A brand-new beam line, H-line, is planned to be constructed as the fourth beam line in MUSE. The new beam line is designed to have a large acceptance, mo-mentum tunability, as well as the ability to use a kicker magnet and a Wien ilter. This beam line will provide an intense beam for experiments that require high sta-tistics, and need to occupy the experimental areas for relatively long periods. Several experiments in the ield of fundamental physics have been proposed pertaining to the H-line [2-4].
In the primary stage of the MUSE construction, only the D line and the front-end magnets in the S line were installed, then the front-end magnets in the U line were installed in 2009. In the H-line, temporary radia-tion-shield blocks were placed. J-PARC has been in op-eration since 2008, and thus the activation around the muon production target has become more serious with every passing year. According to the evaluation using a Monte-Carlo code [5], the dose rate near the target chamber was estimated to be close to 1 Sv/h, and the summer shutdown in 2012 was the actual deadline for installation of the front-end magnets in the H-line. Thus, the installation of the front-end devices was almost
completed in 2012 and the remainder inished in 2014, as shown in Fig. 2.
In the other high-intensity beam line, the U line, we adopted only axial focusing magnets to obtain high-transmission eiciency [6]. However, in the H-line, the beam captured by an axial focusing large-aperture sole-noid magnet is transported through bending magnets, although these non-axial focusing magnets increase the beam loss. To compensate for this and achieve a high transmission eiciency, large-aperture magnets and other devices are adopted in the H-line.
The conceptual design work for the major compo-nents in the experimental hall, i.e. magnets, vacuum components, etc., has been almost completed for the irst phase of the H-line, where the beam-line was con-structed up to the irst experimental area, as shown in Fig. 1.
The design work for the radiation shield was per-formed in the same manner as in the other beam lines [5]. Along the beam-line, a few meters-thick con-crete shield will be required to enclose the streaming neutrons and other radiation sources. Because large ap-erture devices were adopted, the efect of the stream-ing neutrons will be more serious than in the other beam lines. The evaluation of the streaming neutrons is important not only for radiation safety but also to de-termine its efect on the detectors and other devices in the experimental area. Figure 3 shows a typical result of the simulation. During the proton beam operation,
the dose rate in the experimental area is expected to reach 100 mSv/h, and no one can enter this area even if no muon beams are being delivered. By inserting a beam blocker made of a 40-cm thick copper block, the dose rate is decreased by about 1/10. Using the beam blocker as well as switching of the bending magnet, HB2, can guarantee radiation safety. Herewith, a per-sonal protection interlock system can be introduced.
In 2014JFY, supplemental budget was secured to reinforce the radiation shield against a 1-MW proton beam. A part of the H-line shield was designed and fabri-cated to unite the reinforcement shield in experimental hall #1. These shield blocks were delivered in the end of March 2015. Then, during this iscal year, we assembled all of these blocks into the H-line up to the irst experi-mental area, the H1 area, which is covered with deep blue shield blocks, as shown in Fig. 4. Although the as-sembly was completed about 10 days behind schedule, the work was done without any major problems.
The application for change in the shield was accept-ed by the regulatory agency after the inspection in ear-ly November, just after restarting the beam operation.
Early completion of the H-line construction is antici-pated by the usercommunity. We aim to deliver the beam to the irst experimental area in the irst phase of the con-struction. After that, during the second phase, the H-line will be extended for g-2/EDM measurement and also for the transmission muon microscope, as shown in Fig. 5.
[1] N. Kawamura et al. 2013 Journal of Physics: Conference Series 408 012072.
[2] K. Shimomura et al. ibid.
[3] N. Saito et al. ibid.
[4] S. Mihara et al. ibid.
[5] N. Kawamura et al. 2009 NIM A 600 114.
[6] K. Nakahara et al. 2010 AIP Conf. Proc. 1222 420.
N. Kawamura1,2, MuHFS collab., DeeMe collab., and g-2/EDM collab.
1Muon Science Laboratory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK); 2Muon Science Section, Materials and Life Science Division, J-PARC center
Figure 3. A typical simulated result of the radiation dose around the H-line.
(a) blocker out (b) blocker in
100 µSv/h 10 µSv/h
blocker
Figure 4. The radiation shield of the H-line assembled in ex-perimental hall #1.
Figure 5. Beamline layout in the second phase.
H line extension
1. Radiation safety
(Adopting “low-surface contamination area” at the MLF Experimental halls)
To prepare for the upcoming high-beam-power op-eration of MLF, a new classiication of the radiation-con-trolled-area at the MLF experimental halls, “low-surface contamination area”, was adopted in November 2016.
Its purpose is to avoid surface-contamination problems caused by a sample, an environmental atmosphere, contamination and so on, and to expand the lexibility of the experimental conducted at MLF.
The low-surface contamination area is deined in the local radiation protection rule of J-PARC and is in-cluded in the 1st-class radiation-controlled area. In the area, a concentration of surface contamination equal to or lower than the standard value (0.04 Bq/cm2 for alpha-emitting radioisotopes and 0.4 Bq/cm2 for non-alpha-emitting radioisotopes) should be kept. If the contamination in the area exceeds the standard value, it should be removed immediately. An operation with any surface contamination in the area can’t be planned.
However, any accidental contamination is acceptable (and of course, it should be removed immediately). The limitation of gas and liquid used in the experiment is mit-igated. And challenging experiments can be conducted more easily. The low-surface contamination area is not applied to the BL11 experimental room and the 3rd ex-periment preparation room because the contamination is assumed during the experiment or the operation.
To introduce the low-surface contamination, a mon-itor for take-out articles and 2 hand-foot-clothes moni-tors were installed. More than 20 survey meters were prepared and can be used at each neutron instrument due to easy operation by users and stafs. Lockers were prepared in the locker room to reduce the number of ar-ticles brought to the experimental halls. Users and stafs can always take an article out of the radiation controlled-area, excluding irradiated articles and sample because of the installed monitor for articles that are being taken out. Periodic survey service (once a day) to take out large articles also started. In the summer maintenance period, the classiication of the radiation-controlled area at the experimental halls temporarily changes to 2nd class to make it easy to maintain the instruments.
(Radiological License Upgrade)
The two applications for radiological license up-grades in FY2016 were approved on September 27,
2016, and February 2, 2017.
Updated items on September 27, 2016:
(1) Change of the contamination survey areas for preparation to apply the 1st-class radiation-controlled area in the MLF experimental halls (2) Added storage and usage of several sealed
ra-dioisotopes (6 Cs-137)
(3) Preparation of the H-line installation of Muon beam line (change of shield structures)
(4) Change of the drainage equipment for radioac-tive liquid waste (position change of the con-nection to the tank lorry)
Updated item on February 2, 2017:
(1) Added gas folders in the of-gas system.
2. Chemical safety
The usual chemical safety checks of user-brought chemical materials, such as specimen and reagents, to evaluate their toxicity and the stability of their actual physical state – powder, solid, liquid or gas, were per-formed successfully by the chemical-safety team, along with approval of the actual materials for use by individ-ual beamline stafs. As a result, the experiments were performed without serious problems. Figure 1 shows a trend for the number of chemical materials for safety check. As for the form of the sample, solid was used most frequently, then powder, liquid, and gas. From the viewpoint of organic or inorganic matter, inorganic matter was used more frequently. In 2016, because of stably available beam time (approximately 153 days), the total number of chemical materials was increased, compared with 2015 (approximately 62 days), that was the highest number ever.