Optimizing the configuration of a superconducting photonic band gap accelerator cavity to increase the maximum achievable gradients

Self Cite

We present a study of higher order mode (HOM) damping in the first multicell superconducting radiofrequency (SRF) cavity with a photonic band gap (PBG) coupler cell. Achieving higher average beam currents is particularly desirable for future light sources and particle colliders based on SRF energyrecovery linacs (ERLs). Beam current in ERLs is limited by the beam breakup instability, caused by parasitic HOMs interacting with the beam in accelerating cavities. A PBG cell incorporated in an accelerating cavity can reduce the negative effect of HOMs by providing a frequency selective damping mechanism, thus allowing significantly higher beam currents. The five-cell cavity with a PBG cell was designed and optimized for HOM damping. Monopole and dipole HOMs were simulated. The SRF cavity was fabricated and tuned. External quality factors for some HOMs were measured in a cold test. The measurements agreed well with the simulations.

Section: Design Of the Five-cell Srf Cavitymentioning

confidence: 99%

Section: Design Of the Five-cell Srf Cavitymentioning

confidence: 99%

Higher order mode damping in a five-cell superconducting rf cavity with a photonic band gap coupler cell

Arsenyev

Temkin

Shchegolkov

et al. 2016

Self Cite

“…Photonic band-gap (PBG) structures continue to be a topic of experimental and theoretical interest in accelerator structure design. PBG accelerator research is conducted at microwave and optical wavelengths and in room temperature and superconducting structures [1][2][3][4][5][6][7][8][9][10]. Photonic crystals use a lattice of metallic or dielectric rods to prevent propagation of electromagnetic waves through the lattice at certain frequencies that fall into the band gap [11,12].…”

Section: Introductionmentioning

confidence: 99%

Experimental high gradient testing of a 17.1 GHz photonic band-gap accelerator structure

Munroe

Zhang

et al. 2016

We report the design, fabrication, and high gradient testing of a 17.1 GHz photonic band-gap (PBG) accelerator structure. Photonic band-gap (PBG) structures are promising candidates for electron accelerators capable of high-gradient operation because they have the inherent damping of high order modes required to avoid beam breakup instabilities. The 17.1 GHz PBG structure tested was a single cell structure composed of a triangular array of round copper rods of radius 1.45 mm spaced by 8.05 mm. The test assembly consisted of the test PBG cell located between conventional (pillbox) input and output cells, with input power of up to 4 MW from a klystron supplied via a TM 01 mode launcher. Breakdown at high gradient was observed by diagnostics including reflected power, downstream and upstream current monitors and visible light emission. The testing procedure was first benchmarked with a conventional disc-loaded waveguide structure, which reached a gradient of 87 MV=m at a breakdown probability of 1.19 × 10 −1 per pulse per meter. The PBG structure was tested with 100 ns pulses at gradient levels of less than 90 MV=m in order to limit the surface temperature rise to 120 K. The PBG structure reached up to 89 MV=m at a breakdown probability of 1.09 × 10 −1 per pulse per meter. These test results show that a PBG structure can simultaneously operate at high gradients and low breakdown probability, while also providing wakefield damping.

“…By removing a few central elements of the periodic structure, a "defect" can be formed to confine electromagnetic fields [1][2][3]. During the past decades, experimental and theoretical studies on PBG structures have been conducted involving room temperature metallic materials and superconducting materials, as well as dielectric materials [4][5][6][7][8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…The gradients and breakdown probabilities achieved by the metallic PBG structures were found to be comparable with those of conventional disk-loaded waveguide (DLWG) cavities [16,17]. Wakefield damping has been studied in simulation for metallic PBG structures including both room temperature cavities and superconducting cavities [13,18]. A superconducting PBG cavity for damping high order modes in a superconducting structure has recently been successfully tested [19].…”

Section: Introductionmentioning

confidence: 99%

High power experimental studies of hybrid photonic band gap accelerator structures

Zhang

Munroe

et al. 2016

This paper reports the first high power tests of hybrid photonic band gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM 02 mode, with suppression of both lower order modes, such as the TM 11 mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19 MV=m, corresponding to a surface electric field of 78 MV=m, with a breakdown probability of 5 × 10 −1 per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20 MV=m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.