2012/10/15

Attendees: Chagani, Codoreanu, Kennedy, Mandic, Monin, Radpour.

1. Third stripline installed successfully.
   • Initial problem witnessed with shorts to ground during Run 31. However, the resistance did increase with decreasing temperature.
   • Shorts seemed to have disappeared completely at the start of Run 32, and have not reappeared. The reasons for this are unknown.
2. New 600 mK rod installed and temperature stages polished.
   • No contact witnessed between 600 mK rod and other temperature stages.
   • 600 mK rod replaced with thicker version.
   • Lugs connected with speaker wire designed to improve contact between 600 mK rod and tower.
   • Installation of lugs difficult due to ease of coming into contact with tower faces. Perhaps shaving them down a little would be advisable. Investigate during next tower installation.
3. Mixing chamber thermometer fixed.
   • Seems to be working well.
   • However, there was damage to the tower thermometer wiring during the upgrade, and hence this thermometer is out of action.
   • Chagani & Zhang to order replacement wire.
   • Unless urgently required for Tc measurements, will install when we next open the fridge for either 6“ can installation or move to new building.
4. Fault with pressure sensor.
   • Not urgent. Have been too busy with other work.
   • Chagani to investigate and contact Pfeiffer.
5. Leaky bottom flange.
   • Seems to have been the culprit for the degredation in base temperature during Run 31.
   • Mechanical workshop saw no evidence of warping and scratching on flanges was minimal.
   • Using thicker indium wire of 0.064” diameter, as opposed to 0.04“ diameter, seems to have done the trick. Run 32 is still young though, so time will tell.
   • Mechanical workshop can make indium wire up to a thickness of 0.064”. However, they have none in stock at the moment. Radpour to place order.
   • Use of thicker wire results in gap between flanges, thus making it easier to shear screws. This would be very painful. Should start using torque driver or spanner. Peter has provided recommended and maximum torque settings. Chagani to purchase necessary tools.
   • Although there is no evidence of warping, it may be best to stick with current orientation.
6. Change He-3 & He-4 pump oil.
   • He-3 pump oil was changed during Run 31.
   • He-4 pump oil should be changed soon, once Run 32 has concluded. Chagani & Radpour to change pump oil.
7. New manual valves for IGH.
   • Valve 12A on IGH has been leaky for a while. This is a common problem with these fridges and prevents cleaning of nitrogen cold trap 1 during circulation. Solution is to install speedivalve at this port on back of IGH.
   • While blowing out nitrogen, helium gas pressure does put strain on He-4 pump. This can lead to oil being blown into the pump's exhaust. A speedivalve should be installed here to isolate the pump during this procedure.
   • Chagani to purchase.
8. Degauss nu-metal shield.
   • Although it does not appear to be a problem currently, we should construct an apparatus to degauss the nu-metal shield.
   • Cannot be permanent as dewar rests on nu-metal shield when lowered.
   • Not urgent at the moment. Codoreanu to investigate.

1. Run 30 (Maintenance): Completed.
   • Empty cryostat cooled to liquid nitrogen temperatures and leak check performed during nitrogen blow out.
   • Due to time pressure, cryostat was not cooled to liquid helium temperatures.
   • No leak was witnessed.
2. Run 31 (G103a): Completed.
   • Leak found in one of the upper IVC flanges. Unsure why this did not show up during Run 30.
   • Leak found in bottom IVC flange. Indium seal was replaced. No leak found during second cool down.
   • Base temperature suddenly increased from 62 mK to 80 mK about a fortnight into the run.
   • He-3 pump oil replaced: no positive effect witnessed.
   • 97 mbar (dump pressure) of He-4 added to mixture: no positive effect witnessed.
   • Around 30 mbar (dump pressure) of He-3 added to mixture: no positive effect witnessed. May have run out of He-3 reserves.
   • Difficult to pump helium out of IVC at 7 K. Thought to be due to poor vapour pressure so fridge was warmed up.
   • Caught leak in bottom IVC flange through luck: helium shortage meant no spare helium during weekend, resulting in IVC warming to >200 K forcing a nitrogen transfer. Leak was found during nitrogen blow out.
   • Leak seems to have developed over time.
   • Charge-only data taken. Radpour to investigate stability and charge collection efficiency.
3. Run 32 (G103a): Current Run.
   • Thicker indium wire of diameter 0.064“, rather than 0.04”, used to seal bottom IVC flange.
   • Have reached base temperature of 59.5 mK, but too early to celebrate.
   • Pressure in still line 0.06 mbar and still is a little warm. Would imply that it is running dry. It may be worth adding mixture to see if the temperature can be driven lower. As base temperature is sufficient for our purposes, this can be done at the end of the run and the ideal amount of mixture inside the fridge noted for future reference.
   • Channel C2 still dodgy. Channel B3 has a weird modulation curve, although peak-to-peak amplitude is about 360 mV (as opposed to >500 mV for other channels), so should be fine.
   • Monin to build script to investigate data quality. Data acquisition suspended for a couple of days. Will use time for other tasks.
   • Paul requested phonon pulse decay constants due to fear of superfluid helium film interfering with the TESs during Run 31. Half-an-order of magnitude less He-4 exchange gas used during cool down. First helium transfer performed very slowly to prevent collection of liquid in main bath until He-4 gas extracted. These precautions should minimise any residual He-4 gas in IVC. Monin to investigate.
   • Monin to test position reconstruction algorithm and compare with a more traditional method.
   • Noise PSDs of modified DCRC boards should be acquired and compared with those from previous runs.
   • Aim for yield plot.
4. Run 33 (G101b): Proposed.
   • Early analysis indicates that a higher electric field strength is required for complete charge collection when compared with G102a.
   • Crystal is due to be repackaged soon, so analysis must be finished and case made for retest.
   • Chagani to conclude analysis.
5. Run 34 (G106a): Expected.
   • Crystal has been tested in He-3 fridge.
   • Arrival at UMN expected soon.
6. Run 35 (Flexible Side Coax): Proposed.
   • Copper wire design currently under construction by Standberg & Codoreanu.
   • Possibility exists to squeeze this run in before Christmas.
7. Run 36 (G102a): Proposed.
   • DMC may request additional run with G102a.
   • Investigation of current results with G102a may lead to additional run.
   • Preparation of paper may lead to additional run with G102a.
   • Likely earliest date for this run is January 2013.

1. Cu wire design.
   • Single strand wire coated with graphite-based paint.
   • Wrapped in heat shrink to provide insulation.
   • Copper tape for shield.
   • Work started by Strandberg. Codoreanu has taken over.
   • Codoreanu to finish building cable and test ultrasonic bath.
   • Chagani to design SCUHBA and order necessary components. Alternatively, could acquire SCUHBA from Berkeley if there are any spares.
   • Codoreanu to investigate method to accurately measure capacitance of cable.
2. NbTi wire design.
   • Room S25 contains four fume cupboards, which will be required if using nitric acid to etch copper off these wires.
   • Strandberg provided list of possible suppliers. Chagani to investigate and place orders.
   • Codoreanu to formulate procedure to strip wires and build cable, based on procedure currently used at Berkeley.
3. Circuit design.
   • Circuit has potential to be improved. Gary's modifications seem to have increased noise, which was expected. However, components may partly be to blame. May be worth looking into. Chagani and Codoreanu to investigate. Not urgent.

1. Lack of disk space on masherbrum.
   • Around 10 GB of space required for each hour of data on G103a.
   • Disk on masherbrum close to bursting. Starting from Run 31 and working backwards, Radpour to cross-check raw data files with those recorded in data summary, zip up data series and move them to RAID array on vuk1. Files should be individually zipped.
   • Data should be stored by run number, eg. for Run 31 in /data/vuk1/cdms/k100/run31/raw/byseries/.
2. MIDAS DAQ
   • DAQ workshop 3-4 November 2012.
   • Angie requires access to boards. Zhang has completed most of the ground work.
   • Chagani has requested fixed IP addresses for boards. Chagani to chase up computing services, finish setting up and perform quick tests.
   • Will need to juggle Run 32's data acquisition with Angie's requirements. May be worthwhile conducting overnight runs as laboratory is quieter at this time. The day can be used to analyse the data and check for good quality. If organised well, should not cause any problems or loss of time.
3. LabVIEW DAQ
   • Current version on CVS has a few bugs in it, however writes out header to data files and enables data to be acquired in iZIP format.
   • Version we use in laboratory has ironed out most of the bugs. However, it doesn't have as many of the useful features.
   • Need to checkout DAQ from CVS, reverse engineer and apply our changes, retest DAQ and upload it back to CVS. Very long-term project.
4. Automating data processing
   • Transferring data from DAQ machine to Linux cluster and reducing it is very time consuming. We should strive to automate this.
   • Analysing data quality also time consuming and can potentially be automated as at Soudan.
   • May be best to move to latest version of LabVIEW DAQ to make use of its features before trying to automate.

1. Low energy mono-energetic neutron source.
   • 1“ diameter BeO2 disc in Prisca's possession.
   • Quotation received for Y-88 and Sn-124 sources.
   • Decision made to purchase Y-88 source. Chagani to fill in paperwork and place order.
   • Can test out source externally before deciding if it is worth installing within cryostat.
2. Beta source.
   • Various designs available.
   • Unsure if seal will hold under thermal shock. Chagani to attempt to obtain empty source housing in an effort to run liquid nitrogen and helium dunk tests.
   • Chagani to obtain quotation, fill in paperwork and place order.
   • Unlikely to be available before G106a has been installed. May be worth an additional run.
   • Unsure if source would be useful for G101b. Extremely unlikely to be available in time unless another run is planned.

• Proposal submitted for 6” silicon crystals.
  • IVC designed to accommodate crystals of this size.
  • 600 mK rod was not part of initial design, and may cause problems during assembly. Chagani to investigate.
  • New 30 mK can and 600 mK rod will be required. Chagani to design and submit to workshop.
  • If flexible side coax tests with superconducting wires are successful, it may be possible to throw out tower and 600 mK rod. SQUIDs will have to be in thermal contact with 4 K stage, which may increase noise. May not be disasterous.

1. Gamma shield has been constructed and tested.
   • Bottom lead shield does not appear to have much of an effect.
   • Top shielding completed and tested with HPGe crystal.
   • Installed around cryostat during Runs 31 & 32. Appears to have reduced pile-up significantly.
   • No bottom shield during Run 32. No obvious effect witnessed.
2. Future of High Purity Germanium (HPGe) detector.
   • Kennedy has completed analysis with HPGe detector.
   • Chagani to check with Daniel if further runs are required.
   • If finished, remove HPGe detector from laboratory and arrange furniture back to the way it was to provide an extra desk.
3. K100 Simulation.
   • Ongoing. Kennedy assigned.

• Introduction of daily meetings.
  • Short, daily meetings of length 5-10 minutes will start from Tuesday 16th October 2012. They will be held every weekday at 2:30 pm in Room S34.
  • The purpose behind these meetings is to better organise the work required, and ensure that everybody understands their responsibilities.
  • The trial period is of indefinite length. The frequency of these meetings can change as we determine what works best.