Future upgrade of the neutrino beam-line for multi-MW beam 5 th Hyper-Kamiokande open Vancouver July Yuichi Oyama (KEK) (for T2K neutrino beam-line group)

Introduction When the J-PARC project started, the primary goal of the beam power in the neutrino beam line was 750kW. Upgrade to 4MW was second step in the future. ~750kW beam from the accelerators will be within our reach by ~2017 if the budget is funded timely. It is possible to accept this beam power, with significant improvement for steady operation. For operation beyond 750kW, critical improvements are needed. In this talk, future upgrade required for ~2MW beam power is reported.

Beam History At the beginning, 750kW x 5year operation was officially approved, where 1 year is defined as 10 7 sec = 115.7days. For 30GeV proton beam, it corresponds to 7.81 x protons on target (pot). Stable operation at ~230kW has been achieved. Until June 2014, 7.39x10 20 pot is accumulated. It is ~9% of our goal. 3.2s  3.04s  145kW 2.56s  190kW 2.48s  235kW 2.48s 235kW [6 bunches] Rep=3.52s  50kW Run 1 x10 19 Run 2 Run 3Run 4 Run 5 Recovery from the earthquake Hadron Hall accident Neutrino beam Anti-neutrino beam 1.43x10 20 pot until Mar.11,’ x10 20 pot until Jun.9,’12 ~7.3x10 20 pot until Jun.24,’ x10 20 pot until May.8,’13

Present expected beam parameters for ~750kW will be ~1.3sec Main Ring cycle and ~2.0x10 14 ppp (proton per pulse). Future Improvements for higher beam power T.Koseki in J-PARC symposium 2014 ( jp/j-parc2014/) and T.Ishida in this HK open meeting (if the budget is funded as we hoped)

5 Beam Dump Primary Beam-line ExtractionPoint Muon Monitors 110m 280m 295km To Kamioka Main Ring Target & Horns in Target Station P  Decay Volume Near Neutrino Detectors MLF RCS Neutrino experimental facility at J-PARC

Preparation section 11 normal conducting magnets Final focusing (FF) section 10 normal conducting magnets Arc section 28 superconducting combined func. magnets Primary Beam-line

All magnets in the primary beam-line, thickness of concrete tunnel and surrounding soil are designed by assuming 1W/m energy loss in Arc section, 750W loss in the preparation section, and 250W loss in the final focusing section. When the beam power become multi-MW, emittance of the beam may become drastically larger. Much larger energy loss would be generated. A tuning of the beam orbit as well as the beam size is important to avoid radio-activation. Beam monitors are critical for the tuning. If emittance of the beam becomes much larger, some of the magnets must be replaced with new design of large apertures. Production of new magnets are not difficult from a viewpoint of technology. Production period of a few years, and shut-down for installation of a few month to one year, depending on the new beam parameters, are required.

Decay Volume Target Station Beam Dump OA2 o OA2.5 o Beam Transport From RCS to MLF 6m-thick concrete wall OA3 o Helium Vessel Target and 1st Horn 3rd Horn Beam Window Secondary beam-line 2nd Horn For 3 Horns, See Sekiguchi-san’s talk

26mm  x 910mm Ti-6Al-4V (0.3mm-t) Graphite T~200K ~7MPa (Tensile strength 37MPa) 736 o C 30GeV-750kW (~20kW heat load) CFX analyses He gas cooling: 9Nm 3 /m (v=200m/s) Conductivity 140  20W/mK(rad. damage) Target Carbon Graphite of 26mm  x 910mm are embedded in Ti-6Al-4V of 0.3mm thickness. The design was based on calculation of thermal stress and flow of Helium gas cooling. The present design can accept 3.3x10 14 (ppp) x 5 years with a safety factor of 2. This corresponds to 1.2MW if 1.3sec of Main Ring cycle is assumed. (750kW beam with 3.3x10 14 ppp and 2.1s MR cycle was the initial plan.) Larger beam diameter will be needed for future higher power.

Separate Helium vessel from vacuum in primary line. Double wall of 0.3mm thick Ti-6Al-4V, cooled by He gas (0.8g/s) Stress by partial heat load at the beam spot may break the window ! The present design can accept 3.3x10 14 (ppp) with a safety factor of 2. This corresponds to 1.2MW if 1.3sec of Main Ring cycle is assumed. Change the diameter of the beam and/or upgrade the cooling system is needed for future beam. Beam Window

Radiation damage may change the characteristics of the thermal stress of the material. The radiation damage of the Ti -6Al-4V was reported up to 0.24DPA (displace per atom), which corresponds to ~1.5x10 20 pot. We are already in unknown region. Replacement cycle of the window should be considered. However, 2MW x 1 year beam corresponds to 4x10 21 pot. Replacement more than once per year is impossible. Test of radiation damage is needed. We are planning an international collaboration for this test. Ask Ishida-san. According to the results of the test, use of another target/window material might be needed. Radiation damage for Ti-6Al-4V 0.24DPA 0 DPA 1000MPa Strain (%) 70MPa(220kW) Limit:400MPa ? with fatigue & high temp. 200MPa Ti-6Al-4V Stress (Mpa)

Helium Vessel, Decay Volume and Beam Dump Large fractions of the beam energy are absorbed in HV/DV/BD. Thermal stress may damage the structure of HV/DV. Their temperature must be kept less than 60 degree. The temperature of the beam dump core must be less than 400 degree. They are cooled by cooling water system. At present, the system is adjusted for the 750kW operation. Cooling power can be upgraded by increasing flow rate of the cooling water. Additional pumps and related components as well as the space for them in the machine room are needed. Radioactivity of the cooling water will become higher. This is another serious problem. 750 kWFraction Helium Vessel ~170 kW~23% Decay Volume ~130 kW~17% Beam Dump ~150 kW~20% (Neutrino) ~12 kW~1.6%

Max. temp: 54 ºC Max. stress: 47 MPa Thermal analysis shows that there is safety factor 3 for ~750kW beam. Additional iron shields between the magnetic horns and side wall of the Helium Vessel are required for multi-MW beam. Helium Vessel

Rectangular pipe of 3m(W) x 5m(H)x 100m(L), connected with TS Helium vessel. Total volume with TS Helium vessel is 1500m 3. Cooling water system for the iron walls. Ready for 750kW without any upgrade. Upgrade of cooling water flow rate is needed for multi-MW. Max. temp ： 55  C 14 Decay Volume

Graphite core of 2.8m(W) x 5.3m(H) x 3.2m(L), 14blocks. Max. temperature < 400 degree. Aluminum blocks are cooled by water Ready for 750kW without any upgrade Upgrade of cooling water flow rate is needed for multi-MW. Max. temp:180 ℃ 15 Beam Dump

Radiation Issue Many restrictions about radiation in the neutrino beam-line. Radiation dose outside of the radiation control area: < 0.5  Sv/h Radioactivity in disposed water: for 3 H < 60Bq/cc < 5000GBq/year (from J-PARC) for 7 Be < 30Bq/cc < 1200MBq/year (from neutrino facility) Exhausted Air from stacks of buildings (Target Station): for 3 H < 5mBq/cc for others < 0.5mBq/cc (mainly 41 Ar)

DV/BD cooling water system HV/DV water system （ DV downstream and BD ） （ Helium Vessel and DV upstream ） Horn cooling water system Three independent cooling water systems Cooling Water system and Radioactivity Neutrons and other beam products break Oxygen In H 2 O and many kinds of isotopes are produced as spallation products. They are 3 H, 7 Be, 11 C, 13 N, 15 O, 14 O, 16 N, 14 C. Lifetime  1/2 < 20minutes : 11 C, 13 N, 15 O, 14 O, 16 N  1/2 = 5730 years : 14 C Their contribution can be ignored. The source of radioactivity is 3 H (  1/2 = 12.3 years) and 7 Be (  1/2 = 53.3 days).

B2 tank DP tank All drain water ( 2 tanks are used together) 30m 3 Drain tank 21m 3 Buffer tank Ion exchangers H 2 SO 4 NaOH pH control system Only beam- off Also beam -on TS NU2 (effectively 84m 3 ) Horn CW HV/DV CW Ion exchangers drainage Off limit during beam dilution water Drainage of Radioactive Water One drainage cycle per 3 business days. 42Bq/cc x 84m3 = 3.5GBq of 3 H can be disposed per one drainage cycle. Schematic flow of the drainage system for radioactive water One “drainage cycle” is 1)Buffer Tank -> DP tank 2)dilution and measurement 3)drainage from DP tank

Regulation/ Requirement FY2012FY201XFY202X? Beam power 3.10 x pot (=149kW x 10 7 s eqv.) 15.6 x pot (=750kW x 10 7 s eqv.) 41.6 x pot (=2MW x 10 7 s eqv.) 3H3H< 5000GBq/yr from J-PARC < 60Bq/cc (< 42Bq/cc for safety) 77.6GBq (NU2) 30.0GBq(Horn) 47.6GBq(HV/DV) 15.9GBq (NU3) 93.5GBq (NU2+NU3) 390GBq (NU2) 151GBq(Horn) 239GBq(HV/DV) 95GBq (NU3) 485GBq (NU2+NU3) 1040GBq (NU2) 403GBq(Horn) 637GBq(HV/DV) 253GBq (NU3) 1293GBq (NU2+NU3) Drain- age 1 drainage per 3 business day 27 times x 84m 3 (NU2) 25 times x 17m 3 (NU3) 87 times x 84m 3 (NU2) and 12 times x 16GBq (Tank Truck) ~200 times x ~100m 3 (NU5) and ** times x 16GBq (Tank Truck) Prospect for Radioactive Water Drainage We can ask a part of drainage to another section in JAEA by using a tank truck. Ready for 750kW beam. 3 parallel drainage system with larger disposal tanks are needed for 2MW beam.

20 Beam Dump Primary Beam-line ExtractionPoint Muon Monitors 110m 280m 295km To Kamioka Main Ring Target & Horns in Target Station P  Decay Volume Near Neutrino Detectors MLF RCS We are planning to build new facility buildings for new cooling water system, new disposal tanks, and other facilities. We need ~2 years for construction, and full 1-year shutdown? Present facility buildings are too small to install upgraded facilities. New Buildings in the neutrino beam-line

Radioactivity in Exhausted Air ~1000mBq/cc in machine room ~5000mBq/cc in service pit Leakage of radioactive air through gaps ~3mBq/cc in ground floor Negative pressure ~0.3mBq/cc at stack Ventilation system 13000m 3 /h (must be < 0.5mBq/cc. This radioactivity is monitored in beam (after many efforts)

Air-tight work in Target Station Caulking between concrete shields Air-tight sheet (made of the same material for balloon) Protection sheet (over air-tight sheet) Protection sheet under air-tight sheet Air-tight lamination (in future) Caulking + Air-tight sheet More careful air-tight in future !

Ventilation flow rate 13000m 3 /h cannot be changed Bypass of Ventilation in Target Station By making bypass route of the air, ventilation rate of TS ground floor reduced to be 1/10. Radioactivity in the exhausted air become 1/3 of non-bypass mode. About 60% of 41 Ar (  1/2 ~110mins) decay in ground floor. Radioactivity in the ground floor increased by factor ~3. Further change of the bypass rate will be needed for higher beam power…

Many works are definitely needed to accept ~2MW beam……. Summary Replacement of some of the magnets in the primary beam-line? New design of the target? New design of the Beam Window, and study of the radiation damage? Additional iron plate in Helium Vessel. Upgrade of the cooling water system -> New buildings Upgrade of radioactive water drainage -> New building Upgrade of Air-tight in the Target station building Bypass ventilation system Other works not covered in my talk…… List of works to accept ~2MW beam

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