SXR tomography - electric layout

The SXR tomography of MST was composed initially by two diagnostics, each carrying a SXR probe. One is a manipulator (very similar to those used in MST) called SXR1, while the other is more compact, SXR2. The SXR probe, inserted in one of the 1.5 inch porthole of the MST vessel, contains an array of 20 photodiodes (IRD AXUV-20ELM), with a beryllium filter and a pinhole in its front side; both the SXR probes have 16 micron of beryllium, and the foils are curved. 12 diodes were used for each probe, with a total of 24 lines of sight.

The currents from the diodes are amplified by a set of current-to-voltage transimpedance amplifiers. The SXR1 probe used 12 Femto DLPCA-200 amplifiers (variable gains); see figure1; the box which contains the Femto had to be closed during experiments, and left open during the night, manteinance, or when the data measured by the probes are not important (it gets hot inside, otherwise). The SXR2 probe instead used 12 amplifiers built in the electronic lab of MST, see figure2; these were borrowed from the HSX experiment. The amplifiers were numbered and referred to as Femto1, Femto2, or HSX1, HSX2 etc. The power supplies of the amplifiers were floating, but the shielding of the cables that went from the diagnostic to the amplifiers were grounded to MST.

figure1

figure2

The outputs of the amplifiers were then sent to 24 iso-amplifiers (figure3) and then to the digitizers (Joerger TR612). The iso-amplifiers had also floating power supplies; the cables from these amplifiers to the digitizers were grounded on the CAMAC side (the iso-amplifiers were installed just to ground the cables before and after the amplifiers in different point, that is, before to MST and after to the CAMAC).

figure3

The Femto amplifiers had a single power supply, isolated from the MST ground, and positioned at the base of the rack containing the HSX amplifiers (see figure4). Each HSX amplifier had its own power supply (except two modules, that have a common power supply), all isolated from MST ground (using two isolated transformers, one in the base of the rack of the HSX modules, and another near the rack, see figure5). Finally, the iso-amplifiers were powered with isolated power supplies.

figure4

figure5

For the Femto it is only necessary to rotate the knob; the selected gain, and the associated bandwidth, can be read on a table printed on the amplifier; see figure6. These amplifiers are usually used with the following selections: GND (no bias to the photodetectors), L=low noise, FBW and DC.

figure6

The L/H switch selects a factor of 1 or 100, respectively, so, for a certain position of the knob, the total gain is 1x10^8 when the switch selects L (low noise), 100x10^8 when the swith is in the H (high bandwidth) position.

For the HSX amplifiers one has to open it and add/change a resistor. The amplifier has to be switched off, removed from the rack, and brought to the electronic lab. Then reinstall the module in the same position, using the same cables as before. These modules have been changed often, so it is possible that a certain gain was already used: in this case the corresponding resistor can be found taped on the amplifier. It is important to use the same resistor because these amplifiers have been calibrated, both in amplitude and frequency. Ask Mikhail for any question. The values of the resistor to be added can be found in the following table:

The present (17 july 2002) layout is described in the following Word files, one for each SXR probe. This layout is valid for 400kA discharges, sustained or not, without PPCD.

• SXR1
• SXR2

Other settings, for different types of plasma, are reported in the following table; the numbers are the transimpedance, and so 7=1x10^7, 8=1x10^8, and so on). These values are valid for both the SXR probe, except the last column that is valid ONLY for SXR1 rotated 90 degree (in order to have the lines of sight toroidally):

Each time something is changed (amplifier gain, cables, etc.) please write these modification in the corresponding file, with the shot when these are valid, and send the file(s) to me (P.Franz).

From August 2004 the new electronic system has been installed, with 74 new amplifiers and iso-amps. The gain settings are now 1x,2x,3x 10^5,6,7; diodes 18,19,20 of SXR1 have transimpedance 10^6,7,8.

The optimal gains for various kind of experiment are the following:

• 400kA, standard, F=-0.2 or F=0
• 550kA, standard, F=-0.2
• 200kA, PPCD
• 400kA, PPCD
• 500-550kA, PPCD

and can be found on these files:

• 15 microns on all probes, word or pdf
• two-foil configuration, word or pdf

The exact gains, transimpedance etc. should be written also in the MST pulse-file. An IDL routine can be used to do this. First open a terminal and log into THOR, username MSTDATA (THOR is used because this routine runs during the experiments, and also the shot=-1 has to be changed); then type the following commands:

THOR>cd fd
THOR>@login

(these set IDL and the library of routine to be used) and then start IDL. At the IDL prompt type:

IDL>sxr_gain, shot

where shot is the number of the shot from which the modifications are valid. A widget-type window appears:

The window shows the configuration for the SXR1 probe: you can recognise it by the 'SXR_EXTR' (the original name of the SXR1 probe); also '75 degrees' indicates that the probe is that installed in the 75 degree (poloidal) porthole. Click the '165' button above and the card of the SXR2 configuration will be displayed (this probe is inserted in the 165 degree (poloidal) porthole.

Let's suppose the gain of the diode 5 of SXR1=SXR_EXTR has been changed from 1x10^7 to 1x10^8, and suppose that you do this before shot 1020717010. The operations to be performed are:

• write 1020717010 in the left 'Shot' field;
• click on the 'Shot -1' button to activate it;
• click on the droplist 'Transimp' of the diode 5 (the third row) and select '1.0e8', which means a transimpedance of 10^8; leave the 'gain' droplist to 1;
• click on 'Write' and the new configuration is written in the pulse-file, both for the next shot and the "model" shot (-1).

The configurations of both the SXR probes are written in the pulse-file when clicking on 'Write'. The configuration can be written in the pulse-file also later: write the starting and the final shot in the two fields in the bottom and click on 'Write' to store the data.

Here it follows a brief description of each parameter in the widget:

• 'Ampli' droplist: can be 'Femto' or 'HSX'; next there is the droplist to select the number of the corresponding module. This number is written in the amplifier case (F2 for Femto2, A5 for HSX5);
• The 'module' column summaries the amplifiers used for the diodes;
• 'Gain*sign' select the sign of the signal (Femto are negative, -1, HSX are positive, 1), multiplied by the factor 1 or 100; -100 is used for Femto amplifiers when the High Gain switch is used: this introduces a x100 factor, so that 10^6 in this case equals to 100x10^4. Thus -100 and 1.0e4 should be selected for 'Gain*sign' and 'Transimp'. See also the datasheet for the Femto;
• 'Transimp' is the droplist for selecting the transimpedance of the amplifier; see above for the transimpedance to be used when the Femto amplifier is set to High Gain (H/L switch to H);
• The 'Calibration' column summaries the amplification of each module;
• 'Probe orientation': the orientation of the lines of sight. 'Poloidal' means that the probe is looking at the plasma in a poloidal section; 'toroidal 90' means that the SXR1 probe has been rotated 90 degrees anticlockwise;
• 'Insertion': used to specify the position of the probe of the SXR1 diagnostic (that can be moved up and down). 137.1 mm is the measuring position; 0 mm means that the probe is completely extracted. This is present only for SXR1;
• 'VAT valve': specify if the VAT valve of SXR1 is open or not. Only for SXR1;
• 'Filter thickness': the thickness of the Be filter of the probe, in micron (10^-3 mm). 0 means no filter (detectors used as bolometers);
• 'Filter type': specify a flat or a curved Be filter. Both SXR1 and SXR2 have curved filters;
• 'Read': this button can be used to read the layout of the SXR probes for a particular shot, to be specified in the left field (the field on the right is ignored). This is useful to get a configuration for a certain type of plasma; see the table above;
• 'Write': button to write a certain configuration on the MST pulse-file. All the shots between the values contained in the left and the right field are written; if only the left field contain a value only that shot is written. If the 'Shot -1' is selected the configuration is written also for the shot=-1 ("model" shot). Of course one can specify -1 in the left field;
• 'Help': not available;
• 'Quit': to quit the widget.

When a particular shot is written or read the range of shot for that day is reported on the right-bottom of the widget.