Real-time digital heterodyne interferometer for high resolution plasma density measurements at ISTTOK

Journal Article · Wed Oct 15 00:00:00 EDT 2008 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.2956875· OSTI ID:21266536

Marques, T G; Gouveia, A; Pereira, T; Fortunato, J; Carvalho, B B; Sousa, J; Silva, C; Fernandes, H ^[1]

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1. Associacao Euratom/IST Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

With the implementation of alternating discharges (ac) at the ISTTOK tokamak, the typical duration of the discharges increased from 35 to 250 ms. This time increase created the need for a real-time electron density measurement in order to control the plasma fueling. The diagnostic chosen for the real-time calculation was the microwave interferometer. The ISTTOK microwave interferometer is a heterodyne system with quadrature detection and a probing frequency of 100 GHz ({lambda}{sub 0}=3 mm). In this paper, a low-cost approach for real-time diagnostic using a digital signal programable intelligent computer embedded system is presented, which allows the measurement of the phase with a 1% fringe accuracy in less than 6 {mu}s. The system increases its accuracy by digitally correcting the offsets of the input signals and making use of a judicious lookup table optimized to improve the nonlinear behavior of the transfer curve. The electron density is determined at a rate of 82 kHz (limited by the analog to digital converter), and the data are transmitted for each millisecond although this last parameter could be much lower (around 12 {mu}s--each value calculated is transmitted). In the future, this same system is expected to control plasma actuators, such as the piezoelectric valve of the hydrogen injection system responsible for the plasma fueling.

• OSTI ID: 21266536
• Journal Information: Review of Scientific Instruments, Vol. 79, Issue 10; Other Information: DOI: 10.1063/1.2956875; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ACCURACY
ANALOG-TO-DIGITAL CONVERTERS
CONTROL
ELECTRON DENSITY
GHZ RANGE 01-100
HYDROGEN
INTERFEROMETERS
ISTTOK TOKAMAK
KHZ RANGE 01-100
MICROWAVE RADIATION
NONLINEAR PROBLEMS
PIEZOELECTRICITY
PLASMA
PLASMA DENSITY
PLASMA DIAGNOSTICS
RESOLUTION
SIGNALS
VALVES