A high gradient test of a single-cell superconducting radio frequency cavity with a feedback waveguide

Abstract

The most severe problem of the international linear collider (ILC-type) is its high cost, resulting in part from the enormous length of the collider. This length is determined mainly by the achievable accelerating gradient in the RF system of the collider. In current technology, the maximum acceleration gradient in superconducting (SC) structures is determined mainly by the value of the surface RF magnetic field. In order to increase the gradient, a superconducting traveling wave accelerating (STWA) structure is suggested. Utilization of STWA structure with small phase advance per cell for future high energy linear colliders such as ILCs may provide an accelerating gradient 1.2–1.4 times larger [] than a standing wave structure. However, STWA structure requires a feedback waveguide for power redirecting from the end of the structure back to the front end of accelerating structure. Recent tests of a 1.3 GHz model of a single-cell cavity with waveguide feedback demonstrated an accelerating gradient comparable to the gradient of a single-cell ILC-type cavity from the same manufacturer []. In the present paper, high gradient test results are presented.

Progress towards 3-cell superconducting traveling wave cavity cryogenic test

“…The single cell prototype was tested in the SW regime. An accelerating gradient of 26 MV/m was obtained, comparable to a Tesla single cell cavity with the same surface treatment (BCP only) [4]. Thus, the presence of the feedback waveguide did not limit cavity performance and the next step could be taken towards development of a full sized SC TW cavity.…”

“…the cavity uses a principle similar to that of the traveling wave ring resonator (TWR). The acceleration section of the cavity was optimized [4] such that it could provide a 24% higher accelerating gradient with the same field on the surface as a conventional SW cavity. The smaller phase advance per cell (105 degrees) provides a higher transit time factor.…”

“…The smaller phase advance per cell (105 degrees) provides a higher transit time factor. Also, the TW cavity is significantly less sensitive to manufacturing errors [4], i.e. it could be made much longer then SW cavity, which is length-restricted to 1 meter because of field flatness degradation.…”

“…The SC TW cavity is restricted only by cryomodule length and technological issues: manufacturing and cleaning of long cavities. Thus, for the structures studied here, the real estate gradient may be increased by 22% by eliminating beam pipes that contain no RF field in a cryomodule as long as only one cavity may be employed [4].…”

Higgs-Energy LEptoN (HELEN) Collider based on advanced superconducting radio frequency technology

“…First structure fabrication and testing efforts have started for TW cavity development [38]. With the relatively easier BCP treatment only, the first single cell TW cavity (Figure 10(a)) with recirculating waveguide achieved 26 MV/m accelerating gradient, limited by the high field Q-slope, as expected for BCP.…”