Fast movable remotely controlled Langmuir probe system

A versatile remotely controlled fast reciprocating Langmuir probe has been developed for the TJ-II stellarator. The main components of the system are a removable head, containing the measurement tips, and a displacement system that enables the probe to be displaced in vacuum. The probe displacement system has two different components: a slow one (course length less than or equal to 0.8 m) to set the probe at the initial measurement position, and a fast one (run length = 0.1 m) to obtain the desired measurements within an adjustable time interval during the plasma discharge. The radial movement of the probe is controlled remotely by means of a programmable logical control system, with a radial resolution of better than 1 mm. The fast displacement of the probe (up to 1.7 m/s) is achieved by using a pneumatic system. Its position as a function of time is monitored by means of the on-line response of a linear resistor attached to the fast displacement system. (C) 1999 American Institute of Physics. [S0034-6748(99)61101- 7].