--- categories: Training, Reports format: markdown toc: yes title: Impact of toroidal magnetic and electric fields on the floating potential of the glow discharge on the GOLEM tokamak ... Introduction ============ Goal of this session conducted in 8th November 2012 at GOLEM tokamak was to study spatial floating potential dependence $U_f(z)$ of glow discharge induced in tokamak chamber for various toroidal electric fields (current-drive) in H and He plasma for various initial pressure values. Floating potential sensor deployed on GOLEM consists of linear array of 16 cylindrical tips, each of radius $R=0.35 \mathrm{mm}$ and length $b = 2 \mathrm{mm}$. Array spacing is $a=2.5 \mathrm{mm}$. Every tip is grounded by 1/101 divider consisting of resistors 6 $\mathrm{k\Omega}$ and 600 $\mathrm{k\Omega}$. Tips were oriented radially outward from torus center. Outermost 12 tips were connected through divider to 12 channel 16 bit Data Acquisition Systems (DAS) referred as "Papouch\_Zacek" or "Papouch\_Za" in GOLEM documentation. Channel zero is the tip of the probe neareast its end. Parameters of Papouch\_Zacek are 1 MHz sampling frequency and range $\pm 10 \mathrm V$. One shot consists of about 35 ms of data with 1 $\mu$s resolution. We induced glow discharge in GOLEM tokamak chamber by electrode with potential +1000 V with respect to chamber vessel.
Shot 10250: $U_\mathrm{B}$ = 20 V, peak toroidal field $B_t$ ca 9 mT. Glow discharge destroyed by ca 6 mT toroidal magnetic field. |
Shot 10251: $U_\mathrm{B}$ = 10 V, $B_t$ peak ca 5 mT. Glow discharge plasma altered by magnetic field. Turbulence observed. |
Shot 10252: $U_\mathrm{B}$ = 5 V, $B_t$ peak ca 3 mT. 0.5 mT toroidal magnetic field is enough to noticeable alter plasma. Turbulence observed. |
Shot 10253: $U_\mathrm{B}$ = 2 V, $B_t$ peak ca 140 $\mu\mathrm T$. We didn't detect influence of toroidal magnetic field under 140 $\mu\mathrm T$ (ambient Earth magnetic field is ca 50 $\mu\mathrm T$). Steady state observed. |
Shot 10254: Current drive capacitor bank $U_{\mathrm{CD}}=5\mathrm V$, current drive loop voltage $U_L$ ca 0.6 V peak. |
Shot 10255 Current drive capacitor bank $U_{\mathrm{CD}}=10\mathrm V$, current drive loop voltage $U_L$ 0.6 V peak. |
Data acquisition failure. Shot 10256 Current drive capacitor bank $U_{\mathrm{CD}}=20\mathrm V$, current drive loop voltage $U_L$ 1.2 V peak. |
Shot 10257 Current drive capacitor bank $U_{\mathrm{CD}}=20\mathrm V$, current drive loop voltage $U_L$ 1.2 V peak. |
Shot 10258 Current drive capacitor bank $U_{\mathrm{CD}}=40\mathrm V$, current drive loop voltage $U_L$ 1.8 V peak. |
Shot 10259 Current drive capacitor bank $U_{\mathrm{CD}}=80\mathrm V$, current drive loop voltage $U_L$ 3 V peak, turbulent. |
Shot 10260 Current drive capacitor bank $U_{\mathrm{CD}}=160\mathrm V$, current drive loop voltage $U_L$ 5 V peak, turbulent. |
Shot 10261 Current drive capacitor bank $U_{\mathrm{CD}}=320\mathrm V$, current drive loop voltage $U_L$ 9 V peak, turbulent. |
Shot 10262 Current drive capacitor bank $U_{\mathrm{CD}}=320\mathrm V$, current drive loop voltage $U_L$ 9 V peak, turbulent. Repeated for video record. |