MIT/PSFC, Cambridge, Massachusetts, USA
An overmoded hybrid Photonic Band Gap (PBG) structure used as an accelerator cavity has been theoretically designed. The PBG structure consists of a triangular lattice of dielectric (sapphire) and metallic rods. The birefringence of the sapphire affects the PBG eigenmodes and must be taken into account. The PBG cavity formed by rods in between two copper plates will be operated in a TM02 mode at 17 GHz. Arrangement of the rods for higher-order-mode (HOM) damping demonstrates high frequency selectivity. Comparison with a disk-loaded waveguide (DLW) cavity gives a perspective of the dielectric PBG structure operated at an accelerating gradient of 100 MV/m. Cold test of a single hybrid PBG cell presents a high-Q resonance at 17 GHz. A standing-wave (SW) hybrid PBG structure will be tested in TM02 mode at 17 GHz.
MIT/PSFC, Cambridge, Massachusetts, USA
Metamaterials (MTMs) are artificial electromagnetic materials comprised of sub-wavelength elements. A Double-Negative Metamaterial (DNM) has both negative permittivity and negative permeability and can be described by an effective medium theory. We investigate MTMs at microwave, millimeter wave, and THz frequencies for application as accelerator structures, as interaction circuits of high power microwave vacuum electron devices, and as beam diagnostics tools. In this paper, we propose a new method to retrieve the effective material parameters, i.e., effective permittivity and permeability. We first get the effective permeability analytically and then the effective permittivity numerically according to the dispersion characteristics. This method is different from that for the slab DNMs which is based on the scattering parameters. The approach presented here offers a solid foundation for metamaterial-based accelerator and vacuum electron device applications.
MIT/PSFC, Cambridge, Massachusetts, USA
MIT, Cambridge, Massachusetts, USA
A metamaterial waveguide is proposed for application in a linear accelerator. The waveguide walls are made of a metamaterial that includes complementary split-ring resonators. In such a metamaterial waveguide, the TM-like mode exists and can be excited by the electron bunch. A complementary split-ring resonator is formed by slots in a metallic plate, therefore, this metamaterial waveguide is easy to build. This makes it possible to use in high frequency linear accelerators. The metamaterial waveguide is coupled to single mode rectangular waveguides which can be connected to a microwave network for coupling power into or out of the waveguide. One attractive application of the proposed metamaterial waveguide is in electron beam bunch diagnostics. The metamaterial waveguide is designed using HFSS. The wakefield simulations are carried out using the CST Particle Studio code. The simulations are done for a single bunch as well as for a train of bunches to model the experiment. In this experiment, it is proposed to use the beam line of the Haimson Research Corporation/MIT linear accelerator operating at the frequency of 17.14 GHz.
MIT/PSFC, Cambridge, Massachusetts, USA
Photonic Band-gap (PBG) structures continue to be a promising area of research for future accelerator structures. Previous experiments at X-Band have demonstrated that PBG structures can operate at high gradient and low breakdown probability, provided that pulsed heating is controlled. A metallic single-cell standing-wave structure has been constructed at MIT to investigate breakdown performance of PBG structures with very high surface temperature rise. The MIT standing-wave structure test stand has an available power of 4 MW for a maximum gradient of 130 MV/m; the actual realized gradient may be lower due to breakdown limitations. The MIT test stand will also utilize novel diagnostics, including fast camera imaging and optical spectroscopy of breakdowns.
