Procedure for starting the fridge after either loading the probe or cooling the whole thing from RT.
Cool everything to 4K
After loading the insert, it may not be at 4K because there is no gas to conduct heat. Therefore exchange gas needs to be heated out of the sorb to release the 4He put in the IVC.
- Start 'DR front panel.vi' on the laptop desktop and make it plot data every 1 minute (at the bottom right of the screen)
- under the graphs tab, check ch5,ch6,ch7 and monitor the IVC and still pressure
- Record all temperatures (including the magnet temps) and pressures in the log book before starting.
- Apply 35-40 mA to the SORB heater:
- on TT v2.56.vi (see VectorFieldFridgeThermometryAndHeaterSoftware), select the "TCS Control" tab
- in the I1 (current source one) select range 4 (x1mA) and enter 35-40 in the 'current' box, press enter.
- the value you want should appear under the "Current Source 1" display box. Notice the current has not yet been applied since the 'ON' button is dim.
- Click the"ON/OFF" button under the TCS control tab to turn the heater on.
- Check that the Sorb (Channel 0 on AVS47) gets to >~15K (this did not happen on 9/2/12 cooldown...ch0 stayed at 4K) so that the IVC pressure gets to ~0.1mB (since 3mB of exchange gas was put into IVC at room temp).
- After ~30 minutes record all temperatures (including the magnet temps) and pressures in the log book.
- When the fridge is thermalised, turn the SORB heater off (press "ON/OFF" on the "TCS Control" tab).
- Record all actions and fridge parameters in the log book.
- Turn the clamp knob as tight as possible at the top of the probe to make sure the probe is tightly clamped to the Fridge (a further two turns from when it was first lowered).
Check that lines into the fridge are clean
If the fridge hasn't been used for a while:
- connect up a turbo to Aux port 1.
- Pump out the line up to M3 until Pturbo<1e-5.
- Open A9, 8, 2, 0 . Turn on turbo S1. Pump for a couple of hours or overnight.
- Close 0, 2, 8. Turn S1 off.
- Pump traps out while heating them: Open 5 & heat N2 trap. Close 5, open 16 & heat aux trap.
- Close traps (close 5 & 16).
- Pump line out.
- Close A9, M3.
Cool the N2 traps
- Make sure there is no water in the N2 dewar
- Put traps in & fill with liquid N2 without spilling it everywhere.
- Stuff bubblewrap in the top to stop water freezing.
Condensing the mixture
- Check nitrogen flow to gate valve - N2 tank taps and 2 line taps open - (step 5 updated July 2020)
Pressure in lines should be 6mbar to Vector fridge (and 8mbar to BlueFors fridge). Check pressure on regular mounted on back side of the cabinet.
- Make sure the AVS47 is set to log regularly (6s delay or so)
- Record full set of pressures and temperatures in the log book(and keep doing this every 10-15 minutes).
- Record the mixture pressures (P6 & P7) on page VectorFieldFridgeMixturePressureLog.
- Set the pressure limits for condensing in the GHS software (based on new mixture pressure after 2019 top up VectorFieldFridgeMixtureTopUp2019)
a - Open DR Front Panel on Laptop
b - In Pressure Limits set the following values
c - Press the SET VALUES button.
|reading ||Set Limit |
|P6 Low ||50 |
|P6 high ||1150 |
- Cool the N2 traps (this step missing from the manual): Open 4, 5 and M5 to let mixture from back of pump into traps. P5 drops and should see N2 boil as warm He exchange gas goes in. Note this has been changed from original as Aux trap is now in series with main trap - Matt R 20/10/2021
- Open M1 and M2
- Press "Condensing 3He" and then "Auto" - you should hear a loud hiss and bang as the gate valve opens.
- It takes about 15-20 minutes to condense the He3 in.
- It takes about 2.5 hours to condense the He4 in.
- *As of July 2014, you can go straight to step 9 as the firmware has been updated* The instructions are still here in step 8 just in case:
- There was a bug in the firmware and the system would turn the mixture compressor off as soon as the He4 tank is empty and the mixture compressor is below 2 bar - this crashes the fridge.
- To avoid crashing the fridge - as soon as the system turns the mixture compressor off, turn it back on and reopen 7 (press auto first)!
Keep the mixture compressor on for ~15 mins - Mixture compressor should be below 1 bar, and P5 should be below 300mB.
- Turn the mixture compressor off, close 7. P5 will rise, but should stay below ~800mB (if not turn mixture compressor back on). Flow rate should drop to ~100, still pressure should be dropping.
- Make sure that the thermometry voltages aren't too high! 30uV for sorb, 3uV for everything else.
- Record a full set of logs.
- System will now gradually cool to base.
- Note: this step is optional and actually seems to make base temp worse: When still pressure < 0.1mB, turn the still heater to 5-10mW (7mA as of 18-5-11) on TCS Ch3, to get a Still pressure of about 0.2mB.
- Since the fridge has cooled the clamps for the probe may have contracted and loosened, so you can tighten the clamps more.
- Set the temperature scanner to read every 300s in the TT v2.56.vi since we don't need to keep reading the temperature so often (unless you're doing a temp dependance measurement and need faster readings)
- If leaving unattended, ensure that Compressor monitoring software is running and has your contact details should there be a problem, so it can email/SMS you.
- Remember to refill the LN2 traps every 3 days when the fridge is at base
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