Speaker
Mr
Sergey Bozhenkov
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Description
In this contribution we present details of recent W7-X pellet injection experiments and discuss properties of the achieved plasmas. Hydrogen pellet injections allowed to raise the electron density above $1.2 \cdot 10^{20}$ m$^{−3}$ and to establish: (i) operation above the cut-off for the X2 polarization of the 140 GHz electron cyclotron resonance heating (ECRH); (ii) stable divertor heat flux detachment; (iii) plasmas with the diamagnetic energy above 1 MJ. In the latter case, a series of pellets raised the electron density to almost $10^{20}$ m$^{−3}$ in a hydrogen discharge heated by X2 ECRH with the total power stepped from 2.7 MW to 5 MW. These electron densities are sufficiently high for electron and ion temperatures to equilibrate and to cause a change in the radial electric field. In the reheat phase after the pellet injection, ion temperatures above 3.5 keV could be reached with the ECRH only and a significant plasma pressure is achieved. The volume averaged $\left<\beta\right>$ is about 1%, whereas the peak value $\beta_0$ is about 3.5%. The diamagnetic energy of about 1.1 MJ corresponds to confinement times above 0.2 s. In the middle of the
high energy phase, a sudden crash by about 150 kJ is observed by a number of diagnostics, with an inversion radius present in the ECE and soft X-ray signals. These $\beta$ values allow for the first
time the analysis of the MHD stability and the validation of the Shafranov shift optimization. High central $\beta$ values are also required for the improved confinement of fast ions.
A further improvement of the plasma performance can be achieved by a further increase of the electron density, which requires ECRH heating in the O2 polarization, as the electron densities
are already close to the X2 cut-off. To use the full available ECRH power of 7 MW in the O2 polarization a scenario with a switch of the polarization during the discharge has to be implemented. Such a scenario was successfully tested with initially helium target plasma, because of an easier density control. The hydrogen pellet injection was used to raise the density above the X2 cut-off and to maintain it at this high level for more than half a second. In the second half
of the campaign such a scenario will be attempted for hydrogen target plasmas.
| Country or International Organization | Germany |
|---|---|
| Paper Number | EX/P8-8 |
Primary author
Mr
Sergey Bozhenkov
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Co-authors
Dr
Andreas Langenberg
(Max-Planck-Institut für Plasmaphysik,17491 Greifswald, Germany)
Dr
Christian Brandt
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Daihong Zhang
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Ekkehard Pasch
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Gabor Kocsis
(Wigner Research Center, Association EURATOM, Budapest, Hungary)
Dr
Glen Wurden
(LANL)
Dr
Golo Fuchert
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Mr
Hannes Damm
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Heinrich Laqua
(Max-Planck-Institute for Plasma Physics, Greifswald, Germany)
Dr
Henning Thomsen
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Jens Knauer
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
John Schmitt
(Auburn University, Auburn, AL 36849, USA)
Dr
Juergen Baldzuhn
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Kai Jakob Brunner
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Kian Rahbarnia
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Kieran Joseph McCarthy
(Ciemat)
Dr
Marcin Jakubowski
(Max-Planck-Institut für Plasmaphysik)
Dr
Matthias Hirsch
(Max-Planck-Institut für Plasmaphysik)
Dr
Nerea Panadero Alvarez
(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain)
Dr
Novimir Pablant
(Princeton Plasma Physics Laboratory)
Dr
Ralf Koenig
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Prof.
Robert Wolf
(Max-Planck-Institute for Plasma Physics)
Dr
Samuel Lazerson
(Princeton Plasma Physics Laboratory)
Prof.
Thomas Sunn Pedersen
(Max Planck Institute for Plasma Physics)
Mr
Udo Hoefel
(Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Dr
Yevgen Kazakov
(Laboratory for Plasma Physics, LPP-ERM/KMS)
