CRYOSTAT FOR TESTING SUPERCONDUCTING UNDULATOR MAGNETS

Superconducting undulator (SCU) technology has held tremendous promise for radiation sources in storage rings and free electron lasers for several decades. Many of the technical challenges associated with the design, fabrication, and operation of SCUs have been resolved, with SCUs regularly operating in two light sources worldwide and with plans for several more under consideration. SCUs offer several advantages over permanent magnet undulators as radiation sources including: 1) enhanced magnetic field, yielding shorter undulator periods and broader photon energy tuning range compared with most advanced permanent magnet undulators, especially for hard x-ray photon energies above ~20 keV; 2) flexible magnetic field configurations enabled by flexible winding configurations of the superconducting wire; 3) a compact transverse profile that could enable multiple SCUs in a single cryostat; and 4) longer lifetime due to reduced sensitivity to radiation damage. Grant applications are sought in the following subtopics: a. Development of Cryostat for Testing Superconducting Undulator Magnets This topic seeks the development of a diagnostic cryostat for fast testing of superconducting undulator (SCU) magnets. Superconducting undulator is an emerging accelerator technology offering a high undulator field that can be realized in a variety of configurations including planar, helical, and universal undulator. Various superconductor materials can be used for winding SCU magnet coils, leading to multiple options for SCU magnet design that should be experimentally verified. Diagnostic cryostats are needed for the experimental verification. Undulator magnets are provided by the customer and will be tested using the cryostat described in this topic. The primary components of the cryostat should include: i. Vacuum chamber of length approximately 3 m and transverse dimensions of the order of 1 m to accommodate undulator magnets up to 2 m long and cross-sections up to 0.3 m x 0.3 m in the horizontal orientation. Cryogenic cooling and magnet support systems are also required. ii. Cryogenic cooling system capable of providing at least 4 watts of refrigeration at an operating temperature of 4.2 K. The system should have an operating temperature range between 3 K and 5 K and include appropriate thermal insulation consistent with cryogenic engineering practice. iii. Thermal links or other heat transport mechanism capable of transporting heat from the test magnet to the cooling system. An efficient thermal transport system should minimize the temperature difference between the cryogenic cooling system and the test magnet down to about 0.1 K. iv. Support system to suspend, align, and thermally isolate the test magnet from the cryostat. v. Two pairs of current leads capable of supporting up to 2 kA and six pairs of current leads capable of supporting up to 250 A. Leads should include a high-temperature superconductor component to avoid the need for vapor cooling. vi. Instrumentation sufficient to monitor the operating condition of the cryogenic cooling system, current leads, and the undulator magnet being tested. Estimated quantity of temperature sensors required is 40. vii. Support for a magnetic measurement system to be provided by the customer. Test undulator magnets are measured using Hall probe, wire coils, and pulsed wire techniques. In each case, the probe must traverse the cryostat in the horizontal plane, passing through the magnetic gap in the test magnet. The vacuum chamber ends must accommodate a suitable thermal, mechanical, and vacuum transition to allow the probe to enter the interior of the magnet without disturbing cryogenic operations. viii. The cryostat should provide uninterrupted operation over test durations as long as 6 weeks. Questions - Contact: Eliane Lessner, Eliane.Lessner@science.doe.gov b. Other In addition to the specific subtopic listed above, the Department invites grant applications in other areas that fall within the scope of the topic description above.