Diagnostics for steady state plasmas

Abstract

Problems related to the development of diagnostics for steady state fusion plasma experiments are being discussed. The paper concentrates on those necessities already appearing in nowadays non-burning plasma fusion experiments when extending pulse lengths beyond 10 s, i.e. thermal load, erosion, deposition, and long-time signal integration in magnetic diagnostics. Problems arising from high power ECRH under conditions of incomplete absorption are outlined. Individual standard diagnostic systems are discussed to identify their specific problems as well as the opportunities connected with long pulse operation. Burning plasma experiments characterized by intense n-and g-radiation are briefly reviewed for reasons of completeness, dealing with radiation induced processes in windows, fibres, cables, and mirrors. Methods of data handling, real time monitoring, and plasma control are outlined. Index

Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X

“…The local level of stray radiation depends on the source strength, the plasma absorption which, depending on the heating scenario, is a function of electron density and temperature, and the absorption by in-vessel components. Generally, the expected stray radiation level decreases with increasing distance from the ECRH launchers [58,59], and is expected to vary by a factor of ten in W7-X. All in-vessel components, including diagnostics, cabling, etc., are required to withstand up to 50 kW/m 2 of continuous microwave power flux, corresponding to an operational limit set at a total non-absorbed microwave power of 1 MW.…”

Diagnostics development for quasi-steady-state operation of the Wendelstein 7-X stellarator (invited)

“…Very early on in the diagnostic design phase it became clear that starting off with simple only short pulse compatible designs, followed by a later hardening of diagnostics for quasicontinuous operation is just not feasible. 5,6 In the following, the complexity of the various issues that need to be tackled in a large variety of ways is sketched out and examples of their implementation in a number of typical diagnostics are given.…”

The Steady State Challenge for Soft X-Ray Diagnostics on Wendelstein 7-X Stellarator

“…The challenges posed by long pulse discharges to a plasma diagnostic [1,2] can be divided into three topical groups, which are: protection & safety, measurement quality and steady state data acquisition & online analysis. In Fig.…”

“…The steady state operation of Wendelstein 7-X stellarator presently under construction in Greifswald poses special challenges to the diagnostics development [1,2]. A critical issue is the heat load on plasma facing components (~ 500 kW/m^) over a long discharge time (up to 30 min), which leads to the necessity of active cooling.…”