Cavity Production and Testing of the First C75 Cryomodule for CEBAF

Abstract

The CEBAF cryomodule rework program was updated over the last few years to increase the energy gain of refurbished cryomodules to 75 MeV. The concept recycles the waveguide end-groups from original CEBAF cavities fabricated in the 1990s and replaces the five elliptical cells in each with a new optimized cell shape fabricated from large-grain, ingot Nb material. Eight cavities were fabricated at Research Instruments, Germany, and two cavities were built at Jefferson Lab. Each cavity was processed by electropolishing and tested at 2.07 K. The best eight cavities were assembled into "cavity pairs" and re-tested at 2.07 K, before assembly into the cryomodule. All but one cavity in the cryomodule were within 10% of the target accelerating gradient of 19 MV/m with a quality factor of 8×10 9 . The performance limitations were field emission and multipacting.

Shape Evolution of C75 Large-Grain Niobium Half-Cells During Cavity Fabrication

“…The availability of fast, non-contact, 3D coordinate measuring machines (CMM), allows for more detailed 3D shape measurements than it is possible with traditional CMM. In this contributions we present the 3D shape evolution of several large-grain Nb half-cells during the fabrication of two 1.5 GHz, 5-cell cavities for the C75 cryomodule rework program at Jefferson Lab [4]. The same type of cavities have also been built at RI Research Instruments GmbH, Germany, using the same type of material.…”