Measurement of Local Radial Electric Field by Using Gold Neutral Beam Probe in GAMMA 10

In the tandem mirror GAMMA 10, a gold neutral beam probe (GNBP) has been developed to measure the local electrostatic potential and electric field of the central plasma. The potentials at two points of which separation is about 1cm can be measured simultaneously with high time resolution. The estimation error of the potential is reduced to be ±15V using a new fitting function for the secondary beam profile. The electric field of the plasma maintained by ICRF only (~240 kW) is a little negative (about -5 V/cm), and it increased by about 20 V/cm and became positive due to the plug ECH with the power of 300 kW.