FRIB, East Lansing, Michigan, USA
FRIB driver linac will deliver all heavy ion beams up to uranium with energy above 200 MeV/u, and maximum beam power on target 400 kW for nuclear physics research. Phase and amplitude tuning of the FRIB superconducting cavities – totally about 330 of them, are important to the linac beam commissioning at low power and normal operation at high power. Because relatively low beam energy and high acceleration gradient, beam velocity changes significantly in the cavity RF gaps and the beam bunch cannot preserve perfectly in the further downstream beam diagnostics systems, beam longitudinal tuning algorithms are studied for different FRIB cavities and at different beam energy, which include the acceleration cavities as well as the re-buncher cavities.
FRIB, East Lansing, Michigan, USA
FRIB driver linac will deliver all heavy ion beams up to uranium with energy above 200 MeV/u, and maximum beam power on target 400 kW for nuclear physics research. Strong horizontal-vertical beam coupling exists in the FRIB linac since superconducting solenoids are applied to focus multi charge state beams. Further, the FRIB low beta SRF cavities have raised quadrupole field components. The combined effects make beam transverse matching challenging. In this paper, we study transverse matching of horizontal-vertical coupled beams based on beam profile measurements with multiple wire scanners. There are multiple solutions for the initial linac beams with coupling, and errors of the beam diagnostics and magnet power supplies introduce further complication. Nonetheless, simulation studies show that satisfactory transverse matching can be achieved with proper linac beam tuning.
FRIB, East Lansing, Michigan, USA
Beam Loss Monitoring (BLM) System is an essential part to protect accelerator from machine faults. Compared with the empirical or uniform BLM arrangement in most accelerators, our new optimization approach proposes a “minimum spatial distribution” for BLM network. In this distribution, BLMs shall be placed at a small set of “critical positions” that can detect all failure / FPS trigger-able events of each fault mode. In additional, to implement a more advanced function of fault diagnosis, BLM should also be placed at “discrimination points” for fault-induced loss pattern recognition. With examples of FRIB failure event simulations, the author demonstrates the proof of concept to locate these “critical positions” and “discrimination points” for the minimum spatial distribution of BLMs.
FRIB, East Lansing, Michigan, USA
FRIB is using a charge stripper in folding segment 1 to increase the number of charge states of particles to enhance the acceleration efficiency. To control possible emittance growth after the charge stripper, the 3-dimensional on-stripper beam size should be as small as possible. The original 2-cavity-HWR (HWR stands for half wave resonator) rebuncher cryomodule is responsible for the longitudinal focusing before stripper. In order to accept and transport the beam downstream to linac segment 2, another kind of 3-cavity-QWR (QWR stands for quarter wave resonator) rebuncher cryomodule is baselined after the stripper. However, two kinds of cryomodules would increase the cost in design, therefore would be quite inefficient. In this paper, the FRIB lattice with only single-type 4-cavity-QWR rebuncher cryomodule in folding segment 1 is discussed. Positions of lattice elements are adjusted to accommodate the new type of cryomodule. Beam dynamics is optimized to meet the on-stripper beam requirement. The lattice is then adjusted and rematches.
FRIB, East Lansing, Michigan, USA
Non-axisymmetric superconducting RF cavities have been widely used in accelerator facilities. Because of the geometry, electric and magnetic multipole components, including steering terms, quadrupole terms, and higher order terms, would arise and have potential effects on beam dynamics. In this paper, we start with a simple linac periodic structure to study the effects of higher order terms. The action is defined as a figure of merit to quantify the effects. After that, we move to a more realistic situation of FRIB linac segment 1 (LS1). Multipole terms of quarter wave resonators (QWRs) are firstly calculated using multipole expansion scheme. Then, the scheme is tested using the FRIB linac lattice with QWRs, and the effects of higher order terms on FRIB LS1 are estimated.