The Muon linac project at J-PARC

Kondo, Yasuhiro; Kitamura, Ryo; Fuwa, Yasuhiro; Morishita, Takatoshi; Moriya, Katsuhiro; Takayanagi, Tomohiro; Otani, Masashi*; Cicek, E.*; Ego, Hiroyasu*; Fukao, Yoshinori*; et al.

Proceedings of 31st International Linear Accelerator Conference (LINAC 2022) (Internet), p.636 - 641, 2022/09

https://doi.org/10.18429/JACoW-LINAC2022-WE1AA05

The muon linac project for the precise measurement of the muon anomalous magnetic and electric dipole moments, which is currently one of the hottest issues of the elementary particle physics, is in progress at J-PARC. The muons from the J-PARC muon facility are once cooled to room temperature, then accelerated up to 212 MeV with a normalized emittance of 1.5 mm mrad and a momentum spread of 0.1%. Four types of accelerating structures are adopted to obtain the efficient acceleration with a wide beta range from 0.01 to 0.94. The project is moving into the construction phase. We already demonstrated the re-acceleration scheme of the decelerated muons using a 324-MHz RFQ in 2017. The high-power test of the 324-MHz Interdigital H-mode (IH) DTL using a prototype cavity was performed in 2021. The fabrication of the first module of 14 modules of the 1296-MHz Disk and Washer (DAW) CCL will be done to confirm the production process. Moreover, the final design of the travelling wave accelerating structure for the high beta region is also proceeding. In this paper, the recent progress toward the realization of the world first muon linac will be presented.

Backward estimation of atmospheric release of Cs and I using total cumulative deposition in terrestrial areas following the Fukushima Daiichi Nuclear Power Plant accident

Iijima, Masashi*; Takahara, Shogo

Health Physics, 121(6), p.587 - 596, 2021/12

https://doi.org/10.1097/HP.0000000000001480

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident caused a significant release of radionuclides into the environment. Backward estimations of the source term are generally performed using air concentrations, but they are difficult to measure when radioactive plumes are passing through, and only spatially and temporally limited measurements are available. Therefore, a new method of backward estimation was developed based on the total cumulative deposition density that can provide sufficient measurements by combining the atmospheric transport, dispersion and deposition model calculation. Consequently, our estimations have no significant contradiction with the previous studies that were based on air concentrations and an ambient dose equivalent rate. Further considerations are needed to clarify the source term of the FDNPP accident and explore the extent of uncertainty included in backward estimations considering the difference of model and input data.

Assessment model of radiation doses from external exposure to the public after the Fukushima Daiichi Nuclear Power Plant accident

Takahara, Shogo; Iijima, Masashi*; Watanabe, Masatoshi*

Health Physics, 118(6), p.664 - 677, 2020/06

https://doi.org/10.1097/HP.0000000000001176

Assessment model of radiation doses from external exposures was developed based on the actual measurement of individual doses and ambient dose equivalent rate inside and outside of a house in Fukushima city. The survey on behavioral pattern was also carried out under the same purpose. In addition to the actual measurement and survey by ourselves, we also took into account the latest insights from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Comparisons between the assessed results and the measured ones revealed that the time dependences of doses obtained using the developed models were in good agreement with the results of actual measurements. In addition, we were able to reproduce the distribution of doses for indoor and outdoor workers. Therefore, our probabilistic approach was validated. According to our assessment and actual measurement, no participants received 1 mSv/y or higher in Fukushima city in eight years after the FDNPP accident.

Negative muonium ion production with a C12A7 electride film

Otani, Masashi*; Fukao, Yoshinori*; Futatsukawa, Kenta*; Kawamura, Naritoshi*; Matoba, Shiro*; Mibe, Tsutomu*; Miyake, Yasuhiro*; Shimomura, Koichiro*; Yamazaki, Takayuki*; Hasegawa, Kazuo; et al.

Journal of Physics; Conference Series, 1350, p.012067_1 - 012067_6, 2019/12

https://doi.org/10.1088/1742-6596/1350/1/012067

Negative muonium atom (ee, Mu) has unique features stimulating potential interesting for several scientific fields. Since its discovery in late 1980's in vacuum, it has been discussed that the production efficiency would be improved using a low-work function material. C12A7 was a well-known insulator as a constituent of alumina cement, but was recently confirmed to exhibit electric conductivity by electron doping. The C12A7 electride has relatively low-work function (2.9 eV). In this paper, the negative muonium production measurement with several materials including a C12A7 electride film will be presented. Measured production rate of the Mu were 10/s for all the Al, electride, and SUS target. Significant enhancement on electride target was not observed, thus it is presumed that the surface condition should be more carefully treated. There was no material dependence of the Mu averaged energy: it was 0.20.1keV.

Development of the longitudinal beam profile monitor with high time resolution for realization of low-emittance muon beam in the J-PARC E34 muon g-2/EDM experiment

Yotsuzuka, Mai*; Iijima, Toru*; Iinuma, Hiromi*; Inami, Kenji*; Otani, Masashi*; Kawamura, Naritoshi*; Kitamura, Ryo; Kondo, Yasuhiro; Saito, Naohito; Shimomura, Koichiro*; et al.

Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.814 - 817, 2019/07

https://www.pasj.jp/web_publish/pasj2019/proceedings/PDF/THPI/THPI031.pdf

The J-PARC E34 experiment aims to measure the muon anomalous magnetic moment and the electric dipole moment with a high precision. In this experiment, thermal muonium is produced and ionized by laser resonance to generate ultra-slow muons, which are then accelerated in a multistage muon linac. In order to satisfy the experimental requirements, suppression of the emittance growth during the acceleration is necessary. Because the main cause of the emittance growth is beam mismatching between the accelerating stages, the transverse and longitudinal beam monitoring is important. The longitudinal beam monitor has to measure the bunch length with the resolution equivalent to tens of picoseconds, which is 1% of the acceleration phase of 324 MHz. In addition, it should be sensitive to single muon because the beam intensity is limited during the commissioning phase. To realize above requirements, we are developing a longitudinal beam monitor with a micro channel plate, and the test bench to evaluate the monitor performance. So far, the time resolution of the beam monitor was obtained to be 65 ps in RMS including the jitter on the test bench. We also succeeded in measuring the longitudinal bunch size of the muon beam accelerated by RFQ using the beam monitor. In this paper, the results of the performance evaluation for this beam monitor are reported.

Development of the longitudinal beam monitor with high time resolution for a muon linac in the J-PARC E34 experiment

Yotsuzuka, Mai*; Iijima, Toru*; Inami, Kenji*; Sue, Yuki*; Iinuma, Hiromi*; Nakazawa, Yuga*; Saito, Naohito; Hasegawa, Kazuo; Kondo, Yasuhiro; Kitamura, Ryo; et al.

Proceedings of 10th International Particle Accelerator Conference (IPAC '19) (Internet), p.2571 - 2574, 2019/06

https://doi.org/10.18429/JACoW-IPAC2019-WEPGW042

The J-PARC E34 experiment aims to measure the muon anomalous magnetic moment and the electric dipole moment with a high precision. In this experiment, thermal muonium is produced and ionized by laser resonance to generate ultra-slow muons, which are then accelerated in a multistage muon linac. In order to satisfy the experimental requirements, suppression of the emittance growth during the acceleration is necessary. Because the main cause of the emittance growth is beam mismatching between the accelerating stages, the transverse and longitudinal beam monitoring is important. The longitudinal beam monitor has to measure the bunch length with the resolution equivalent to tens of picoseconds, which is 1% of the acceleration phase of 324 MHz. In addition, it should be sensitive to single muon because the beam intensity is limited during the commissioning phase. To realize above requirements, we are developing a longitudinal beam monitor with a micro channel plate, and the test bench to evaluate the monitor performance. So far, the time resolution of the beam monitor was obtained to be 65 ps in RMS including the jitter on the test bench. We also succeeded in measuring the longitudinal bunch size of the muon beam accelerated by RFQ using the beam monitor. Further improvement of the measurement system is needed to guarantee the required accuracy. In this paper, the results of the performance evaluation for this beam monitor are reported.

External dose evaluation of emergency responder in off-site at the time of Fukushima-Dai-ichi Nuclear Power Station Accident (Contract research)

Shimada, Kazumasa; Sasaki, Toshihisa*; Iijima, Masashi*; Munakata, Masahiro

JAEA-Research 2018-012, 68 Pages, 2019/02

JAEA-Research-2018-012.pdf:4.15MB

The external exposure dose of off-site emergency responders at Fukushima Dai-ichi Nuclear Power Station accident were evaluated in order to consider a radiation protection of emergency responders. The maximum value of individual daily dose of emergency responders whose activities details were recorded from 12th to 31th March 2011 was 650 Sv engaged in evacuation support in Futaba Town on 12th. Next, atmospheric concentrations and deposition of radionuclides were calculated from the source terms estimated by previous studies using atmospheric diffusion and deposit calculation codes, and air dose rates at off-site were estimated. Then, the external exposure dose was calculated for 6 emergency responders whose daily activities and personal doses were continuously recorded. Furthermore, the maximum value and the average value of the calculation external dose of emergency responders in the activity area were compared with the measurement value of the personal dosimeter of them. These results showed that the calculated value of the external exposure dose of emergency responders calculated from the maximum value of the dose rate in the active area roughly includes the measured value.

Muon profile measurement after acceleration with a radio-frequency quadrupole linac

Otani, Masashi*; Sue, Yuki*; Fukao, Yoshinori*; Futatsukawa, Kenta*; Kawamura, Naritoshi*; Mibe, Tsutomu*; Miyake, Yasuhiro*; Shimomura, Koichiro*; Yamazaki, Takayuki*; Iijima, Toru*; et al.

Journal of Physics; Conference Series, 1067(5), p.052012_1 - 052012_7, 2018/09

https://doi.org/10.1088/1742-6596/1067/5/052012

We have measured the muon beam profile after acceleration using a radio frequency quadrupole linac (RFQ). Positive muons are injected to an aluminum degrader and negative muoniums (Mu) are generated. The generated Mus are extracted by an electrostatic lens and accelerated to 89 keV by the RFQ. The accelerated Mus are transported to a beam profile monitor (BPM) through a quadrupole magnet pair and a bending magnet. The BPM consists of a micro-channel plate, a phospher screen, and a CCD camera. Measured profile in the vertical direction is consistent to the simulation. This profile measurement is one of milestones for realizing a muon linac for measurement of the muon anomalous magnetic moment at the Japan Proton Accelerator Research Complex.

First muon acceleration using a radio-frequency accelerator

Bae, S.*; Choi, H.*; Choi, S.*; Fukao, Yoshinori*; Futatsukawa, Kenta*; Hasegawa, Kazuo; Iijima, Toru*; Iinuma, Hiromi*; Ishida, Katsuhiko*; Kawamura, Naritoshi*; et al.

Physical Review Accelerators and Beams (Internet), 21(5), p.050101_1 - 050101_6, 2018/05

https://doi.org/10.1103/PhysRevAccelBeams.21.050101

Muons have been accelerated by using a radio-frequency accelerator for the first time. Negative muonium atoms (Mu), which are bound states of positive muons and two electrons, are generated from through the electron capture process in an aluminum degrader. The generated Mu's are initially electrostatically accelerated and injected into a radio-frequency quadrupole linac (RFQ). In the RFQ, the Mu's are accelerated to 89 keV. The accelerated Mu's are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.

Identification of penetration path and deposition distribution of radionuclides in houses by experiments and numerical model

Hirouchi, Jun; Takahara, Shogo; Iijima, Masashi; Watanabe, Masatoshi; Munakata, Masahiro

Radiation Physics and Chemistry, 140, p.127 - 131, 2017/11

BB2016-0282.pdf:0.39MB

https://doi.org/10.1016/j.radphyschem.2017.02.005