SPARO cooldown instructions for Paolo

1. Preliminaries
2. Pumping out the Vacuum Jacket
3. Flushing the Reservoir and Pumped-pot Line
4. Cooling to LN₂
5. Cooling to ⁴He
6. Preparing for the first ³He cycle

1. Preliminaries

Some of the photos in these cooldown instructions are slightly out of date. Many of them are from 2000. So you can expect that some of the fixtures may look different from what you are using now. But the procedures are the same.
These instructions were originally prepared for Bob Pernic's use, so there is some "English slang" that may not be easy for someone who is not a native speaker. For example, we use the expression "valve off.." to mean "close the valve to...". "Valve off the pump." means "Close the valve that leads to the pump."
The following is a list of items you will need for cooldown. Some items may be in the closet in MAPO that is near to where you are working on SPARO. When you enter this closet, look on the walls, and on the shelf that is directly over your head.

2 Cylinders UHP Helium
2 Helium gas regulators w/2 psi resolution (attached to above)
thin tygon tubing attached to above (see Fig. 11)
LN2 - 50 liters is plenty to cool SPARO
liquid Helium - we need about 120 liters to cool. Plus 120 liters/week, when bubbling warm He-4 through capillary.
Alcatel 2015 mechanical pump (we have two; one white and one orange).
plenty of KF valves are needed. See photos below to figure out what is needed.
Sufficient amounts of KF fittings, tubing, and a conflat 1.33 blankoff w/ copper gasket.
Capacitance manometer gauge and readout
lab temperature breakout box (the same one you used for warmup)
reservoir pumping fixture (see fig. 4)
blowout fixture (see fig. 4)
pumped pot flushing fixture (the same one you installed just after removal of SPARO from Viper - see figs. 11 and 12 of web instructions "Procedure for Removing SPARO from Viper")
working turbo pump station
working hi-vac gauge on the turbo pump station is very helpful
working leak checker
LN2 fill fixture (see fig. 4 - this tends to get borrowed by other p-CARA projects a lot)

The turbo pumping stations at South Pole are very hard to figure out how to use, and their Penning gages are easy to break.
- The manual is worthless. The little paper taped to the top of the station is more helpful, but still very confusing. It always takes me hours to figure out how to use the gages.
- Allan has been asked by pCARA to go over all the vacuum equipment at Pole so that we can determine its status and determine whether any new parts need to be ordered in preparation for the upcoming season. Jesse Wirth of Yerkes is his point-of-contact in the US and has agreed to help him. Thus, Jesse and Allan could be very helpful to you when you are using the vacuum equipment.
- There are two gages on each turbo station: A low-vac gage (Pirani) and a hi-vac gage (Penning). The Pirani only goes down to 10^-3 (not sensitive enough for us). A Penning gage should go down to around 10^-6, which is lower than the lowest vacuum we expect to get in SPARO. However, the Penning gages are very easy to break by air inrush. I have broken many Penning gages over the years despite my best efforts to avoid sudden venting. Last summer, I broke the Penning gages on both of the turbo stations in MAPO.
- Penning gages are usually easy to repair by simply cleaning them. Jesse Wirth is the expert at Penning gage repair.
- In summer, I cooled SPARO with no high-vac gage, using just the Pirani, but its better to have a working Penning (or other hi-vac gage) so you have an indication if there is any trouble with the cooling.
- Given this situation, you might want to first find someone who is more experienced that you with these turbo pumps (Allan or perhaps Chris) and get them to give you some training before you start to use them. Maybe you already have done this.
The green valves that serve to isolate the external He-3 tanks from the He-3 plumbing inside SPARO should be open during cooldown.
- There is one such valve for each of the two He-3 stages (detector and guard). For location of these valves see Fig. 2 of the SPARO web document "Warmup Procedure for SPARO Cryostat".
- They are in fact probably still open as you were supposed to open them during warm-up.
- you will see the pressure very slightly drop on the analog gages as SPARO cools and the fraction of the Helium-3 gas that is inside SPARO also cools. Eventually it will all get sucked onto the charcoal pumps and the pressures will drop to zero in the Helium-3 systems.
The heat switches (HS) should both be closed for the cooldown. You were supposed to close them for warmup so they are probably already closed.

The He-3 pot HS is marked with red tape, and the charcoal pump HS is marked with green tape.
In the "top view" photo in fig 13 below, the He-3 pot HS is at "4 o'clock" and the charcoal pump HS is at "12 o'clock".
Both of the HS close by turning clockwise.
When closing, you will feel the stop. When opening, there is no stop so you must count turns. The He-3 pot HS requires 90 turns to open and the pump HS requires 40 turns. You should also count turns when closing so you know if you reach the true closed position or merely a "sticky" place.
If you want to check if a valve is open or closed you should open by 5 turns and then turn it in the closed direction until it reaches the stop. (If you reach the stop in about 5 turns then it was originally closed.)
The He-3 pot HS has more friction. You may find that when you start from the closed position and open this valve, you will reach a very sticky point after about 5 or 10 turns. It will seem to you as if the shaft is stuck and cannot be turned further. But have no fear - keep turning. It will eventually get unstuck. it will not break (i hope).

Notes about reinstalling the VAT valves:
- Both the SPARO vacuum jacket valve and the SPARO pumped pot valve are the same - they are both metal-seal VAT valves. Don't confuse these two VAT valves. The one that you used on the pumped pot line is contaminated with Helium. (If you get them confused, send me the serial numbers and I'll tell you which is which.)
- when you reinstall the pumped pot VAT valve, pay attention to the length of screw used. The screws should protrude through the bottom of the stainless steel piece that they thread into, and into some holes in the split Aluminum disks that are ~10 cm dia. and ~ 3 mm thick. This is to give some protection against torsion to the pumped pot assembly. if you use the same screws you took out, we should be fine.
- I can't tell from your photos how much of the SPARO vacuum jacket pumping valve assembly you removed. Perhaps you removed only the VAT valve, or perhaps you also removed the conflat "T" that connects the valve to the main body of SPARO. If you removed the "T", be careful that the screws you use to reinstall it to SPARO are not so long that they touch the bottom of the holes. These holes are not very long. Again, if you use all the same screws in all the same locations, then you will be fine.
- When redoing the "conflat" (copper gasket) connections, (a) clean everything very well, and (b) use washers if at all possible, and (c) tighten with an L shaped Allan wrench and turn hard to really compress the copper. Just as for indium seals, tighten sequentially. I.e., after you have tightened all the screws go around and tighten them again. Keep going around and around until they are all really tight.
The cooldown will take about 3 days to complete. During this time, a power outage or tripped cricuit-breaker in MAPO could cause major damage to SPARO if oil from a pump is gets sucked into SPARO's pumped pot line or vacuum jacket.
- A simple thing like someone using a bandsaw in the machine shop in the past caused the power to trip off on SPARO's pumps due to circuit breaker overload. For this reason, it is good to have someone monitoring SPARO as much as possible during the cooldown, to avoid the dangers of oil contamination of SPARO.
- Once SPARO is at 4 K, with UHP Helium bubbling through the capillary, then there is no worry about oil suckback due to AC power failure.
- Hopefully, oil suckback would not happen even if we did have a power outage at a pump. All the mechanical pumps used have anti-suckback protection, and there is an additional anti-suckback valve (Leybold) that is available, and we have used in the past. Still, it is best to be aware of the danger.

2. Pumping out the Vacuum Jacket

First step is to get SPARO on the turbo. You will need to "rough it out" with a mechanical pump first. When "roughing", I keep a pressure of about 10 Torr on the pump (you will hear it working hard) and it takes about 30 minutes to get the air out. Then you can turn on the turbo pump and the pressure will drop fast. Of course you will need to reinstall the VAT valve to pump out the vacuum jacket. (See notes above on copper gaskets.) But you don't want to open and close this valve a lot because for any all-metal valve the number of open/close operations is limited. Accordingly, put a KF o-ring valve in series with this valve (see photo below). Leave the VAT valve open and use the KF valve to open and close the SPARO vacuum jacket as needed during cooldown.

photos of vacuum jacket pumpout

click to enlarge	Fig 1 - SPARO on turbo: close-up of valves
click to enlarge	Fig 2 - SPARO on turbo

when pressure is low enough, move to leak checker and leak check (a pressure of 1 x 10^-4 mmHg should be low enough)
- Do not leak-check the snout as you will be sure to find a leak through the silicone O-ring that seals quartz window to aluminum snout.
- Leak checking should be done on 10^-9 scale of Alcatel
- Blow He down into main Helium reservoir
Put SPARO back on the turbo pump.
After about 15 hours on turbo-pump, pressure should go to about 3 x 10^-5 mmHg. You can move forward to step 3 (flushing the reservoir and pumped-pot line) while waiting for jacket to reach this pressure.

3. Flushing the Reservoir and Pumped-pot Line

Next you set up the SPARO Alcatel 2015 mechanical pump (see photo below) so that it is possible to pump either the main Helium reservoir, or the pumped pot line, or both. This setup should include the additional possibilities of (1) backfilling the reservoir with UHP Helium, and (2) flushing the capillary by applying back-pressure to the pumped-pot line. To achieve this set-up you will use the "reservoir pumping fixture" and the "flushing fixture" (that you already used for warmup) and also other gages and valves as shown below. If you follow the arrangement shown in the photos below you will be able to easily accomplish the whole pre-cool flushing procedure.

The "diagram" below is only meant to introduce you to the general idea of the flushing setup - the detailed arrangement shown in the photos is the one that should be used. (reminder: some photos are out of date as they are from 2000.)
Don't put the mechanical pump (2015 Alacatel) on the same cart as SPARO. We did this once and the vibrations from the pump caused a plugged capillary in SPARO.

diagram and photos of flushing operations

click to enlarge	Fig 3 - Diagram of flushing setup, giving the general idea
click to enlarge	Fig 4 - photo of reservoir pumping fixture (and other fixtures used later)
click to enlarge	Fig 5 - "flushing fixture" connected to SPARO pumped-pot (This is 2000 photo. See Figs. 11 and 12 of Web instructions "Procedure for removing SPARO from Viper" to see "flushing fixture" used in 2003. The function is the same.)
click to enlarge	Fig 6 - flushing setup: connections to Alacatel 2015
click to enlarge	Fig 7 - wide-angle view of flushing setup

Set up to read temperatures and pressures:
- Attach lab breakout box to SPARO (you used this for warmup; see photos below). This attaches to the "cycling" connector on SPARO. Don't confuse the cycling connector with the preamp connectors.
- Silicon diode thermometer: You can read out the Silicon diode thermometer that is located on the SPARO's Helium-4 surface (near the charcoal pump) by using a 10 micro-Amp current source.
- Attach the capacitance manometer gage to the capacitance manometer gage readout (see photo below). The reading is in Torr, with an accuracy of about ten milliTorr.

photos showing temperature and pressure readouts

click to enlarge	Fig 8 - capacitance manometer readout
click to enlarge	Fig 9 - capacitance manometer readout and lab breakout box
click to enlarge	Fig 10 - how to attach lab breakout box to SPARO

Begin pumping on the reservoir with the pumped pot line valved off.
When the reservoir pressure gets to 20 mTorr (Note: it should take 5-10 minutes to get the valve completely open and another 10 min to an hour to get down to 20 mT), begin pumping on the pumped pot line while continuing to pump on the reservoir.
After another 10-20 minutes, prepare to apply back-pressure to the capillary by following these steps:

Blow some Helium out into the room through the tygon hose that connects to the UHP He cylinder. This will purge this line of other gases. Then hook this line up to the "flushing port" on the "flushing fixture" that attaches to SPARO's pumped pot line (see diagram and photos above).
Next, purge the volume near the "flushing port" needle valve by the following "pinching operation": Pinch off a section of the tygon flushing line, near to the "flushing port", and open the needle valve so as to pump out the pinched off section of the line. Then re-close this valve and release (unpinch) the hose.

photo showing idea of "pinching operation"

click to enlarge

Fig 11 - "pinching operation" on "reservoir pumping fixture" (similar to the procedure described above for "flushing fixture")

Next, apply back-pressure to the capillary as follows:

Close the KF valve of the "flushing fixture", thus breaking the connection between the Alcatel 2015 pump and the pumped-pot line.
Gently open the needle valve of the "flushing fixture" in order to begin flushing UHP He gas through the pumped pot (use a pressure of ~10 psi).

This backpressure to be applied continuously through to the end of step 6.

4. Cooling to LN₂

Valve off pump to reservoir (but keep back pressure on pumped pot)
Gently fill reservoir with UHP Helium gas using the "reservoir fill port" (see diagram in section 3) to admit the gas. Note the following.

set the pressure on the regulator to about 1 lb. of pressure, no more.
use the same two step flushing and pinching technique as described in section 3 to purge the tygon line from the cylinder and to purge the volume near the needle valve by pinching (see last photo in sec. 3).
When you are ready to admit the UHP Helium gas into the reservoir, proceed as follows:
- turn off the mechanical pump so the room is quiet.
- put your ear near to the valve near reservoir fill port
- open the valve slowly until you hear the gas flowing through the line.

fill with LN₂ using the LN₂ fill fixture (pump liquid in directly from transfer dewar)
- photo of LN₂ fill fixture can be seen in section 3 above.

set up the flowmeter assembly on SPARO:

photos of SPARO flowmeters

click to enlarge	Fig 12 - flowmeter assembly used with SPARO
click to enlarge	Fig 13 - Top view showing flowmeter attached to SPARO Helium reservoir
click to enlarge	Fig 14 - A safety feature in case of buildup of pressure in reservoir

Record Silicon diode voltage reading during cooldown
Open and close both heat switches when the dewar reaches a temperature of in the range of 175-125 K. The purpose is to make sure that they don't get jammed closed by the thermal contraction. Note that opening the charcoal pump heat switch can be a frustrating experience. this is dicussed in section 1 above.
Let soak at LN₂ for ~ 5 hours or more
- 3 hours after beginning the nitrogen fill:
  - flow ~ 50 on 11 LPM flowmeter;
  - Pressure should be about 2-3 x 10^-6 (with some large upwards jumps)
- 20 hours after beginning the nitrogen fill:
  - flow should be about 8 on 11 LPM flowmeter;
  - Pressure should go to about 1-2 x 10^-6
- dewar is near 75K (boiling point of liquid nitrogen) when charcoal pump diode reads around 1.025V.

5. Cooling to ⁴He

Blow out LN₂, using the LN₂ blowout fixture and UHP Helium gas. There is a photo of the SPARO LN₂ blowout fixture below and another photo of this fixture appears in section 3 above. Two lbs. of pressure on the LN₂ blowout fixture should be sufficient to blow out the LN₂.
It is important to get all of the LN₂ out of the reservoir so as to avoid plugging the capillary. While you are blowing out the LN₂, you will see the liqiud coming out of the hose. When it stops coming out, you know that you have emptied the reservoir. However, to make sure that you get all of the LN₂ out, push the blowout fixture down so that it touches the bottom of the reservoir and poke it around down there for a while to be sure you get all the liquid. Then, when you are sure that you have all the liquid out, don't remove the blowout fixture yet. Keep it in there for an additional ten minutes. In doing so, you will be blowing more warm Helium gas into the reservoir that will be sure to warm up the sides of the reservoir enough to expel any residual LN₂.

photo of LN₂ blowout fixture in use

click to enlarge

Fig 15 - closeup of LN₂ blowout fixture on SPARO

Re-attach flowmeter and allow reservoir to warm to about 85 K, which corresponds to a voltage of 1.00 V on the Silicon diode thermometer. This should take about 8 hours.
Re-attach "reservoir pumping fixture" and pump on reservoir for about 3 hours. Record pressure - it should go to 100-150 milliTorr if the capillary is not plugged.
gently back fill reservoir with UHP He gas. (Keep flushing pressure on pumped pot line.) Use the back-fill technique descibed in section 4.
Valve off the dewar case, using KF valve. Remove from pump. Put tape on valve so no one inadvertently opens this valve.
Begin LHe transfer
- Maintain flushing pressure on pumped pot line
- monitor and record Silicon diode voltage and ³He gas pressures
depending on speed of transfer, dewar may be cold before reservoir is full
- Flow meter readings:
  - 2 hours after beginning fill: flow is 30-50 on 30 LPM flowmeter;
  - 5 hours after beginning fill: flow is 15-20 on 30 LPM flowmeter;
  - 15-20 hours after beginning fill: flow is 25-55 on 11 LPM flowmeter, depending on the flow through the capillary;
- dewar is near 4 K when ⁴He surface diode reads around 1.6V
SPARO normally has a ⁴He hold time of 3-4 days indoors, but when bubbling Helium-4 through the capillary the hold-time could be much less, as little as a day and a half.

6. Preparing for the first ³He cycle

When the ³He pressures on the Ashcroft analog gages both read zero, this means all the ³He gas has been sucked onto the charcoal pumps. (Zero pressure is minus 1 atm on these differential gages, i.e. about minus 14 inHg). At this point, you can close both green valves located near the external ³He reservoirs. See discussion in section 1 above. By doing this, you will make sure that the ³He gas is confined to the inside of the cryostat, and you will be ready for the ³He cycle.
After SPARO has been at 4 K for about 12 hours, you should open the ³He pot heat swich. This heat switch is marked with Red tape. You need to open it 90 turns. Unfortunately, opening this heat switch can be a frustrating experience. See discussion of heat switches in section 1. This heat switch will remain open until SPARO is warmed again.

Last updated Sept 6, 2003 GN