Thermal considerations in the cryogenic regime for the BNL double ridge higher order mode waveguide

Brookhaven National Laboratory (BNL) has proposed to build an electron ion collider (EIC) as an upgrade to the existing Relativistic Heavy Ion Collider (RHIC). A part of the new design is to use superconducting radio frequency (SRF) cavities for acceleration, which sit in a bath of superfluid helium at a temperature of 2 K. SRF cavities designed for the BNL EIC create a standing electromagnetic wave, oscillating at a fundamental frequency of 647 MHz. Interaction of the charged particle beam with the EM field in the cavity creates higher order modes (HOM) of oscillation which have adverse effects on the beam when allowed to propagate down the beam tube. HOM waveguides are thus designed to remove this excess energy which is then damped at room temperature. As a result, these waveguides provide a direct thermal link between room temperature and the superconducting cavities adding a static thermal load. The EM wave propagating through the warmer sections of the waveguide creates an additional dynamic thermal load. This study calculates these thermal loads, concluding that the dynamic load is small in comparison to the static load. Temperature distributions are mapped on the waveguide and the number of heat intercepts required to efficiently manage thermal loads have been determined. In addition, a thermal radiation study has been performed and it is found that this contribution is around three orders of magnitude smaller than the static conduction and dynamic loads.

Figure 1

Figure showing layout of the proposed electron ion collider at BNL.

Figure 2

Figure (a) shows the full length view of the waveguide. Figure (b) shows the waveguide atttached to the BNL4 cavity [10].

Figure 3

Variation of thermal conductivities of copper and stainless steel with temperature.

Figure 4

Variation of surface resistance of copper with temperature.

Figure 5

Temperature as a function of position on the waveguide.

Figure 6

Heat loads at first and second intercepts with change in distance and operating temperatures.

Figure 7

Q variation with thickness of Cu, SS and stage length (a) from 300 K to 85 K (b) from 85 K to 25 K and (c) from 25 K to 6.5 K

Figure 8

Temperature distribution obtained numerically.