Design Issues for Cryogenic Cooling of Short Period Superconducting Undulators

Abstract

Superconducting insertion devices, which produce periodic magnetic fields, have been built and installed in a number of synchrotron-light source storage-rings. For the most part, these devices have been wigglers, which have relatively long period lengths. This report concerns itself with the special cryogenic issues associated with short period undulators. The motivation for considering the incorporation of superconducting technology in insertion device designs is to achieve higher magnetic fields than can be achieved with more conventional permanent magnet technology. Since the peak field decreases sharply with increased magnet gap to period ratio, the cryogenic design of the magnet system is crucial. In particular, the insulation required for a warm vacuum bore device is impractical for short period undulators. This report describes the issues that are related to a cold bore (~4 K) and an intermediate temperature bore (30 to 70 K) designs. The criteria for the use of small cryocoolers for cooling a short period undulator are presented. The problems associated with connecting small coolers to an undulator at 4.2 K are discussed.

Development of a Cryogenic Calorimeter for Investigating Beam-Based Heat Load of Superconducting Undulators

“…The cryogen-free calorimeter has simplicity for the design of cryostat, and has easy maintenance [4]. With conduction cooling using one SRP-082B of Sumitomo Heavy Industries and one PT415 of CRYOMECH cryocoolers, first stage cold heads cool the 50 K thermal shield and second stage cold heads cool the two paralleled beam plates via the measurement blocks.…”

The Mice Focusing Solenoids and Their Cooling System

“…Figure 4 shows a method for distributing the cooling using a thermal siphon heat pipe between the cold head and the load. The thermal siphon heat pipe has the following advantages over a copper strap for distributing cold to the focusing magnet coils [7]: 1) Liquid helium can be all around the coil so that the DT within the magnet is minimized. 2) If the heat pipe is correctly designed, the DT between the 2 nd stage cold head and the magnet can be as low as 0.05 K.…”

“…The focusing magnet must be cooled down using liquid cryogens. With proper design, the DT between the cooler second stage cold head and the hottest point in the magnet can be less than 0.2 K [7].…”

Results from the Cooler and Lead Tests

“…This ensures that the cold is evenly distributed within the magnet volume [11]. The connection between the cooler second-stage and the cold mass will be made using a natural convection thermal siphon type of circuit that condenses helium gas from the magnet and distributes the liquid helium back to the magnet cold mass [12], [13]. The system should be designed to minimize the temperature drop between the magnet hot spot and the second stage cold heads [14].…”