High Charge State Ion Beams Research Articles

Production of multiply charge-state ions in a multicusp ion source

High charge state ion beams are commonly used in atomic and nuclear physics experiments. Multiply charged ions are normally produced in an ECR or in an EBIS. Multicusp generators can confine primary electrons very efficiently. Therefore, the electrical and gas efficiencies of these devices are high. Since the magnetic cusp fields are localized near the chamber wall, large volumes of uniform and high density plasmas can be obtained at low pressure, conditions favorable for the formation of multiply charged state ions. Attempts have been made at LBNL to generate multiply charged ion beams by employing a 25-cm diam by 25-cm long multicusp source. Experimental results demonstrated that charge states as high as 7+ can be obtained with argon or xenon plasmas. Multiply charged metallic ions such as tungsten and titanium have also been successfully formed in the multicusp source by evaporation and sputtering processes. In order to extend the charge state to higher values, a novel technique of injecting high energy electrons into the source plasma is proposed. If this is successful, the multicusp source will become very useful for radioactive beam accelerators, ion implantation, and nuclear physics applications.

Two-frequency plasma heating in a high charge state electron cyclotron resonance ion source

The performance of the Lawrence Berkeley Laboratory (LBL) advanced electron cyclotron resonance ion source, which is a single stage source designed to operate at 14 GHz alone (single-frequency heating), is enhanced by heating the plasma simultaneously with microwaves of 10 and 14 GHz (two-frequency heating). Production of high charge state ions was increased a factor of 2–5 or higher for the very heavy ions such as bismuth and uranium, as compared to single- frequency heating. Plasma stability was improved and the ion charge state distribution shifted to higher charge state. With two-frequency heating, the source can produce more than 1×109 pps of fully stripped argon. High charge state ion beams of bismuth and uranium produced by the source were injected into the 88-Inch Cyclotron at LBL. After acceleration to energies greater than 6 MeV/nucleon, the extracted beam intensities were 1×106 pps or higher for Bi50+,51+ and 238U52+,53+.

Intense high charge state ion sources (invited)

A review of Penning ionization gauge (PIG), duoplasmatron (DP), laser-plasma ion source (LPIS), Electron cyclotron resonance ion source (ECRIS), and electron beam ion source (EBIS) used for the production of intense and high charge state ion beams is given. The outputs of high charge states of different elements of the Periodic Table from ion sources of these types are compared. Bare nuclei up to Ar can be obtained from EBIS and ECR and Xe+54 from EBIS. Comparisons are made of compilations of the output (high average current of 107–1017 pps) for different charge states of Xe for PIG, DP, ECRIS, EBIS ion sources and Ta, Pb for different charge states of the LPIS. The present level and perspectives of development (a pulsed gas feed, stationary electric field) of the PIG ion source are presented. The beam performance and future development of these intense and high charge state ion sources are discussed from the point of view of the perspectives of the cyclotron programs at FLNR and JINR.

Review of the Eleventh International Workshop on ECR ion sources (invited)

At the Workshop, the operation of various new and existing ECR ion sources was reported, with most of the emphasis on new methods to improve the performance and extend the variety of species. Much attention was paid to theoretical aspects, in particular to the basic question of electron heating; a complete investigation is still considered to be a long term project. A number of measurements of diagnostic character were presented. The strong radial component of the field in the magnetic trap turns out to play a crucial role in the confinement of hot electrons and hence in the production of very high charge state ion beams. A donor for cold electrons in any form—like a biased probe, plasma cathode, or electron gun—contributes strongly to increased output and stability of operation of the ECR ion source.

A high charge state multicusp ion source

Attempts have been made to generate high charge state ion beams by employing a multicusp plasma source. Three experimental investigations have been performed at Lawrence Berkeley Laboratory (LBL) and at Gesellschaft fuer Schwerionenforschung, Darmstadt (GSI) to study the charge state distributions and the emittance of the extracted beam. Results demonstrate that charge state as high as +7 can be obtained with argon or xenon plasmas. The brightness of a 11-mA xenon ion beam is found to be 26 A/(π mm mrad)2.

Performance of the LBL ECR ion source

The LBL Electron Cyclotron Resonance (ECR) ion source in test operation since January 1984 has produced a wide variety of high charge state ion beams suitable for injection into the 88-inch Cyclotron. Two recent developments have dramatically improved the capability of the ECR source. The first development was the production of metallic ions. The intensities of aluminum ions produced were 36, 22, 10, and 0.065 eμA for charge states 6, 7, 8, and 11, respectively. Calcium ion intensities were 36, 31, 4.6, and 0.20 eμA for charge states 8, 9, 12, and 14, respectively. The second development was the replacement of the sextupole magnet used in all other high charge state ECR sources with an octupole structure. This modification resulted in a dramatic improvement in the intensities of the high charge state beams and a significant upward shift in the charge state distribution (CSD). The ECR-octupole or “OCTIGUN” has produced 89, 52, 9, and 2.5 eμA. of Ar 8,9,11,12+ and 21, 10, and 0.34 eμA of Kr 10,14,18+, respectively. For the high charge states of argon and krypton the improvement gained by using the octupole is typically a factor of 5 to 10.