A Commercial HTS Dipole Magnet for X-Ray Magnetic Circular Dichroism (XMCD) Experiments

A commercial HTS magnet was designed, built and tested by HTS-110 Ltd for X-ray Magnetic Circular Dichroism (XMCD) experiments. The magnet was integrated with a XMCD UHV (Ultra High Vacuum) chamber and installed at an existing soft X-ray beamline at Singapore Synchrotron Light Source (SSLS). The dipole magnet has a bore of 40 mm in diameter and a gap of 90 mm to accommodate the XMCD chamber with nine access ports for sample manipulation and XMCD analysis. To achieve a UHV of 10^-10 mbar inside the chamber, an independent bakeout system was developed for this magnet to allow the XMCD UHV chamber to be baked out at a temperature over 100 degrees Celsius without affecting the HTS magnet. A small GM type cryocooler is employed to cool the magnet coils down to 17 K by thermally intercepting the heat load from the 2nd stage to the 1st stage. The magnet can provide variable magnetic fields up to 2.16 T and with the field homogeneity better than 0.1% over a 1 cm diameter sphere. Limited by the peak voltage of the bipolar power supply used for the magnet, the minimum time of full field energizing is around 20 seconds and the minimum time of full field reversal is around 40 seconds. The technical issues related to UHV compatibility and ramping rate in developing similar HTS applications are discussed in this paper.