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Title: H{sup -} ion beam extraction from a transformer coupled plasma source with triode extraction system

Abstract

A continuous-mode H{sup -} ion source has been developed in SNU by using rf transformer coupled plasma source for long lifetime. Recently, its plasma confinement has been improved by modifying the main cusp magnet system that covers rf antenna and plasma electrode regions. The extraction system has also been upgraded to triode extraction system, where permanent magnets in dipole configuration are embedded in extraction electrode to provide additional magnetic field for filtering out fast electrons. Electrode shape, extraction hole size, and gap distance are optimized for high beam currents with low emittance by using PBGUNS code. With new configuration, H{sup -} beam currents of up to 1.67 mA with 1.7 kW, 13.56 MHz rf power are extracted in a continuous mode. Low e/H{sup -} ratios down to 8 are achieved by increasing total filtering field strength up to 190 G.

Authors:
; ; ; ;  [1]
  1. Department of Nuclear Engineering, Seoul National University, Seoul 151-742 (Korea, Republic of)
Publication Date:
OSTI Identifier:
20779021
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: 10.1063/1.2172341; (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; ANTENNAS; BEAM CURRENTS; BEAM EXTRACTION; ELECTRODES; EXTRACTION; HYDROGEN IONS 1 MINUS; ION BEAMS; ION SOURCES; PERMANENT MAGNETS; PLASMA; PLASMA CONFINEMENT; TRANSFORMERS

Citation Formats

Jeong, H.S., Kim, Y.J., Hong, I.S., Park, D.H., and Hwang, Y.S. H{sup -} ion beam extraction from a transformer coupled plasma source with triode extraction system. United States: N. p., 2006. Web. doi:10.1063/1.2172341.
Jeong, H.S., Kim, Y.J., Hong, I.S., Park, D.H., & Hwang, Y.S. H{sup -} ion beam extraction from a transformer coupled plasma source with triode extraction system. United States. doi:10.1063/1.2172341.
Jeong, H.S., Kim, Y.J., Hong, I.S., Park, D.H., and Hwang, Y.S. Wed . "H{sup -} ion beam extraction from a transformer coupled plasma source with triode extraction system". United States. doi:10.1063/1.2172341.
@article{osti_20779021,
title = {H{sup -} ion beam extraction from a transformer coupled plasma source with triode extraction system},
author = {Jeong, H.S. and Kim, Y.J. and Hong, I.S. and Park, D.H. and Hwang, Y.S.},
abstractNote = {A continuous-mode H{sup -} ion source has been developed in SNU by using rf transformer coupled plasma source for long lifetime. Recently, its plasma confinement has been improved by modifying the main cusp magnet system that covers rf antenna and plasma electrode regions. The extraction system has also been upgraded to triode extraction system, where permanent magnets in dipole configuration are embedded in extraction electrode to provide additional magnetic field for filtering out fast electrons. Electrode shape, extraction hole size, and gap distance are optimized for high beam currents with low emittance by using PBGUNS code. With new configuration, H{sup -} beam currents of up to 1.67 mA with 1.7 kW, 13.56 MHz rf power are extracted in a continuous mode. Low e/H{sup -} ratios down to 8 are achieved by increasing total filtering field strength up to 190 G.},
doi = {10.1063/1.2172341},
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 effect of rf wave frequencies on the production of H{sup -} ion is investigated in a transformer coupled plasma H{sup -} ion source at Seoul National University. A Langmuir probe is installed to measure the plasma density and temperature, and these plasma parameters are correlated to the extracted H{sup -} beam currents at various frequencies. The Langmuir probe is also used to measure the density of H{sup -} ions at the ion source by generating photodetachment with an Nd:YAG laser. The extracted H{sup -} currents decrease to a minimum value until 13 MHz and then, increase as the drivingmore » frequency increases from 13 MHz while the relative H{sup -} population measured by photodetachment monotonically decreases as the driving rf frequency increases from 11 MHz to 15 MHz. A potential well formed at the extraction region at high frequencies of more than 13 MHz is considered responsible for the increased H{sup -} beam extraction even with a lower photodetachment signal. The variation in the driving rf frequency not only affects the density and temperature of the plasma but also modifies the plasma potential with the existence of a filtering magnetic field and consequently, influences the extracted H{sup -} current through the extraction as well as formation of H{sup -} ions.« less
  • A vessel for extraction and source plasma analyses (VESPA) is operational at the Rutherford Appleton Laboratory (RAL). This project supports and guides the overall ion source R&D effort for the ISIS spallation neutron and muon facility at RAL. The VESPA produces 100 mA of pulsed H{sup −} beam, but perveance scans indicate that the source is production-limited at extraction voltages above 12 kV unless the arc current is increased. A high resolution optical monochromator is used to measure plasma properties using argon as a diagnostic gas. The atomic hydrogen temperature increases linearly with arc current, up to 2.8 eV formore » 50 A; whereas the electron temperature has a slight linear decrease toward 2.2 eV. The gas density is 10{sup 21} m{sup −3}, whilst the electron density is two orders of magnitude lower. Densities follow square root relationships with arc current, with gas density decreasing whilst electron (and hence ion) density increases. Stopping and range of ions in matter calculations prove that operating a high current arc with an argon admixture is extremely difficult because cathode-coated cesium is heavily sputtered by argon.« less
  • A method to estimate H{sup -} density and velocity in the extraction region of a negative ion source plasma without a Langmuir probe is developed. It utilizes the laser photodetachment with a Faraday cup (PD-FC). The H{sup -} parameters estimated by PD-FC are compared to the results measured by laser-photodetachment with a Langmuir probe (PD-LP). The result shows that H{sup -} velocity estimated by PD-FC is in good agreement with the PD-LP result. Meanwhile, H{sup -} density estimated by PD-FC is twice larger than the PD-LP result. Though a more detailed research, including more effects that are ignored in thismore » study, is needed for H{sup -} density measurement, PD-FC will be a very useful tool for H{sup -} measurements especially near an extraction hole in negative ion sources.« less
  • The ISIS H{sup -} Penning surface plasma source has been developed to produce beam currents up to 70 mA and pulse lengths up to 1.5 ms at 50 Hz. This paper details the investigation into beam extraction and beam transport in an attempt to understand the beam emittance and to try to improve the emittance. A scintillator profile measurement technique has been developed to assess the performance of different plasma electrode apertures, extraction electrode geometries, and postextraction acceleration configurations. This work shows that the present extraction, beam transport, and postacceleration system are suboptimal and further work is required to improvemore » it.« less
  • H{sup -} beam was successfully extracted from a cesium seeded ion source operated using a field effect transistor inverter power supply as a radio frequency (RF) wave source. High density hydrogen plasma more than 10{sup 19} m{sup -3} was obtained using an external type antenna with RF frequency of lower than 0.5 MHz. The source was isolated by an isolation transformer and H{sup -} ion beam was extracted from a single aperture. Acceleration current and extraction current increased with the increase of extraction voltage. Addition of a small amount of cesium vapor into the source enhanced the currents.