SLAC, Menlo Park, California, USA
We present the design for a rapid proton energy modulator with radio-frequency (RF) accelerator cavities. The energy modulator is designed as a multi-cell one-meter long accelerator working at 2.856 GHz. We envision that each individual accelerator cavity is powered by a 400 kW low-voltage klystron to provide an accelerating / decelerating gradient of 30 MV/m. We have performed beam dynamics simulations showing that the modulator can provide ± 30MeV of beam energy change, with an energy spread of 3 MeV for a 7 mm long (full length) proton bunch. A prototype experiment of a single cell is in preparation at the Next Linear Collider Test Accelerator (NLCTA) at SLAC.
THYBB4
SLAC, Menlo Park, California, USA
MIT/PSFC, Cambridge, Massachusetts, USA
MIT, Cambridge, Massachusetts, USA
INFN/LNF, Frascati, Italy
There is an ongoing interest in linear accelerators operating at 100s of GHz and THz frequencies due to their small size and potentially high efficiency. Vacuum RF breakdown is one of the fundamental factors limiting performance of these linacs. Accordingly, study of RF breakdown physics in mm-wave high gradient accelerating structures is needed, which includes understanding of dependencies of the breakdown rate on electromagnetic, geometric, and material properties. In our previous work, we have tested beam-driven 100 GHz and 200 GHz metallic accelerating structures. In this work we report results of high power tests of a 110 GHz single-cell standing wave accelerating cavity powered by a 1 MW gyrotron. The RF power is coupled into the accelerating structure using a "Gaussian to TM01" mode converter. In order to characterize high gradient behavior of the cavity, including the RF breakdown probability, we have measured RF signals and field-emitted currents. The cavity is driven by 10 ns, 100s of kilowatt pulses. These short pulses were cut from microsecond-long gyrotron pulses using a fast optical switch, with accelerating gradients up to 150 MV/m.
THYBB5
RadiaBeam, Santa Monica, California, USA
SLAC, Menlo Park, California, USA
RadiaBeam Systems, Santa Monica, California, USA
MIT/PSFC, Cambridge, Massachusetts, USA
MIT, Cambridge, Massachusetts, USA
The development of novel mm-wave accelerating structures with > 200 MV/m gradients offers a promising path to reduce the cost and footprint of future TeV-scale linear colliders, as well as linacs for industrial, medical and security applications. The major factor limiting accelerating gradient is vacuum RF breakdown. The probability of such breakdowns increases with pulse length. For reliable operation, millimeter-wave structures require nanoseconds long pulses at the megawatt level. This power is available from gyrotrons, which have a minimum pulse length on the order of microseconds. In this paper, we will describe the laser-based RF switch capable of selecting 10 ns long pulses out of the microseconds long gyrotron pulses, thus enabling the use of the gyrotrons as power sources for mm-wave high gradient linac. The principle of operation of this device and its achieved parameters will be discussed. We will also report on the experimental demonstration of the RF switch with the high power gyrotron at the Massachusetts Institute of Technology.