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Nishimori, Nobuyuki; Nagai, Ryoji; Hajima, Ryoichi; Yamamoto, Masahiro*; Honda, Yosuke*; Miyajima, Tsukasa*; Muto, Toshiya*; Iijima, Hokuto*; Kuriki, Masao*; Kuwahara, Makoto*; et al.
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.995 - 997, 2010/09
Ao, Hiroyuki
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.357 - 361, 2010/09
The budget of the J-PARC linac energy upgrade up to 400 MeV was started from March 2009. The current output energy of the linac was decreased at 181 MeV in the first stage, so that the output power of the 3-GeV Rapid Cycling Synchrotron (RCS) is expected as 600 kW at maximum because of the beam-loss limitation due to a space-charge effect. The 400-MeV injection is therefore essential for the 1-MW operation of the RCS. This energy upgrade requires total 25 Annular-ring Coupled Structure (ACS) modules, 25 high-power RF sources, low-level RF systems and additional beam monitors. In this paper, we summarize the developments and fabrication status of these accelerator components with briefly reviewing their results.
Miura, Akihiko; Sako, Hiroyuki; Wei, G.; Ikegami, Masanori*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.587 - 589, 2010/09
Residual gas in beam line essentially affects the beam loss and residual radiation on the accelerator. It is important to understand a cause of beam loss and relation between beam loss and residual gas pressure. We measured beam loss at the normal and worse vacuum condition in both SDTL and A0BT sections. The result indicates that the beam loss depends on the residual gas pressure and position where the beam loss occurs is about 20 to 30 meter downstream. This suggests the optimum position for installation of vacuum system to minimize the beam loss. In this paper, we describe the experimental result and its discussions. In addition, the cause of the beam loss is considered to be a stripping from negative hydrogen ions to neutral hydrogen atoms (H
).
Miura, Akihiko; Sako, Hiroyuki; Yamamoto, Kazami; Kikuzawa, Nobuhiro; Maruta, Tomofumi; Sato, Susumu; Imai, Kenichi; Adachi, Satoshi; Sugimura, Hitoshi; Igarashi, Zenei*; et al.
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.590 - 592, 2010/09
Ar-CO
gas proportional counters are employed for the measurement of beam loss in the current linac operation, but they are also sensitive to background noise of X-ray emitted from RF cavities. In SDTL section, protons, secondary hadrons and 
rays would be mainly generated as a beam loss, but it is not easy to estimate real beam loss using the proportional counter. The plastic scintillation counters with less X-ray sensitivity and 
He proportional counters with high thermal neutron sensitivity will be also employed to measure the beam loss. This paper reports the signals obtained during the beam operation using the Ar-CO gas proportional counter and the plastic scintillation counter. Finally, a measurement of emission position and angle distributions of protons due to negative hydrogen ion (H
) beam loss is being planed. This plan is introduced and this result would lead to clarify the source of beam loss.
Wei, G.; Ikegami, Masanori*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.947 - 949, 2010/09
Sako, Hiroyuki; Wei, G.; Miura, Akihiko; Ikegami, Masanori*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.563 - 565, 2010/09
In J-PARC linac at 15 mA, horizontal and vertical emittance after DTL is reduced by 12% and 10%, respectively by setting the amplitudes of the first and second bunchers to 120% and 90% with respect to the designed settings. The resulting normalized horizontal and vertical emittance is 0.230 and 0.205 mm mrad. At 20 mA measured in Jan 2010, horizontal and vertical rms emittance is reduced by 17% and 10% respectively by setting the amplitudes of the first and second bunchers to 110% and 80% with respect to the designed settings. The resulting normalized horizontal and vertical emittance is 0.273 and 0.253 mm mrad. At 15 mA, we further investigated dependence of emittance on quadrupole magnetic field in MEBT1. With the most downstream quadruple magnet field at MEBT1 enhanced by 20% from the designed values, the emittance is further reduced to 0.171 and 0.200 mm mrad. These results are compared with the IMPACT simulation.
Hasegawa, Kazuo
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.449 - 451, 2010/09
Beam commissioning of the J-PARC linac started in November 2006 and 181 MeV acceleration was successfully achieved in January 2007. The linac had delivered beams for commissioning of accelerators and experimental facilities. Trip rates of the RFQ, however, unexpectedly increased in Autumn 2008, and that was the primary limitations of the operation days and power ramp up. We tried to recover by improvement of vacuum properties, tender conditioning and so on. By taking these measures, we can lengthen the continuous operation days and stand user operations. We ramped up the beam power from 20 kW to 120 kW for 3 GeV beam users in November 2009. This corresponds to the linac beam power of 7.2 kW and the linac has delivered beams at this power since then without significant troubles. And also we successfully demonstrated 300 kW at 3 GeV for 1 hour in December. We present the performance and operation experiences of the J-PARC linac.
Oguri, Hidetomo; Namekawa, Yuya; Okoshi, Kiyonori; Ueno, Akira; Ikegami, Kiyoshi*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.1016 - 1018, 2010/09
A cesium-free H ion source driven with a LaB
filament is being operated for J-PARC. As of June 2010, there have been 34 beam commissioning or supply runs. In these runs, the ion source has been successfully operated in two different modes such as low current mode of 5 mA and high current mode of 30 mA. According to the task of the run, one of the two modes was selected. However, the beam current has been restricted to less than 15 mA for the stable operation of the RFQ linac which has serious discharge problem from September 2008. The beam run is performed 1 month cycles, which consisted of a 4-5 weeks beam run and 4 days down-period interval. At the recent beam run, about 600 hours continuous operation was achieved, which is satisfied with the requirement of the ion source lifetime for the J-PARC first stage. At every runs, the beam stop time due to the ion source failure is about one hour, which correspond to the ion source availability of 99%.
Morishita, Takatoshi; Kondo, Yasuhiro; Hasegawa, Kazuo; Naito, Fujio*; Yoshioka, Masakazu*; Matsumoto, Hiroshi*; Hori, Yoichiro*; Kawamata, Hiroshi*; Saito, Yoshio*; Baba, Hiroshi*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.521 - 523, 2010/09
The fabrication of a new RFQ has been started as a backup machine for the J-PARC linac. The RFQ cavity is divided by three unit tanks in the longitudinal direction. The unit tank consists of two major vanes and two minor vanes, those are brazed together. A one-step vacuum brazing of a unit tank was adopted to unite these four vanes together with the flanges and ports. At the first tank brazing, the vacuum leak has been occurred due to the non-uniform temperature rise during the heating. Repair of this leakage and the results of the improved brazing of the second tank are reported.
Kondo, Yasuhiro; Ikegami, Masanori*; Naito, Fujio*; Qiang, J.*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.911 - 913, 2010/09
For the beam current upgrade of the J-PARC linac, a new RFQ (RFQ III) is developing. The peak beam current of RFQ III is 50 mA. To increase the peak current form the existing RFQ (RFQ I), the longitudinal and/or transverse emittances are expected to be increased. However, the increase of the longitudinal emittance will affect the performance of the RF chopper system. In this paper, detailed simulations of the RF chopper system are described.
Morishita, Takatoshi; Kondo, Yasuhiro; Hasegawa, Kazuo; Kawamata, Hiroshi*; Naito, Fujio*; Yoshioka, Masakazu*; Matsumoto, Hiroshi*; Hori, Yoichiro*; Saito, Yoshio*; Baba, Hiroshi*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.518 - 520, 2010/09
The fabrication of a new RFQ has been started in the J-PARC linac. The RFQ cavity is divided by three unit tanks in the longitudinal direction. The unit tank consists of two major vanes and two minor vanes, those will be brazed together. To reduce the costs and periods to develop the special formed bite for the modulation machining, a numerical controlled machining using a conventional ball-end-mill was adopted for the vane modulation cutting instead of the wheel shape cutter. The dimension accuracy was confirmed by cutting test pieces. Moreover, the obtained surface seems smooth enough for the operation. Results of the ball-end-mill machining for the vanes are described.
Ito, Takashi; Nammo, Kesao*; Kubota, Chikashi*; Naito, Fujio*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.566 - 568, 2010/09
An operation of a DTL and a Separated type DTL (SDTL) of a J-PARC started in November 2006. The DTL and SDTL are currently running stable and accelerating the beam. To maintain the stable operation of the DTL and SDTL, we have done the maintenance of various equipment for the tank and solved many troubles. In this paper, we will present the operation experiences of the DTL and the SDTL.
Naito, Fujio*; Nammo, Kesao*; Tanaka, Hirokazu*; Asano, Hiroyuki; Ito, Takashi
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.569 - 571, 2010/09
X-ray radiation from the SDTL of J-PARC linac has been observed with the beam loss monitor by the cavity. The results show that the X-ray intensity depends not only on the RF power level of the tank but also on the RF structure of the tank. In the paper we will show the results of the investigation for the origin of the X-ray radiation from the tank.
Kobayashi, Tetsuya
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.253 - 255, 2010/09
For 400-MeV upgrade of the J-PARC linac. ACS (Annular Coupled Structure) cavities, which are driven by 972-MHz RF, will be installed. The ACS cavity has complicated structure. Its Q-value is very low and the operation frequency is three times high in comparison with that of the SDTL cavity. So the stabilizing control of the ACS accelerating field will be more difficult than present RF system. Further more the chopped beam loading compensation is required. Especially, a debuncher, which has ACS structure, will be located very far from the klystron, consequently the feedback loop delay will be about 1.5 
s. This paper will show the simulation results of the feedback control of the ACS cavity field including long loop delay. As the result, it was found that the required stability could be satisfied by giving high integral gain in FB control.
Kobayashi, Tetsuya; Ikegami, Masanori*
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.256 - 258, 2010/09
The function of the chopped beam loading compensation was implemented into the digital feedback/feed-forward control system of the J-PARC Linac LLRF system to stabilize the ACS cavity fields for the 400-MeV upgrade. The beam test of the chopped beam loading compensation was performed with the present 324-MHz cavity system. Consequently the chopped beam loading was successfully compensated and that this system is valid.
Kawamura, Masato*; Fukui, Yuji*; Naito, Fujio*; Chishiro, Etsuji; Yamazaki, Masayoshi*; Suzuki, Hiroyuki*; Shinozaki, Shinichi; Hasegawa, Kazuo
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.887 - 889, 2010/09
This paper describes the present status, technical specifications, operating experience, and upgrade plane for the power supply system (PS system) for the klystrons in the J-PARC. The PS systems include both the high voltage DC power supplies (DCPSs), which drives one or four modulating-anode klystron each, and the anode-modulators, one per klystron. Currently, the energy output of the J-PARC linac is 181 MeV, which includes the energy necessary to run twenty 324 MHz klystrons. In 2012, the linac will add twenty-five 972 MHz klystrons and upgrade the energy output to 400 MeV.
Umemori, Kensei*; Furuya, Takaaki*; Sakai, Hiroshi*; Takahashi, Takeshi*; Shinoe, Kenji*; Sawamura, Masaru
Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.404 - 406, 2010/09
In order to obtain technology needed for construction of the ERL main linac cryomodule, several developments have been performed. A prototype of 9-cell superconducting cavity was fabricated. Its performance was confirmed through vertical tests. Prototypes of coupler components were also fabricated and tested at the high power test stand. They could successfully pass the specified RF power. A prototype of HOM absorber without ferrite was made. It is under cooling tests. Design work of cryomodule is in progress.
