Session report, 7 February 2019

Author: Kateřina Jiráková

For Daniela Kropáčková’s SOČ, I have promised to perform a couple more discharges which can be used in her work, which involves measurement of Mach number profile using a tunnel probe in the clockwise and anticlockwise field configuration. Her original discharges are located around #29287.

Session goal

The goal is to perform 8 high quality discharges (and possibly a small number of check discharges) which contribute to Daniela’s work. The discharge parameters are:

Gas pressure: 20 mPa
Working gas: H
Preionization: Upper el. gun
CBt capacitors charged to: 1300 V, triggered 5.0 ms
CBD capacitors charged to: 0 V, triggered 5.0 ms
CCD capacitors charged to: 500 V, triggered 5.0 ms
CST capacitors charged to: 0 V, triggered 5.0 ms

4 of these discharges are at clockwise field configuration, 4 at anti-clockwise field configuration. The tunnel probe needs to be installed, the tunnel facing the toroidal direction, with all four electrodes (2 back plates and 2 tunnels) biased to the voltage of -104 V using an array of batteries. In each of the discharge series, the tunnel probe needs to be installed at the following diameters:

\(r\) = 60, 70, 80, and 90 mm

At the same time, the double rake probe is to be installed and the bolometer array should be functional. All the pins in the double rake probe are to be biased at … V, measuring in the Isat regime. This measurement, like the bolometer array, should eventually yield an estimate of plasma movement during the discharge.

##Session discharges and notes

###29444 Master test, testing if I can use the command line to issue discharges. (Without the command line access, I can’t specify clockwise/anti-clockwise orientation.)

###29445 Shot at target parameters, \(p_H=20\) mPa, CW.

###29446 Seeing that the last shot didn’t look like Daniela’s shots, I realised that there was an error in her current SOČ version - her discharges were at \(p_H=10\) mPa, not 20. Fixed this. The desired shot wasn’t reproduced again (high \(U_{loop}\), short shot).

###29447 Tried to reproduce a very nice discharge from this morning (#29440). For some reason, this discharge lasted only 10 ms when its predecessor lasted 16 ms. I am confused.

###29448 Tried the same discharge, but ACW. Like… it’s better than before, at least \(U_{loop}\) doesn’t climb as much during the discharge, but it’s still 12 ms!

##Session end

In the end, I consulted the matter with Vojta and we came to a semi-positive result: The session goal was unrealistic to begin with. There is a huge difference in plasma performance between shots that were made 3 hours apart; it’s foolish to try and reproduce the conditions from two-month-old discharges. Plans were then made to perform baking and glow discharge tomorrow and shoot the entire series at once, replacing the old data.