The Target

• Tandem target configuration - total length 1.5 m. The same beam penetrates oppositely polarized target halves to minimize the effect of beam flux variations. The method requires, however, that the spin directions are frequently reversed to cancel the false asymmetry due to the drift of the muon spectrometer acceptance ratio and the different amount of material in the target halves. This is done by synchronously operating the longitudinal and the vertical fields to rotate the field direction at 0.5 T.
• Placed inside a microwave cavity for dynamic nuclear polarization (DNP)
• Target material has to be kept in its glassy state doped with Chromium complex ions which requires that the temperature stays below 100 K permanently. The target holder with the target material is loaded submerged in liquid nitrogen.
• Magnetic field generated by a superconducting magnet - 2.5 T with homogeneity better than 20 ppm over the target volume
• Cooled by a dilution refrigerator to temperatures below 30 mK. Millikelvin temperatures are essential because the spins "freeze" as the spin-lattice relaxation time increases with decreasing temperature. At sufficiently low temperatures the direction of the polarized nuclei can be rotated with negligible loss of polarization

The Dilution Refrigerator

• Dilution refrigeration is necessary to obtain sufficient cooling capacity at low temperatures.
• Mounted to the Superconducting magnet with common isolation vacuum
• The target material is cooled inside the dilution refrigerator mixing chamber immersed in the helium mixture.
• The target cooling is dependent on two helium circulating systems - one for 3He and another for 4He.
• The pumps that circulate 3He comprise a system of 8 roots blowers connected in series to obtain low enough pressure in the still.

The Superconducting Magnet

• 2.5 T field over a 1.5 m long target volume
• Field homogeneity better than 20 ppm over the target volume

The Coldbox

Both the dilution refrigerator and the magnet use liquid 4He. A 100 l/h liquifier (Sulzer TCF 100) on a balcony above the target provides the experiment with liquid 4He. Both the dilution refrigerator and the superconducting magnet is fed with liquid helium via a 2000 l buffer dewar.

The Control Room

• houses the microwave power supplies and the control of the microwaves as well as the control equipment of the superconducting magnet and the dilution refrigerator.
• User-friendly graphical interface, based on a commercial software package SL-GMS, and running in a Unix workstation and X terminals, has been implemented to control the dilution refrigerator and the superconducting magnet. The control programs are running in VME processors.
• More than 100 cryogenic parameters are logged by the programs which also generate alarms. Most readout instruments are read via a GPIB bus, either directly or using a 32-channel data logger/plotter.

The power supplies for the superconducting magnet and the NMR-electronics are located on the platform next to the target cryostat.