LANL, Los Alamos, New Mexico, USA
SLAC, Menlo Park, California, USA
Small, lightweight, few-MeV electron accelerators that can operate with low-voltage power sources, e.g., solid-state transistors running on 50 VDC, instead of high-voltage klystrons, will provide a new tool to enhance existing applications of accelerators as well as to initiate new ones. Recent advances in gallium nitride (GaN) semiconductor technologies * have resulted in a new class of high-power RF solid-state devices called high-electron mobility transistors (HEMTs). These HEMTs are capable of generating a few hundred watts at S-, C- and X-bands at 10% duty factor. We have characterized a number of GaN HEMTs and verified they have suitable RF characteristics to power accelerator cavities **. We have measured energy gain as a function of RF power in a single low-beta C-band cavity. The HEMT powered RF accelerators will be compact and efficient, and they can operate off the low-voltage DC power buses or batteries. These all-solid-state accelerators are also more robust, less likely to fail, and are easier to maintain and operate. In this poster, we present the design of a low-beta, 5.1-GHz cavity and beam dynamics simulations showing continuous energy gain in a ten-cavity C-band prototype.
* See for example, http://www.wolfspeed.com/downloads/dl/file/id/463/product/174/cghv59350.pdf
** J.W. Lewellen et al., Proceedings of LINAC2016, Paper MO3A03
SLAC, Menlo Park, California, USA
MIT/PSFC, Cambridge, Massachusetts, USA
MIT, Cambridge, Massachusetts, USA
INFN/LNF, Frascati (Roma), Italy
We will preliminary testing results for single-cell accelerating structures intended for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures consist of pi-mode standing-wave cavities fed with TM01 circular waveguide mode. We fabricated of two structures one in copper and the other in CuAg alloy. Cold RF tests confirm the design RF performance of the structures. The geometry and field shape of these accelerating structures is as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with a MW gyrotron oscillator that produces microsecond pulses. One megawatt of RF power from the gyrotron may allow us to reach a peak accelerating gradient of 400 MeV/m.
Euclid TechLabs, LLC, Solon, Ohio, USA
SLAC, Menlo Park, California, USA
Conventional traveling wave or pi-phase advance standing wave structures use coupling of the microwave power through the beam pipe. This feature constrains the cavity shunt impedance (efficiency) to relatively small values. As microwave power flows through the accelerating cells in such structures, the probability of breakdown in high gradient operation is greatly increased. In this paper we present results from an accelerating structure prototype with distributed microwave coupling, an approach invented at SLAC. These structures include one or more parallel waveguides which are loaded by accelerating cavities. In this configuration accelerating cavities are fed independently and completely isolated at the beam pipe. Thus there is no microwave power flow through the accelerating cavity, making this geometry favorable for high gradient operation and maximizing the shunt impedance.
INFN-Roma1, Rome, Italy
UCLA, Los Angeles, California, USA
INFN/LNF, Frascati (Roma), Italy
INFN/LNS, Catania, Italy
SLAC, Menlo Park, California, USA
Rome University La Sapienza, Roma, Italy
Sapienza University of Rome, Rome, Italy
University of Catania, Catania, Italy
LANL, Los Alamos, New Mexico, USA
SLAC, Menlo Park, California, USA
NASA Goddard Space Flight Center, Greenbelt, USA
Los Alamos National Laboratory, in collaboration with SLAC and Goddard Space Flight Center, have begun developing a high-duty-factor, MeV-range linear accelerator intended for use on satellites, specifically to probe the magnetosphere-ionosphere linkage. The design makes use of low-beta C-band cavities operating at moderate gradients, individually powered by 500-W RF amplifier chips. We present the current state of the design, and technology maturation efforts including RF amplifier performance studies, cavity tuner design and an initial acceleration test using a DC beam source and single RF cavity.
SLAC, Menlo Park, California, USA
We present comprehensive efficiency equations and useful scaling laws to optimally determine design parameters for high efficiency rf linacs. For the first time we have incorporated the parasitic losses due to the higher order cavity modes into the efficiency analysis of the standing wave (SW) and travelling wave (TW) accelerators. We have also derived the efficiency equations for a new kind of attenuation-independent-impedance travelling wave (ATW) accelerators where the shunt impedance can be optimized independent of the group velocity. We have obtained scaling laws which relate the rf to beam efficiency to the linac length, beam aperture radius , phase advance per cell, and the type of accelerating structure: SW versus TW, disk-loaded (DL) versus nose-cone (NC). We give an example of using these scaling laws to determine a feasible set of parameters for a 10 MeV, 10 MW linac with 97.2% efficiency.
SLAC, Menlo Park, California, USA
We have used our accelerator design toolbox equations to design three high efficiency and high power CW accelerators for the environmental and medical applications. These are: 2MeV-1MW, 10MeV-10MW, and 10MeV-1MW linacs. These are all 10 m long, 1.3 GHz, π-mode standing wave structures with design efficiencies of 96.8, 97.4 and 86.5 %, and optimal coupling coefficients of 32.9, 43.5, and 7.45, respectively. We present the detailed design parameters of these linacs. The study of single-bunch beam breakup for these linacs and the simulations results from ABCI are also included. The initial cavities are optimized according to the speed of the electron bunch to maximize the shunt impedance. The plots of peak surface fields on these cavities are also presented. We have also included a detailed thermal analysis of these linacs. Finally, we present the results of ASTRA simulations of the three linacs with magnetic focusing. We have also included the complete design of rf-distributed-coupling manifold for the third linac along with the HFSS® simulation results.