Development of a High Temperature Superconducting YBCO for Ultrashort Period (< 10 mm) Undulators

This project proposal is for nanometer wavelength undulators with a low energy electron beam (1-2 GeV) and with a ultrashort period (less than 10 mm) which meet the requirements for the next generation of undulator radiation sources. The proposed design will have a deflection parameter K=1 and a peak gap field B & gt; 1 T. We have performed feasibility studies on second generation high temperature superconducting (2G HTS) YBCO wires and we concluded that, at 4.2 K, a coil with an average current density of 1,500 A/ mm2 can be designed and used to construct an ultra short period undulator with a period less than 10 mm and generate 1.1 T peak field at 3 mm beam gap. The proposed YBCO wire will be 3 mm width x 0.1 mm thick with kapton insulation, and is available from Superpower Inc. It is proposed to have an iron pole of 1.6 to 2.0 mm in thickness and an overall axial coil thickness equal to 6 mm for a pair of adjacent YBCO coils wound as double pancake. Thus, the period will be 9.6 mm to 10.0 mm. We shall compute coil forces and perform finite element stress analysis to confirm that a critical tensile coil stress will be less than 550 MPa and conductor critical axial tensile strain will be less than 0.45%. Today, YBCO wire can be obtained from Superpower Inc for a reasonable price of $50-$60 per 50 A-m for a continuous length of 50-100 m. A typical 50 pole YBCO undulator magnet will need an approximately 2500 m length of 2G HTS wire. Thus, the total wire cost for a 50 pole undulator magnet will be about $150K. These wires can be connected with a lap-joint at the outermost turns of a YBCO double pancake coil. A lap joint made by soft soldering can achieve a resistivity of about 40-50 n-cm2. In Phase 1, we shall design a race track YBCO coil with a minimum bending diameter of 12.5 mm which is feasible as compared with the critical bending diameter of 11 mm for both tension and compression. In addition, we shall complete the cryostat design for the YBCO undulator coils. The cryostat will have a clear cold beam aperature of 3 mm. Furthermore, we shall develop a 5-pole prototype YBCO SCU and perform test in an open dewar. In Phase 2, the 50-pole YBCO SCU magnet will be built and operated at 4.2 K in open dewar. Then, we shall install in a two-cooler-cryostat with a gold plate OFHC cold beam duct. The beam duct will have a clear beam aperature of 3 mm. We shall completely test the YBCO undulator and its coil cryostat. When Phase 2 is successfully completed, the system will be ready to be installed for use in USA & apos;s advanced light source facilities.