HEOX

Oxford Intruments 3He Sorption Cryostat

HEOX is a 3He cryostat with a sorption 3He pump. All gas handling is inside the cryostat, there are therefore no tubes to a pump outside.

After putting into operation, some questions are still open:

• The sample space has a diameter of about 40 mm. Around this tube, there is 4.5 mm liquid helium. This produces background, especially on inelastic measurements. A test on TASP shows background count rates of the order of 40 counts/min. which seems to be inacceptable.

• In principle, it should be possible to combine the 3He insert with the MA09 cryomagnet. It is not yet clear, if it really works, and there will also be the problem with the LHe background.

• For powders, it is not clear if the thermal contact inside the sample container is good enough to ensure the expected sample temperature.

Some test results

Hold times:

LS340 Settings:

• Sensor A : 1K-pot
• Sensor B : Sorb. (thats the cryo pump for the 3He)
• Sensor C : 3He-pot Cernox for 1.2K<T<320K
• Sensor D : 3He-pot Speer for T<10K
• Sorb heater: 34 Ohm
• 3He-pot heater: 200 Ohm

Inelastic background on TASP

Operation with two heaters:

Heox starts up with the second PID loop (Analog Out2) enabled and loop 1 to control the temperature of the Sorb (Ch B)

The switch on the heater cable allows to operate the Sorb on loop 1 (the main loop) and simultaneously heat the 3He-pot with loop 2 and visa versa.

For low Temperature experiments <10K it is recommended to use: Sorb = loop1, 3He = loop2 while for higher temperatures Sorb = loop2, 3He = loop1 should be used. note: for the high temperatur setting the Cernox (channel C) should be used as the primary thermometer

You can operate the system by regulating the Sorb and the 3He-pot temperature independently (controlmode 0) or by using both heaters cooperatively to control the 3He-pot temperature (controlmode 1) in this case the setpoints for both loops should have the same value.

INPORTANT: both heaters are disabled if any setpoint is exactly zero. In order to control the Temperature using only 1 heater the other set value should be small (not reachable)

sea_commands

tt controlmode <n> ...sets control channel of loop 1 to B (n=0) or D (n=01)

tt set2 <n.n> ... setpoint of loop 2 in K

tt send pid n:P,I,D ... set PID values of loop n (1 or 2)

tt send cset n:<channel>,<unit>,<off/on>,<power enable> ...sets the channel (A,B,C,D) which will be used by loop <n> (e.g. tt send cset 2:D,1,1 sets loop 2 to control the 3He-pot heater

tt send pid?n query PID settings of loop n

tt send cset?n query control settings of loop n