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Electron cloud instability is presented in most of the high intensity proton rings. During the Slow beam extraction (SX) mode at Main Ring of J-PARC, signals related with its formation were observed. An electron cloud detector is installed downstream of the ElectroStatic Septum (ESS), to measure the electron signal. Additionally, scintillation detector with photomultiplier, a proportional counter and photo-diode were set closely to the electron cloud detector to observe the beam lost. This paper presents the measurements of the electron cloud and some of the conditions which support its creation, for instance the signal of lost particle from the beam loss monitors, the residual gas in the vacuum duct by using vacuum pressure gauges, etc., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The resistive wall impedance is one of the major contributors of the impedance in the Main Ring of J-PARC. The present model assumes round chambers of stainless steel with perfect magnet boundary conditions for its surroundings. This work presents the model of the resistive wall impedances taking into account the different chamber geometries of Main Ring, the materials and more realistic surroundings. The models were benchmarked with measurements of the coherent tune shift of the Main Ring of J-PARC. The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Monthly Notices of the Royal Astronomical Society, 451 (1), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

Beam Position Monitor (BPM) is one of the essential elements in a synchrotron facility. It provides the accurate beam positions, which are used to correct the closed orbit distortion. Each BPM is installed with the electronics which enable to acquire the data of the turn-by-turn beam positions. Here, we define the "gain" as the proportionality coefficient between the signal detected at the ADC and the ideal signal without any errors. The signal strength from a BPM electrode varies depending on 1) transmission characteristics of a long cable, 2) processing circuit, and 3) contact resistance at the connected parts. These are the origin of the gain deviations. In order to correct the deviations, a Beam Based Gain Calibration (BBGC) method has been proposed *. Development of a new method for adequate gain calibration is required because any calibration method for routine operation has not been established for BPMs with diagonal-cut electrodes used at J-PARC Main Ring. The results of analysis will be presented using the Total Least Square fitting as an adequate method for the BBGC with sufficient accuracy within 0.6% in one standard deviation., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

We will report the development of a new broadband (bandwidth of around 100MHz) feedback system for suppression of intra-bunch oscillations and reduction of particle losses at the J-PARC Main Ring (MR). A new BPM has been designed based on the exponential coupler stripline type (the diameter of 134 mm and the length of 300 mm) and it is now under fabrication. In this BPM system, the frequency characteristics are corrected using the equalizer as bunch signals are differentiated. The design detail and the performance of the new BPM as well as preparation of newly installed exciter and power amplifiers will be presented. We will also report beam test results of head-tail mode suppression at 3 GeV with the bunch length of 150-250 ns., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

A new data acquisition system has been developed to improve band-width and dynamic range of the beam loss monitor systems. It consists of isolation current amplifiers with the gain of 1M and the band-width of DC-100kHz, and VME-based 24bit ADCs with the band-width of DC-300kHz and the noise level of 100uV peak to peak. The waveform data of 1MS/s and 1KS/s, and the charge count which is the integrated waveform data are generated and these are compared with alarm levels for the machine protection system. Long-term ground-level stability is essential to monitor residual dose activities. Some beam loss signals include effect of radiations from activated devices, and thus its fractions should be excluded. If the residual dose activities just before the beam injections can be monitored, these fractions would be roughly estimated. Furthermore, on-line monitoring of the residual dose activities after a beam operation will be useful for activation control of the devices at the high level activation area like the collimator and the slow-extraction area. A shot by shot DC offset cancellation is adopted to ensure high ground level stability., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

We have developed an accurate and efficient analysis method with a multi-conductor transmission line model for beam position monitors (BPMs). This method combines the two-dimensional electrostatic analysis including beams in the transverse plane and the transmission line analysis in the longitudinal direction. The loads are also included in the boundary condition of the transmission line analysis. Calculation of 2D electrostatic fields can be easily performed with the boundary element method. The BPM response to a beam is compared with that to a stretched wire., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

High power protons from the J-PARC main ring is slowly extracted using the third integer resonance and delivered to the experimental hall for various nuclear and particle physics experiments. The slow extraction device comprises two electro static septa (ESS), ten magnetic septa, four bump magnets, eight resonant sextupole magnets and their power supply. One of the critical issue of the slow extraction is radiation caused by the beam loss during the slow extraction. We have developed the electrostatic and magnetic septa with thin septum thickness. A unique scheme with large step size and small angular spread of the extracted beam enables hit rate on the ESS less than 1% level. In January 2009, first 30 GeV proton beam has been successfully delivered to the fixed target. Quadrupole magnets and a DSP feedback control system to obtain a uniform beam spill structure were implemented in 2009 summer shutdown period. We will report the extraction efficiency, extracted beam profiles and spill structure obtained by the beam commissioning so far. We will also mention a upgrade plan based on some new ideas to aim a higher performance., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In the J-PARC Main Ring (MR), the bending, quadrupole, sextupole, and steering magnets can be controlled on the operating interfaces (OPI). The optics parameters for all magnets are calculated by using SAD, and are converted to BL tables (ex: 2000 points for a steering magnet) for each power supplies. The BL tables are made from the parameters of optics, pattern timing, and beam energy at flat bottom and flat top. For MR beam studies, the BL tables are adjustable with offset and factor. This system is useful for COD correction, beta function measurement, aperture survey, and slow extraction. In this proceeding, the structure of the magnet control system and OPIs for beam studies will be shown., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In J-PARC 50GeV synchrotron ring, large vacuum pressure rises above 10⁻³ Pa are found at 30GeV acceleration final stage of intensity over 10¹³ protons per pulse in the chambers of the in-vacuum electrostatic septum magnet for the slow-extraction(SX), magnetic septum for SX, and the kicker magnet for the fast-extraction. This pressure rise depends on beam intensity and peak-current, and can be reduced by continuous beam operations, such as scrubbing with proton beam, secondary emission electrons and other cations of remaining gasses or desorptions., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

A single-wire proportional counter which has the maximum gain of 6·10⁴ is used as a beam loss monitor (p-BLM), thus low-level beam loss can be monitored. However, it involves gain reduction problem by the space charge effect. It is essential to estimate the space charge effect to utilize a proportional counter for beam loss monitoring. The calibration procedure is discussed for the p-BLMs for 3-50BT and MR. Measurements of residual dose were made and some nuclei were identified. Radiation from the short-life nucleus, Fe53 (T1/2=8.51m), may be a good index to predict a residual dose after a long term beam operation., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The J-PARC RCS is an M-Watt class rapid cycling synchrotron and it has delivered an intensive beam to the neutron target and the MR. In order to overcome large space charge effect, its physical aperture is designed to be more than 250mm in diameter. Even though its chamber size is very large, the BPM system gives precise data to determine beam optics parameters of the ring. For this purpose, only relative positions and resolutions are important. However, for much higher intensity, the absolute beam position and accurate COD correction are indispensable. We have carefully installed the BPM and measured the position with respect to the quadrupole magnet (QM) nearby. But it is also necessary to estimate its absolute position by using beam. If each QM could be controlled independently, the simple beam based alignment technique can be utilized, but it is not the case for RCS. There are seven families of QM, and only each family can be controlled at one time. We developed a new technique by expanding the simple method for the case of multiple QM focusing changed simultaneously, and applied to the J-PARC RCS. The paper describes this method and discussed about experimental results., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

A nondestructive beam profile monitor using a nitrogen-molecule gas-jet sheet has been developed for intense ion beams. The density of the gas-jet sheet corresponds to 1 x 10⁻³ Pa. A light emitted from nitrogen excited by an ion beam collision is measured with a high sensitive camera attached a radiation hard image intensifier. In tests, beam profiles of 6 MeV/u full-stripped oxygen beams whose peak current was 600 μA. were measured. This paper describes characteristics of the instruments and the beam test results., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan