Design and Vertical Tests of SPS-series Double-Quarter Wave (DQW) Cavity Prototypes for the HL-LHC Crab Cavity System

• Main Authors: Verdú-Andrés, S, Artoos, K, Belomestnykh, S, Ben-Zvi, I, Boulware, C, Burt, G, Calaga, R, Capatina, O, Carra, F, Castilla, A, Clemens, W, Grimm, T, Kuder, N, Leuxe, R, Li, Z, McEwen, E. A, Park, H, Powers, T, Ratti, A, Shipman, N, Skaritka, J, Wu, Q, Xiao, B. P, Yancey, J, Zanoni, C
• Format: Journal Article
• Language: English
• Published: 21-05-2018
• Subjects: Physics - Accelerator Physics
• DOI: 10.48550/arxiv.1805.08123

Phys. Rev. Accel. Beams 21, 082002 (2018) Crab crossing is essential for high-luminosity colliders. The High Luminosity
Large Hadron Collider (HL-LHC) will equip one of its Interaction Points (IP1)
with Double-Quarter Wave (DQW) crab cavities. A DQW cavity is a new generation
of deflecting RF cavities that stands out for its compactness and broad
frequency separation between fundamental and first high-order modes. The
deflecting kick is provided by its fundamental mode. Each HL-LHC DQW cavity
shall provide a nominal deflecting voltage of 3.4 MV, although up to 5.0 MV may
be required. A Proof-of-Principle (PoP) DQW cavity was limited by quench at 4.6
MV. This paper describes a new, highly optimized cavity, designated DQW
SPS-series, which satisfies dimensional, cryogenic, manufacturing and impedance
requirements for beam tests at SPS and operation in LHC. Two prototypes of this
DQW SPS-series were fabricated by US industry and cold tested after following
conventional SRF surface treatment. Both units outperformed the PoP cavity,
reaching a deflecting voltage of 5.3-5.9 MV. This voltage - the highest reached
by a DQW cavity - is well beyond the nominal voltage of 3.4 MV and may even
operate at the ultimate voltage of 5.0MVwith sufficient margin. This paper
covers fabrication, surface preparation and cryogenic RF test results and
implications.