Experimental demonstration of particle acceleration with normal conducting accelerating structure at cryogenic temperature
Mamdouh Nasr, Emilio Nanni, Martin Breidenbach, Stephen Weathersby, Marco Oriunno, Sami Tantawi
Abstract
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 $150\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, corresponding to a peak surface electric field of $375\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. 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.