Zap SQUIDs and SQUID Tuning

1. Zap SQUIDs
2. Trigger on Test Signal. Turn on Test Signal.
3. Connect Test Signal to feedback, 400 Hz, maybe 100 mVpp
4. Set Polarity to OPEN and ADCsource to PREAMP
5. Start with QET bias = 0, Lockpoint = 0, SQUID bias = 0, Driver offset = 0
6. Increase SQUID bias (negative for RevC.1, positive for RevC) to maximized modulation depth (Vpp) while avoiding cusps
7. Increase Lockpoint (negative for RevC.1, positive for RevC) so that x-axis intersects at point with high slope
8. then set back to normal: turn off test signal, disconnect test signal, set ADCsource to FEEDBACK, set Polarity to NON-INVERTING

In order to take Tc and IbIs measurements and collect phonon data, the SQUIDs need to be tuned. For them to be tuned, you need to remove trapped flux from the SQUIDs by zapping them. The process is outlined below. You should also look at the Soudan SQUID Tuning Procedure to get more background information on SQUID tuning:

1. Open the programs necessary for tuning the SQUIDS:
   1. Go to Labview/DCRCv3/20110303 2.
   2. Open DCRC.llb.
   3. In DCRC.llb open SCDMS DetectorControl.vi.
   4. In DCRC.llb open SCDMS DetectorReadout.vi.
2. In the Detector Control vi under the FrontEnd Settings tab, uncheck “Auto Write” if it’s been selected.
3. At the top of each vi, select the board address for the DCRC board you wish to access.
4. Run both programs that you just opened by pressing the white arrow.
5. In the Detector Readout vi, press the ”Run” button.
6. Under the Front End Settings tab in the Detector Control vi, make note of the phonon channel you’re working on (A, B, C or D).
7. Read from the board its settings.
8. Check “Auto Write”.
9. Set Front End Gain and Output Gain = 1.
10. Set Driver Offset, SQUID bias, Lockpoint, and QET bias = 0.
11. Choose the polarity to be “Grounded” or “Open Loop”.
12. You are now going to zap the SQUIDs. This is necessary to remove trapped flux from the SQUIDs. Go the the “Heat, Flash, Snap, and Zap” tab on the control vi. Towards the bottom right of the vi you will see “Zap Control”. Select ‘Zap All’. You’ll see that it will take some time for this operation to ‘charge’ and then zapping will occur. You should be able to note a slight increase in the tower temperature. When the tower temperature begins to decrease zap all of the SQUIDs once more.
13. For the phonon channel you wish to tune, select “Feedback” as the signal source.
14. Under the Test Signal tab, click the feedback line of the phonon channel you are tuning. Set the wave settings to 300 mVpp at 100 Hz. Correction: as of 2015 and probably earlier, the standard amplitude is 200 mVpp.
15. Start the test signal (click “Start Pulser”) and look at the Readout vi. Select the appropriate phonon channel to view. You should see a triangle wave on the Responsivity window. Check the trace length settings - make sure it’s 16.384 ms (with 400 us look back time) and set the trigger mode to “External”.
16. When you see the triangle wave, go back to the Control vi and switch the signal source to “Pre-amp”. You are now ready to tune the SQUIDS.
17. Increase the SQUID bias by pressing the “+” sign for the SQUID bias scale. Monitor the shape of the signal and stop increasing the bias (by pressing the same button again) when you feel you’ve reached the maximum modulation depth. You can also look at what the signal peak-to-peak in volts is on the Readout vi. This is another indication for whether you’ve reached the maximum modulation depth. If you have achieved this, the shape of the signal should look sinusoidal (there will be a somewhat mirrored image of a sine wave). If you overshoot on the SQUID bias, which would result in the signal magnitude decreasing, you can press the “-” sign to lower the SQUID bias.
    • The ideal of shape of the sinusoidal wave isn’t always a perfect wave. Sometimes it’s better to choose a modulation depth where the top of the wave is slightly flat. It will make it easier to choose a lockpoint in the next step.
    • If the signal has wiggles in it, for example at the peak of the wave, this means there is still some trapped flux and you will need to zap the phonon channels again.
18. Note that there is a second window below the signal window that is labeled “Derivative”. This window will help you determine where to set the lockpoint. The goal is to set the value for the lockpoint such that the greatest slope on the sinusoidal curve is aligned with zero on the y-axis. To do this, increase the lockpoint values by pressing the “+” sign, and press it again when you wish the movement to stop. If you overshoot, you can press the “-” sign.
19. Now it is time to determine what polarity to set the channel on. Switch from “Pre-amp” to “Feedback” and select “Non-Inverting”. A triangle wave should appear in the responsivity window again. However, it will probably look slightly curved. If the signal looks horribly different from a triangle wave, then switch the polarity to “Inverting”. Hopefully you will get a signal closer to the shape of a triangle. If not, you will choose the lesser of two evil signals to designate the polarity. You may also want to make sure that the SQUIDs are still free of flux. Sometimes the SQUIDs still maintain some flux and this will affect the signal. If so, you should stop the pulser and go back to the original settings designated at the beginning of this procedure and re-zap the SQUIDs.
20. Now you may stop the pulser by clicking “Start Pulser” again. The triangle wave should disappear and you should see the noise baseline again.
21. Though not necessary at this point, it is a good idea to determine an approximate value for the QET bias. This value is important because it tells us where to bias the phonon channels in order to have the superconducting sensors transition to normal when an event occurs. Similar to how you varied the SQUID bias, you will change the QET bias gradually. However, you will go in the negative direction, thus initially pushing “-”. Note that the values change in steps of 10. Go slowly when you make the change. Usually QET bias values will range between 40-90 uA. When you reached a value where the pulses become clear, you can stop.
22. Now you can save the information for that phonon channel in a file. You will name the file in such a way that identifies which board and dib you are using and whether there is a QET bias in the file. For example, if you are using Dib 1 and DCRC32 and there is no QET bias value set yet, you can name the file Dib1 DCRC32 0V.xml. If there is a QET bias, then change “0V” to “QET”.
    • These phonon values are necessary to take phonon data. When creating the DAQ files to take data, you will be calling up these xml files you’ve created. Thus, you MUST have QET bias values in them. You may wait until after IbIs measurements to finalize the QET bias values for each channel.
23. Record the values you’ve found for the SQUID bias, the lockpoint, modulation depth, QET bias, and polarity in a table in the run diary. Sometimes the SQUID loses its lock, and instead of trying to find all these values from the start again, you can refer to the values in the run diary for automatic tuning.
24. Uncheck “Auto-Write” and switch to the next phonon channel you wish to tune. Repeat all of the steps above to tune that channel until you reach the step to save these values. All four channels will be saved within the same file (for example, Dib1 DCRC32 0V.xml ). Thus, when you go to save the second channel, it will have the same file name as the first channel. HOWEVER, DO NOT CLICK ON THE ALREADY CREATED FILE TO FILL IN THE FILE NAME SLOT. If you do, then you will be overwriting the information from the previous channel. The vi has a bug that makes it do this. Instead, just type out the exact same name of the file you created. It will save these values as a distinct channel. More minor details to be aware of:
    • Make sure that when you switch between phonon channels that “Auto-Write” is not checked.
    • If you want to upload phonon values to the control vi, you have to upload the file four times- once for each channel. Additionally, each time you upload the file, press “Write to Board” to make sure the values have been entered. To further check that this is the case, press “Read from Board”. It is a good idea to often check this because it’s very easy to make a mistake during the saving process or when switching between phonon channels. This is why we record values in the run diary first.
    • Sometimes the SQUIDs become unlocked. To re-lock them, make sure the QET bias is at zero. Then switch the polarity from “Inverting”/“Non-Inverting” to “Grounded”/“Open Loop”. Afterwards, switch back to the proper polarity determined for that channel.
25. Once you are done with one dib, stop the readout and control vi’s you are running by pressing the “STOP” button (NOT the stop sign). Switch to the a new board and repeat the above process. When you’ve finished with all three boards, the SQUIDs will have all been tuned.