Bridging Metal Additive Manufacturing and RF Accelerator Design: Development of a 704.4 MHz Crossbar H-Mode Linac for Efficient Beam Acceleration

TL;DR

This paper reports the development of a 704.4 MHz crossbar H-mode linear accelerator cavity fabricated entirely via metal additive manufacturing, demonstrating high-gradient beam acceleration with innovative cooling and high-frequency design.

Contribution

It introduces the highest-frequency CH cavity fabricated with MAM, integrating complex cooling networks and achieving significant energy gain rates for UHF linacs.

Findings

Achieved 1.4-1.5 MeV/m energy gain in CW mode.

Achieved 4.6-4.8 MeV/m energy gain in pulsed mode.

Maintained peak surface temperature around 60°C.

Abstract

The development of Ultra-High Frequency (UHF) linear accelerators via Metal Additive Manufacturing (MAM) is a strategic research focus of the RACERS team at GSI. The 704.4 MHz Crossbar H-mode (CH) cavity, proposed in 2021 to facilitate efficient frequency jumps and downsize accelerator footprints, represents both the highest-frequency CH structure to date and the first of its kind fabricated entirely through MAM. This study demonstrates the structure's capability for efficient beam acceleration in both Continuous Wave (CW) applications (e.g., accelerator-driven systems) and pulsed operations (e.g., spallation neutron sources). By operating in the UHF regime, the cavity inherently enhances sparking resistance, shifting the physical bottleneck away from surface electric field constraints to enable higher accelerating gradients. To manage the resulting thermal loads within compact dimensions, this study utilizes the design freedom of MAM to integrate a sophisticated "lotus-root-like" cooling network, which is a geometry unachievable through conventional subtractive machining. In combination with a kind of high-strength and high-conductivity alloy, CuCr1Zr, the cavity can achieve energy gain rates of 1.4-1.5 MeV/m (CW) and 4.6-4.8 MeV/m (pulsed), while maintaining a peak surface temperature of approximately 60 degrees Celsius. These results indicate that bridging additive manufacturing with advanced RF design provides a robust framework for next-generation UHF linac structures to go beyond current accelerating-gradient limits.