Abstract
Wendelstein 7-X (W7-X) is a large optimized stellarator (B=2.5T, V=30m3) aiming at demonstrating the reactor relevance of the optimized stellarators. In 2015 W7-X will begin its first operation phase (OP1.1) with five inertially cooled inboard limiters made of graphite. Assuming the heat loads can be spread out evenly between the limiters, 1 second discharges at 2 MW of ECRH heating power could be run in OP1.1. The expected plasma parameters will be sufficient to demonstrate the readiness of the installed diagnostics and even to run a first physics program. The diagnostics available for this first operation phase, including some special limiter diagnostics, and their capabilities are being presented.A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics
Highlights
To quasi-continuous operation with the beginning of OP2, currently foreseen to start in 2019
The plasma parameters expected to be achievable under these conditions (Te < 3.5 keV, Ti < 0.9 keV, ne < 2 1019 m−3) are expected to be sufficient to demonstrate the readiness of the installed diagnostics and even to run a small first physics program, initially with helium and possibly even a few weeks with hydrogen
In order to enable the short physics program, a group of 8 high priority diagnostics essential for OP1.1 had been defined. This set of essential diagnostics consists of the neutron counters, the flux surface measurements to demonstrate that the magnetic field accuracy has been achieved, the interferometer, Electron cyclotron emission (ECE) and video diagnostic for basic plasma parameter determination and monitoring, and the basic limiter diagnostics, like the limiter thermo-couples, the limiter Langmuir probes and the limiter infrared/visible observation systems, to allow some first SOL physics experiments
Summary
The central system consists of 5 counter tubes of different sensitivity to thermal neutrons, whereas the two peripheral ones contain 4 counter tubes, inserted in a specially designed moderator. The detectors have different sensitivities in order to allow measurement of the neutron yield of the plasma over more than five orders of magnitude with < 15% statistical uncertainty in time intervals of 5 ms. The design aims of the neutron monitors were confirmed by investigations in the reference radiation fields at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany, in 2014. A relative standard uncertainty of < 3% has been achieved for the calibration factors, i.e. the ratio of the neutrons starting from the calibration source and the number of counts observed with the monitors
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