As the TE polarization of nucleons increases to low temperatures and high magnetic fields, polarization studies are conducted at low temperatures of about 1 Kelvin and below as well as at field intensities greater than 2.5 Telsa. This places high demands on the measurement setups.
The Bochum working group "Polarized Target" operates three measuring stands for this research:
This is a helium-4 bath cryostat. As the name suggests, liquid helium serves as a coolant. At atmospheric pressure the boiling point of helium is about 4.2 Kelvin. However, the temperature can be lowered further by reducing the pressure over the cooling liquid. The boiling point adjusts itself according to the vapor pressure curve. In this way temperatures of about 1 Kelvin can be achieved.
The polarizing magnet used here is a normal-conducting C magnet whose maximum field strength is limited to 2.5 Tesla.
As with the measuring stand "SOPHIE", this is also a helium-4 bath cryostat. However, better thermal insulation can reach temperatures around 850mK.
Another special feature of CHRISTA is that here a superconducting solenoid magnet is used as a polarizing magnet. It can reach field strengths of up to 7.5 Tesla, but is must be cooled down below its Curie temperature, which complicates the handling of this system compared to SPOHIE.
With this dilution cryostat temperatures of less than 100mK can be reached. The coolant used here is a mixture of liquid helium-4 and helium-3. From a temperature of about 860mK, two phases are formed in this mixture, which differ in their helium-3 concentration from each other. If helium-3 passes from the enriched phase to the impoverished phase, this is equivalent to a phase change; Helium-3 evaporates practically. This phase transition is accompanied by a decrease in temperature.
The magnetic field is also realized here by a superconducting magnet and amounts to a maximum of 7.5 Tesla
In contrast to the other systems, this is not a cryostat but am ESR system. With the help of electron paramagnetic resonance certain properties of the prepared target material can be examined more closely.
More detailed information about the EPR can be found under the section "NMR & EPR".