15th Topical Conference on High Temperature Plasma Diagnostics, 19 a 22 de Abril de 2004, San Diego, USA

	Operation of a Multiple Cell Array Detector in Plasma Experiments with a Heavy Ion Beam Diagnostic
	B. Goncalves, A. Malaquias, I.S. Nedzelskiy, L. Pereira, C. Silva, C.A.F. Varandas, J.A.C. Cabral, S.M. Khrebtov, N.B. Dreval, L.I. Krupnik, C. Hidalgo e J. Depablos
	Resumo
	A multiple cell array detector (MCAD) has been developed to investigate the spatial structure of plasma turbulence in fusion plasmas. This system is expected to provide simultaneous measurements of edge and core density fluctuations with both temporal and spatial resolution , extending the range and number of the sample volumes simultaneously recorded by a heavy ion beam diagnostic (HIBD). Since the detector (usually located close to the vessel wall of a plasma device) operates in a strong plasma radiation environment, the effective shielding of the detector presents a special problem. This paper describes and compares the MCAD operation conditions on TJ-II and ISTTOK. In these stellarator and tokamak the MCAD is placed inside the main magnetic field region, enabling partial suppression of the secondary electrons created on the detector surface by secondary ions and plasma ultraviolet radiation. As a result of such a natural magnetic filtering, the observed signal-to-noise ratio is improved, avoiding the implementation of a more sophisticated detector. However, a cross-talk effect due to possible interchange of the secondary electrons between MCAD cells can impair the measurements. Such an influence on the measurements of the ne e seff profile has been identified in HIBD experiments on ISTTOK. To minimize this effect on the TJ-II stellarator, the MCAD cells are miniature Faraday cups. Experimental results of the detector performance will be presented together with the first measurements of ne e seff and density fluctuation profiles of the TJ-II plasmas.