increased thermal and structural effects, combined with elevated chemical reactivity significantly reduce the ovens ability to operate in this envelope. The oven has been redesigned with higher thermal efficiency, improved structural strength and chemically compatible species in order to produce the desired high intensity, high charge state uranium beams. Aspects of the engineering development are presented.

DIANA - A deep underground accelerator for nuclear astrophysics experiments

DIANA (Dakota Ion Accelerator for Nuclear Astrophysics) is a proposed facility designed to be operated deep underground. The DIANA collaboration includes nuclear astrophysics groups from Lawrence Berkeley National Laboratory, Michigan State University, Western Michigan University, Colorado School of Mines, and the University of North Carolina, and is led by the University of Notre Dame. The scientific goals of the facility are measurements of low energy nuclear cross-sections associated with sun and pre-supernova stars in a laboratory setup at energies that are close to those in stars. Because of the low stellar temperatures associated with these environments, and the high Coulomb barrier, the reaction cross-sections are extremely low. Therefore these measurements are hampered by small signal to background ratios. By going underground the background due to cosmic rays can be reduced by several orders of magnitude. We report on the design status of the DIANA facility with focus on the 3 MV electrostatic accelerator.

Simulation-driven optimization of heavy-ION production in ECR sources

Next-generation heavy-ion beam accelerators require a wide variety of high charge state ion beams (from protons to uranium) with up to an order of magnitude higher intensity than that demonstrated with conventional electron cyclotron resonance (ECR) ion sources. Optimization of the ion beam production for each element is therefore required. Efficient loading of the material into the ECR plasma is one of the key elements for optimizing the ion beam production. High-fidelity simulations provide a means to understanding the deposition of uncaptured metal atoms along the walls. This information would help to optimize the loading process into the ECR plasma. We are currently extending the plasma simulation framework VORPAL with models to investigate effective loading of heavy metals into ECR ion source via alternate mechanisms, including vapor loading, ion sputtering and laser ablation. First results of the ion production for different loading scenarios are presented.

Particle-in-Cell Simulations of the Venus Ion Beam Tranpsort System

The next-generation superconducting ECR ion source VENUS serves as the prototype injector ion source for the linac driver of the proposed Rare Isotope Accelerator (RIA). The high-intensity heavy ion beams required by the RIA driver linac present significant challenges for the design and simulation of an ECR extraction and low energy ion beam transport system. Extraction and beam formation take place in a strong (up to 3T) axial magnetic field, which leads to significantly different focusing properties for the different ion masses and charge states of the extracted beam. Typically, beam simulations must take into account the contributions of up to 30 different charge states and ion masses. Two three-dimensional, particle-in-cell codes developed for other purposes, IMPACT and WARP, have been adapted in order to model intense, multi-species DC beams. A discussion of the differences of these codes and the advantages of each in the simulation of the low energy beam transport system of an ECR ion source is given. Direct comparisons of results from these two codes as well as with experimental results from VENUS are presented.

Development of the 3D Parallel Particle-In-Cell Code IMPACT to Simulate the Ion Beam Transport System of VENUS (Abstract)

The superconducting ECR ion source VENUS serves as the prototype injector ion source for the Rare Isotope Accelerator (RIA) driver linac. The RIA driver linac requires a great variety of high charge state ion beams with up to an order of magnitude higher intensity than currently achievable with conventional ECR ion sources. In order to design the beam line optics of the low energy beam line for the RIA front end for the wide parameter range required for the RIA driver accelerator, reliable simulations of the ion beam extraction from the ECR ion source through the ion mass analyzing system are essential. The RIA low energy beam transport line must be able to transport intense beams (up to 10 mA) of light and heavy ions at 30 keV.For this purpose, LBNL is developing the parallel 3D particle‐in‐cell code IMPACT to simulate the ion beam transport from the ECR extraction aperture through the analyzing section of the low energy transport system. IMPACT, a parallel, particle‐in‐cell code, is currently used to mo...

Commissioning of the superconducting ECR ion source VENUS at 18 GHz

Commissioning of the Superconducting ECR ion source VENUS at 18 GHz D. Leitner, S.R. Abbott, R.D. Dwinell, M.A. Leitner, C. Taylor, C.M. Lyneis, Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 O 6+ Xe 20+ Xe 27+ Bi 25+ Bi 29+ Bi 41+ Bismuth optimized on low charge states 1a) O O O M/Q Analyzed FC Current (euA) COMMISSIONING RESULTS AT 18 GHZ In 2002 and 2003 initial commissioning at 18 GHz was carried out. During this commissioning period, a number of improvements were made to the cryostat system, the 18 GHz microwave system, and the magnet power supply control system [1,2]. Novel heat exchangers for the two cryocoolers were de- signed, and they enable VENUS to operate in closed loop operation without the addition of liquid helium. Recently a third cryocooler was added in preparation for the 28 GHz operation. The third cryocooler adds 1.3 W of additional cooling power to the cryostat system and enables to run the magnet at the design temperature of 4.2 K. It also provides ample cooling power compensating the expected increased heat load at 28 GHz operation due to the x-ray load produced by hot plasma electrons colliding with the plasma chamber. VENUS is now operational at the full capacity of the 2 kW, 18 GHz klystron. The operation experience has been excellent. In table 1 a few exemplary ion beam intensities from VENUS are presented. The performance of VENUS exceeds the performance of the LBNL AECR-U in all areas. Table 1: Ion beam intensities extracted from VENUS O 7+ In August 2003 a high temperature oven has been installed in VENUS. A prototype of this oven has been developed and successfully tested previously with the existing LBNL ECR ion sources for temperatures up to 2000 degree C. Bismuth was selected as the first metal ion beam to be produced with VENUS. Figures 1a and 1b show a Bi spectrum optimized for high and low charge states. Analyzed FC Current (euA) During the last year, the VENUS ECR ion source was commissioned at 18 GHz and preparations for 28 GHz operation are now underway. During the commissioning phase with 18 GHz, tests with various gases and metals have been performed with up to 2000 W RF power. The ion source performance is very promising [1,2]. VENUS (Versatile ECR ion source for NUclear Science) is a next generation superconducting ECR ion source, de- signed to produce high current, high charge state ions for the 88-Inch Cyclotron at the Lawrence Berkeley National Labo- ratory. VENUS also serves as the prototype ion source for the RIA (Rare Isotope Accelerator) front end. The goal of the VENUS ECR ion source project as the RIA R&D injector is the production of 240eµA of U 30+ , a high current medium charge state beam. On the other hand, as an injector ion source for the 88-Inch Cyclotron the design objective is the production of 5eµA of U 48+ , a low current, very high charge state beam. To meet these ambitious goals, VENUS has been designed for optimum operation at 28 GHz. This frequency choice has several design consequences. To achieve the required magnetic confinement, super- conducting magnets have to be used. The size of the super- conducting magnet structure implies a relatively large plasma volume. Consequently, high power microwave cou- pling becomes necessary to achieve sufficient plasma heating power densities. The 28 GHz power supply has been deliv- ered in April 2004. Bismuth optimized on high charge states O 4+ O 1b) O 2+ 35+, C 2+ M/Q Fig.1 Analyzed Bi current for an ion source tune optimized for low (1a) and high (1b) charge states. Note the different current scales in the spectra. REFERENCES [1] D. Leitner, S. R. Abbott, R. D. Dwinell, M. Leitner, C. Taylor, and C. M. Lyneis, APS Proceedings of the Particle Accelerator Conference (PAC03), Portland, Or, 2003). [2] C.M. Lyneis, D. Leitner, S.R. Abbott, R.D. Dwinell, M. Leitner, C.S. Silver, C. Taylor, RSI75, in print, 2004