A new diagnostic method for local particle transport, which is based oninjection of the tracer-encapsulated solid pellet (TESPEL), was appliedfor the first time in experiments on the CHS device. Such aconfiguration of the pellet allows the lithium hydride tracer to reachthe core plasma region and be deposited within a few centimetres in theradial direction, which was confirmed by measurements withphotomultipliers and CCD imaging. The radial diffusion of the fullyionized tracer is observed by means of charge exchange recombinationspectroscopy with the heating neutral beam as a source. The local tracerdeposition and complete ionization of the tracer greatly simplify thetransport analysis and allow the use of analytic expressions forderiving the diffusion coefficient, D. With this procedure, thediffusion coefficient was determined for various plasma conditions andwas found to be larger for discharges with higher electron temperature.An impurity transport code was also applied to the experimental data,which allowed more precise calculation of the transport coefficientsincluding the pinch velocity, V. It is expected that a higher accuracywill be achieved for the case of TESPEL injection into a larger-scaleplasma.
Overview of recent TJ-II stellarator results