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Beam Profile Monitor for Intense, Negative, Hydrogen-Ion Beams in the J-PARC Linac
Akihiko Miura,Kazuo Hasegawa,Tomoaki Miyao,Tomofumi Maruta,Yong Liu,Kazuhiko Horioka 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.6
Tracking the beam halo and its growth are essential to mitigate the beam dynamics problem in high-current accelerators. In the J-PARC linac, a beam halo has been reported to appear at the place of a mismatched magnet and/or an inaccurately set cavity. The beam loss becomes more significant as the beam’s output power increases. We developed a sensitive wire scanner monitor (WSM) to measure the transverse root-mean-squared (RMS) size of a negative hydrogen-ion beam for the transverse matching between quadrupole magnets. Although the dynamic range of 10+2 is sufficient to evaluate the RMS beam size, we set a dynamic range goal of 10+4 because we intend to observe the beam halo at the same time. We achieved a dynamic range over 10+4 by selecting a proper combination of wire material and diameter by considering the interactions between the beam and the wires. This enabled a measurement of the beam halo evolution in the linac. We discuss the mechanism that enabled the wider dynamic range compared with proton-beam WSMs. In addition, we propose a new chopper-phase-tuning method, which is realized because of the wide dynamic range of the WSM. This method may provide an accurate tuning scheme for not only the present operation but also the high-peak beam-current operation of the linac.
Design and Delivery of Beam Monitors for the Energy-upgraded Linac in J-PARC
Akihiko Miura,Nobuo Ouchi,Hidetomo Oguri,Kazuo Hasegawa,Tomoaki Miyao,Masanori Ikegami 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.3
In the J-PARC (Japan Proton Accelerator Research Complex) linac, an energy-upgrade projecthas started to achieve a design beam power of 1 MW at the exit of the downstream synchrotron. To account for the significant beam parameter upgrades, we will use the newly-fabricated beammonitors for the beam commissioning. This paper discusses the design and assembly of the beamposition monitor, phase monitor, current monitor, transverse profile monitor, and beam loss monitorfor the energy-upgraded linac. We periodically installed the newly-fabricated monitors for theupgraded beam line, as well as for longitudinal matching, because of the frequency jump betweenthe original RF cavity and the newly-developed cavity. We employed two debunchers to correctfor momentum spread and jitter. To account for the new debunchers, we fabricated and installedadditional pairs of phase monitors in order to tune the debunchers to the adequate RF set point. Finally, we propose commissioning plans to support the beam monitor check. We will begin toestablish the 181-MeV operation to confirm the proper functioning of beam monitors. Herein, wewill examine the response to changes of the knobs that control the quadrupole magnets after theenergy upgrade. After proper functioning of the beam monitors is confirmed, we will use the newbeam monitors to establish the 400-MeV acceleration operation.