KEK, Ibaraki, Japan
Mitsubishi Electric System & Service Co., Ltd, Tsukuba, Japan
J-PARC, KEK & JAEA, Ibaraki-ken, Japan
A two-dimensional beam profile monitor having a high dynamic range approximately six orders of magnitude by using of Optical Transition Radiation (OTR) and fluorescence screens has been operated in the injection-beam transport (3-50BT) line of the J-PARC main ring (MR) [1]. This device contributes to the diagnosis of beam core and halo of intense proton beams before injection to MR, particularly measurement of beam cut effects by beam collimators located in upstream of the device is useful for beam shaping. We have been developing the second device to be installed into MR for diagnosing on injected beams. By using the both of first and second devices, beam core and halo can be diagnosed in different phases. Moreover, by using the second device, beam profiles including halo can be measured with circulating beams in almost twenty turns after injection. This measurement allows us to diagnose beam cut effect by the MR beam collimators by observing beam halo phase space distribution. Property tests of the device have been conducted at a test bench to install it in the ring. In the structure of the device, its longitudinal coupling impedance close to 10 Ω (by Z/n value) is an issue, especially due to high-frequency resonance in the in-vacuum optical system and the target section by beam wake fields. As a countermeasure, we have been studying the absorption of the power of such high frequency resonances up to about 1 GHz using SiC. We have been studying to keep the coupling impedance as low as possible. In a current simulation, we obtained the result that the impedance can be reduced to about 0.5 Ω or less. At the end of this fiscal year, we plan to conduct a characteristic test with SiC mounted device. In this presentation, we will discuss the characteristics of the developing device to be put in the ring and the simulation result of suppressing the coupling impedance.
[1] Y. Hashimoto, et al., Proc. HB2014, East-Lansing, p.187-191.
