Speaker
Mr
David DOUAI
(CEA, IRFM, Association Euratom-CEA, 13108 St Paul lez Durance, France)
Description
Wall conditioning will be required in JT-60SA to control fuel and impurity recycling and to improve plasma performance and reproducibility. In addition to glow discharge cleaning, operable only in the absence of toroidal field, Electron Cyclotron Wall Conditioning (ECWC) plasmas created with its ECRF launchers are envisioned. ECWC has been successfully operated in Helium at the first harmonic in JT-60U, allowing recovering from disruptions. However, in JT-60SA (R = 2.96 m, a = 1.18 m, B_T= 2.25 T), with gyrotrons frequencies f = 110 or 138 GHz, ECWC discharges will have to be operated at the second harmonic of the EC wave.
This paper reports on Helium ECWC experiments on TCV in support of JT-60SA operation. About forty discharges have been produced in TCV, at a toroidal field B_T = 1.3-1.54 T, with gyrotrons at 82.7 GHz in X2 mode. Hence, the cold ECR layer lies in TCV at R = 0.78-0.92 m, mimicking operation in JT-60SA. Helium pressures ranged between 0.5 and 2x10^-^2 Pa and ECRH powers up to 480 kW, using different launchers. Horizontal and vertical poloidal fields with amplitudes typically 0.1 to 2% of B_T have been used, aiming at extending the discharge vertically and radially. Discharge homogeneity was estimated from the electron density radial profile measured with Far Infrared Interferometry (FIR) and from visible CCD images, while wall coverage was assessed from the ion saturation current measured by the TCV array of wall-mounted Langmuir probes located at the high and low field sides, and at the bottom of the device. Electron densities of 5-15x10^18 m^-^2 and temperatures of 20-40 eV have been measured with the TCV FIR and Thomson Scattering systems. Typical edge temperatures were found to be 3 eV at the probes.
The efficiency of ECWC was assessed from the amount of released D_2 fuel, measured in the exhaust gas using optical Penning gauges connected to the vacuum vessel. About 2x10^2^0 D_2 molecules could be removed with the forty He-ECWC discharges operated in TCV. Despite this, the initiation of a standard ohmic D2-plasma could not be sustained after conditioning. Thus, demonstration of the ability of ECWC, operated in X2 mode, to recover to normal operation still remains to be done. For this, a larger operational domain will need to be investigated, e.g. higher pressures, different field patterns, and longer ECWC operation will be needed.
| Country or International Organization | France |
|---|---|
| Paper Number | EX/P8-31 |
Primary author
Mr
David DOUAI
(CEA, IRFM, Association Euratom-CEA, 13108 St Paul lez Durance, France)
Co-authors
Dr
Akihiko Isayama
(Japan Atomic Energy Agency)
Dr
Alessandro Moro
(Istituto di Fisica del Plasma CNR, Milano, Italy)
Dr
Carlo Sozzi
(Istituto di Fisica del Plasma CNR, Associazione EURATOM-ENEA)
Dr
Christian Theiler
(Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland)
Dr
Daria Ricci
(Istituto di Fisica del Plasma CNR, Milano, Italy)
Dr
Kevin Verhaegh
(Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland)
Dr
Lorenzo Figini
(Istituto di Fisica del Plasma CNR, Milano, Italy)
Dr
Masakatsu Fukumoto
(Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan)
Dr
Miguel Silva
(Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland)
Dr
Patrick Blanchard
(Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland)
Dr
Saul Garavaglia
(Istituto di Fisica del Plasma CNR, Milano, Italy)
Dr
Stefano Coda
(CRPP-EPFL)
Mr
Stéphane Vartanian
(CEA, IRFM, F-13108 St-Paul-Lez-Durance, France)
Dr
Timothy Goodman
(EPFL - CRPP)
Dr
Tom Wauters
(Laboratory for Plasma Physics - ERM/KMS, 1000 Brussels, Belgium, TEC Partner)
Dr
Yoshiaki Miyata
(Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan)
