Experimental demonstration of particle acceleration with normal conducting accelerating structure at cryogenic temperature

In this paper, we present an experimental demonstration of the high-gradient operation of an X-band, 11.424 GHz, 20-cells linear accelerator (linac) operating at a liquid nitrogen temperature of 77 K. The tested linac was previously processed and tested at room temperature. Low-temperature operation increases the yield strength of the accelerator material and reduces surface resistance, hence a great reduction in cyclic fatigue could be achieved resulting in a large reduction in breakdown rates compared to room temperature operation. Furthermore, temperature reduction increases the intrinsic quality factor of the accelerating cavities, and consequently, the shunt impedance leading to increased rf-to-beam efficiency and beam loading capabilities. We verified the enhanced accelerating parameters of the tested accelerator at cryogenic temperature using different measurements including electron beam acceleration up to a gradient of 150 MV/m, corresponding to a peak surface electric field of 375 MV/m. We also measured the breakdown rates in the tested structure showing a reduction of 2 orders of magnitude compared to their values at room temperature for the same accelerating gradient.

Automated summary

This paper presents an experimental demonstration of high-gradient operation of an X-band linear accelerator at liquid nitrogen temperature, showing enhanced performance at low temperatures including increased yield strength, reduced surface resistance, and improved rf-to-beam efficiency. Measurements confirmed the accelerator's improved parameters at cryogenic temperatures, with electron beam acceleration reaching up to 150 MV/m and breakdown rates significantly reduced compared to room temperature operation.