Design and testing of a 7.8 GHz power extractor using a cylindrical dielectric-loaded waveguide

Abstract

Dielectric-loaded power extraction is a method for the generation of high-power radio frequency (rf) waves under development for future particle accelerators. In this method, a high-charge electron beam drives a wakefield in a dielectric-loaded waveguide (the decelerator) and an rf output coupler extracts the rf power into an external waveguide. We report on the experimental demonstration of a 7.8 GHz dielectricloaded power extractor at the Argonne Wakefield Accelerator facility. We have generated more than 30 MW of rf power with a pulse length of approximately 1.7 ns by passing a single 66 nC electron bunch through the power extractor. We have also used a train of 4 electron bunches to show a clear signature of field superposition. Test results are in good agreement with predictions.

High-power radio frequency pulse generation and extration based on wakefield excited by an intense charged particle beam in dielectric-loaded waveguides.

“…When a single on-axis particle bunch travels through a circular DL waveguide, it excites azimuthally symmetric TM 0n modes, and generally the power generated in one mode decreases with an increasing n. For simplicity, we assume the waveguide is lossless, and the beam is ultrarelativistic with a particle velocity of c. Without loss of generality, for an excited mode which may or may not be intentionally chosen as an interaction mode, with a synchronous frequency f 0 (at which v p = c), the on-axis longitudinal e-field detected at the down stream end of the decelerator is (Gao 2008):…”

“…In this section, the RF power level and RF pulse duration excited by a drive beam (a bunch or bunch train) in a DL waveguide are described (Gao 2008).…”

“…(Sessler 1982) and one of the best known applications is the CERN-CLIC system (Braun 1998). As shown in the figure, a typical TBA scheme consists of three stages: i) RF power is extracted from a lowenergy, high-current beam (drive beam) within decelerating sections; ii) RF power is coupled out of the decelerating sections into output waveguides; and iii) RF power is delivered into accelerating sections for acceleration of the high-energy, low-current beam (Gao 2008). This option may overcome some of the limitations of high-power RF generation, transfer, and pulse compression compared to a traditional klystron-based system (Braun 1998;Kübner 1992) at frequencies above X-band (Danly 1995) and power levels beyond a few hundred megawatts (Gai 2001).…”

Linear analysis of active-medium two-beam accelerator

“…The two electron beams move along parallel lines which do not coincide. At Argonne National Laboratory (ANL) [2] and Yale University (Omega P) [3] a similar program is pursued except that extraction units consist of a dielectric loaded waveguide-thus the name dielectric wakefield accelerator (DWA). In another configuration of DWA a Cherenkov wake produced by the drive beam traveling along the a dielectric-loaded waveguide may be used to accelerate a trailing beam in the same structure.…”

Interaction of an Ultrarelativistic Electron Bunch Train with aW-Band Accelerating Structure: High Power and High Gradient

“…In our experiment, the bunch train was generated directly from an RF photoinjector illuminated by a series of laser pulses with variable spacing to provide a tunable drive bunch train and witness bunch [25]. The electron bunch train has the same time structure as the laser pulse train.…”