7th International Reflectometry Workshop for Fusion Plasma Diagnostics, 9-12 de Maio de 2005, Garching, Alemanha

	Further Development of Reflectometry Diagnostics for Measurement of Alfvén Cascades on the JET Tokamak
	S. Hacquin, S. Sharapov, B. Alper, D. Borba, C. Boswell, J. Fessey, L. Meneses, M. Walsh e os Contributos do JET EFDA
	Resumo
	A new class of Alfvén Eigenmodes, so-called Alfvén Cascades, was recently observed in the JT-60U, JET, TFTR and Alcator C-Mod tokamaks. The excitation and observation of these Alfvén Cascades is important for the diagnosis of advanced plasma scenarios. In addition to the determination of the magnetic field topology, the time evolution of the minimum of the safety factor – which is an useful parameter for the triggering of the internal transport barriers - can be inferred from their measurement. It was shown on TFTR that Xmode reflectometry could provide more information on the Alfvén Cascades than the external magnetic pick-up coils generally used for their detection [1]. On JET a new approach based on O-mode measurement in the interferometry regime proved to give an unprecedented clear picture of the Alfvén Cascades [2]. In this paper are discussed the main characteristics of the technique used and some illustrative results are presented.