Abstract
Electron cyclotron resonance heating (ECRH) is the main heating mechanism in the Wendelstein 7-X stellarator (W7-X). W7-X is equipped with five absolutely calibrated sniffer probes that are installed in each of the five modules of the device. The sniffer probes monitor energy flux of unabsorbed ECRH radiation in the device and interlocks are fed with the sniffer probe signals. The stray radiation level in the device changes significantly during the start-up phase: Plasma is a strong microwave absorber and during its formation the stray radiation level in sniffer probes reduces by more than 95%. In this paper, we discuss the influence of neutral gas pressure and gyrotron power on plasma breakdown processes.
Highlights
Wendelstein 7-X (W7-X) is an optimized stellarator with n = 5 symmetry operating in Greifswald, Germany
In its first experimental campaign, OP1.1, it was equipped with 4 MW of Electron cyclotron resonance heating (ECRH) power as a sole source of heating
Influence of the input power and neutral gas pressure on delay time and plasma evolution In Fig. 2 the plasma breakdown time, defined by interferometer is plotted against neutral gas pressure in module 5, measured by a manometer [μA]
Summary
The plasma start-up time is usually defined as time from the beginning of heating, needed for theHα emission to reach its maximum. It was shown [5] that the maximum of the Hα emission corresponds to the moment when interferometer starts detecting first plasma in the vessel and ae-mail: dmitry.moseev@ipp.mpg.de shows that the line integrated density is greater than zero. There the time traces from 02.02.2016, 15:39 UTC show (from top to bottom) the total RF power injected into the vessel, stray radiation energy flux in module 3, and line integrated density measured by interferometer.
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