Existing Ion Source Research Articles

Novel Approaches for Intensifying Negative C60 Ion Beams Using Conventional Ion Sources Installed on a Tandem Accelerator

We developed novel methods for producing negative C60 ion beams at the accelerator facility Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) to increase the current intensity of swift C60 ion beams accelerated to the MeV energy region using a tandem accelerator. We produced negative C60 ion beams with an intensity of 1.3 µA, which is several tens of thousands of times greater than the intensity of beams produced using conventional methods based on the Cs sputtering process. These beams were obtained by temporarily adding an ionization function based on electron attachment to an existing ion source that is widely used in tandem accelerators. The high-intensity swift C60 ion beams can be made available relatively easily to institutes that have tandem accelerators and ion sources of the type used at TIARA because there is no need to change existing ion sources or install new ones.

Ion beam enhancement in 236UO− measurement by AMS using Si powder as the binder

UO− has so far been the ion of choice for 236U measurement by AMS, but high and stable ionization efficiency for UO− production has been difficult to obtain with some models of Cs+ sputter ion sources. We have experienced considerable difficulties in producing sustainable UO− current even at 10 nA levels using the SO-110B source at A. E. Lalonde AMS Laboratory, University of Ottawa. This source is presently not configured for delivering Cs+ sputter beams at levels greater than 0.5 mA reliably, while ∼1.5 mA is reported to be needed for producing steady UO− currents in the 150–300 nA range. Various tests were undertaken to increase and stabilize the UO− current using the SO-110B source in its present configuration. The test included the addition of several fine powders as binders, including Al, C, Ta, Si, and SiC, to uranium oxide to form the sputter target. Si and Ta + Si were found to provide a significant enhancement to the UO− current production, which enabled us to carry on the 236U measurement using UO− with the existing ion source, although the achieved enhancement is still far short of the 150–300 nA UO− current reported elsewhere.

Diffusion processes in microwave discharge ion source and consequences on the upgrade of existing ion sources.

Several experiments have shown that the insertion of insulator materials within the plasma chamber may lead to a general improvement of microwave discharge ion source performances. In particular, the insertion of alumina into the chamber walls and borum nitride into extraction and injection flanges permits to increase the extracted current and the proton fraction and leads to a general decrease in the beam ripple. These beneficial effects have been usually explained by considering the secondary electron emission of insulators hit by plasma electrons. This paper tries to illustrate that these effects can be explained by taking into account the modification of the diffusion regime induced by the insulator materials. This approach will be used to comment on the results obtained with the versatile ion source by changing the wall conditions.

Development of $$\hbox {H}^{-}$$ H - multicusp ion source

The ion source is one of the key devices for the high-intensity cyclotron, which exerts influence on the beam intensity and applications of the machine. This paper will provide an introduction to current measures and present relevant experimental study as well as the beam test results. The existing ion source of the accelerator has a 2-mA output current. Our aim is to increase the current to roughly 5 mA to decrease the reaction time of cyclotron. Therefore, a new ion source was developed. To this end, some simulations were performed, and the simulated ion source was constructed, and then some measurements were noted. The CST code is used to simulate the chamber and extraction system. For construction, some materials such as copper and stainless steel are used. Tungsten wire of 2.1 mm diameter was developed to reach high beam current. Turbo and rotary pump is chosen for system evacuation. Faraday cup can be used for readout. The magnets for plasma confinement are made of Nd–Fe–B material. The source assembly consists of a tubular plasma chamber (inner diameter: 100 mm; length: 150 mm) with 12 columns of permanent magnets (Nd–Fe–B material) to provide a stronger multicusp field, a three-electrode extraction system, and a top cover with a confinement magnet inside. Now, 5 mA $$\hbox {H}^{-}$$ beam can be extracted from the ion source with a plasma electrode aperture of 13 mm under an arc power of 6 kW. The optimum $$\hbox {H}_{2}$$ gas flow rate and the change of pressure found during the tuning process of the ion source are presented.

Artificially Structured Boundary for a high purity ion trap or ion source

A plasma enclosed by an Artificially Structured Boundary (ASB) is proposed here as an alternative to existing ion source assemblies. In accelerator applications, many ion sources can have a limited lifetime or frequent service intervals due to sputtering and eventual degradation of the ion source assembly. Ions are accelerated towards the exit canal of positive ion sources, whereas, due to the biasing scheme, electrons or negative ions are accelerated towards the back of the ion source assembly. This can either adversely affect the experiment in progress due to sputtered contamination or compromise the integrity of the ion source assembly. Charged particle trajectories in the proximity of an ASB experience electromagnetic fields that are designed to hinder ion–surface interactions. Away from the ASB there is an essentially field free region. The field produced by an ASB is considered to consist of a periodic sequence of electrostatically plugged magnetic field cusps. A classical trajectory Monte Carlo simulation is extended to include electrostatic plugging of magnetic field cusps. The conditions necessary for charged particles to be reflected by the ASB are presented and quantified in terms of normalized parameters.

Ion optic calculations and installation of a modified SIMS ion source

The NRL trace element accelerator mass spectrometer facility has recently added a modified Cameca IMS 6F SIMS instrument as a high-performance ion source. It includes the Cs primary column, the sample chamber, and the secondary ion column. The NRL accelerator facility supplants the normal mass spectrometer portion of the IMS 6F instrument. To enable uncompromised injection from both the IMS 6F SIMS at 10keV and from the existing ion source at 70keV, a new compound Einzel lens was added inside the pressure tank of the Pelletron accelerator. The high-energy beam line was completely reconfigured to form an angle-focusing and energy-focusing mass spectrometer. These modifications will provide improved mass spectrometry performance, both for surface analysis using the new SIMS source and for radiocarbon measurements with the older multi-cathode ion source.

Plans for expanded 14C analyses at the NOSAMS facility – a status and progress report

After completion of the original main program – radiocarbon analysis of over 13000 seawater samples from the World Ocean Circulation Experiment (WOCE) – the NOSAMS Facility has entered a new phase of its operation. Major areas of concentration will be: (a) Continuation of analyses of “normal size” marine samples (including additional seawater samples from WOCE follow-up studies), (b) analysis of small samples (≪100 μg C), (c) analysis of individual compounds or compound classes, and (d) continuous-flow AMS (see contribution elsewhere in these proceedings). While (a) could be considered routine work, we intend to intensify our efforts to drive down the systematic uncertainties of our analyses. The other three areas all yield small samples, requiring new techniques in sample handling and AMS analysis. The facility plans to devote one of its two existing ion sources (134-sample NEC MC-SNICS) to the “routine” work, the other (59-sample “846”) will be upgraded to better accommodate small samples, and a new, separate small AMS system will be developed for continuous-flow AMS. The latter is expected to become the instrument of choice for individual-compound work. Until that device comes online, tests of the continuous-flow injector are planned on the main AMS system, temporarily adding a third injector leg. A planned enlargement of the facility will house the new AMS system, additional staff and laboratory space.

Plans for expanded 14C analyses at the NOSAMS facility ? a status and progress report

After completion of the original main program – radiocarbon analysis of over 13 000 seawater samples from the World Ocean Circulation Experiment (WOCE) – the NOSAMS Facility has entered a new phase of its operation. Major areas of concentration will be: (a) Continuation of analyses of “normal size” marine samples (including additional seawater samples from WOCE follow-up studies), (b) analysis of small samples (≪100 μg C), (c) analysis of individual compounds or compound classes, and (d) continuous-flow AMS (see contribution elsewhere in these proceedings). While (a) could be considered routine work, we intend to intensify our efforts to drive down the systematic uncertainties of our analyses. The other three areas all yield small samples, requiring new techniques in sample handling and AMS analysis. The facility plans to devote one of its two existing ion sources (134-sample NEC MC-SNICS) to the “routine” work, the other (59-sample “846”) will be upgraded to better accommodate small samples, and a new, separate small AMS system will be developed for continuous-flow AMS. The latter is expected to become the instrument of choice for individual-compound work. Until that device comes online, tests of the continuous-flow injector are planned on the main AMS system, temporarily adding a third injector leg. A planned enlargement of the facility will house the new AMS system, additional staff and laboratory space.

Testing the atomic structure of beryllium with AMS

If the Pauli exclusion principle were violated, the electronic structure of Be could be 1s 4 (denoted by Be ′) rather than 1s 22s 2. This paper describes the results of an experimental search for Be ′, carried out at PRIME Lab, the Purdue Rare Isotope Measurement Laboratory. In the process of setting stringent constraints on Be ′ using samples of metallic Be, Be ore, natural gas, and air, we made several modifications to the PRIME Lab facility. These included a new Be-free source and the construction of a gas introduction system which coupled to the existing ion source. The modifications permitted us to reach limits which are a factor of nearly 300 better than those obtained in previous experiments.

Laser ion source torch for highly charged ions

The article describes a laser ion source torch designed on the basis of a CO2 laser at Efremov Institute of Electrophysical Apparatus in collaboration with the Institute for Nuclear Research of the Ukrainian Academy of Science, Kiev. The ion extraction from the laser plasma is done by means of spherical grid electrodes. This permits to improve the efficiency several hundred times compared to the existing ion sources and to increase the ion beam correspondingly, including highly charged ions. The charge composition of the beam, the pulse frequency, and the extracted beam are determined by the operational mode of the laser.

Atomic mass spectrometry of materials

Texas Instruments and the University of North Texas (UNT) are collaborating on the design of an accelerator mass spectrometry (AMS) system dedicated primarily to the analysis of impurities in electronic materials and metals. An AMS beamline consisting of high-resolution magnetic ( M dM > 350) and electrostatic ( E dE > 700) analysis followed by a surface barrier detector has been installed on the NEC 9SDH pelletron at UNT, and a “clean” ion source is under development. An existing ion source (NEC Cs sputter source) has been used in conjunction with the AMS beamline to generate computer controlled molecule-free mass analyses of solid samples. Through a careful choice of isotopes and charge states a robust algorithm can be developed for removing molecular interferences from the mass analysis for essentially all materials. Examples using graphite, Si and CdZnTe are discussed.

Ion sources for light-ion fusion (invited)

Light-ion drivers offer a potentially efficient and low-cost method to compress and heat an inertial-confinement fusion (ICF) target. In order to produce a significant thermonuclear burn of the fuel, focused ion-beam intensities of 100 TW/cm2 are required. The ion sources for these pulsed-power drivers should produce a single-ion species and should be capable of providing current-density levels up to 5 kA/cm2, in pulse widths of 10–20 ns, at voltages up to several tens of megavolts. Most ion sources used in the past have produced multiple-ion species, including protons and heavier ions, such as carbon and oxygen. In the last few years there has been a substantial research effort to produce single-species sources. The major effort since 1983 has been directed towards developing a pure, high-current Li+ source for the light-ion fusion accelerator, PBFA II. There are two types of ion sources being used for intense ion-beam generation: (1) passive sources which are produced directly or indirectly by the diode voltage itself; and (2) active sources, in which a preformed plasma is generated before the arrival of the power pulse. A survey of existing ion sources and those under development will be given. Emphasis will be given to the lithium-ion sources being developed at Sandia National Laboratories (SNL).

Gas utilization in the Tokamak Fusion Test Reactor neutral beam injectors

Measurements of gas utilization were performed using hydrogen and deuterium beams in the Tokamak Fusion Test Reactor (TFTR) neutral beam test beamline to study the feasibility of operating tritium beams with existing ion sources under conditions of minimal tritium consumption. (i) It was found that the fraction of gas molecules introduced into the TFTR long-pulse ion sources that are converted to extracted ions (i.e., the ion source gas efficiency) was higher than with previous short-pulse sources. Gas efficiencies were studied over the range 33%–55%, and its effect on neutralization of the extracted ions was studied. At the high end of the gas efficiency range, the neutral fraction of the beam fell below that predicted from room-temperature molecular gas flow (similar to observations at the Joint European Torus). (ii) Beam isotope change studies were performed. No extracted hydrogen ions were observed in the first deuterium beam following a working gas change from H2 to D2. There was no arc conditioning or gas injection preceding the first beam extraction attempt. (iii) Experiments were also performed to determine the reliability of ion source operation during the long waiting periods between pulses that are anticipated during tritium operation. It was found that an ion source conditioned to 120 kV could produce a clean beam pulse after a waiting period of 14 h by preceding the beam extraction with several acceleration voltage/filament warm-up pulses. It can be concluded that the operation of up to six ion sources on tritium gas should be compatible with on-site inventory restrictions established for D–T, Q=1 experiments on TFTR.

The Production and Acceleration of Metal Ions in the Harwell Variable Energy Cyclotron

The range of ions accelerated by the V.E.C. has recently been extended to metal ions. For example, a 5 to 10 μA beam of 48 MeV 58Ni6+ is now available and has been used by a customer. This beam has become possible as a result of success in adapting the normal ion source for the production of metal ions. The problem was to add to the ion source a controlled source of metal vapour without increasing the size of the ion source or adding separate oven heaters and controls. This has been achieved by inserting a graphite liner into the existing ion source chimney, the metal being embedded in the liner and out of direct contact with the arc. Provided the arc power exceeds a few kilowatts, the metal becomes molten and the vapour diffuses through the graphite into the arc which then becomes self-sustaining. With nickel (the most widely tested so far), intensity at full radius of between 10 and 20 μA of 6+ ions and 1μA of 8+ ions is readily obtained and source life averages about 4 hours. Other metals such as cobalt, iron, chromium and copper give similar results.