Optimization of a traveling wave superconducting radiofrequency cavity for upgrading the International Linear Collider

TL;DR

This paper explores the optimization of traveling wave superconducting RF cavities, demonstrating potential for higher gradients and efficiency improvements over existing standing wave designs for the International Linear Collider upgrade.

Contribution

It introduces a novel design approach for niobium-based traveling wave structures that surpass current standing wave limits in gradient and heat load reduction.

Findings

Traveling wave structures can achieve >70 MV/m gradient.

R/Q is approximately doubled compared to TESLA structures.

Proposed methods to prevent multipactor effects.

Abstract

The Standing Wave (SW) TESLA niobium-based superconducting radio frequency structure is limited to an accelerating gradient of about 50 MV/m by the critical RF magnetic field. To break through this barrier, we explore the option of niobium-based traveling wave (TW) structures. Optimization of TW structures was done considering experimentally known limiting electric and magnetic fields. It is shown that a TW structure can have an accelerating gradient above 70 MeV/m that is about 1.5 times higher than contemporary standing wave structures with the same critical magnetic field. The other benefit of TW structures shown is R/Q about 2 times higher than TESLA structure that reduces the dynamic heat load by a factor of 2. A method is proposed how to make TW structures multipactor-free. Some design proposals are offered to facilitate fabrication. Further increase of the real-estate gradient (equivalent to 80 MV/m active gradient) is also possible by increasing the length of the accelerating structure because of higher group velocity and cell-to-cell coupling. Realization of this work opens paths to ILC energy upgrades beyond 1 TeV to 3 TeV in competition with CLIC. The paper will discuss corresponding opportunities and challenges.