Development of a compact bushing for NBI

H. de Esch , A. Simonin (1) , C. Grand (2) , Bruno Lepetit (3) , Didier Lemoine , M. Márquez-Mijares , T. Minea (4) , L. Caillault (4) , B. Seznec (4) , T. Jager (4) , E. Odic (5) , Michael J Kirkpatrick (5) , Ph. Teste (5) , Philippe Dessante (5) , K. Almaksour

1 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique
2 ADEME - Agence de l'Environnement et de la Maîtrise de l'Energie
3 Théorie (LCAR)
4 LPGP - Laboratoire de physique des gaz et des plasmas
5 GeePs - Laboratoire Génie électrique et électronique de Paris

Research into a novel type of compact bushing is being conducted through the HVIV (High Voltage holding In Vacuum) partnership between CEA-Cadarache 1 , GeePs-Centralesupélec 4 , LPGP 3 and LCAR 2. The bushing aims to concentrate the high electric field inside its interior, rather than in the vacuum tank. Hence the field emission current is also concentrated inside the bushing and it can be attempted to suppress this so-called dark current by conditioning the internal surfaces and by adding gas. LCAR have performed theoretical quantum mechanical studies of electron field emission and the role of adsorbates in changing the work function. LPGP studied the ionization of gas due to field emission current and the behavior of micro particles exposed to emissive electron current in the vacuum gap under high electric fields. Experiments at Geeps have clarified the role of surface conditioning in reducing the dark current. Geeps also found that adding low pressure nitrogen gas to the vacuum is much more effective than helium in reducing the field emission. An interesting observation is the growth of carbon structures after exposure of an electrode to the electric field. Finally, IRFM have performed experiments on a single stage test bushing that features a 36 cm high porcelain insulator and two cylindrical electrode surfaces in vacuum or low-pressure gas. Using 0.1 Pa N 2 gas, the voltage holding exceeded 185 kV over a 40 mm "vacuum" gap without dark current. Above this voltage, exterior breakdowns occurred over the insulator, which was in air. The project will finish with the fabrication of a 2-stage compact bushing, capable to withstand 400 kV.

Domaines: Physique [physics]; Sciences de l'ingénieur [physics]

H. de Esch, A. Simonin, C. Grand, Bruno Lepetit, Didier Lemoine, et al.. Development of a compact bushing for NBI. FIFTH INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS, BEAMS AND SOURCES (NIBS 2016), Sep 2016, Oxford, United Kingdom. pp.060003, ⟨10.1063/1.4995790⟩. ⟨hal-02071160⟩