Rapid Prediction of Long Range Wakefields for Beam Impedance and Power Loading in Complex Accelerator Structures

The successful design and operation of accelerating structures depends on understanding how particles excite extraneous signals (wake fields) as they pass through the structures. The wake fields are a complicated superposition of hundreds to sometimes thousands of oscillating electromagnetic modes, which in turn can depend critically on detailed aspects of the cavity and coupler shapes. Wake fields can lead to undesirable emittance growth, instability within subsequent bunches, undesirable high-order modes (HOMs), and undesirably large power loading. The use of computational models to predict wake field behavior is quite challenging, as existing tools and techniques are insufficient for the task, or require impractically long run times. This project will combine two approaches ¿ (1) augmenting existing parallel processing software with the Time-Domain Extrapolation Method, and (2) applying and evaluating the recently demonstrated and validated Filter Diagonalization mode-analysis technique ¿ to speed up the computation of wake fields for nuclear physics accelerator cavities. Both approaches will be used to compute a quantity called the Beam Impedance, which characterizes the wake fields seen by a given bunch, due to the passage through the cavity of preceding bunches. Commercial Applications and other Benefits as described by the awardee The development of a wake field computational capability would have a major positive impact on cavity design, which is critical for accelerator facilities throughout the DOE portfolio. A better design capability would lead to higher current beams with less wake field losses.