M. Kasa

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.

Development of a Planar Superconducting Undulator for the Advanced Photon Source

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.

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

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 superconducting undulator for the APS

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.

Feasibility and electromagnetic analysis of a REBCO superconducting undulator

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.

Feasibility of a Short-Period Superconducting Undulator Using 2G HTS Tapes

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.

Design of a REBCO thin film superconducting undulator

Recent developments have shown that superconducting undulators, mainly NbTi- based, outperform the existing devices. However, cooling these undulators is a challenge. REBCO (RE = rare earth, barium copper oxide) coated conductors (CCs) have been found to be a promising alternative to these materials due to their larger temperature stability margin and high engineering current densities. Here, we have investigated the feasibility of building an undulator magnetic structure using REBCO coated conductors and conducted experiments to evaluate their performance. The undulator coil has been wound with no inter-layer insulation. The critical current measurements at 77K showed that the winding of the undulator does not noticeably deteriorate the performance of the tape. Transient behaviour of the undulator has also been investigated and found to be characterized by long magnetic field decay times that result from current sharing between the windings. Steady-state operation was found to be very suitable for most undulator applications.

Cryostat design and development for a superconducting undulator for the APS

The Advanced Photon Source (APS) upgrade project at Argonne National Laboratory includes the implementation of superconducting undulator insertion devices. A development program is under way to build, test, and operate a prototype device in the storage ring. We present the overall design concept including superconducting magnet structure, cryocooler-based cooling system, and cryostat as well as a status report on the R&D program. Results of cryocooler performance characterization using a model magnet in a test cryostat are described.

Fabrication and assembly of a superconducting undulator for the advanced photon source

A prototype superconducting undulator magnet (SCU0) has been built at the Advanced Photon Source (APS) of Argonne National Laboratory (ANL) and has successfully completed both cryogenic performance and magnetic measurement test programs. The SCU0 closed loop, zero-boil-off cryogenic system incorporates high temperature superconducting (HTS) current leads, cryocoolers, a LHe reservoir supplying dual magnetic cores, and an integrated cooled beam chamber. This system presented numerous challenges in the design, fabrication, and assembly of the device. Aspects of this R&D relating to both the cryogenic and overall assembly of the device are presented here. The SCU0 magnet has been installed in the APS storage ring.

DSP methods for correcting dispersion and pulse width effects during pulsed wire measurements

Measuring a magnetic field by pulsing electrical current through a wire placed in the magnetic field, followed by measuring the displacement of the wire as a travelling wave passes a displacement sensor, is a technique typically referred to as a pulsed wire measurement. The goal of these measurements is to extract the magnetic field distribution of the magnet from the time dependent wire displacement data. The described technique could be used for measurements of any type of magnet, including undulators.