Simultaneous measurement of ion and electron temperatures in the scrape-off layer of a small tokamak

Abstract

This article describes a system composed of an electrostatic ion probe associated with an electronic circuit designed and constructed to be used in the scrape-off layer of the TBR-1 tokamak for simultaneous measurements of local electron and ion temperatures. The electronic circuit is discussed. Details of the mechanical structure and dimensions of the probe can be found in another article [Rev. Sci. Instrum. 57, 2205 (1986)]. The circuit is composed of a sweep generator followed by an amplifier. The sweep time can be varied from 50 μs to 50 ms and the probe voltage amplitude from 0 to 200 V. The circuit supplies a maximum current of 250 mA, is short-circuit protected, and provides cable capacitance neutralization. The ion current is detected by a current transformer sensitive to currents as low as 20 μA. The total probe current is measured by the voltage drop in a resistor inserted in the circuit. The system has been tested in the TBR-1 boundary plasma and showed good performance with a time resolution better than 500 μs. The obtained results showed that, for TBR-1 boundary plasma, the ion temperature is about two times the electron temperature.