Numerical simulation of the RF plasma discharge in the Linac4 H− ion source

This paper presents a Particle-In-Cell Monte Carlo Collision simulation of the Radio-Frequency (RF) plasma heating in the Linac4 H− ion source at CERN. The model self-consistently takes into account the electromagnetic field generated by the RF coil, the external static magnetic fields and the resul...

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Bibliographic Details
Main Authors: Mattei, S., Nishida, K., Onai, M., Lettry, J., Tran, M. Q., Hatayama, A.
Format: Conference Proceeding
Language:English
Subjects:
CERN
Collision dynamics
Computer simulation
Electromagnetic fields
Electron density
Electron energy
Emission analysis
Mathematical models
Optical emission spectroscopy
Particle in cell technique
Plasma
Plasma heating
Plasma jets
Radio frequency
Simulation
Spatial distribution
Temperature distribution
Vibrational states
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Summary:This paper presents a Particle-In-Cell Monte Carlo Collision simulation of the Radio-Frequency (RF) plasma heating in the Linac4 H− ion source at CERN. The model self-consistently takes into account the electromagnetic field generated by the RF coil, the external static magnetic fields and the resulting plasma response, including a kinetic description of the charged species (e−, H+, H 2 + , H 3 + , H−), as well as the atomic and molecular (vibrationally resolved) populations. The simulation is performed for the nominal operational condition of 40 kW RF power and 3 Pa H2 pressure. Results show that the plasma spatial distribution is non-uniform in the plasma chamber, with a density peak of n e = 5 · 1019 m −3 in the RF coil region. In the filter field region the electron density drops by two orders of magnitude, with a substantial reduction of the electron energy as well. This results in a ratio e/H− ≈ 1 in the extraction region. The vibrational population is characterized by a two temperature distribution, with the high vibrational states showing a factor 2 higher termperature. A very good agreement is found between the simulation results and optical emission spectroscopy measurement performed on a dedicated test stand at CERN.
ISSN:0094-243X
1551-7616
DOI:10.1063/1.4995738