Multi-harmonic test setup for RF breakdown studies

Structure-based, high transformer ratio collinear two-beam accelerator

“…Recently, we proposed a class of novel cavity designs with unconventional spatiotemporal distributions using multi-harmonic mode superposition to suppress RF breakdown [2] and pulsed heating [3]. Multi-harmonic cavity structures can, in principle, be powered by two or more types of klystrons at two or more harmonic frequencies [4]. But we have reached the conclusion that the two-beam configuration is more appealing for a large-scale high-gradient accelerator, based on the same arguments put forward by the CLIC group [1].…”

Multi-harmonic cavity for suppressing surface pulsed heating

“…The first phenomenon is the suppression of field emission due to the anode-cathode effect [1,2]. In a longitudinally asymmetric cavity [1,2], phase-locked two-frequency operation with the 2 nd mode at a frequency double that of the fundamental, can allow the electric field pointing into one wall (cathode-like) to be significantly smaller than the field pointing out of that wall (anode-like), as shown in Fig. 1(a) and (b).…”

“…The specific design of multi-harmonic cavity to make such an effect prominent has been discussed in details in Ref. [1]. The related experimental effort to explore the anode-cathode effect will be pursuit in parallel to the experiment described in this paper.…”

“…Similarly, the surface RF H-field is . Pulsed heating temperature rise can then be approximately scaled in terms of and as (1) where the frequency term is related to the ratio of surface resistivities, , and the cross term averages out over one period. Fig.…”

Multi-harmonic RF test stand for RF breakdown studies

“…This multi-harmonic RF test stand is a unique facility, built to provide mutually phase-locked multi-MW ~1 µs pulses at 2.856 and 5.712 GHz with continuously-adjustable amplitudes and relative phase difference [4]. It is anticipated that deepened understanding of RF breakdown, perhaps through studies of the sort described here, could lead to improved design of warm structures with higher accelerator gradient and lower breakdown probability than can be built at present.…”