Alfvén eigenmode and energetic particle research in JT-60U

Abstract

Recent results on investigations of Alfvén eigenmodes, fast ionconfinement and fast ion diagnostics in JT-60U are presented. It wasfound that toroidicity induced Alfvén eigenmodes (TAEs) were stablein negative shear discharges with a large density gradient at theinternal transport barrier (ITB). If the density gradient was smallat the ITB, multiple TAEs appeared around the q = 2 surface (pitchminimum) and showed a large frequency chirping (Δf ≈ 80kHz). In low-q positive shear discharges, the location of the TAEschanged from outside to inside the q = 1 surface, owing to a temporalchange of the q profile. A significant depression of themegaelectronvolt ion population was observed only with high-n (nup to 14) multiple TAEs inside the q = 1 surface. Non-circulartriangularity induced Alfvén eigenmodes were observed for the firsttime. Considerable depression of the triton burnup was observed innegative shear discharges. Orbit following Monte Carlo simulationsindicated that ripple loss was responsible for the enhanced tritonlosses. The fast ion stored energies in ICRF heated negative sheardischarges were comparable to those of positive shear plasmas. Tailion temperatures in high (second to fourth) harmonic ICRF heatingexperiments were first analysed with an MeV neutral particleanalyser. The behaviour of MeV ions produced by ICRF heating wasstudied with gamma ray diagnostics. A scintillating fibre detectorsystem for detecting the 14MeV neutron emission was developed forthe triton burnup studies. Ion cyclotron emission measurementsdiscriminating between parallel and perpendicular components of theelectric field were carried out for the first time.