Month: December 2012

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Pump station testing

Completed tests:

1.  Changed oil, rebuild plumbing, wired up extension cord and changed plug, demonstrated basic function.

2. Checked base vacuum: 1*10^-2Torr within ~ a minute and stable over ~5 hours.  For comparison, Andrea thesis (pg 139) reports 0.3 Torr ultimate pressure while pumping on the empty column.

3. Plumbed up a flow meter in series with a needle valve.  Air flow was adjusted from 8-18 CFH (0.13-0.30 CFM), calibrated for CO2, with corresponding input pressures 0.25 – 1.1 Torr.  Andrea estimates a purge flow of 0.1cfm for the exo200 filter.  For comparison, Andrea’s thesis (pg 141) shows tank pressures of 4-16 Torr over a purge flow range of 1-4 l/s (2-8 cfm), with the columns loaded.

4.  System ran for 7.5hrs on 12/21/12 and for 26hrs on 1/2/13 with no gas load to check for stability.  Base pressure was stable at 1*10^-2 Torr and no “hot electronics” smell in either case.

5. System ran from 1/3 to 1/7 with about 10cfh (as calibrated for CO2) of air.  Base pressure stable around 0.2 Torr.  No excessive heat or noise, some smell of pump oil.

6. Pumpdown tests on column 1/9.  Column was blanked off on one side, connected to ISO80 valve input on the other with (all) the 3″ plastic tubing.  Test sequence (repeated 3 times) was:

  1. Column full, valve closed.
  2. Pump started, pressure noted
  3. Valve opened, pressure noted
  4. Pump stopped, system vented
  5. Valve closed, oil level noted.

Plot of pressure vs time while pumping out one column below. The system reaches 2*10^-2 Torr in about a minute.

The oil level for the backing pump at the end of each trial (pump off) varied between the “off” and “on” marks that Andrea put on the sight glass. No trend observed.

Pressure vs time for pumpstation evacuating one column.
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FFT analysis, influence of vacuum pump, and leakage current

I collected the data with the pump on/off and bias=0, 1.4kV for each situation. I then ran some fast Fourier transform analysis on this data to find if the spike at ~25.4 kHz is due to the pump vibrations or other electronic influence. These are the FFT output graphs over the summation of 400 events.

[Please ignore the titles of the histograms, for some reason ROOT did not use the titles I inserted on the canvas when I saved to jpg.]

All data sets have: temp=room_temp, power=linear_regulated, source=in_chamber

pump off no bias

pump on no bias

bias pump on (spike ~25.4 kHz)

bias pump off (spike ~25.4kHz)

The final graph has a large chunk missing due to a computing error involving the limit of summed amplitudes for root FFT to output to a histogram, but it is largely irrelevant.

We see that the spike is NOT influenced by the pump as much as i is influenced by the HV bias. This seems to be a consequence of the irregularly large leakage current on the Front End Card interface (FEC). The next test to run is to increase the bias by .1kV intervals and do FFT analysis at each step to see if the magnitude of the frequency spike changes, and/or the frequency itself.

Ultimately, the FEC needs to physically be analysed, looking for ground loops or sources of noise of that specific frequency. We can possibly clean it with soap and water as suggested by Liang Yang (I am scared to do this). Also, we can avoid the DAQ board altogether and buy the Ortec 142H preamp for a different circuit set up.

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Game Plan

As the semester comes to a close, I’d like to asses my progress and propose an itinerary for the new semester.

With regards to the liquefaction system, I am waiting the return of our product from 9Scale Vacuum. This will certainly be back by January 19th when I return and so my first plan of action is to reassemble the system and run a couple of cooling tests.

In the mean time, I need to:

1) Meet with Cameron and test my vacuum gauge in the clean tent with his to make sure it is reading accurately.

2) Work on the purification system piping/item organization

3) Build a temperature controller for the heaters

For the first, I’m just waiting for a convenient time when Cam and I are not terribly busy and can get that done. For the second, I need anyone else to help me as moving the pieces around alone does not seem like a good idea (I’d like to have one person hold the piece while the other secures it to the Unistrut). For the last, I need to find the remaining pieces that will go inside the controller. Once I have these, I can properly mark the chassis we have so Sereres (and maybe I) can properly machine it. After that, assembling the controller shouldn’t take more than an hour or two.

A side project is running a special thermal analysis for Andrea. Currently, I am learning how to use SolidWorks Flow Simulation option to properly describe the convection heat transference that will occur in the actual model. I will update this post with a picture of my simplified assembly when I can. Hopefully I will finish this by the end of the semester.

Thus, by early next semester, I hope to finish the three items mentioned above and run some informative cooling tests. After that, the plan will be to finish the purification system and try to liquefy some xenon.