Ion temperature measurements on JT-60 using He beam scattering (invited)

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Abstract
In order to measure the ion temperature of the JT‐60 tokamak, we have developed a Rutherford scattering system using a helium atom beam. A positive‐ion beam generated by an ion source which has a capability of beam energy 200 keV and drain current 3.5 A is converted to a helium atom beam by collision with cold helium gas. The He atom beam, equivalent to 0.6 A, reaches the center of the vacuum chamber of the JT‐60 tokamak. The scattering angle is 7.0°. Scattered helium atoms are analyzed by an E∥B‐type neutral particle energy analyzer with a gas stripping cell. This scattering system has been applied to investigate additionally heated plasmas by the method of neutral beam injection (NBI), ion cyclotron wave (ICRH), lower hybrid wave (LHRH), and combined heating of NBI+LHRH or ICRH in a parameter range of Bt=4.0 to 4.5 T, Ip=1.0 to 3.2 MA, and n̄e≲1×1020 m−3. The ion temperatures obtained by the system are consistent with those measured by Doppler broadenings of Ti xxi and Ti xxii resonance lines. To investigate the influence of ion temperature and density profiles and the beam component of NBI heating on the determination of ion temperature, we have evaluated an energy spectrum of scattered atoms by using a simulation code. The result shows that in JT‐60 plasmas the beam component hardly exerts an important influence on the determination of ion temperature by this diagnostic system.