High-energy ion linacs based on superconducting spoke cavities

Abstract

The applicability of superconducting TEM-class spoke cavities to high-energy ion linacs is discussed, and detailed designs for two TEM-class, triple-spoke-loaded superconducting niobium resonant cavities are presented. The 345 MHz cavities have a velocity range of 0:4 < < 0:75 and a beam aperture of 4 cm. Spoke-loaded cavities offer several advantages compared with the higherfrequency elliptical-cell cavities that are currently being developed for this range of particle velocities. The proposed triple-spoke cavities can provide broader velocity acceptance, more accelerating voltage per cavity, reduced heat-load operation at 4.2 K, and increased longitudinal acceptance through the high-energy section. Application to the proposed U.S. rare-isotope accelerator driver linac is discussed in detail.

Superconducting Hadron Linacs

“…This class is topologically identical to the one used at β = 1, but with a reduced cell length. We will refer to these two classes of cavity geometry as TM and TEM geometries [20], respectively. TEM and TM cavity geometries differ in three major respects: the transverse dimensions, the cell-to-cell coupling, and the localization of the electromagnetic field.…”

Superconducting spoke cavities for high-velocity applications

“…Spoke and other low-frequency, low-velocity cavities were primarily intended for 4.2 K operation; however, recent developments in fabrication and processing techniques [7,13,14] have produced results which indicate that 2 K operation may be more economical for large machines, even taking into account the differences in refrigerator efficiency [9]. For smaller machines, on the other hand, 2 K operation may not be practical, in which case, spoke cavities offer a viable 4.2 K option [15].…”

“…Since the late 1980s there has been a growing interest in higher velocity protons and ions [3,5], and TEM structures have been designed for higher and higher velocities [7], while TM structures have been designed for lower and lower velocities, until the two have overlapped in what is referred to as the medium-velocity region corresponding to 0 $ 0:5-0:6 [8,9]. The majority of superconducting accelerating structures in use or under development, and included in the medium-0 regime, fall under these two broad categories.…”

Design of 325 MHz Single and Triple Spoke Resonators at FNAL

“…In the Front End, after a standard RFQ, room-temperature triple-spoke resonators are used to accelerate the beam from 2.5 to 10 MeV. Three types of superconducting spoke resonators, two single spoke resonators (SSR1 at β=0.22 and SSR2 at β=0.4) and a triple spoke resonator (TSR at β=0.62) are used to accelerate protons from 10 MeV to 400 MeV [2].…”