Search

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 ��� (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 ��� 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., Proceedings of the 10th International Beam Instrumentation Conference, IBIC2021, Pohang, Rep. of Korea

The beam commissioning for the RIKEN Heavy-ion Linac (RILAC) upgrade, including the new Superconducting Linac (SRILAC) has been successfully completed. These RILAC upgrade aims at promoting super-heavy element searches and the radioactive isotope (RI) production for medical use. When we accelerate the beam by the SRILAC, we must definitely reduce the beam loss under 1 W/m. To constantly monitor the beam nondestructively, we have developed the new system (BEPM) measuring simultaneously not only the beam position but also the beam energy by measuring the time of flight of the beam. This system has the great advantage that can handle time-chopped beam by synchronizing the measurement system with the beam-chopping signal. At the beginning of the commissioning, the beam was chopped to 3% duty to make the SRILAC cavity protected from the beam loss. Even though the beam intensity was 15 enA, the beam position and energy were accurately measured. We measure the beam position to an accuracy of ±0.1 mm and the beam energy to that of several 10⁻⁴. Here, we present details concerning the BEPM system and commissioning results., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

Upgrades for the RIKEN Heavy-ion Linac (RILAC) involving a new Superconducting Linac (SRILAC) are currently underway to promote super-heavy element searches and Radio Isotope (RI) production (211At) for medical use at the RIKEN radioactive isotope beam factory (RIBF). If destructive monitors are used, since they generate outgassing, it becomes difficult to maintain the Q value and surface resistance indicating the performance of the superconducting radio frequency (SRF) cavities over a long period of time. Therefore it is crucially important to develop nondestructive beam measurement diagnostics. We have developed a beam energy position monitor (BEPM) system which can measure not only the beam position but also the beam energy simultaneously by measuring the time of flight of the beam. By using parabolic cut, ideal linear response of the quadrupole moments is realized, keeping a good linear position sensitivity at the same time. We fabricated 11 BEPMs and the position calibration system employing a wire method has been used to obtain the sensitivity and offset of BEPMs. We will describe details concerning the BEPM, calibration system and measured results., Proceedings of the 8th International Beam Instrumentation Conference, IBIC2019, Malmö, Sweden

For J-PARC, 16 electrodes beam-monitors are developed. It is possible to measure the transverse moments of beams from the induced voltages. A beam size is calculated from these in two locations with different values of beta functions. Beam-monitors such as a Flying Wire Monitor and an Ionization Profile Monitor (IPM) are already installed. However, the two monitors have issues in measuring higher intensity beams. The former is that the wire gets easily burned out and the latter is that there is a sign of the saturation by a space charge effect. Therefore, these aim at measuring the sizes of high intensity proton beams up to 4.2·10⁺¹³ protons/bunch, which corresponds to 1.3 MW in 1.16 s cycle operation of the MR. Furthermore, with high accuracy measurements, the injection mismatch from the RCS is to be decreased. In the beam test in February 2019, the signal-noise ratio (SNR) of this monitor in bunch-by-bunch measurements was nearly 40 dB and lower than the SNR > 50 dB which is comparable to IPM. To improve the SNR, we developed new LPFs for anti-aliasing and improved signal processing. In addition, the second monitor will be installed in August 2019 and tested with beams in November., Proceedings of the 8th International Beam Instrumentation Conference, IBIC2019, Malmö, Sweden

Extracted-beam profiles in slow extraction at J-PARC has been measured by using secondary electrons emitted from a target array made by multi-layered graphen, in real time during spill time of around 2 seconds. The target array consists of 20 ribbons with width of 1 mm, pitch of 2 mm, and thickness of 1.1 micron. Secondary-electron current at each channel is measured by a current amplifier having sensitivity more than 1 pA. These configuration produces useful information for beam dynamics in slow extraction. We have set this monitor at the entrance of a septum magnet, then we can also measure the last few-turns beam with the extracted beam simultaneously. We will discuss about features of this instrument and recent beam study with 51 kW extracted-beams., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

One of the important ingredient in the intra-bunch transverse feedback is a kicker. The frequency characteristics of the kicker suffers from the transit-time factor, sin(kl)/kl. We examine the frequency characteristics of multiple kickers system. Relation between the excitation patterns of the multiple kickers and the frequency characteristics are presented., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

For the T2K neutrino oscillation experiment upgrade programs of J-PARC are on-going for higher beam intensity. The ultimate goal is to achieve a beam power of 1.3 MW in the main ring, a significant increase more than triple intensity compared to the presently achieved power of 470 kW. Beam loss is a cause of the limitation on the proton bunch intensity. A precise orbit correction is necessary in order to reduce the beam loss. Beam position monitor (BPM) is a vital element providing accurate measurements of the beam positions for the control of closed orbit distortion (COD). Currently an apparent dependence of COD RMS on the beam intensity is observed (about 30 μ m). In order to understand the nature of the phenomenon, investigations are being made on the BPM response and its intensity dependence as well as on the effects of wake field, beam bumps to COD and septum. Status of the studies will be discussed. Also presented are new design of BPM for improved position resolution and stability, and its expected performance., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

We measure dipole and quadrupole moments of the beam using the BPMs in the beam transport line 3-50BT of J-PARC and obtain differences of squared horizontal- and vertical-rms-sizes for those BPMs. Then we obtain rms emittances and rms momentum by fitting with given Twiss parameters., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The tapered-coupler stripline beam position monitor has been used for the intra-bunch feedback system in the J-PARC MR. It should be realized with a special shaped striplines, for example, whose width is tailored exponentially and whose gap distances between the inner surface of the beam pipe should be also decreasing as a exponential function in order to keep the characteristic impedance 50 ohm. This 3D varying geometry makes it difficult to achieve the good balance between the electrode responses to the beam. We present a new design method with a groove, which may give simpler geometry and flatter frequency response., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

Fukushima nuclear accident of March 11, 2011, soil and water had been contaminated by radioactive cesium. Moreover, radioactive cesium was found in the ocean sludge in Tokyo Bay flowing from rivers. Cesium which is adsorbed to the sludge cannot be easily removed. One of the authors developed decomposition and purification system, a circulation-type system by fine bubbles, that is, by creating aerobic state, aerobic bacteria are activated resulting to decomposition and purification of ocean sludge. Based on the hypothesis that radioactive cesium is adsorbed on the surface of the sludge deposition. It is considered that cesium can be eluted after decomposing the deposited sludge. Once the cesium is eluted in the water, it can fix to a mineral such as zeolite. Eluting and fixing cesium adsorbed on sludge takes so much time. In this case, the concept of removing the left sludge by flocculation method and then followed by coagulating sedimentation method is studied. In this study, our objects are to show the effectivity and efficiency of using flocculation and coagulating sedimentation in removing radioactive cesium. As the results, we pointed out this method is very good.

Transverse multipole moments (quadrupole and more) of the beam may give important informations of the beam such as beam sizes, nonlinear resonances and so on. However higher moments are difficult to measure because signal-to-noise-ratio becomes smaller proportional to the n-th order of the beam-radius-to-vacuum-duct-radius ratio. In order to increase the SNR and to extend the multipole order, we developed and installed a 16 electrode beam monitor in the J-PARC MR, which consists of guard-potential-separated 16 striplines. The calibration method, beam test results will be presented., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The new beam loss monitor (BLM) system now in operation at the main ring of J-PARC consists of an isolated front-end current to voltage converter, a VME-based 24 bit ADC system. A dual detector system employs a proportional-type gas chamber (PBLM) and an air-filled ionization chamber (AIC). The system shows a wide dynamic range of 160 dB. It can detect the low level signal that would arise in the case of the detection of residual dose in the ring itself after the beam has been turned off as well as an event such as high level beam loss at the collimators. The signal rise time of the waveform obtained is 17 us which fast enough to meet the speed requirement of the Machine Protection System (MPS); which is that the MPS should dump the beam within 100 us when the beam loss signal exceeds the reference levels set in the ADC system., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The RCS at J-PARC is a kicker-impedance dominant machine, which violates the impedance budget from a classical viewpoint. Nevertheless, we have recently succeeded to accelerate a 1-MW equivalent beam by making maximum use of the space charge effect on the beam instabilities. In this report, we explain the manipulation to suppress the beam instability, at first. Then, we discuss some issues to suppress the beam instabilities for beams with much smaller transverse emittance, as well as the present status of our efforts to reduce the kicker impedance toward the realization of the higher beam power at the RCS., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

In high intensity proton synchrotrons, linear and nonlinear betatron resonances cause beam loss. When the betatron tune spreads over a resonance line, the oscillation amplitude will get larger, causing a large beam loss. Our study aims for a direct measurement of the betatron tune spread by using a quadrupole kicker and a 4-electrode monitor. The monochromatic rf signal is inputted to the kicker and we induce an oscillation by kicking the beam. The amplitude of the quadrupole oscillation will depend on the number of particles having a certain tune. In the beam test at J-PARC MR, the dipole kicker was used as a quadrupole kicker by exciting the two facing electrodes in-phase. We measured the response to the kick at several frequencies. We observed that the amplitude depends on the kicker frequency and the number of particles per bunch. This demonstrates that the quadrupole oscillation can be induced by a kicker and the possibility of measuring the number of a particular tune particle from the response. We will present the result of the beam test and our prospect and the comparison between the experimental result and a numerical calculation., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

We are looking for feasible and quantitative method to evaluate space charge induced beam loss in J-PARC MR. One possible way is space charge simulation and theory based on measured Twiss parameter. Twiss parameter measurement using turn-by-turn monitors is presented. Resonance strengths of lattice magnets and space charge force are estimated by the measured Twiss parameters. Emittance growth and beam loss under the resonance strengths are discussed., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A nondestructive Ionization Profile Monitor (IPM) is widely used to measure transversal profile. At J-PARC Main Ring (MR), three IPM systems have been used not only to measure emittances but also to correct injection miss matchings. To measure injection 3GeV beam profiles, the high external E field of +50kV/130mm at the maximum is used to guide ionized positive ions to a position sensitive detector; transversal kick force originating from space charge E field of circulating beam is a main error source which deteriorates profile. The strong B field is also used to compensate the kick force. To measure 30GeV bunched beam at the flat top on the fast extraction mode in good resolution, the strong B field of about 0.2T is needed. One set of magnet system, which consists of a C-type and two H-type magnets, were developed and installed in one IPM system. The IPM chamber was inserted between the 2 poles of the C-type magnet. To make the line integral of B field along the beam axis zero, the H-type magnets have the opposite field polarity to that of the C-type magnet and were installed on both sides of the C-type magnet. Details of the magnet system and its first trials will be presented., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain