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Title: Extraction of single-ion beams from helicon ion source in high plasma density operation mode: Experiment and simulation

Abstract

Tests of a high plasma density high-brightness helicon ion source for nuclear microscopy applications are underway. Experiments were performed with hydrogen, helium, and argon. Different extraction structures of the helicon rf ion source were investigated with an imposed external magnetic field. We present measurements of the extracted current as a function of the extraction voltage and rf power. The source has been diagnosed by a microwave interferometer. Plasma densities in the vicinity of the emission hole of up to 7.2x10{sup 12} cm{sup -3} (for argon), 1.6x10{sup 12} cm{sup -3} (for helium), and 6.0x10{sup 11} cm{sup -3} (for hydrogen) were obtained for working gas pressure of <5 mTorr and rf power <350 W (f{sub rf}=27.12 MHz). The ion current density was 80 mA/cm{sup 2} with high percentage of protons in the beam ({approx}80%). In the extraction structure, the cathode channel has a 3 mm length and a 0.6 mm diameter. The phase set degradation due to aberrations in the extraction structure of the helicon rf ion source was simulated for a fourth-order approximation in series expansion of the electrostatic potential and third-order approximation in series of the magnetic fields, by the matrizant method. The calculations were performed involving experimental data onmore » ion energy spread, average ion energy, and plasma density of the helicon rf ion source with permanent magnets.« less

Authors:
; ; ; ; ; ;  [1]
  1. Institute of Applied Physics, National Academy of Sciences of the Ukraine, Sumy (Ukraine)
Publication Date:
OSTI Identifier:
20779083
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 77; Journal Issue: 3; Conference: 11. international conference on ion sources, Caen (France), 12-16 Sep 2005; Other Information: DOI: 10.1063/1.2147739; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ARGON; BEAM EXTRACTION; BEAM-PLASMA SYSTEMS; BRIGHTNESS; CATHODES; HELIUM; HYDROGEN; INTERFEROMETERS; ION BEAMS; ION SOURCES; IONS; MAGNETIC FIELDS; PERMANENT MAGNETS; PLASMA; PLASMA DENSITY

Citation Formats

Mordyk, S., Miroshnichenko, V., Nahornyy, A., Nahornyy, D., Shulha, D., Storizhko, V., and Voznyy, V.. Extraction of single-ion beams from helicon ion source in high plasma density operation mode: Experiment and simulation. United States: N. p., 2006. Web. doi:10.1063/1.2147739.
Mordyk, S., Miroshnichenko, V., Nahornyy, A., Nahornyy, D., Shulha, D., Storizhko, V., & Voznyy, V.. Extraction of single-ion beams from helicon ion source in high plasma density operation mode: Experiment and simulation. United States. doi:10.1063/1.2147739.
Mordyk, S., Miroshnichenko, V., Nahornyy, A., Nahornyy, D., Shulha, D., Storizhko, V., and Voznyy, V.. Wed . "Extraction of single-ion beams from helicon ion source in high plasma density operation mode: Experiment and simulation". United States. doi:10.1063/1.2147739.
@article{osti_20779083,
title = {Extraction of single-ion beams from helicon ion source in high plasma density operation mode: Experiment and simulation},
author = {Mordyk, S. and Miroshnichenko, V. and Nahornyy, A. and Nahornyy, D. and Shulha, D. and Storizhko, V. and Voznyy, V.},
abstractNote = {Tests of a high plasma density high-brightness helicon ion source for nuclear microscopy applications are underway. Experiments were performed with hydrogen, helium, and argon. Different extraction structures of the helicon rf ion source were investigated with an imposed external magnetic field. We present measurements of the extracted current as a function of the extraction voltage and rf power. The source has been diagnosed by a microwave interferometer. Plasma densities in the vicinity of the emission hole of up to 7.2x10{sup 12} cm{sup -3} (for argon), 1.6x10{sup 12} cm{sup -3} (for helium), and 6.0x10{sup 11} cm{sup -3} (for hydrogen) were obtained for working gas pressure of <5 mTorr and rf power <350 W (f{sub rf}=27.12 MHz). The ion current density was 80 mA/cm{sup 2} with high percentage of protons in the beam ({approx}80%). In the extraction structure, the cathode channel has a 3 mm length and a 0.6 mm diameter. The phase set degradation due to aberrations in the extraction structure of the helicon rf ion source was simulated for a fourth-order approximation in series expansion of the electrostatic potential and third-order approximation in series of the magnetic fields, by the matrizant method. The calculations were performed involving experimental data on ion energy spread, average ion energy, and plasma density of the helicon rf ion source with permanent magnets.},
doi = {10.1063/1.2147739},
journal = {Review of Scientific Instruments},
number = 3,
volume = 77,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H{sup -} ion beams in a filament-driven discharge. In this kind of an ion source the extracted H{sup -} beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H{sup -}more » converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H{sup -} ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H{sup -} ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H{sup -} production (main discharge) in order to further improve the brightness of extracted H{sup -} ion beams.« less
  • A helicon based pre-ionization source has been developed and installed on the Helicity Injected Torus with Steady Inductance (HIT-SI) spheromak. The source initiates plasma breakdown by injecting impurity-free, unmagnetized plasma into the HIT-SI confinement volume. Typical helium spheromaks have electron density reduced from (2–3) × 10{sup 19} m{sup −3} to 1 × 10{sup 19} m{sup −3}. Deuterium spheromak formation is possible with density as low as 2 × 10{sup 18} m{sup −3}. The source also enables HIT-SI to be operated with only one helicity injector at injector frequencies above 14.5 kHz. A theory explaining the physical mechanism driving the reductionmore » of breakdown density is presented.« less
  • The currently employed converter-type negative ion source at Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H{sup -} ion beams in a filament-driven discharge. The extracted H{sup -} beam current is limited by the achievable plasma density, which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which degrades the performance of the H{sup -} conversion surface. In order to overcomemore » these limitations we have designed and tested a prototype of a surface conversion H{sup -} ion source, based on excitation of helicon plasma wave mode with an external antenna. The source has been operated with and without cesium injection. An H{sup -} beam current of over 12 mA has been transported through the low energy beam transport of the LANSCE ion source test stand. The results of these experiments and the effects of different source parameters on the extracted beam current are presented. The limitations of the source prototype are discussed and future improvements are proposed based on the experimental observations.« less
  • The currently employed converter-type negative ion source at Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H{sup -} ion beams in a filament-driven discharge. The extracted H{sup -} beam current is limited by the achievable plasma density, which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which degrades the performance of the H{sup -} conversion surface. In order to overcomemore » these limitations we have designed and tested a prototype of a surface conversion H{sup -} ion source, based on excitation of helicon plasma wave mode with an external antenna. The source has been operated with and without cesium injection. An H{sup -} beam current of over 12 mA has been transported through the low energy beam transport of the LANSCE ion source test stand. The results of these experiments and the effects of different source parameters on the extracted beam current are presented. The limitations of the source prototype are discussed and future improvements are proposed based on the experimental observations.« less
  • Despite of high plasma density, helicon plasma has not yet been applied to a large area ion source such as a driver for neutral beam injection (NBI) system due to intrinsically poor plasma uniformity in the discharge region. In this study, a radio-frequency (RF) ion source with multi-helicon plasma injectors for high plasma density with good uniformity has been designed and constructed for the NBI system of Versatile Experiment Spherical Torus at Seoul National University. The ion source consists of a rectangular plasma expansion chamber (120 × 120 × 120 mm{sup 3}), four helicon plasma injectors with annular permanent magnetsmore » and RF power system. Main feature of the source is downstream plasma confinement in the cusp magnetic field configuration which is generated by arranging polarities of permanent magnets in the helicon plasma injectors. In this paper, detailed design of the multi-helicon plasma injector and plasma characteristics of the ion source are presented.« less