Ion temperature fluctuation measurements using a retarding field analyzer

Journal Article · Fri Apr 15 00:00:00 EDT 2011 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.3581219· OSTI ID:22062298

Nedzelskiy, I S; Silva, C; Duarte, P; Fernandes, H ^[1]

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1. Associacao EURATOM/IST, Instituto de Plasma e Fusao Nuclear- Laboratorio Associado, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

The retarding field analyzer (RFA) is a widely used diagnostic tool for the ion temperature measurement in the scrape-off-layer (SOL) of the thermonuclear plasma devices. However, the temporal resolution in the standard RFA application is restricted to the ms timescale. In this paper, a dc operation of the RFA is considered, which allows for the measurement of the plasma ion temperature fluctuations. The method is based on the relation for the RFA current-voltage (I-V) characteristic resulted from a common RFA model of shifted Maxwellian distribution of the analyzed ions, and the measurements of two points on the exponentially decaying region of the I-V characteristic with two differently dc biased RFA electrodes. The method has been tested and compared with conventional RFA measurements of the ion temperature in the tokamak ISTTOK SOL plasma. An ion temperature of T{sub i}= 17 eV is obtained near the limiter position. The agreement between the results of the two methods is within {approx}25%. The amplitude of the ion temperature fluctuations is found to be around 5 eV at this location. The method has been validated by taking into account the effect of fluctuations in the plasma potential and the noise contamination, proving the reliability of the results obtained. Finally, constrains to the method application are discussed that include a negligible electron emission from the RFA grids and the restriction to operate in the exponentially decaying region of the I-V characteristic.

• OSTI ID: 22062298
• Journal Information: Review of Scientific Instruments, Vol. 82, Issue 4; Other Information: (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ELECTRIC CONDUCTIVITY
ELECTROMAGNETIC FIELDS
ELECTRON EMISSION
EV RANGE
FLUCTUATIONS
GRIDS
ION TEMPERATURE
ISTTOK TOKAMAK
NOISE
PLASMA POTENTIAL
PLASMA SCRAPE-OFF LAYER
RELIABILITY
TEMPERATURE MEASUREMENT
TIME RESOLUTION