C. Doose

A Design Concept for a Planar Superconducting Undulator for the APS

A superconducting planar undulator is under development at the Advanced Photon Source. The R&D phase culminated in the successful testing of several short magnetic structure prototypes. Work is now focused on a complete design for the first undulator. The conceptual designs for its superconducting magnet, the cooling system, and the cryostat are described in this paper.

Design and development of a short-period superconducting undulator at the APS

A planar superconducting undulator (SCU) with a period of 15 mm is under development at the Advanced Photon Source (APS). The SCU is designed to achieve a peak field of 0.8 T on the beam axis for an 8 mm pole gap and a current density in the coil of 1.0 kA/mm/sup 2/. Short sections of low-carbon-steel cores with 12 and 22 periods were fabricated, and coil windings were completed with NbTi superconducting wire. After training by means of quenches, the SCUs were able to charge up to near the critical current density j/sub c/ of 1.43 kA/mm/sup 2/. Using a thin-film heater attached to the inner surface of a vacuum chamber wall, steady-state heat fluxes were applied to the coil/pole face of the 12-period SCU in 4.2 K liquid He (LHe). The heat flux densities needed to quench the SCU were measured. At 0.998j/sub c/ and 0.8j/sub c/ the thermal stability margins were about 1.3 mW/mm/sup 2/ and 2 mW/mm/sup 2/, respectively. The thermal stability margin of the SCU was affected by the latent heat of vaporization of LHe.

RaD of Short-Period NBTI and Nb 3 Sn Superconducting Undulators for the APS

Superconducting undulators (SCUs) with a period of 14.5 mm are under development for the Advanced Photon Source (APS). The undulators have been designed to achieve a peak field on the beam axis higher than 0.8 T with an 8 mm pole gap and current densities over 1 kA/mm2in the NbTi and Nb 3 Sn coils. Upper-half NbTi SCUs of short sections have been fabricated and were charged up to near the critical current density of 1.43 kA/mm2to achieve a peak field about 1 T. The stability margin of the SCU was measured by imposing steady-state heat fluxes on the pole/coil face of the SCU in a pool-boiling liquid He (LHe) dewar at 4.2 K. Near the critical current density, where the temperature stability margin is minimal, the heat flux density to quench the SCU was about 1.3 mW/mm2, of which 60% was attributed to LHe at the interface of the SCU and the vacuum chamber. The peak fields of the SCU were mapped along the beam axis using a Hall probe in a vertical dewar. The first test of a Nb 3 Sn short-section SCU was charged to an average current density of 1.45 kA/mm2, slightly higher than the critical current density for the NbTi SCU.

Development of Short-Period

Superconducting undulators (SCUs) with a period of 14.5 mm are under development for the Advanced Photon Source (APS) using Nb3Sn superconductors. The initial goal is to install a SCU with a 19- to 29-keV tuning range for the first harmonic photon energy. The design of the SCU assembly includes the interface with the beam chamber as an integral part of the assembly. A four-period Nb3Sn half SCU was fabricated and tested. After a number of quenches, the SCU was charged to an engineering current density of 1.92 kA/mm 2 in the coil pack. This corresponds to a peak field of 1.08 T on the beam axis with a pole gap of 8.5 mm. The achieved current density was approximately 90% of the engineering critical current density for the design calculations. With an operating current density of 1.6 kA/mm 2 , the SCU will operate at a peak field of 0.95 T with some degree of stability.

{\rm Nb}_{3}{\rm Sn}

A planar superconducting undulator (SCU) with a period of 15 mm is under development at the Advanced Photon Source (APS). The intended users require a photon energy that can be tuned from 19 to 28 keV for inelastic X-ray scattering studies. The SCU design consists of two low-carbon-steel cores that are positioned above and below the beam chamber. There are 20 turns of NbTi/Cu superconducting (SC) wire within a coil cross section of 4.3 /spl times/ 4.0 (w /spl times/ h) mm/sup 2/. At a pole gap of 8 mm, the necessary average current density in the coil will be about 1 kA/mm/sup 2/ to achieve a peak field of 0.8 T on the beam axis. The design and fabrication progress of a 12-period prototype SCU are presented, and some challenging requirements are discussed.

Superconducting Undulators for the APS

Superconducting technology offers the possibility of creating undulators for synchrotron light sources with better performance than conventional hybrid or pure permanent magnet technologies. A superconducting planar undulator is under development at the Advanced Photon Source (APS) with the goal of providing the APS users with higher photon fluxes at higher photon energies. A magnetic design has been developed and several short magnetic structure prototypes have been built. A phase error of less than 2 degrees rms has been achieved without any magnetic shimming. The team is now working on the manufacture of the first full-scale undulator for the APS. The results of the prototype tests are described in this paper. The designs for the superconducting magnet, the cooling system, and the cryostat are presented, as well as the status of the project.

Development of a short-period superconducting undulator at APS

The first superconducting planar undulator (SCU0) at the Advanced Photon Source (APS) has been built with the goal of providing the APS users with higher photon fluxes at higher photon energies. The undulator magnetic structure is wound with NbTi superconducting wire. The magnet is indirectly cooled by liquid helium circulating in a closed circuit. The cooling of the helium circuit, the current leads, and the thermal shields are provided by four cryocoolers. After a rigorous stand-alone cold test the undulator has been installed into the APS storage ring. The results of the SCU0 cold test are presented in this paper.

Development of a Planar Superconducting Undulator for the Advanced Photon Source

As the western hemispheres premier x-ray synchrotron radiation source, the Advanced Photon Source (APS) continues to advance the state of the art in insertion device technology in order to maintain record high brightness, especially in the hard x-ray wavelength region. Due to the unique bunch pattern used for normal APS operations and its ultimate capabilities, the APS has chosen superconducting technology for its future hard x-ray undulator sources. In the last several years, the APS in collaboration with the Budker Institute of Nuclear Physics has being developing the technology for planar, small-period superconducting undulators (SCUs). These developments include the design and construction of several prototypes and the construction of the necessary mechanical, vacuum, and cryogenic infrastructure at the APS site. Several prototypes of the SCU magnetic structure have been built and tested. The first SCU is assembled and will be installed in the APS storage ring at the end of 2012. Expected SCU performance in terms of x-ray brightness should noticeably exceed that of existing APS undulators. Immediately after commissioning, the SCU will be used at APS Sector 6 as the radiation source for high-energy x-ray studies.

Test Results of a Planar Superconducting Undulator for the Advanced Photon Source

Recent advances in second-generation (2G) high temperature superconducting (HTS) coated conductors (CCs) have made them very attractive for new applications such as undulators. In this paper, we have, for the first time, experimentally evaluated a design to validate applicability of 2G-HTS tapes for next generation undulator magnetic structures. A two-period undulator magnetic core was fabricated and 2G-HTS CCs were successfully wound onto the undulator core. The performance of the undulator magnetic structure was investigated and the highest engineering current density, J e, in such configuration reported yet was obtained. A new U-slit tape configuration was used to reduce the number of resistive joints and it was shown that with this new technique affordable levels of resistance values can be achieved for short length undulators. The ferromagnetic core was designed such as to accommodate winding the U-slit tapes. Test results indicated that the winding and the soldering procedures are successful and do not deteriorate the performance of the 2G-HTS tapes.

Development of a superconducting undulator for the APS

This paper presents a design concept of a planar-type superconducting undulator (SCU) using YBCO high-temperature superconductor (HTS) tapes. The SCU has a period length of 15 mm, and the tape conductor has dimensions of 4-mm width and 0.1-mm thickness. It has been shown that the conductor transition from one coil groove to the one in the next period is possible by making a semi-circular concave loop of the tape for continuous winding in the same direction. Non-uniform current distribution in the tape may cause field quality degradation. Assuming a uniform current density in the tape, the engineering critical-current density of the HTS in the coil for the design and the corresponding achievable on-axis peak field at 4.2 K were calculated.