J. Kyynäräinen

The SMC polarized target

Abstract The Spin Muon Collaboration (SMC) at CERN uses the largest solid polarized target in operation to measure the spin-dependent structure functions of the nucleons. The target is made of butanol, doped with EHBA-Cr(V), and has a volume of 2 × 1280 cm 3 . The target halves are dynamically polarized to opposite directions to minimize many systematic errors, and the spin orientation can be reversed by rotating the magnetic field in the frozen spin mode without losses. Frequency modulation of the microwaves is used to increase the maximum polarization and the growth rate. The polarization is measured with 10 series Q -meters with an accuracy of 3–5%.

Properties of the deuterated target material used by the SMC

The target material used in the SMC experiment NA47 at the CERN SPS is described. The arguments for selecting the material are given and the problems of the production and their solutions are presented. Relevant properties with respect to the scattering experiment are discussed and parameters like polarization build-up rate and relaxation times are highlighted.

Polarized targets as dark matter detectors

Abstract The strong electron paramagnetic resonance (EPR) of polarized targets can be used to search for axions as dark matter candidates in the range of (1–100) GHz. Once the axions are absorbed they can provide the communications gate for spin thermal contact between different nuclei that were kept artificially at different temperatures.

Computer control of the SMC polarized target

Abstract The SMC polarized target is controlled through VME crates driven by CPUs working under the VxWorks operating system. The CPUs are connected to a SUN workstation which provides the user interface due to a graphical package named SL-GMS. This results in user friendliness, high modularity and flexibility. The system allows the control of: (1) the superconductive solenoid and the transverse dipole: control of the power supplies; automatic reversal of the spin direction by field rotation; acquisition, display and storage of the electric and cryogenic parameters; generation of alarms; and (2) the dilution refrigerator: evaporator level control; acquisition, display and storage of ≈ 100 cryogenic parameters; and generation of alarms.

Cross-relaxation between protons and 13C nuclei

Abstract In an applied microwave field, the free electron spin-spin interaction reservoir in polarized target material couples strongly to the Zeeman interaction reservoirs of different nuclei. This leads to an effective cross-relaxation between different nuclei, which was studied at different levels of microwave power between protons and 13 C nuclei in the large SMC target using butanol as material.

13C cross‐relaxation measurements

The time constants τ of the spin coupling between protons and 13C‐nuclei in the SMC butanol target was measured as a function of the applied microwave power. A clear decrease of τ in the presence of a microwave field was found. This has to be related to the cross‐relaxation between the different spin species. The application for cold dark matter detection is outlined.