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Development and characterization of thermal helium beam diagnostic with four helium lines for RFX-mod2 experiment
M Agostini1, P Scarin1, R Milazzo1
1Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), C.so Stati Uniti 4, 35127 Padova, Italy.
The Review of Scientific Instruments
|December 2, 2020
Summary
The upgraded Thermal Helium Beam diagnostic now measures a fourth spectral line, improving accuracy for electron density and temperature in fusion plasmas. This enhancement utilizes new Multi-Pixel Photon Counters for better signal collection near the plasma edge.
Area of Science:
- Plasma Physics
- Fusion Energy Research
- Diagnostic Techniques
Background:
- The Thermal Helium Beam (THB) diagnostic is crucial for measuring electron density (ne) and temperature (Te) in fusion plasma boundary regions.
- Standard THB relies on three HeI lines, but radiation re-absorption at high neutral densities requires accounting for a fourth line (501.6 nm).
Purpose of the Study:
- To upgrade the THB diagnostic by incorporating the measurement of the fourth HeI line (501.6 nm) for improved accuracy.
- To replace traditional photomultiplier tube (PMT) detectors with magnetic field-insensitive Multi-Pixel Photon Counters (MPPCs).
- To prepare the enhanced THB for installation on the new RFX-mod2 experiment for edge plasma characterization.
Main Methods:
- Acquisition of the fourth HeI line (501.6 nm) intensity using a Czerny-Turner spectrograph.
- Replacement of multichannel PMT detectors with two 16-channel MPPC array modules, enabling 32 signal acquisitions (4 lines x 8 spatial points).
- Installation of MPPCs close to the experimental device to minimize optical fiber length and maximize signal intensity.
Main Results:
- The new system successfully integrates the fourth HeI line measurement, crucial for correcting radiation re-absorption effects.
- MPPCs demonstrate comparable or superior performance to PMTs and are insensitive to magnetic fields, allowing closer proximity to the plasma.
- The upgraded THB system is ready for deployment on RFX-mod2, capable of measuring edge electron density and temperature profiles in various plasma conditions and magnetic configurations.
Conclusions:
- The upgraded THB diagnostic with MPPC technology provides more accurate measurements of edge plasma parameters by accounting for radiation re-absorption.
- The system's design facilitates installation and enhances signal collection efficiency, crucial for future fusion experiments like RFX-mod2.
- This advancement supports the goal of detailed edge plasma characterization in both reversed field pinch and tokamak modes in RFX-mod2.
