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index

Aim: to measure VA characteristics on the shot to shot basis.

##Experimental setup

##Theory

###Initial configuration:

Date: Afternoon 261114
LP position of 1st pin from the vessel center \(LP_{pos}=107\) mm,
\(V_{bias}\) off,
\(R=100\) Ohm:
LP orientation: pins ahead SouthEast (in the port direction), i.e. probe is oriented perpendicularly to the magnetic field lines
Discharge setup: –UBt 800 –Ucd 500 –Tcd 10000 –Tres 2000 –pressure 1 –preionization 4
Preionization: ECR wave
\(V_{bias}\) measured with 1:100 divider

###Minutes of the experiment:

Aim	Shot(s)	Comments
Reference shot	#17717
Switching on \(V_{bias}\) to ~ 10V	#17718	OK, \(V_{bias}\) goes to ~0.1V
Lp to position \(LP_{pos}\) = 54 mm	#17719	\(I_{sat}\) too high ~ 100 mA
Galvanic insulation implemented for V_bias power supply	#17720	Satisfactory, no problem
Since \(I_{sat}\) is too high, Let’s decrease R to 50 Ohm	#17721	Better, but still \(V_R\) ~9V
Since \(I_{sat}\) is still too high, Let’s take out LP to position 68 mm	#17722 to #17726 fails
	#17727 OK	No effect, still \(V_R\) ~9V
HS discussion: configuration OK reverse \(V_{bias}\) polarity to -10 V to measure \(I_{is}\)	#17728 to #17733 fails
	#17734 OK	Hopefully good result
\(V_{bias}\) = {-20,-30,-40} V	#17735,#17736,#17737	OK, ready for scan
Scan \(V_{bias}\) = {-40,-35,-30,-25,-20,-15,-10,-5,0,1,2,3,4,5,6,7,8,9,10,12} V	From #17739 to #17762	see Figs. 1, 2, 3, 4

###Final experiment configuration:

LP position of 1st pin from the vessel center \(LP_{pos}=68\) mm,
\(V_{bias}\) from -40V (#17739) to 12V (#17762),
\(R=50\) Ohm:
LP orientation: pins ahead SouthEast (in the port direction) i.e. probe is oriented perpendicularly to the magnetic field lines
Discharge setup: –UBt 800 –Ucd 500 –Tcd 10000 –Tres 2000 –pressure 1 –preionization 4
Preionization: ECR wave
\(V_{bias}\) measured with 1:100 divider
Length of pin: 2 mm, diameter of the pin: 0.7 mm => pin surface ~ 3.140.7210^-6 m^2 ~ 4.410^-6 m^2

##Reference shot #17743

Reproducibility of the GOLEM tokamak discharge from #17739 to #17762

\(I_{p}\) scan - alltogether (jpg, svg,canvas,script)

##Raw experimental data

Fig.1: \(V_{bias}\) scan - alltogether (jpg, svg,canvas,script)

Fig.2: \(V_{bias}\) scan - ion side (jpg, svg,canvas,script)

Fig.3: \(V_{bias}\) scan - electron side (jpg, svg,canvas,script)

Fig.4: \(V_{bias}\) scan - alltogether \(U_{bias}\) (jpg, svg,canvas,script)

##Analysis ### Raw data - VA characteristics at specific time with \(10\mu s\) averaging.

The reason for the VA char vanish in the end of the discharge could be fact, that the GOLEM plasma is normally moving up as can be seen here (#11405):

Note the rake probe seen in the photo.

Raw data directory
- <#ShotNo>v_r: \(V_R\) reflecting current via Langmuir Probe @ \(R=50\Omega\)
- <#ShotNo>param_2: abs(Biasing voltage)
\(10\mu s\) averaged data at specific times directory
- <#Time>raw.dat, where #Time \(in <14000,28000> \mu s\) with \(10 \mu s\) step in 2 column format: \(V_{bias}\), \(V_R\).
Files in directory, where #Time \(\in <14000,28000> \mu s\) with \(10 \mu s\) step
- <#Time>raw.dat in 2 column format: \(V_{bias} [V]\), \(I_{Lprobe} [A]\).
- <#Time>Bt.dat in 1 single data format: \(B_t [T]\).
- <#Time>d2f.dat: second derivative of the VA characteristics fit (available during plasma life from 17100 to 20800 us).
- <#Time>eedf.dat: Experimental EEDF (available during plasma life from 17100 to 20800 us).
- <#Time>fm.dat: Maxwell-Boltzman fit to experimental EEDF (available during plasma life from 17100 to 20800 us).
- <#Time>fd.dat: Druyvesteyn fit to experimental EEDF (available during plasma life from 17100 to 20800 us).
Individual figures directory, where #Time \(\in <14000,28000> \mu s\) with \(10 \mu s\) step
Toroidal magnetic field evolution \(B_t\) of the #17743

[Annette Meiners @COMSOL: Electron Energy Distribution Function](http://www.comsol.com/blogs/electron-energy-distribution-function/)

Electron saturation current	Ion saturation current	Electron density	Ion density
Electron temperature	Floating potential	Plasma potential	\(I_{es}/I_{es}\) ration