Building economical, high-power rf accelerating cavities
The Advanced Wakefield Accelerator (AWA) group of Argonne’s High Energy Physics (HEP) Division has recently demonstrated a highly economical method for building high-power rf accelerating cavities. The estimated cost savings is greater than a factor of three when compared to previous approaches. This method was developed by means of collaboration with SLAC and an industrial partnership with a local vendor, Hi Tech.
The economy of the new method is due to the efficiency of moving directly from 3D electromagnetic simulation to fabricated cavity in a single step, without any prototyping. Previous rf cavity fabrication was a time consuming process wherein the rf subassemblies went through many costly iterations of a two-step process: a machining step followed by an rf measurement step. The reason for the many iterations was that the rf properties of the cavity could only be simulated in a 2D model and were therefore not accurate enough to rely on only a mechanical measurement of the cavity dimensions. Using SLAC’s ACE3P code run on the NERSC supercomputer, a complete 3D electromagnetic model of the rf cavity was accurately simulated. Other keys to cost reduction were due to push-pull rf tuners that could correct for minor errors, and the use of well understood braze joints designs developed by SLAC and LANL.
The first of six rf cavities was delivered by Hi Tech to Argonne in the beginning of February 2012. Initial rf characterization of the cavity revealed a cavity that was nearly perfect out of the box and only a small amount of tuning and balancing was required. The cavity is vacuum-tight, the frequency and field balance are correct and high power testing will commence shortly. We have notified the vendor to proceed with fabricating the remaining five rf cavities. This is the first proof that production ready cavities can be directly produced from 3D electromagnetic simulations, resulting in reducing the cost for accelerators.