Bias Effects on the Reynolds Stress Using the Multi-Purpose Probe in IR-T1 Tokamak

The effect of the positive bias on Reynolds stress (RS) and its effect on the radial turbulent transport at the edge plasma (r/a=0.9) and scrape-off layer (SOL) region of plasma in tokamak are investigated. The radial and poloidal electric fields (E_\rm r, E_\rm p) and ion saturation current (I_\rm s) are measured by multi-purpose probe (MPP). This probe is fabricated and constructed for the first time in the IR-T1 tokamak. The most advantage of this probe is that the variations of E_\rm r and E_\rm p can be measured in different radii at the single shot. Thus the information of different radii can be compared with high precision. The bias voltage is fixed at V_\rm bias=200 V and it has been applied with the limiter bias that is fixed in r/a=0.9. Moreover, the phase difference between radial and poloidal electric fields, and temporal evolution of the RS spectrum detected by MPP are calculated. RS magnitude on the edge (r/a=0.9) is more than its value in the SOL (r/a=1.02). With the applied bias 200 V, RS and the magnitude of the phase difference between E_\rm r and E_\rm p are increased, while the radial turbulent transport is decreased simultaneously. Thus it can be concluded that RS affects radial turbulence. Temporal evolution of the RS spectrum shows that the frequency of RS is increased and reaches its highest value at r/a=0.9 in the presence of bias.