Development of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments

We have developed a novel and economical neutral-beam injection system by employing a washer-gun plasma source. It provides a low-cost and maintenance-free ion beam, thus eliminating the need for the filaments and water-cooling systems employed conventionally. In our primary experiments, the washer...

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Bibliographic Details
Published in:Review of scientific instruments 2012-08, Vol.83 (8), p.083504-083504
Main Authors: Ii, Toru, Gi, Keii, Umezawa, Toshiyuki, Asai, Tomohiko, Inomoto, Michiaki, Ono, Yasushi
Format: Article
Language:English
Subjects:
ACCELERATION
BEAM CURRENTS
BEAM EXTRACTION
Beams (radiation)
COMPACT TORUS
COOLING SYSTEMS
CURRENT DENSITY
Electric potential
ELECTRON DENSITY
ELECTRON TEMPERATURE
Extraction
HIGH-BETA PLASMA
Injectors
ION BEAMS
ION TEMPERATURE
MAGNETIC FIELDS
Neutral beams
PARTICLE ACCELERATORS
PLASMA BEAM INJECTION
PLASMA DENSITY
PLASMA GUNS
SPACE CHARGE
TOKAMAK DEVICES
Voltage
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Summary:We have developed a novel and economical neutral-beam injection system by employing a washer-gun plasma source. It provides a low-cost and maintenance-free ion beam, thus eliminating the need for the filaments and water-cooling systems employed conventionally. In our primary experiments, the washer gun produced a source plasma with an electron temperature of approximately 5 eV and an electron density of 5 × 1017 m−3, i.e., conditions suitable for ion-beam extraction. The dependence of the extracted beam current on the acceleration voltage is consistent with space-charge current limitation, because the observed current density is almost proportional to the 3/2 power of the acceleration voltage below approximately 8 kV. By optimizing plasma formation, we successfully achieved beam extraction of up to 40 A at 15 kV and a pulse length in excess of 0.25 ms. Its low-voltage and high-current pulsed-beam properties enable us to apply this high-power neutral beam injection into a high-beta compact torus plasma characterized by a low magnetic field.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.4744960