Multipoint Thomson scattering measurements in a lowhyphen;density plasma

摘要

A multipoint Thomson scattering apparatus has been constructed to measure electron temperature and density at several spatial locations in a lowhyphen;density toroidal plasma discharge. A multianode microchannelhyphen;plate photomultiplier tube detector is used to provide the multipoint capability of this device. This detector, along with a simple and efficient optical collection system, allows for lowhyphen;density measurements. Critical for lowhyphen;density operation is a low stray light level from the laser, which has been achieved through careful design of the laser beam handling optics. The plasma parameters in which this device operates are in a regime where Langmuir probes are the usual diagnostic method. The design of this device is presented, along with electron temperature and density profiles of an electron cyclotron heated plasma in the Interchangeable Module Stellarator. Comparison is made with Langmuir probe measurements of similar discharges. Discrepancies between these methods are seen, and are attributed to plasma perturbations by the probe.