Theory

The aim of this work is to measure radial profile of tokamak GOLEM and determine electron temperature using ball pen and langmuir probes, where calibration coefficient of ball pen was determined in previous measurement.

\[T_{e} = \frac{U_{float}^{bpp} - U_{float}^{lp}}{\alpha},\]

Where \(U_{float}^{bpp}\), \(U_{float}^{lp}\), \(\alpha\) are parameters we meassure. Using equation (1) can we detemine electron temperature \(T_{e}\) in each position of probes.

Experiment configuration

1. Gas pressure 0.13 - 18 mPa

2. Working gas: hydrogen

3. Pre-ionization: Upper el. Gun

4. \(C_{Bt}\) capacitors charged to: 1300 V, triggered 5.0 ms

5. \(C_{CD}\) capacitors charged to: 350 V, triggered 5.0 ms

The numbers of shots, used for measurement are: \(\# 25980\) to \(\# 25984\), \(\# 25987\), \(\# 25989\) to \(\# 25990\), \(\# 25992\) to \(\# 25995\) and \(\# 25997\) to \(\# 25999\). The radius is set from 105 to 55 mm with a step of 5 mm. During measurement, there is no voltage on LP.

Minutes of the experiment

1. Scan via \(r = \{ 105, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55 \} \ mm\)

2. Altough the value of preassure was set to 20 mPa again, the pressure was 18 mPa during all the shots.

3. There were problems with almost each shot during measurement, because of instabilities and short shot times. We had to repeat some of the shot more then three times.

Data analysis

To measure radial profile and electron temperature, in each position, we used equation (1), where potentials were meassured for each probes position and calibration coefficient of ball pen probe, \(\alpha\), was determined during previous measurement, as \(\alpha = 2.6 \pm 0.7\). Radial profile of electron temperature is in Table and Figure 1.

\(r[mm]\) & 105 & 100 & 95 & 90 & 85 & 80 & 75 & 70 & 65 & 60 & 55
\(T_{e}[eV]\) & 0,23 & 0,33 & 2,78 & 7,12 & 8,74 & 9,21 & 11,47 & 15,60 & 17,16 & 15,99 & 12,41

Conclusion

To sum up, in previous measurement we have found out calibration coefficient of ball pen probe, which we had determied to \(\alpha = 2.6 \pm 0.7\). To find electon temperature dependence on radial range of both probes, we have measured potentials of both probes in each radial range. We have determined electron temperature, using equation (1) a find radial profile for each time interval. Results the results match the expectations, expect last two closest ranges, where probes probably disrupt plasma.