Investigation of advanced materials for fusion alpha particle diagnostics

Fusion alpha particle diagnostics for ITER remain a challenging task. Standard escaping alpha particle detectors in present tokamaks are not applicable to ITER and techniques suitable for fusion reactor conditions need further research and development. The activation technique is widely used for the characterization of high fluence rates inside neutron reactors. Tokamak applications of the neutron activation technique are already well developed whereas measuring escaping ions using this technique is a novel fusion plasma diagnostic development. Despite low alpha particle fluence levels in present tokamaks, promising results using activation technique combined with ultra-low level gamma-ray spectrometry were achieved before in JET. In the present paper, the use of new advanced detector materials is reported. The material properties beneficial for alpha induced activation are i) ultra-high purity which reduces neutron-induced background activation and ii) isotopic tailoring which increases the activation yield of the measured activation product. Two samples were borrowed from GERDA, an experiment aimed at measuring the neutrinoless double beta decay in 76Ge. These samples, made of highly pure (9N) germanium highly enriched to 87% in isotope Ge-76, were irradiated in real D-D fusion plasma conditions inside the TEXTOR tokamak. Comparison of the calculated and the experimentally measured activity shows good agreement. Compared to previously investigated high temperature ceramic material, this candidate detector offers better prospects for signal to background S/B ratio, energy resolution and particle selectivity due to a unique alpha particle signature. Applicability to ITER is discussed. Finally, research needs for further development of this diagnostic technique are outlined.

BONHEURE Georges;  VAN WASSENHOVE G.;  HULT Mikael;  GONZALEZ DE ORDUNA Raquel;  STRIVAY D.;  VERMAERCKE P.;  DELVIGNE T.;  CHENE G.;  DELHALLE R.;  HUBER A.;  SCHWEER B.;  ESSER G.;  BIEL W.;  NEUBAUER O.; 

2013-11-26

ELSEVIER SCIENCE SA

JRC80523

0920-3796,   

http://www.sciencedirect.com/science/article/pii/S0920379613000380,    https://publications.jrc.ec.europa.eu/repository/handle/JRC80523,   

10.1016/j.fusengdes.2013.01.029,