TJ-II:Charge exchange spectroscopy
At TJ-II, the ion temperature profile has been measured using a charge exchange neutral particle analyser (CX-NPA). The CX-NPA gives the energy spectrum of plasma ions at one point per shot, and the ion temperature can be calculated from this spectrum assuming a Maxwellian energy distribution function. The analyser can perform a poloidal scan covering a low magnetic field section at constant toroidal angle near φ = 85º. Moreover, the particle flux is collimated in order that the tested plasma volume is small (the diameter is about 10 mm on magnetic axis). Due to the geometry of the device, the collected particle beam is very narrow and positioned almost perpendicular to magnetic field, therefore, the pitch of the collected particles is very small, tan-1(v ||/vper) ≤ 3.1·10–2 rad, which means that only the perpendicular velocity of trapped particles is measured. A radial profile is obtained using a series of reproducible discharges. [1] [2]