High-Gradient, Millimeter Wave Accelerating Structure

TL;DR

This paper proposes a high-gradient millimeter wave all-metallic accelerating structure combining linear acceleration and beam cooling, with simulations and initial low-power test results indicating promising performance for advanced particle accelerators.

Contribution

It introduces a novel millimeter wave accelerating structure that integrates acceleration and cooling functions using specific eigen modes, supported by simulations and initial tests.

Findings

Shunt impedance up to 100 MOhm/m in simulations

Successful initial low-power tests at 30 GHz

Potential for >100 MeV/m gradient in acceleration

Abstract

The millimeter wave all-metallic accelerating structure, aimed to provide more than 100 MeV/m gradient and fed by feeding RF pulses of 20-30 ns duration, is proposed. The structure is based on a waveguide with small helical corrugation. Each section of 10-20 wavelengths long has big circular cross-section aperture comparable with wavelength. Because short wavelength structures are expected to be critical to wakefields excitation and emittance growth, we suggest to combine in one structure properties of a linear accelerator and a cooling damping ring simultaneously. It provides acceleration of straight on-axis beam as well as cooling of this beam due to the synchrotron radiation of particles in strong non-synchronous transverse fields. These properties are provided by specific slow eigen mode which consists of two partial waves, TM01 and TM11. Simulations show that shunt impedance can be as high as 100 MOhm/m. Results of the first low-power tests with 30 GHz accelerating section are analyzed.