Laboratory-based validation of the baseline sensors of the ITER diagnostic residual gas analyzer

Abstract

The divertor-specific ITER Diagnostic Residual Gas Analyzer (DRGA) will provide essential information relating to DT fusion plasma performance. This includes pulse-resolving measurements of the fuel isotopic mix reaching the pumping ducts, as well as the concentration of the helium generated as the ash of the fusion reaction. In the present baseline design, the cluster of sensors attached to this diagnostic's differentially pumped analysis chamber assembly includes a radiation compatible version of a commercial quadrupole mass spectrometer, as well as an optical gas analyzer using a plasma-based light excitation source. This paper reports on a laboratory study intended to validate the performance of this sensor cluster, with emphasis on the detection limit of the isotopic measurement. This validation study was carried out in a laboratory set-up that closely prototyped the analysis chamber assembly configuration of the baseline design. This includes an ITER-specific placement of the optical gas measurement downstream from the first turbine of the chamber's turbo-molecular pump to provide sufficient light emission while preserving the gas dynamics conditions that allow for ~1 s response time from the sensor cluster [1]. K: Plasma diagnostics -interferometry, spectroscopy and imaging; Mass spectrometers; Nuclear instruments and methods for hot plasma diagnostics 1Corresponding author.

Sub-divertor fuel isotopic content detection limit for JET and its impact on ICRF core heating and DTE2 operation

“…With state-of-the-art, passive optical spectroscopy used for DTE1, one can see in figure 2(b) that the H minority species is spectrally well separated from D. As such, it seems to be affected primarily by the relatively low spectral line signal over the random noise. On the other hand, the close spacing of the D and T components means that the It is worth noting that a similar (~1%) isotopic detection limit was concluded in a recent, laboratory-based study, using H as a proxy for T in H/D mixtures, for an equivalent subdivertor gas analysis system designed and prototyped for ITER [5]. The system included the same plasma excitation source as was used in DTE1 and until presently (i.e.…”

“…This difference, which has most impact at the low isotopic contents of interest in the present study, is presently attributed to isotopic exchanges processes with the metallic surfaces of the Penning cold-cathode gauges, which is used as the emission source for this spectroscopic technique (see e.g. discussion on surface interaction in the plasma source in [5]). Direct, laboratory studies of these interactions, using the same plasma sources and deploying baking under controlled conditions, as well as a model to describe these processes, are presently under way [16].…”

“…The upgraded sub-divertor gas analysis system for JET-DTE2 has many of the same features as for the corresponding system being designed for the ITER divertor, including the Penning-OGA measurement, whose recently improved detection limits for trace He (down to 0.1%) in a mostly D 2 divertor effluent will benefit both JET-DTE2 and ITER [5]. Thus, a demonstration, in an ILW environ ment, of getting also the fuel isotopic measurement down to the lowest achievable levels, but also the significance of achieving particularly low (<~1%) detection minima on DT plasma performance, are both of great importance to the design of measurement capability for ITER, in particular for its nuclear phase, where the measurement is most challenging.…”

Wisconsin In Situ Penning (WISP) gauge: A versatile neutral pressure gauge to measure partial pressures in strong magnetic fields

“…At such low concentrations the neutral He emission line gets weaker and the molecular spectra of hydrogen isotopes can dominate the emission within the spectral band around the He-I line. Instead of using filtered photodetectors, another study utilized dispersive spectroscopy to avoid such interference and achieved measurements down to the 0.1 % level 21 .…”

First results from the implementation of the ITER diagnostic residual gas analyzer prototype at Wendelstein 7-X

“…The existing P-DRGA was lab-validated at ORNL [6]. It consists of an actively pumped analysis chamber equipped with a commercially available quadrupole mass spectrometer (MKS MV2), a spectroscopically observed Penning trap (Alcatel CF2) and some total pressure gauges for operational purposes.…”