JLab/UVa Polarized Fusion Discussion Weekly Meeting Minutes





9/18/2015 9/11/2015
8/21/2015 7/31/2015 6/26/2015 6/5/2015 5/29/2015 5/08/2015 5/01/2015 4/24/2015 4/17/2015



  • 09/18/2015

  1. Participants: Wilson Miller, Xiangdong Wei, Kevin Wei, Michael Lowry, Alexandre Deur, Andy Sandorfi, Xiaochao Zheng.
  2. JLab's picture of the L-tube test cell filled with two pellets: SPF L-tube tests Sept 18.pdf
    1. the jlab setup needed weights to keep the L-tube in place due to pressure. This should not be necessary if we use plastic tubing (and cutting a groove around the tube for the O-ring to sit in).
    2. two pellets were lost/broken during the fill process. In order to remove static electricity from the pellets for them to drop into the L-tube, the pellets were washed in ethanol and then pumped in an oil bath at 200C for 18 hours. Then the 4He permeation at dry-ice temperature was measured again but it appeared the permeation has changed w.r.t. before the ethanol wash (page 2 of slides, lower right, black data points.)
  3. Wilson sent an updated image of 3 plastic beads (2mm dia), with improved resolution: MR image 9-10-2015.png
  4. Alexandre will move the complete support structure from JLab to UVa.
  5. Alexandre will move one pressure-reducing tube to JLab for measuring the pressure drop.

  • 09/11/2015

  1. Participants: Wilson Miller, Xiangdong Wei, Kevin Wei, Alexandre Deur, Andy Sandorfi, Xiaochao Zheng.
  2. Andy's summary on thermal tests: Summary JLab Thermal Tests.pdf The essence is the following:
    1. we can easily go from 200 C directly to Dry Ice at -78 C in seconds without any problems or signs of damage to the glass.
    2. the temperature of He gas inside the L-tube follows the change in bath temperature, but a little more slowly - time constant of 28 sec.
    3. there is negligible mixing of the hot gas at the bottom of the L-tube with the cold gas above it. As a result a pressure differential will be created as we cool the pellet, so we need to make sure we don't buckle the shell as we cool the L-tube.
    4. The buckling pressure for the thin shells at 200 C is 3.8 atm, but goes to 21 atm at Dry Ice. We need to keep the pressure differential across the pellet wall below about 1/2 the buckling pressure to have some safety margin. (The thicker walled shell could go higher.)
    5. With the thin shells we should start off trying to fill to 4 atm at 200 C. That would certainly be safe. I will do a proper calc taking into account.
      the time constants for cooling the gas.
  3. Andy's calculation on pressure due to cooling: Differential pressure from cooling.pdf
    1. I've calculated the time evolution of the pressures within the pellets when going from 200 C to either dry ice (top panels in the attached plot) or to LN2 (bottom panels). The theoretical buckling pressure limits are shown as the blue (14 micron wall) and red (26 micron) curves. The 26 micron wall pellets are never a problem - we should start with these.
    2. However, at 8 atm (left panels) the calculated pressures (red points) come too near the 14 micron limits (blue curves). With the thinner pellets weshould limit the initial pressure to about 5 atm.
  4. Design for the multi-stage filling tube:
    1. Xiaochao's initial sketch: cell_2015_3.png
    2. Andy measured the volume of one of the L-tubes, see L-tube volume.pdf
      1. the 5.5 cc includes 0.5cc in the thick walled bottom 10 cm length and 5 cc in the upper part that ends in the valve seat). This is V1 in the sketch.
      2. The cell part of V2 is 9.0-5.5=3.5cc.
    3. measured I.D.: chem-thread is 0.307in or 7.80mm; valve is 0.215in or 5.46mm on both sides. We want to max the fill pressure (as long as it is below 4-5 atm). So want to minimize the fill-valve portion of V2 and maximize V3. Also,Wilson mentioned the O-ring might pop off  in the bottom valve of the original sketch.
    4. So here is a modified sketch: cell_2015_3c.png. Assuming the "minimized" length of V2 is 2cm, then V2=3.5cc+(2cm)*pi*(5.46mm/2 to 7.8mm/2)^2 = 3.5cc+(0.47cc to 0.96cc) = 3.97cc to 4.46cc; V3=(20cm)pi(5.46mm/2)^2 = 4.68 cc.
    5. Estimate of fill pressure using the calculated volume: If we fill V3 with 8atm, the filling pressure would be 8atm*(V3)/(V1+V2+V3)=8atm*(4.68)/(5.5+3.97+4.68) to(4.68)/(5.5+4.46+4.68) = (0.33 to 0.32) * 8atm. People seem to be happy with this ratio.
  5. Xiangdong's coil support design:
    1. drawing: MRI Coil Form Assembly-Half View.pdf
    2. video: Explosion1_1.wmv
  6. Wilson updated from the imaging side: gas self-diffusion may be the ultimate limit on imaging resolution. This effect should be temperature-dependent but we are not sure how much it will change. Wilson is trying to find a way to deal with this, aiming for 0.5mm in all directions.
  7. We talked about safty: need a pexi-glass shield, face-shields, ear plugs, gloves.
  8. We talked about the test sequence:
    1. setup the L-tube, the filling valves, the manifold from the polarizer;
    2. put the L-tube in the oil bath, pump out the system;
    3. let the polarized 3He in from polarizer, fill the pellet in multiple stages;
    4. close the valve plunge the L-tube into dry-ice, then either measure the cell, or open the valve again, use manifold to pump out gas outside the pellet, for imaging the pellet.
    5. disconnect from the manifold, walk down the hall for imaging;
    6. If we measure the filled cell, the polarization outside the pellet is supposed to be similar to the polarization in the polarizer.
    7. We will start with 2 pellets, so if one breaks, the other still works.
    8. We will repeat this process at liquid nitrogen temperature. There has been some evidence that T1 would drop in the temperatue range of 70-100K due to increased dwell time of 3He on the wall surface and thus a longer exposure to paramagnetic impurities, see this figure from Price & Haeberli NIM-A349(94)321. We need to find at what temperature this effect becomes significant.

  • 08/21/2015

  1. Participants: Wilson Miller, Xiangdong Wei, Andy Sandorfi, Xiaochao Zheng.
  2. General updates since last meeting:
    1. The two broken cells had been repaired and shipped to Andy.
    2. Andy has ordered some glass tubing from Mike to check the thermal shock.
  3. Andy showed a presentation: 3He-pellet-conf-Aug21-topics.pdf
    1. page 2: calculated buckle pressure is 4.8 atm for the thinnest pellet. Would like to keep pressure < 2atm for safety.
    2. page 5: summary of all permeation measurement for 4He. All three batches of pellets gave similar results. The measurement was done at 5 temperatures: dry ice, 0C, room, 100C and 200C, per pellet, and using 2-3 different methods.
    3. page 6: 3He and 4He have almost identical permeation. snapshot: 10sec at 200C, 2hrs at dry ice, and 317 years at LN2
  4. We discussed the test procedure (page 1 of Andy's presentation). A few discussions:
    1. At some point we discussed pumping 3He out of the test cell and image the pellet only. The current plan is to start with imaging the filled cell, and pellet-only image will be measured only if necessary.
    2. Andy suggested we start with 2atm test cell first.
    3. We need to fill the cell in <2atm steps. The plan is to design a small two-valve system and control the filling by volume ratio.
    4. Question: how much density is needed for a good image? Wilson: not sure, but last test was done with 3-4atm at room temp.
    5. Question: why is T1 measured so short, 45min?  Calculation showed tens of hours (see 4/24/2015 minutes). Wilson: could be O2 (manifold of the polarizer is leaky); in his experience with this polarizer (bags, cells, etc.) never saw T1 longer than 1 hour. Impression is it is limited by wall relaxation.
  5. To do list:
    1. Jlab will continue working on flushing the cell and design of the thermal system;
    2. Wilson will continue working on improving the image resolution;
    3. Design the two-valve system -- Xiaochao
      1. info: polarizer cell is about 4"-dia sphere with volume 340mL. Our test cell is about 5cc.
    4. figure out details of the dry ice, LN2 etc at physics -- Xiaochao
      1. Gordon has a 10L thermos we might be able to borrow. Demo lab has two, 5L and 10L, but occasionally need both for the classrooms; LN2 from the physics dewar is about $1/liter; Need a PATEO# if we take any.
      2. we don't have dry ice in the department. Need to order if needed. Demo lab sometimes order 30-70 lbs that cost ~$40.
  6. next meeting will be Friday Sept. 4th.

  • 07/31/2015

  1. Participants: Wilson Miller, Xiangdong Wei, Kevin Wei, Andy Sandorfi.
  2. Wilson has made a first image of the L-shape tube. 3-4atm room-temperature polarized 3He, T1~45min. See meeting minutes by Andy here: 3He fusion conf July 31 summar.pdf 

  • 06/26/2015

  1. Participants: Wilson Miller, Xiangdong Wei, Kevin Wei, Andy Sandorfi, Xiaochao Zheng, (Alexandre joined near the end).
  2. Andy visited Wilson's lab on June 17. Here are pictures of the coil (with cables) and the cell with two glass beads in.
  3. Andy, Xiangdong and Kevin have been doing the permeation test in the past three weeks.
    1. Repeated the measurement for different pressure and temperatures. The result did not change much compare to the 6/5 meeting. Concluded the present test setup limits reaching higher precisions so will stop here. The permeation time is similar to what were reported in the literature.
    2. Prepared individual pellets: put them in to test vials (one pellet per vial) and flushed with 4He gas. Wilson pointed out O2 could be a problem here due to the high depolarization effect -- 0.1 amg O2 would cause a 20-s T1. Measured the O2 content with an RGA (residue gas analyzer) of the 4He gas used and found ~0.1% O2 for the "ultra pure" and even higher for the "ultra ultra pure" helium gas. The O2 in 3He gas used for the hyperpolarizer is not a problem since it reacts out with the alkali vapor right away, but for our test we need to leave the He-flushed test tubes pumping a long time (probably overnight)
    3. one pellet (out of 12) exploded/shattered. Don't know how it happened. But fortunately no damage was done and no safety report was required.
    4. Todo:
      1. continue the flushing practice.
      2. calculate the permeation time of O2 to determine the minimum pumping time for the actual test.
  4. Wilson has been tuning the RF coils
    1. The current RF coil works should work with a linear polarization adaptor box ("LP" box) connecting to the MRI setup. Has both a LP and a circular polarization (CP) box but for some reason the LP box does not work correctly. (Here the LP and CP refers to the x and y component of the excitation B1 field).
    2. When trying to fill the glass cells with pellets, found it was difficult to turn the valve on two of the three cells, and eventually these two cracked. Here is a picture of the cracked valve.  Could it be that the glass-blowing process altered the valve somewhat?
    3. Filled the unbroken glass cell with two beads.
    4. Todo:
      1. will make the LP box work
      2. first will try measuring the thermal 3He polarization in the cell, by filling the cell with 1atm of 3He and 1atm O2. Here the O2 is to decrease T1 so the thermal polarization can be reached as soon as the cell is placed in the MRI setup.  Hopefully these can be done within a week. Then will try the hyper-polarized 3He.
  5. Also discussed the test: we should have the glass cells tested (empty) at UVa first, then flush/fill with 4He at JLab, then back to UVa for the final test.
  6. Other todos:
    1. Xiaochao will talk to Mike Souza about the broken cells. Will see if Mike or Al can fix them (if we purchase new valves).

  • 06/05/2015

  1. Participants: Andy Sandorfi, Xiaochao Zheng; (Wilson is out of town, Xiangdong is at Disneyland, Alexandre's location is unknown).
  2. Andy's update on the permeation test: permeation-June5update.pdf. We discussed the following:
    1. page 1 shows the relevant formula. D: diameter of pellet; w: wall thickness of pellet; kappa: permeation constant.
    2. On page 2, the left graph is for a 2atm filled pellet, the right is for am empty pellet. There is a linear term in pressure due to off-gasing of the pellet and the chamber.
    3. For the filled pellet test (p2 left), it is hard to get a good fit with the (exponential+linear) function.
    4. page 3: fit to various time ranges shows tau=(540\pm 30)sec at 297K, consistent with literature
    5. To dos:
      1. measure chamber off-gasing without the pellet. This will help to quantify how much off-gasing is from the pellet (and how it will eventually affect our polarized pellet)
      2. will repeat the test for other pellets and at different temperatures (we should know the temperature dependence of the off-gasing too)
  3. Detailed information on the glass material from Mike Souza:
    1. Here is the glass handbook from Corning. "Pyrex" is a trademark from Corning when they introduced their borosilicate glass in 1915. However, they also used "pyrex" for glasses made from other materials.
    2. The specific glass used for our test cells is Corning 7740
    3. Information relevant to the thermal and mechanical properties are on page 828 (Table 4), 834 and 838, and are summarized below:
      1. In Table 4, the properties of Corning 7740 are the same as (or at least very similar to) the table summarized below under "5/29" minutes.
      2. On page 834, the equation to calculate thermal stress differ from Xiaochao's simple model by 2(1-nu) where nu=0.20-0.23 for borosilicate is called Poisson's ratio. This causes a factor 1.6 higher thermal shock than Xiaochao's calculation. However, this is almost irrelevant because both the simple and the handbook equations depend on the ultimate strength of the glass, which in reality varies from sample to sample. I would suggest that we adhere to the max thermal shock of 160K (3.2mm thick) to 90K (12.7mm thick) shown in the handbook.
      3. More details of the thermal shock test are given: The max thermal shock of 160K (3.2mm)  to 130K (6.4mm) to 90K (12.7mm thick) were obtained by plunging a 15x15cm^2 plate from a hot temperature into a cold reservior. All surfaces are cooled uniformity. This means the stress is between the center and the surface which for the 160K result is effectively across a 1.6mm thickness. Our test cell wall is probably close to 2-3mm thick which means we might want to limit the shock to 100K.
    4. Xiaochao will bring some pyrex test tubes to JLab to check thermal shock
    5. Xiaochao will calculate the time constant of the glass test cell, to determine how long we need to keep it in boiling water/ice water etc.

  • 05/29/2015

  1. Participants: Andy Sandorfi, Xiangdong Wei, Alexandre Deur, Kevin Wei, Xiaochao Zheng, Wilson Miller
  2. Summary of the past two weeks:
    1. Cells arrived from Princeton and are now in Wilson's lab. Wilson had a first attempt of the RF coil, see a picture here.
  3. Andy, Xiangdong and Kevin have been working on the permeation on one sphere with 23um wall (the other two values available are 14um and 26um)
    1. permeation time is 700-800 seconds at room temperature. Calculation of Andy showed similar values.  At 200C we expect a few tens of seconds.
    2. Next will measure activation energy EK (for formula see Andy's slide from May 1) which can be determined by measuring the permeation time for different wall thicknesses and different temperatures. This will allow calculation under any other pressure and temperature conditions.
    3. if we want 1atm at room temperature for imaging then we need 1.6atm at 200C.
  4. Discussions:
    1. How to put >1atm into the pellet?
      1. We previously talked about using the syringe. But since the polarizer gives 8atm/60%/300ml. Can dispense the gas directly into the test cell.
      2. The gas still need to be cooled first before dispensing.
      3. The manifold connecting the polarizer cell and the dispensing point has a volume of about 20cc and is about 1 foot long.
      4. We can control the dispensing pressure by the several valves available. Note that the pellets' buckling pressure at room temperature is 5atm with burst pressure 15atm (no safety added). So it should be okay if we fill the cell at ~2atm steps.
    2. Heating of the pellets?
      1. We talked about 80C previously, but now we are aiming for 200C for faster permeation.
      2. We talked about Kapton heaters previously, but given the uncertainty of the induced magnetic field it is probably easier to use an oil pot. Oil is heated on a hot plate and then be moved to near the test cell. (We also don't want the hot plate to be around the cell because of the field reason).
      3. We need the heater designed in a way that the test cell can be quicly removed from the oil and dip into ice water or liquid nitrogen.
      4. Calculation on if pyrex glass can sustain the temperature shock? For the simplest model assuming instantaneous establishment of a constant temperature gradient through the full thickness, the max temperature shock is (dT)_max = (F/A)_max /E/alpha where (F/A)_max is compressive or tensile strengh, E is Young's modulus and alpha is thermal expansion coefficient. This simple calculation is independent of the glass thickness. See table below for results (data weblinks are shown below the table)
        Type of glass
        		 borosilicate glass (I guess this is typical pyrex glass)
        		 soda lime (Corning 0080) (I guess this is typical ordinary glass)
        E
        		 64GPaa,b 72GPaa
        alpha
        		 3.3E-6 K-1a,b,c 9.4 E-6 K-1a,c
        compressive strength
        		 2GPab
        (delta T)_max (plunging into cold)
        		 9400 K (calculated)
        tensile strength
        		 282MPab
        (delta T)_max (plunging into hot)
        		 1300 K (calculated)
        max thermal shock from web searches
        		 90K(12.7mm thick) -> 130K (6.4mm thick) -> 160K(3.2mm thick)a 35K (12.5mm thick) -> 65K (3.2mm thick)a
         
        1. http://www.quartz.com/pxtherm.pdf
        2. http://www.udel.edu/chem/GlassShop/PhysicalProperties.htm
        3. Physics for scientists and engineers (textbook), Giancoli.
      5. Findings:
        1. The calculation is based on instantaneous establishment of a constant temperature gradient. The reality differs from the simple model due to finite thermal conductivity. Comparison between the calculation (1300K for tensile) and the max temp shock from the web (90-160K) differ by factor 8-10 possibly due to 1) finite thermal conductivity (which introduce dependence on the thickness; 2) impurity and nonuniformity of glass; and 3) safety factors.
        2. Max thermal shock should be 7-8 times higher for compressive (plunging into cold) than for tensile (plunging into hot). The 90-160K limit is likely for the tensile case, which means the max shock is much higher for the compressive case.
        3. Our glass wall is likely <3mm thick which means the max shock for tensile case is probably slightly higher than 160K, and 7-8 times higher for compressive case. This means:
          1. moving the test cell from hot oil (200K) to liquid nitrogen is probablly okay, but it would provide a high safety factor if we move it first to ice water then to liquid nitrogen, so the thermal shock is always <200K (recall this would be for compressive case so the max shock should be higher than 160K by factor 7-8).
          2. moving the test cell from room temperature to hot oil (200K) may be risky (this is the tensile case where pyrex is expected to have 90-160K max thermal shock. Even if our wall is <3.2mm we may be too close to the max value). So we may want to move the cell from room temp to boiling water first, then to hot oil.
  5. Plan:
    1. Andy's group will continue on permeation test, oil pot design, and cooling pot design.
    2. Wilson will continue working on the RF coil and tuning the imaging conditions.
    3. Andy may visit UVa on June 16.

  • 05/08/2015

  1. Participants: Andy Sandorfi, Alexandre Deur, Xiaochao Zheng
  2. Xiaochao ordered 3 cells from Mike Souza and they should arrive at UVa next week. (Total cost ~$850, anyone want to chip in?) Still need to order the Ethylene Propylene (E.P.) o-rings because Mike ordered valves with the viton o-ring.
    1. Update: Chemglass has discontinued all E.P. o-rings!
  3. Xiaochao will bring pellets to Alexandre during the weekend, so Xiangdong can do the permeation test next week at JLab.
  4. Andy will make some solenoids for the holding field.
  5. Next friday we will have to meet on Friday afternoon instead of 11am.

  • 05/01/2015

  1. Participants: Andy Sandorfi, Alexandre Deur, Wilson Miller, Xiangdong Wei, Xiaochao Zheng
  2. Andy's slide on permeation. References: J Mem Sci 282(06)245.pdf, SandiaTechRef8100 H2.pdf, NIM A615(10)267.pdf,  J Vac Sci Tech A4(86).pdf. Existing data differ by about a factor two for He3 permeation. The last slide shows a proposed test to measure the membrane permeation time. Xiangdong can do this in the week of May 11-15.
  3. Wilson's comments:
    1. shorter imaging time --> poorer image quality; longer time --> better image.
    2. RF can be a Holmholtz-coil-like structure, to allow accommodation of the long liquid N2 holder (see below)
    3. The MRI bore is about 50cm across.
  4. Discussion of the cell design sketch (updated at the meeting):  cell, cell shown with RF. Xiaochao will send these to Mike at Princeton. JLab side will design the LN2 holder.
  5. Discussion of followup items from below.

  • 04/24/2015 discussions only (updated 5/1)

  1. T1 calculation(AD):
    1. dipolar: 744hr/[He](amg);
    2. wall: 90h for average nuclear cell; gradient: (1/90h)*(|gradient of Bx|^2+|gradient of By|^2)/B_z^2.
    3. based on http://galileo.phys.virginia.edu/research/groups/spinphysics/thesis/sol-gel-talk.ps, wall relaxation for 1-in spherical cell are shown below, with extrapolation to 3mm dia x 50mm tube:
      from report sol-gel-talk.ps, all are 1in-dia spherical cells (S/V=3/r=2.36cm-1)
      		 extrapolated to 3mm dia x 50mm tube, 1amg, assuming no pressure dependence. S/V=2/r=13.3 cm-1
      		 extrapolated to 3mm dia x 50mm tube, 10amg, assuming no pressure dependence of wall relaxation
      glass
      		 density (amg)
      		 dipolar (hrs)
      		 wall (hrs)
      		 dipolar
      		 wall
      (assuming no pressure dependence)      		 dipolar
      		 wall
       (assuming no pressure dependence)
      coated pyrex
      		 1.9
      		 392
      		 2809
      		 744h
      		 500h
      		 74.4h 500h
      uncoated pyrex
      		 2.0
      		 372
      		 684
      		 744h
      		 121h
      		 74.4h 121h
      coated GE-180
      		 2.4
      		 310
      		 2693
      		 744h 478h
      		 74.4h 478h
      coated GE-180
      		 2.5
      		 298
      		 2169
      		 744h 385h
      		 74.4h 385h
      uncoated GE-180
      		 2.5
      		 298
      		 190
      		 744h 34h
      		 74.4h 34h
      nuclear (coated pyrex)
      		 8.4
      		 87
      		 136
      		 744h 2-3 (uncoated), 36h (coated)
      		 74.4h

    4. there is a paper on T1 wall-relaxation dependence on pressure and also at 4.2K: http://arxiv.org/pdf/1203.3897v1.pdf, but I have not understood it yet.
      1. Andy's explanation: below 77K (depending on the coating), the sticking time is very high. So 3He would stick to the wall and depolarize very fast.
    5. Conclusion: T1 looks promising.
  2. heater: can use kapton heater (cole parmer) but need to study the field. Xiaochao got a heater and a temperature sensor from JLab. If building an oven can use alumina silicate ceramic (master-carr). There was also suggestion that we can just use boiling water, simpler and with very good knowledge of the temperature.
  3. XZ talked to Al and coating and 4He flushing. 4He is not a problem but Al doesn't recommend coating. It takes some effort and there is no clear evidence that it can improve the cell. (He said he made several for Duke and some of them simply turned out bad for no known reason).
  4. holding field: basic requirement is <10mG/cm gradient (2mG/cm would be even better), 10G or larger. But we decided to start with no holding field and trust the Earth field to be good enough.
  5. small pyrex beads: Al has some, in size 1mm, 2mm and 3mm (diameter)

  • 04/17/2015 meeting

  1. Participants: Andy Sandorfi, Xiangdong Wei, Alexandre Deur, Annalisa D'Angelo, Xiaochao Zheng
  2. Xiaochao's report on the setup in Snyder and an idea for the 3He test: slides
  3. Discussions and to-do's:
    1. T1 calculation -- A.D. (to start with)
      1. start from 3-mm dia x 50mm long tube, that's going to be our minimal size;
      2. T1 vs. field magnitude?
      3. T1 vs. temperature?
    2. Make 4 cells. X.Z. will contact Al about sol-gel coating and 4He flushing in Physics building.
    3. Look for different sizes of glass beads (sub-mm would be great)
    4. Alternate syringe? -- need valve to measure pressure, valve for better sealing, and better control of volume -- X.W.
    5. Make a small RF coil -- XZ will contact Wilson. Small RF will allow much faster imaging and help to increase S/N.
    6. Oven with controller, must be nonmagnetic. JLab can help?
    7. Jlab side can help with a holding field?
    8. A container for holding ice water and/or dry ice and/or liquid nitrogen
    9. Schedule: 1) May 14 (R), 15 (F), 19 (M)? Then week of May 25 and June 1?