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Title: Pressure optimization for H{sup -} ion production in an electron cyclotron resonance-driven and a filamented source

Abstract

The negative ion density as a function of the hydrogen pressure (1-8 mTorr) in the electron cyclotron resonance-driven version of the magnetic multipole volume source 'Camembert III' is measured by means of the photodetachment technique. An optimum value is observed between 4 and 5 mTorr, yielding a H{sup -} ion density of about 1.5x10{sup 9} cm{sup -3} in the center of the source. The electron density monotonously increases in the range {approx}(0.5-2.5)x10{sup 10} cm{sup -3} and the electron temperature decreases ({approx}1.25-0.5 eV). The optimum pressure for H{sup -} production is equally reported for a conventional filamented multipole source, in which the influence of rovibrationally excited hydrogen molecules in the electronic ground state on the formation of H{sup -} is analyzed. The physical mechanism which determines the existence of this ion density maximum is discussed.

Authors:
; ; ;  [1];  [2]
  1. LPTP, Ecole Polytechnique, UMR 7648 du CNRS, 91128 Palaiseau (France)
  2. (Germany)
Publication Date:
OSTI Identifier:
20779017
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: 10.1063/1.2172343; (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; ELECTRON CYCLOTRON-RESONANCE; ELECTRON DENSITY; ELECTRON TEMPERATURE; GROUND STATES; HYDROGEN; HYDROGEN IONS 1 MINUS; ION BEAMS; ION DENSITY; ION SOURCES; ION TEMPERATURE; OPTIMIZATION; PLASMA DENSITY; PLASMA DIAGNOSTICS

Citation Formats

Svarnas, P., Breton, J., Bacal, M., Mosbach, T., and Institut fuer Laser- und Plasmaphysik, Universitaet Duisburg-Essen, Campus Essen, D-45117 Essen. Pressure optimization for H{sup -} ion production in an electron cyclotron resonance-driven and a filamented source. United States: N. p., 2006. Web. doi:10.1063/1.2172343.
Svarnas, P., Breton, J., Bacal, M., Mosbach, T., & Institut fuer Laser- und Plasmaphysik, Universitaet Duisburg-Essen, Campus Essen, D-45117 Essen. Pressure optimization for H{sup -} ion production in an electron cyclotron resonance-driven and a filamented source. United States. doi:10.1063/1.2172343.
Svarnas, P., Breton, J., Bacal, M., Mosbach, T., and Institut fuer Laser- und Plasmaphysik, Universitaet Duisburg-Essen, Campus Essen, D-45117 Essen. Wed . "Pressure optimization for H{sup -} ion production in an electron cyclotron resonance-driven and a filamented source". United States. doi:10.1063/1.2172343.
@article{osti_20779017,
title = {Pressure optimization for H{sup -} ion production in an electron cyclotron resonance-driven and a filamented source},
author = {Svarnas, P. and Breton, J. and Bacal, M. and Mosbach, T. and Institut fuer Laser- und Plasmaphysik, Universitaet Duisburg-Essen, Campus Essen, D-45117 Essen},
abstractNote = {The negative ion density as a function of the hydrogen pressure (1-8 mTorr) in the electron cyclotron resonance-driven version of the magnetic multipole volume source 'Camembert III' is measured by means of the photodetachment technique. An optimum value is observed between 4 and 5 mTorr, yielding a H{sup -} ion density of about 1.5x10{sup 9} cm{sup -3} in the center of the source. The electron density monotonously increases in the range {approx}(0.5-2.5)x10{sup 10} cm{sup -3} and the electron temperature decreases ({approx}1.25-0.5 eV). The optimum pressure for H{sup -} production is equally reported for a conventional filamented multipole source, in which the influence of rovibrationally excited hydrogen molecules in the electronic ground state on the formation of H{sup -} is analyzed. The physical mechanism which determines the existence of this ion density maximum is discussed.},
doi = {10.1063/1.2172343},
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}
}
  • A 2.45 GHz microwave ion source was developed at China Institute of Atomic Energy (CIAE) for proton beam production of over 60 mA [B.-Q. Cui, Y.-W. Bao, L.-Q. Li, W.-S. Jiang, and R.-W. Wang, Proceedings of the High Current Electron Cyclotron Resonance (ECR) Ion Source for Proton Accelerator, APAC-2001, 2001 (unpublished)]. For various proton beam applications, another 2.45 GHz microwave ion source with a compact structure is designed and will be built at CIAE as well for high current proton beam production. It is also considered to be used for the test of H{sub 2}{sup +} beam, which could bemore » injected into the central region model cyclotron at CIAE, and accelerated to 5 MeV before extraction by stripping. The required ECR magnetic field is supplied by all the permanent magnets rather than electrical solenoids and six poles. The magnetic field distribution provided by this permanent magnets configuration is a large and uniformly volume of ECR zone, with central magnetic field of a magnitude of {approx}875 Gs[T. Taylor and J. S. C. Wills, Nucl. Instrum. Methods Phys. Res. A 309, 37 (1991)]. The field adjustment at the extraction end can be implemented by moving the position of the magnet blocks. The results of plasma, coupling with 2.45 GHz microwave in the ECR zone inside the ion source are simulated by particle-in-cell code to optimize the density by adjusting the magnetic field distribution. The design configuration of the ion source will be summarized in the paper.« less
  • H{sub 2} microwave (2.45 GHz) pulsed plasma is produced from seven elementary electron cyclotron resonance sources installed into the magnetic multipole chamber 'Camembert III' (Ecole Polytechnique-Palaiseau) from which H{sup -} extraction takes place. The negative-ion and electron extracted currents are studied through electrical measurements and the plasma parameters by means of electrostatic probe under various experimental conditions. The role of the plasma electrode bias and the discharge duty cycle in the extraction process is emphasized. The gas breakdown at the beginning of every pulse gives rise to variations of the plasma characteristic parameters in comparison with those established at themore » later time of the pulse, where the electron temperature, the plasma potential, and the floating potential converge to the values obtained for a continuous plasma. The electron density is significantly enhanced in the pulsed mode.« less
  • The permanent magnet 2.45 GHz electron cyclotron resonance ion source at Peking University can produce more than 100 mA hydrogen ion beam working at pulsed mode. For the increasing requirements of cluster ions (H{sub 2}{sup +} and H{sub 3}{sup +}) in linac and cyclotron, experimental study was carried out to further understand the hydrogen plasma processes in the ion source for the generation of cluster ions. The constituents of extracted beam have been analyzed varying with the pulsed duration from 0.3 ms to 2.0 ms (repetition frequency 100 Hz) at different operation pressure. The fraction of cluster ions dramatically increasedmore » when the pulsed duration was lower than 0.6 ms, and more than 20 mA pure H{sub 3}{sup +} ions with fraction 43.2% and 40 mA H{sub 2}{sup +} ions with fraction 47.7% were obtained when the operation parameters were adequate. The dependence of extracted ion fraction on microwave power was also measured at different pressure as the energy absorbed by plasma will greatly influence electron temperature and electron density then the plasma processes in the ion source. More details will be presented in this paper.« less
  • A metal ion source prototype has been developed: a combination of magnetron sputter technology with 2.45 GHz electron cyclotron resonance (ECR) ion source technology—a so called magnetron ECR ion source (MECRIS). An integrated ring-shaped sputter magnetron with an Al target is acting as a powerful metal atom supply in order to produce an intense current of singly charged metal ions. Preliminary experiments show that an Al{sup +} ion current with a density of 167 μA/cm{sup 2} is extracted from the source at an acceleration voltage of 27 kV. Spatially resolved double Langmuir probe measurements and optical emission spectroscopy were usedmore » to study the plasma states of the ion source: sputter magnetron, ECR, and MECRIS plasma. Electron density and temperature as well as Al atom density were determined as a function of microwave and sputter magnetron power. The effect of ECR heating is strongly pronounced in the center of the source. There the electron density is increased by one order of magnitude from 6 × 10{sup 9} cm{sup −3} to 6 × 10{sup 10} cm{sup −3} and the electron temperature is enhanced from about 5 eV to 12 eV, when the ECR plasma is ignited to the magnetron plasma. Operating the magnetron at constant power, it was observed that its discharge current is raised from 1.8 A to 4.8 A, when the ECR discharge was superimposed with a microwave power of 2 kW. At the same time, the discharge voltage decreased from about 560 V to 210 V, clearly indicating a higher plasma density of the MECRIS mode. The optical emission spectrum of the MECRIS plasma is dominated by lines of excited Al atoms and shows a significant contribution of lines arising from singly ionized Al. Plasma emission photography with a CCD camera was used to prove probe measurements and to identify separated plasma emission zones originating from the ECR and magnetron discharge.« less
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