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DTSTAMP:20260522T153154Z
UID:https://www.ipp.mpg.de/events/23479/4986152
DTSTART:20200306T093000Z
DTEND:20200306T110000Z
CLASS:PUBLIC
CREATED:20200109T135911Z
DESCRIPTION:Änderungsmitteilung: Cancelled\nWendelstein 7-X is the first l
 arge optimized stellarator that was designed with reactor relevant require
 ments in mind. Its design criteria include reduction of the neoclassical h
 eat transport\, minimization of the bootstrap plasma current\, improved fa
 st-ion confinement and a suitable divertor concept. The ultimate goal of t
 he project is to validate the viability of this design line as a fusion re
 actor that could allow a true steady state operation without hazardous dis
 ruption events. W7-X came into operation in 2015 after a lengthy construct
 ion phase and it has now completed two experimental campaigns\, including 
 a short limiter phase and a test divertor phase. This presentation reviews
  the most prominent experimental results from the point of view of the ove
 rall plasma performance. Although the initial experimental time was largel
 y devoted to technical but necessary aspects\, such as commissioning of pl
 asma diagnostics\, error field correction\, first wall conditioning and he
 ating power upgrade\; some prominent physics results that are likely to re
 main relevant in the future were already obtained. In particular\, it is f
 ound that the plasma performance is well below pure neoclassical predictio
 ns in the vast majority of discharges. Typical energy confinement times ar
 e at the level at or below the empirical ISS04-scaling. The ion temperatur
 e in such discharges is limited below 1.6 keV\, with profiles reminiscent 
 of stiffness in tokamaks. Furthermore\, almost no dependence on the effici
 ency of collisional coupling between ions and electrons and on magnetic co
 nfiguration (effective helical ripple) is observed. But\, a significant an
 d serendipitous improvement of the plasma performance is observed after th
 e injection of a series of frozen hydrogen pellets that leads to very peak
 ed density profiles. Ion temperatures above 3 keV and energy confinement t
 imes above the ISS04-scaling\, were achieved in post-pellet phases. This c
 onditions correspond to the highest triple product realized in stellarator
 s so far. At least two important conclusions can be drawn from the describ
 ed observations. Firstly\, the record parameters obtained with pellet inje
 ction strongly suggest that the W7-X transport optimization is effective. 
 Secondly\, the findings in non-pellet cases imply that the plasma performa
 nce in W7-X is otherwise dominated by anomalous losses. Even though a deta
 iled understanding of turbulent losses still needs to be elaborated with t
 he help of e.g. gyro-kinetic GENE simulations\, presently it appears that 
 peaking of the density profile is important for improving the plasma perfo
 rmance. Future experiments to validate this conjecture will benefit from f
 urther improved experimental capabilities\, such as first wall cooling\, a
 ctive pumping\, continuous pellet injection\, increased heating power. Apa
 rt from that\, a truly steady state plasma operation will soon become poss
 ible after installation of water cooled targets.\nVortragender: S. A. Bozh
 enkov 
LAST-MODIFIED:20200305T115523Z
LOCATION:IPP Greifswald\, Raum: HGW S1 (Übertragung Hörsaal D2)
ORGANIZER;CN=Dmitry Moseev:mailto:dmitry.moseev@ipp.mpg.de
SUMMARY:Institutskolloquium: WENDELSTEIN 7-X ON THE WAY TO HIGH-PERFORMANCE
  PLASMAS
URL;VALUE=URI:https://www.ipp.mpg.de/events/23479/4986152
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