The GrAHal experiment (Grenoble Axion Haloscope), is based on the use of the superconducting outsert coil of the Grenoble hybrid magnet (LNCMI) providing the unprecedented figure of merit of B2V ~34.5 T²m³, within a volume ~0.48 m³ and a central magnetic field of ~8.5 T.  The RF cavity installed in the center of the coil needs to be cooled at 50 mK to reduce the thermal radiation noise. 
The cryogenic system has to be operated within that high magnetic field environment. An important constraint is to mount high sensitivity squid amplifiers closed to the RF cavity that requires to mount a ‘superconducting compensation magnet’.
We will present the cryogenic system design based on several cooling loops in order to keep the active cryocoolers at a location where the stray field is compatible with the electrical motors and the control electronics operation (< 5 mT).
The flexibility of the system offers several configurations in order to address various experimental needs : 1) a ’50 K’ large volume cooled by a high pressure cryogenic cooling loop that couples the facility to the remote cryocoolers placed at ~5 meter from the magnet center; 2) a ‘4 K’ configuration with a compensated magnetic field volume (~ 10^-3 m³) ; 3) the ’50 mK RF cavity’ configuration for the Haloscope cooled by a dilution insert.
 

Keywords
cryogenics|particles|axion|haloscope|magnet