Traveling Wave Accelerating Structure for A Superconducting Accelerator

Abstract

We present a superconducting traveling wave accelerating structure (STWA) concept, which may prove of crucial importance to the International Linear Collider. Compared to the existing TESLA cavity design, the traveling wave structure can provide ~20-40% higher accelerating gradient for the same aperture and the same peak surface RF magnetic field. The recently achieved SC structure gradient of 35 MV/m can be increased up to ~50 MV/m with the new STWA structure design. The STWA structure is supposed to be installed into the superconducting resonance ring and is fed by one or two couplers (depending on the required input power) with appropriate phase advance to excite a traveling wave inside the structure. We discuss the structure design, optimization of the parameters, tuning requirements and plans for further development.

The International Linear Collider (Report to Snowmass 2021)

“…1. Optimized travelling wave (TW) superconducting structures [149,150,151] with effective gradients up to 70 MV/m, along with 100% increase in R/Q. This reduces the dynamic heat load by 40% due to increase of GR/Q, where G is the geometry factor of TW structure.…”

“…First structure fabrication and testing efforts have started for TW cavity development [149,150]. With the relatively easier BCP treatment only, the first single cell TW cavity (Fig.…”

RF Technologies for Future Colliders

“…Traveling wave (TW) structures [32] offer several main advantages compared to standing wave ones: substantially lower peak magnetic field, lower peak electric field, and substantially higher R/Q. To achieve the highest possible accelerating gradient, the main emphasis of design optimization is to lower H pk /E acc as much as possible.…”

A tuner for a superconducting traveling wave cavity prototype

“…Thus, there is a gap between cavities (220 mm) which reduces the accelerating rate by 22%. A superconducting traveling wave accelerating structure was proposed in our previous publications [9][10][11][12]. It requires a feedback waveguide from one end of accelerating structure to the other in order to make a closed loop for power distribution.…”

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Use of a superconducting traveling wave accelerating (STWA) structure with small phase advance per cell for future high energy linear colliders may provide an accelerating gradient 1.2-1.4 times larger [1] than a standing wave structure. However, the STWA structure requires a feedback waveguide [1]. Recent tests of a 1.3 GHz model of a single-cell cavity with waveguide feedback demonstrated an accelerating gradient comparable to the gradient in a single-cell ILC-type cavity from the same manufacturer [2].

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