Warming up the cryostat (Liquid He Version):
This is utilized in most of the cryostat troubleshooting steps.
- Leave the sample rod secured in place.
- VERY IMPORTANT! Make sure the sample space is opened to vacuum- the sample space valve is open and the vacuum line is open to pump on the cryostat. If the valve is closed while heating, the cryostat windows can pop and it could end your experiment for several hours, if not for the rest of your time!!
- Note the position of the flow control needle valve on the flow controller, you will return the knob to this position at the end. Reduce the flow by rotating the knob clockwise but do not completely shut off the helium flow. (could probably use a picture here)
- Set the temperature to 85 K by holding the "set" button down and changing the value using the Adjust "Raise" and "Lower" buttons.
- On the temperature controller, push the button for "Auto," - this will put the cryo heater in a programmed automatic ramp up to a set temperature.
- As the temperature increases, the pressure in the cryostat may increase (observed on the Hastings Gauge highlighted in photo below). Most likely once it gets over 60. If there is too much of a pressure increase, you may want to decrease the heater output (depress and hold the Heater "man" button and use the Adjust "lower" button to adjust power to a lower value) until the pressure settles back down, then press the "auto" button again to resume heating to 85 K.
- Once the cryostat has reached 85 K, the cryostat can be cooled back down. Depress and hold the "man" button and use the "lower" button to reduce the heater output to 0. The set point can be left at 85 unless the user is using the heater in "auto" to stabilize the temperature at a particular value (not the usual mode of operation). Open the flow controller needle valve (rotate know counter-clockwise) to the original position noted earlier in the process.
- Close the sample space valve so you are not actively pumping while cooling back down (this could pull air through and result in more ice in the cryostat), and wait for the temperature to come back down to the temperature you were running at.
- Examine the o-ring on the sample rod that was removed. If it is cracked or damaged do not re-use that rod until the o-ring has been replaced.
Warming up the cryostat (7-3 Cryocooler):
These will be similar to the instructions for a cryostat being cooled from a LHe dewar, the cryostat being cooled from a closed loop cryocooler, but not entirely the same.
Follow the above instructions for opening the cryostat sample space to vacuum.
Instead of adjusting the flow controller on top of the temperature controller boxes, you will adjust the flow controller strapped to the shelf inside of the 7-3 hutch. It should be up around 100. When heating up the cryostat, decrease this to ~40.
Continue following the above instructions for turning up the temperature controller heater.
Once the cryostat has reached 85K, you can turn the heater output back down to 0. Increase the flow on the cryocooler flowmeter back to ~100. The user should run through the same cycles of vacuum - He gas - vacuum - etc. that they would when putting a sample rod into the cryostat, and then leave the sample space under He flow while closing the sample space valve (knob on the left most (downstream) part of the cryostat). Then close the He valve on the black box. Wait until the cryostat cools down to the desired temperature (this could take over an hour).
Sample rod is stuck:
- If you cannot pull the rod straight up and out of the cryostat, do not attempt to remove by twisting. Re-insert the rod in the cryostat (you might need to tap it loose if it's stuck part way out), open the sample space valve to vacuum, and safely warm up to 85K to get rid of the ice. Once at elevated temperature you can try again to remove the sample rod.
Sample rod wont go into the cryostat:
- Much the same as the case for the sample rod being frozen into the cryostat, if there is so much resistance that the user cannot put their sample into the cryostat properly, follow protocol for warming up to 85K and try again once the ice is gone.