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22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
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High density and high performance operation with pellet injection in W7-X

26 Oct 2018, 14:00
4h 45m
Mahatma Mandir Conference Centre

Mahatma Mandir Conference Centre

Gandhinagar (nearest Airport: Ahmedabad), India
Poster P8 Posters

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)

Presentation Materials

Paper