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Superconducting Wave Length Shifters and Multipole Wigglers Developed in Budker Inp

This paper is available in a repository.
This paper is available in a repository.

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Abstract

Several high-field superconducting wigglers (SCW) and wavelength shifters (WLS) are fabricated in Budker INP for generation of synchrotron radiation. Three-pole WLS with the magnetic field of 7.5 T are installed on LSU-CAMD and BESSY-II storage rings for shifting of radiation spectrum. WLS with the field of 10.3 T will be used for generation of slow positrons on SPring-8. The creation of 13-pole 7 T wiggler for BESSY-II and 45-pole 3.5 T wiggler for ELETTRA now is finished. The main characteristics, design features and synchrotron radiation properties of SCW and WLS created in Budker INP are presented in this article. Last few years in Budker INP several high-field superconducting wigglers (SCW) and wavelength shifters (WLS) which used as insertion devices (ID) for storage rings are developed and fabricated for generation of synchrotron radiation (SR). Such devices are used for shifting of photon critical energy to the hard X-ray range due to high magnetic field and for magnification of photon flux by using of many poles. This gives new possibilities for the existing SR sources and allows to conduct new experiments. In addition this ID can be used to control the emittance of storage ring, decrease the polarization time of electron or positron beam and others. In the Table 1 the main features of SCW and WLS which are produced by Budker INP are presented. 2 MAGNETIC SYSTEM Such devices as SCW and WLS are not the main elements of the storage ring lattice and do not reduce reliability of the machine. The compensation of the wiggler effects on beam dynamic has to be performed. One of the main demands for the wiggler field distribution is the minimization of the field integrals along the ID for closing of the beam orbit. Only the central pole of three-pole PLS-WLS (1) has high-field level of 7.5 T and used for generation of SR. Two side poles with low-level field of 1.5 T are needed for closing of the beam orbit. The side pole field level is selected as low as possible for spectral separation of SR from the central and the side poles to reduce contribution of the so-called "second source". Some inconvenience of using of three-pole wiggler is deviation of the equilibrium electron orbit and shifting of the radiation point at the different field level. Therefore for the next three-pole 7.5 T WLS (CAMD-WLS (2), BAM-WLS (3) and PSF-WLS) two additional usual steering magnets were placed at the both ends of the ID straight section for compensation of the orbit deviation. In this case the geometry of the SR experiments is not changed at any field level since the radiation point is fixed in the center of WLS. The distribution of magnetic field and electron beam orbit along BAM-WLS straight section is presented in Fig.1. The three-pole wiggler magnetic system (see Fig.2) consists of two halves of an iron yoke with three superconducting dipoles which are located above and below of the vacuum chamber. The iron yoke is designed so that whole magnetic flux is closed inside of the magnet and there are no stray magnetic fields outside of wiggler. The key element of three-pole wigglers is high-field superconducting racetrack central pole with the iron core. The coils are reeled up from superconducting Nb-Ti wire with diameter of 0.85 mm and impregnated with epoxy compound. The critical current of used wire is equal to 360 A at a field of 7 T. Each of the central coils is separated into two sections to optimize field - current relationship and reach the maximum field. To feed the coils two independent power supplies are used. The inner and outer sections of the central coils and all side coils are powered by the first power supply with the current of ~150 A. The second power supply with the current of ~100 A feeds the outer section of the central coils. In this way the currents are summarized at the outer sections and the value of current is equal to ~250 A. Thus each section is energized by the optimal current and