Research in Support of the Development of a Plasma Pulse-Resolving, Fuel-Cycle Exhaust-Gas Analyzer for the ITER Divertor*

The ITER Diagnostic Residual Gas Analyzer (DRGA) will measure the distribution of gas species, i.e., H, D, T, and impurities, in the divertor exhaust stream and in the plasma periphery. Recently restarted, final design activities are strongly benefiting from testing of prototypical DRGA components and methods on current fusion devices under international collaboration programs. Advances include recent demonstration of simultaneous H/D/T and ³He/⁴He absolute concentration measurements on JET with an upgraded, DRGA-like optical gas analyzer and with detection down to 0.1% levels [1]. Experience with this measurement is currently extending to T containing plasmas and has direct implications for operating ICRH in ITER PFPO-2 [2].  A US-ITER developed, prototype quadrupole mass spectrometer, using custom compensation circuitry to extend the cable length by over 10x the state-of-the-art, has also been successfully demonstrated in JET pre-DTE2 plasma operations [3]. The Molfow+ MC simulation code, applied to the divertor DRGA configuration, has confirmed previously estimated response times [4]. Comparison of this simulation to measurements from a prototype ITER DRGA analysis station on W7X, operated in the OP1.2b campaign, revealed a backflow issue for light gas species, which can limit fuel cycle gas isotopic detection limits and whose mitigation is now included in the ongoing final design plan for ITER.