Asymmetric dual axis energy recovery linac for ultrahigh flux sources of coherent x-ray and THz radiation: Investigations towards its ultimate performance

Abstract

In order for sources of coherent high brightness and intensity THz and X-Ray radiation to be accepted by university or industrial R&D laboratories, truly compact, high current and efficient particle accelerators are required. The demand for compactness and efficiency can be satisfied by superconducting RF energy recovery linear accelerators (SRF ERL) allowing effectively minimising the footprint and maximising the efficiency of the system. However such set-ups are affected by regenerative beam-break up (BBU) instabilities which limit the beam current and may terminate the beam transport as well as energy recuperation. In this paper we suggest and discuss a SRF ERL with asymmetric configuration of resonantly coupled accelerating and decelerating cavities. In this type of SRF ERL an electron bunch is passing through accelerating and decelerating cavities once and, as we show in this case, the regenerative BBU instability can be minimised allowing high currents to be achieved. We study the BBU start current in such an asymmetric ERL via analytical and numerical models and discuss the properties of such a system.

Experimental studies of 7-cell dual axis asymmetric cavity for energy recovery linac

“…A field flatness of around 85% was observed. As in previous studies [11] the eigenmodes associated with the resonant coupler [ Fig. 2(c)] have similar structures and are localized inside the coupling cell and the contour plots are similar to those observed before, for the 11-cell cavity.…”

“…The port numbering is used throughout the text as shown. (b) Part of the technical drawing indicating the cavity cells similar to models studied in [11]. the studies were conducted in the frequency range from 1 to 2.5 GHz.…”

“…The dual axis asymmetric energy recovery linac (AERL) in which acceleration and deceleration are separated, while the cells are individually tuned and linked via a resonant coupler has recently been suggested [11][12][13][14] to mitigate the development of the instability. The theoretical studies of an 11-cell cavity [11] indicated the possibility to increase the BBU starting current, thus stimulating the research.…”

“…To demonstrate scalability of the conceptual design i.e. conservation of the basic properties predicted in [11] with variation of the cavity length, to speed up the cavity manufacturing and save the cost of machining a 7-cell cavity ( Fig. 1) was considered for the first prototype studies.…”

“…In the conclusion we will discuss further steps to realize asymmetric energy recovery Linac (AERL). We note that the numerical studies were carried out using a 3D CST MW Studio software package, instead of ACE3P electromagnetic suite (developed at SLAC) and used in the previous work [11]. The new software was used to check validity of the conceptual model and compare the capabilities of the broadly available commercial product 3D CST Microwave Studio with highly reputable specialist software ACE3P.…”