Abstract
Energy recovery linear accelerators (ERLs) rely upon single-axis superconducting radio frequency (SRF) cavities to be an efficient source of relativistic electrons for high energy and nuclear physics. SRF cavities are also considered relevant for next-generation photon factories and radio-isotope production facilities. The ultimate energy recovery capability for the accelerator would be the ability to operate with a sufficiently spent beam and decrease the energy of the beam before the beam dump to a value lower than the beam injection energy. This is especially important for high current accelerators, where the beam injection energy could be as high as several MeV, and systems where partial beam loss can be expected. The efficient operation of energy recovery in linear accelerators is adversely affected by the typical degradation of the beam quality and current loss. This hinders the application of the ERLs in research and industry, and enabling the use of spent (partially lost current), degraded beams should broaden their application. We suggest that the use of the asymmetric operating mode observed in the dual-axis asymmetric cavities will enable such ultimate capabilities. We discuss the advantages of the application of fields of different amplitude along the cavity accelerating and decelerating axes and demonstrate that the fields can be tuned separately in each axis of the dual-axis cavity. The design of such a cavity and ways to optimize the energy recovery of a spent electron beam by tuning the dual-axis asymmetric SRF cavity are discussed.
Highlights
The concept of an asymmetric, dual-axis superconducting radio frequency (SRF) cavity (Fig. 1) has recently been proposed followed by preliminary studies of the electromagnetic properties of such a structure [1,2,3,4]
We suggest to use a dualaxis cavity, previously proposed to increase the beam breakup (BBU) start current via localization of the higher-order modes (HOMs), to exhibit the asymmetric operating mode which has different accelerating and decelerating field profiles
Research presented here has demonstrated that the dualaxis asymmetric SRF cavity can support accelerating and decelerating fields of different amplitudes
Summary
The concept of an asymmetric, dual-axis superconducting radio frequency (SRF) cavity (Fig. 1) has recently been proposed followed by preliminary studies of the electromagnetic properties of such a structure [1,2,3,4]. Single-axis ERL cavity, the accelerating and decelerating electron beam bunches propagate along the same axis, experiencing identical amplitudes of the electric rf fields. We show a contour plot of the electric fields of the operating TM010 π mode employed for acceleration (axis 1) and deceleration (axis 2). The ability to tailor the field experienced by the decelerated beam independently from that experienced by the accelerating beam becomes important To realize such an asymmetric operating mode, a dual-axis asymmetric cavity [1], which previously has been considered to increase BBU instability start current via localization of the HOMs should be considered. Ep=Ea Bp=Ea (mT/MV/m) R=Q (Ohm) axis 1 R=Q (Ohm) axis 2 Vz (MV) axis 1a Vz (MV) axis 2a R=Q (Ohm)—axis 1 nearest mode R=Q (Ohm)—axis 2 nearest mode G, (Ohm)—operating mode aAt 1 J stored energy
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