A BULK HIGH-TC SUPERCONDUCTOR STAGGERED ARRAY UNDULATOR

At Institute of Advanced Energy, Kyoto University, we propose new staggered-type undulator with bulk high critical temperature superconductor magnets to achieve short period undulator. The new undulator consists of bulk superconductor magnets with same magnetization direction and then they can be magnetized by an external solenoid field. In this paper, we show the measurement result of transverse field, which are produced by magnetized bulk superconductor magnets in 3-period prototype. We show the dependence of transverse field on reversed solenoid field. We also show that calculation results with simple assumption related to bulk superconductor magnets provide good agreements with experimental results. INTRODUCTION Short period undulators bring in several advantages, short lengths FEL with low electron beam energy, high gain with same undulator length. To achieve short period undulator with the same K value, we have to obtain strong undulator field. There are two main way to obtain strong undulator field. One is the undulator with superconducting wires. Another is the In-vacuum undulator. The former can generate 10 times higher magnetic field than the latter. However, the superconducting wires have to be cooled down near liquid Helium boiling point (4.2 K), and large thermal insulation area between beam line and superconducting wires is needed. The undulator field in the former is not stronger than the latter. Undulator with bulk HTSC (high critical temperature superconductor) magnets is promising for short period undulator. Bulk HTSC magnets as represented by YBaCuO bulk can trap magnetic field of several teslas. Recent research progress reports that a YBaCuO bulk trap the magnetic field of 17 teslas [1]. Moreover bulk HTSC magnets can be used at a temperature above liquid Nitrogen boiling point (77 K). Therefore, present refrigerator systems make it possible for the bulk HTSC magnets to be used near the beam line. However, to use bulk HTSC magnets, we have to magnetize them below Tc (critical temperature). Magnetization method is main issue for using HTSC bulk magnets [2], [3]. At our institute, we proposed staggered structure to magnetize HTSC [4]. The conventional Staggered Array Undulator consists of ferromagnetic and nonmagnetic pieces [5]. Bulk HTSC Staggered Array Undulator consists of Bulk HTSC and nonmagnetic pieces. Hybrid Staggered Undulator structure, which consists of ferromagnetic and magnets, is also good candidate for using Bulk HTSC magnets in place of permanent magnets [6]. A schematic of new type undulator is shown in Figure 1.It have bulk HTSC magnets with the magnetization direction to +z. In this structure bulk HTSC can be magnetized by an external solenoid field. The objective of out experiment is to check the conecept of this new undulator. EXPERIMENTAL SETUP Figure 2 shows a schematic of experimental setup and a photograph of 3-period prototype of the new undulator. Table 1 shows parameters of experimental setup. HTSC Magnetization Vector