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VERSION:2.0
PRODID:-//Memento EPFL//
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SUMMARY:First ECRH plasmas in the Wendelstein 7-X Stellarator
DTSTART:20160620T140000
DTEND:20160620T150000
DTSTAMP:20260501T211110Z
UID:90f57e79383d66f36822b27f98963dd7a4167a795a8faab8b91a81f6
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Torsten Stange - Max-Planck-Inst. für Plasmaphysik\, Grei
 fswald\, D\nOn 10th December 2015\, after 15 years of construction\, the f
 irst plasma was created in Wendlstein 7-X (W7-X). It is the world's larges
 t optimized stellarator\, with 3-D shaped superconducting modular coils\, 
 and aims to achieve reactor relevant plasma parameters in steady state ope
 ration. The exclusive heating method in the first operational phase of W7-
 X (OP1.1) is electron cyclotron resonance heating (ECRH) at 140 GHz in X2 
 mode. In combination with the steady-state confining magnetic field at 2.5
  T\, the ECRH system allowed for very fast progress in OP1.1\, with keV pl
 asmas generated by 4 MW of input power already after 3 days of operation\,
  even though the vacuum vessel was not conditioned by glow discharge clean
 ing in advance resulting in an early radiation collapse of the plasma. How
 ever\, OP1.1 was a campaign primarily dedicated to the integral commission
 ing of the heating system\, the diagnostics and the critical components of
  the device itself\, such as the vacuum vessel and coil system. The discha
 rge time was limited by the heat capacity of the uncooled graphite limiter
 s installed on the high-field side (HFS) in each of the five W7-X modules\
 , whereas the gyrotrons are capable of steady-state operation. Up to six g
 yrotrons were used in OP1.1 at power levels usually between 2 and 4 MW. Th
 is talk will focus on physical investigations based on the flexible use of
  the ECRH system\, e.g. shaping of electron temperature and density profil
 e by change of on- and off-axis power deposition\, current drive scenarios
  for compensation of the bootstrap current and advanced heating scenarios 
 like O2-heating. Furthermore\, ECRH power modulation was used for first tr
 ansport studies by use of the ECE diagnostic. The ECE radiometer of W7-X i
 s\, unlike many other ECE diagnostics\, absolutely calibrated and consists
  of 32 channels with additional 16 flexible channels with higher radial re
 solution. The resultant confinement times can be compared with an analytic
 al model for the power balance. The non-absorbed power is determined by st
 ray-radiation probes mounted in each of the five modules\, as well as an e
 lectron cyclotron absorption (ECA) diagnostic\, consisting of 128 mono-mod
 e waveguide antennas incorporated in the HFS graphite tiles opposite to th
 e ECRH launchers. The excellent reliability of the stray radiation monitor
 s enables the use as a plasma operation interlock. Comparing the stray rad
 iation level with the electron cyclotron absorption measurements opposite 
 to the ECRH launchers allows distinguishing poor absorption due to a decay
 ing plasma from poor absorption because the cut-off density has been reach
 ed. The operation of W7-X was started with helium as discharge gas\, follo
 wed by hydrogen\, allowing a direct comparison of start-up and plasma perf
 ormance for both gas species.
LOCATION:PPB 019
STATUS:CONFIRMED
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