WEZBA1
ORNL, Oak Ridge, Tennessee, USA
FRIB, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
Facility for Rare Isotope Beams (FRIB) at Michigan State University is based on a high power heavy ion linac and beam commissioning is under way. For evaluation of beam Twiss parameters and rms emittance, we routinely use multiple profile measurements while the strength of an upstream quadrupole is varied. The change of the quadrupole strength results in a beam mismatch downstream of the profile monitor which can cause beam losses. This is not acceptable in a high energy beamline. To avoid this transverse mismatch, we developed a beam matching procedure by optimization of quadrupoles’ setting downstream of the profile monitor. Using this procedure we were able to eliminate beam losses during the quadrupole scan, and evaluate beam Twiss parameters and rms emittance. Examples of using this procedure in the folding segment of the FRIB linac will be reported.
WEZBA4
University of Tennessee, Knoxville, USA
CNMS, Oak Ridge, USA
ORNL RAD, Oak Ridge, Tennessee, USA
ORNL, Oak Ridge, Tennessee, USA
The 1.4 MW Spallation Neutron Source (SNS) uses nanocrystalline diamond (NCD) foils to strip 1 GeV H− ions to protons during injection into the accumulator ring. The SNS Proton Power Upgrade will double the power deposited into the NCD foils by increasing the beam current by 50% and linac energy by 30%. This makes understanding the failure modes of the NCD foils increasingly important. In this work we report on experiments using a 30 keV, 5 mA electron gun capable of simulating SNS PPU time structure and energy deposition in NCD foils. We analyze changes to the foil with an RGA, FLIR camera, faraday cup, high definition photography, SEM, and Raman spectroscopy. We examine failure mechanisms for foils subjected to equivalent PPU conditions. Preliminary results have shown characteristic signs of foil thinning and different failure mechanisms between the electron gun and SNS beam line. Additionally, membrane cantilever structures have been synthesized and characterized to understand the material properties of the NCD. Finally, finite element thermal simulations of the suspended diamond foils have been performed, which will be used to assess and direct future foil modifications.
Fermilab, Batavia, Illinois, USA
A Marx-topology modulator has been designed and developed at the Fermi National Accelerator Laboratory under the Proton Improvement Plan (PIP). This modulator replaces the previous triode hard-tube design, increasing reliability, lowering operational costs, and maintaining waveform accuracy. The Marx modulator supplies the anode of the 7835 VHF power triode tube with a 35 kV, 375 Amp, 460 µs pulse at 15 Hz. It consists of 54 individual Marx cells, each containing a 639 µF capacitor charged to 900 Volts, combined in series with IGBT switches to create the desired output waveform. This requires variable rise and fall times, flattening of capacitive droop, and feedforward beam loading compensation. All five 201.25 MHz RF systems have been upgraded to Marx modulators to ensure continued operation of the linear accelerator.
CCR, San Mateo, California, USA
Fermilab, Batavia, Illinois, USA
CPI, Beverley, Massachusetts, USA
Calabazas Creek Research, Inc., Fermilab, and Communications & Power Industries, LLC, developed a 100 kW peak, 10 kW average, 1.3 GHz, magnetron-based, RF system for driving accelerators. Efficiency varied between 81% and 87%. Phase locking uses a novel approach that provides fast amplitude and phase control when coupled into a superconducting accelerator cavity [1]. The system was successfully tested at Fermilab and produced 100 kW in 1.5 ms pulses at a repetition rate of 2 pps. A locking bandwidth of 0.9 MHz was achieved with a drive signal of 269 W injected through a 4 port circulator. The phase locking signal was 25 dB below the magnetron output power. The spectrum of the phase locked magnetron was suitable for driving accelerator cavities. Phase modulation was demonstrated to 50 kHz (the limit of the available driver source). The average power was limited by available conditioning time. Scaling indicates 42 kW of average power should be achievable. Estimated cost is less than $1/Watt of delivered RF power, exclusive of power supplies or modulators. System design and performance measurements will be presented.
[1] B. Chase, R. Pasquinelli, E. Cullerton, P. Varghese, "Precision Vector Control of a Superconducting RF Cavity driven by an Injection Locked Magnetron," Jou. of Instrumentation, Vol. 10 March 2015.