Assembly, Installation, and Commissioning of the Atlas Upgrade Cryomodule

Abstract

A new cryomodule containing seven low-beta superconducting radio frequency (SRF) cavities has been added to the ATLAS heavy ion linac, providing an additional 15 MV accelerating potential to the existing accelerator. We describe the final stages of cryomodule assembly, commissioning, and installation in the ATLAS accelerator. The clean techniques used to achieve low-particulate rf surfaces are presented, as are the module design features which enable clean assembly and reliable high-gradient operation. The thermal performance of the cryomodule is described, along with performance data for the SRF cavities. Details on subsystem performance including helium and nitrogen systems, vacuum systems, thermal and magnetic shields, slow and fast tuners, and survey/alignment systems are given.

SRF acceleration for heavy ions: ATLAS decadal operation and evolution

“…[21,22]. The coupler design has evolved from the original inductively coupled, adjustable units built for the prototype quarter-wave and half-wave cavities to a more general purpose design appropriate for cavity frequencies up to 345 MHz [23]. We have also developed an adjustable capacitive coupler which is installed on one of the cavities.…”

“…In addition, the liquid nitrogen static load is 100 Watts. The details of the EUC commissioning have been reported in several conference papers [30]- [33].…”

Low- to medium-β cavities for heavy ion acceleration

“…In HI linacs, the typical configuration of most low-β cryomodules is the top-down one, i.e. with the cold mass hanging from the cryomodule removable top plate (see figure 22, left) which hosts all RF, electrical, cryogenic and cavity vacuum interfaces [85,86]. One advantage of this configuration is that cold masses can be made very long and they can undergo even large thermal contraction without creating dangerous structural tension.…”

“…This 109 MHz closed cavity with steering correction provided by beam port tilting can be seen as a precursor of the above one, the main conceptual difference being in the cylindrical OC shape [86] (figure 42). Having a β 0 λ=0.41 m, almost two times higher than the β=0.077 QWR, its OC diameter is rather large without being conical.…”

“…It should be mentioned that the choice for this cavity of defining as active length the minimum distance between beam ports (0.25 m=0.41) can be somehow confusing; to compare the published results with the ones of other similar cavities which use the standard β 0 λ definition, E a should be multiplied by ∼0.61 (renormalized values will be reported in parentheses). The vertical test performance of the cavities [54] were reproduced on line: an average quench field of 11.3(6.9) MV m -1 , and an average operation gradient of 8.3 (5.1) MV m -1 [86]. The large cavity size results in an average gain of 2.1 MV per cavity at a Q=10 9 (with the best cavities able of 3.75 MV), realizing a cryomodule with 'real estate' gradient of 3.2 MV m −1 .…”