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KEK:Y. Makida, H. Ohata, O. Araoka, M. Iida

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1 KEK:Y. Makida, H. Ohata, O. Araoka, M. Iida
Status of a Cryogenic System for J-PARC Neutrino - Availability, Tritium creation, Volatilization of the ammonia etc. - KEK:Y. Makida, H. Ohata, O. Araoka, M. Iida T. Ogitsu, N. Kimura, T. Okamura, T. Nakamoto, K. Sasaki, M. Iio, M. Yoshida

2 Contents J-PARC and T2K Overview. Cryogenic Plant for T2K.
Status of Cryogenic Plant. History and Rate of Operation Initial Failure at Turbine and Pump Watching Impurities and Unexpected Volatilization . Creation of Tritium and Radiation Control Conclusion

3 J-PARC (Japan Proton Accelerator Research Complex)
Hadron Experimental Facility Material and Life Science Facility Transmutation Experimental Facility (in future) Apr., Neutrino Beam Neutrino Facility To Super - Kamiokande Nov, GeV Main synchrotron 1500 m circ., 25 Hz 30 GeV (in future 50GeV) 3 Gev rapid cycle synchrotron (RCS) 350 m circ. , 25 Hz Linac 330 m Jan, 2007, 181 MeV Dec, 2008 MR beam The J-PARC accelerator complex consists of 3 accelerators, a linear accelerator, a rapid cycle synchrotron (RCS, 3GeV) and a 50 GeV (now 30 ) synchrotron. Each accelerator provides a high intensity beam for the experimental facilities (materials and life science, hadron physics, neutrinos, transmutation). The secondary particles, such as neutrons and mesons as well as neutrinos, are produced by bombarding a target with the proton beam. 3

4 Purpose of T2K experiment
The T2K (Tokai to Kamioka) experiment is a neutrino-oscillation experiment to study nature of neutrinos. Artificial neutrino beam generated in the J-PARC is shoot toward the 50kton water Cherenkov detector, Super-Kamiomande, which is located about 1000m underground in Kamioka mine (Gifu) and is 295km away from Tokai. 4

5 T2K neutrino facility in J-PARC http://j-parc
Target-Horn System Target Station MR Muon Monitoring Pit Final Focusing Section 295km to Super-Kamiokande Nu Preparation Section 100m 30 GeV (50 GeV) The proton beams emitted by the Main Ring synchrotron are directed westward through the primary beam line, where many normal-conducting / super-conducting magnets and beam monitors are placed along the trajectory. At the target station the protons collide with a target composed of graphite rods and produce numerous daughter particles. Among these particles, the positively charged π-mesons –the parents of muon neutrinos– converge in the forward direction under the effect of magnetic horns.Magnetic horns are magnets designed to focus charged π-mesons by applying a few hundred thousand amperes of pulsed current synchronized with each beam shot. The π-mesons then decay into pairs, each comprising a muon and muon neutrino, during the flight in a 100-m-long tunnel (decay volume). All the neutrinos (and a small fraction of muons) escape from the facility, whereas all the other particles such as the remaining protons and undecayed π-mesons are absorbed by a beam dump composed of large graphite blocks. SC combined func mags Near Neutrino Detector Beam Dump Decay Volume P beams accelerated up to 30 GeV are directed westward through the Primary Part . A string of SC. Mag is a core part in the Primary Part. P collide with a graphite target and produce -mesons, which decay into neutrinos. 5

6 Present status of T2K 20kW, upto 240 kW 65x1019 for physics analysis
History of accumulated proton number and beam power improvement 20kW, upto 240 kW 65x1019 for physics analysis HD hall radiation accident Electron-neutrino candidate in Super Kamiokande Although two long shut-down periods due to an earthquake and a radiation accident, T2K resumed data taking. Statistic of P beam became enough to announce its experimental result. The international T2K collaboration announced a definitive observation of muon neutrino to electron neutrino transformation on July 2013.  T2K saw its first event in antineutrino beam mode on June 2014.

7 Contents J-PARC and T2K Overview. Cryogenic Plant for T2K.
Status of Cryogenic Plant. History and Rate of Operation Initial Failure at Turbine and Pump Watching Impurities and Unexpected Volatilization . Creation of Tritium and Radiation Control Conclusion

8 Primary line components - One string of Superconducting Magnets -
The neutrino beam line has a bending section with a radius of 105 m, where single string of 28 superconducting magnets has been installed. The magnet design is very unique. It has a combined function of 2.6 T dipole field with 19.6 T/m quadrupole field gradient by a left-right asymmetric distribution of conductors. 8

9 Cryogenic Plant overview
Cryogenic devices, 4 He tanks, 1 LN2 CE, a compressor, a cold box, a sub-cooler and a current lead box, are set on surface. The magnets are at -12 m under ground and coolant SHE is transported between them. Pacific Ocean (5m Tsunami arrived) LN2 CE He Tank S.C. Magnet MCP, CB, Sub-cooler, CLB 9

10 Overall Layout (Ground Plan)
Magnet String & Transfer Line Inventor 3900 ℓ, Cold mass 225 ton(Fe) 90 m transfer line with SC bus Heat Leak 220 W + Beam Loss max 150 W Neutrino Beam Line Superconducting Magnet Arc in main tunnel at -12m level Radius 105m, Length 150m Main Synchrotron Recovery Vessel (for Quench) As Storage Vessel for Inventory Volume 100m3×3 Cold Box、Subcooler SHE Max 300 g/s 4.5 K LHe pot : 800 ℓ C/L flow : 1 g/s Superconducting Magnet 10 m Main Compressor (MCP) : 570 kW, 1.4 MPa, 150g/s LN2: ℓ Only pre-cooling & cold purification pre-cool 300 – 100 K Buffer Vessel (for MCP) Volume 100m3×1

11 Conceptual Flow Diagram @ excitation
LN2 is consumed for pre-cooling and gas purification. The two-stage oil injected screw compressors with five-stage oil separators pressurize helium gas up to 1.4 MPa with a flow rate of 160 g/s. The refrigerator is basically Claude type with three turbines. A part of pressurized helium with a flow rate of 150 g/s is divided into a two-stage expansion turbine unit, where the helium gas with a flow rate of 70 g/s works adiabatically with a pressure release from 1.4 MPa to 0.13 MPa. Before reaching the turbine unit, the divided helium gas goes the long way around the radiation shield line in the magnets. At third expansion turbine, the rest part of pressurized helium gas with a flow rate about 80 g/s adiabatically expands to SHE region with a pressure of 0.4 MPa. The SHE is transferred into a sub-cooler, where the SHE is liquefied with a expansion to 0.13 MPa through the JT valve. A centrifugal pump installed into the sub-cooler circulates SHE flow with a nominal rate of 300 g/s through the magnet as coolant. Its maximum pressure head is 0.1 MPa. The pumped SHE stream is after-cooled down to 4.5 K in heat exchanger with liquid helium in the reservoir tank and the magnets can be kept under 4.8 K. The return SHE stream from the magnets is pre-cooled for stable pump inlet condition. The pressure in the connection line among the SHE turbine outlet, SHE pump outlet and the JT valve inlet was kept at 0.4 MPa by the JT valve feed-back operation. This control scheme spontaneously complements the current leads cooling gas which falls out from the pumped circulation. And base pressure in pumped SHE circulation is controlled by the JT valve, too. A cascade refrigerating system , composed a Claude cycle refrigerator with a centrifugal pump , supplys 4.5 K, 0.4 MPa, 300 g/s She. Turbine flow goes through radiation shield cooling line in the magnet . 1.4MPa, 150 g/s He gas is supplied by the compressor. 70 g/s flow expands and works at turbines, and the rest expand at JT valve in the sub-cooler.

12 Power saving mode. Refrigerator capacity 1500 W need the 900 W offset by using LHe level control heater. Saving refrigerator capacity by reducing unloader and supply pressure results in lower power consumption at the compressor. Saving 1.5 MYen/month

13 Contents J-PARC and T2K Overview. Cryogenic Plant for T2K.
Status of Cryogenic Plant. History and Rate of Operation Initial Failure at Turbine and Pump Watching Impurities and Unexpected Volatilization . Creation of Tritium and Radiation Control Conclusion

14 History and Rate of Operation
6/5 7/3 15/3 17/5 11/12 8/12 4/12 8/12 Earthquake 11/3 FY2011 FY2012 After MSS Miss Trigger trouble is solved, Nu cryogenic system has caused no interruptions of T2K experiment. Rate of operation (availability) is beyond 0.99. Although cryogenic system did not stop, some devices did abnormal movement. It was only lucky.

15 History and Rate of Operation
FY2013 FY2014 J-PARC operation was not admitted until improved radiation management was established. HD Radioactive Material Leak Accident on 23/May About HD radiation material leak accident please refer To restart J-PARC operation, Radiation control management became severe. Nu cryogenic facility and its maintenance method were examined in radiation evaluation committee. T2K experiment resumed on April 2014. On May 23, 2013, the electromagnets for slow extraction of proton beams from the 50-GeV MR malfunctioned, and an intense peaked beam beyond a designed value was delivered to the gold target in HD hall. Part of the gold target was damaged and the radioactive material dispersed form the target. It leaked into the environment outside of the radiation control area.

16 Contents J-PARC and T2K Overview. Cryogenic Plant for T2K.
Status of Cryogenic Plant. History and Rate of Operation Initial Failure at Turbine and Pump Watching Impurities and Unexpected Volatilization . Creation of Tritium and Radiation Control Conclusion

17 Notches in Turbine We found some notches at 2nd turbine blades by the visual inspection after 2009 autumn operation. We observed abnormal start movement of 2nd turbine. LINDE TED turbine needs bearing gas supply during only start-up. And bearing gas stops, after the rotation reach to normal speed. But 2nd turbine could not start with bearing gas, and it could start when bearing gas stopped. Once start-up, 2nd turbine rotated normal condition during the beam operation, and cooling power did not degrade. Measured mechanical strength of the turbine material is rather low. Linde also reported that the bearing gas pressure at 14 bar in Nu cold box is higher than its design pressure of >10 bar in standard liquefiers. New turbine made with inspected material was set. Pressure reducing valve was installed into the bearing gas supply line. PRV addition into bearing line Remade 2nd Turbine and 1st Turbine HP CP MAG LP

18 Rubbing of SHE pump We found burrs on the pump impeller blades by the visual inspection after 2010 autumn -> 2011 winter operation. We heard abnormal large and shrill noise during the operation. But flow rate of 300 g/s at nominal rotation improved 310 g/s. So, the operation continued. Lower position of the pump impeller caused scratch of the impeller blades with the pump housing. New tool and gage to set the blade at the design position are prepared. Cold bearing is Exchanged annually by Taiyo Nippon Sanso, Main contract of Nu cryogenics . And removed bearing is inspected by Barber Nichols to analyze its operation life. Tuning Bolt of Rod Length Cold Bearing

19 Contents J-PARC and T2K Overview. Cryogenic Plant for T2K.
Status of Cryogenic Plant. History and Rate of Operation Initial Failure at Turbine and Pump Watching Impurities and Unexpected Volatilization . Creation of Tritium and Radiation Control Conclusion

20 Watching and measuring impurities
Inner Detectors (Measured gas go to the LP line) Dew-point meter : MICHLL Ins. Water detection < - 60 ۫C ( before cool down ), -90 ۫C (usually) Discharge light spectrometer : KEK original N2, < 1 ppm Gas chromatograph : SHIMAZU → LINDE multi component detector N2, O2, CO, CO2 < 1 ppm Gas sampling ( at warm-up 25 K ) Quadruples mass spectrometer : ULVAC & JAEA H2 < 1 ppm H2 from polymers in the magnets by beam irradiation. Liquid scintillator : Radiation Control Equipment HT < 7 Bq/cc, HTO < 5 mBq/cc (Radiation control criteria) Tritium transmuted from 3He H

21 Oil separation check Screw Compressor 1st Separator Demister
2nd & 3rd Separator Filter Element Coalescence 4th Separator Active Charcoal Adsorption 5th Separator Molecular Sieve Adsorption Water Cooler Oil must be ≦0.001vol.ppm Oil check sampling annually. Daily check through sight glass. Oil return Solenoid valve with Counter and Action signal Level Switch Sight Glass Action Signal Controller Counting Interval check Filter element selection is important. Activity of DOMINICK HUNTER is short. This element caused RIKEN Oil diffusion accident. TAIHEIYOU filter is activate longer. So, filters in 2nd separator were exchanged. Controller checks oil return valve action interval. If the interval become longer, that means filter elements are saturated.

22 Unexpected Volatilization : Ammonia from Magnet
Ammonia Origin Ammonia Properties Molecular Formula NH3 Molecular Mass g/mol Density 0.86 kg/m3 (1.013 bar at boiling point) 681.9 kg/m3 at −33.3 ℃ (liquid) Melting point −77.73 °C (195.42 K) Boiling point −33.34 °C (239.81 K) Glass-reinforced Phenolic Thermosets Rin=102 mm, t=20 mm, L= 100 mm *PM9640 by Sumitomo Bakelite, Arisawa Atmosphere Atmosphere We found that irritant odor in vent helium gas from the magnet at maintenance. Gas analyzing showed that the odor material is ammonia. Search found the plastic spacer is its origin. Why the Nu refrigerator was not blocked up? Molecular Sieve (Crystalline Zeolite) in 5th oil separator can adsorb large quantity of ammonia. 5th separator has large enough quantity of MS, which can adsorb 79 kg ammonia. And MS can be re-activate by heating at 150 ℃. Pump Ammonia Detector He Recovery MS (13X) Adsorb Thermo-meter Dew point mater Heater He ppm NH3 to watch adsorption He for carburation N2 gas for reactivation

23 Contents J-PARC and T2K Overview. Cryogenic Plant for T2K.
Status of Cryogenic Plant. History and Rate of Operation Initial Failure at Turbine and Pump Watching Impurities and Unexpected Volatilization . Creation of Tritium and Radiation Control Conclusion

24 Measurement Record of Tritium (HT & HTO)
HT (BP 25K) and HTO inside Beam Time -> Sampling at > 25 Return from MAG HT (Bq/L) HTO (Bq/L) Beam P (kW) May/2010 0.082 ~ 80 July/2010 Sep./2012 48.2 2.4 ~ 200 Dec./2012 28 ~ 220 Mar./2013 19 ~ 230 May/2013 40.5 Aug./2013 37.5 July/2014 ~ 250 Sample gas is analyzed by Liquid scintillater with precision of 5Bq/L. Analysis is done at RT, AP. Larger Beam Power may produce more tritium. HT HTO Boiling Point (K) 25 373 Melting Point (K) 20.4 277.5 A. Limit * (Bq/L) 7000 5 << A. Limit Regulation Law Concerning Prevention from Radiation Hazards due to Radio‐Isotopes, etc. (≈ ICRP90) * Allowable limit in discharging gaseous radioactive waste Radiation Management in J-PARC require Gaseous waste must be vent through authorized vent stack with radiation monitor. Even small gas vent from maintained equipment must follow the guideline. The work place, where gaseous waste is vent, is set as a radiation management area temporally.

25 Same Operation and Modified Maintenance due to Tritium
But Radiation Management in J-PARC accept Nu cryogenic system, which is designed and is inspected by High Pressure Gas Regulation, holds enough air-tightness to prevent tritium leakage. Consequently, Nu cryogenic area on surface need not become radiation management area permanently. It is only set, when the helium gas part is exposed. Otherwise Vent Stack Air Temporal Radiation Management Area C/L Box Tank Subcooler Evaporator Tank CB Evaporator Air Tank Yard Cryo. Room Tank Oil Separator MCP

26 Guide Line of Temporal Radiation Management
Cryogenics Room = Temporal Backup Seal Temporal Vent Line Existing Vent Stack Temporal 1st Seal Backup Seal Vac. Pump Radiation Monitor CL BOX Sub- Cooler CB MCP Tank Surface Under Ground Radiation Management Magnet He Vent Line Beam Pipe Vacuum Vessel 1 mm Metal Mesh 0.1 mm Metal Mesh

27 Actual Method : Filter Exchange at 2nd,3rd Oil Separator
Setting Management Area Radiation Safety Check By gas sampling and smearing. Analysis takes 1day 400 m3/h blower exhausts air from the room to the vent line. Oil Filter Exchange 1st seal Oil Separator Unit is covered by an air-tight plastic sheet room. Backup seal Cryogenic Room becomes radiation management area. Radiation Safety Check By smearing. Analysis takes 1day Cancel Management Area

28 Actual Method : Relief Valve Exchange at outdoor Tanks
RV vent RV Setting Management Area Radiation Safety Check By smearing. Analysis takes 0.5day Stop Valve He must be vent before RV removal Wrench is kept inside plastic bag as 1st seal. Back up seal is rope. Rope set management area . Rope is back-up seal ??? Radiation Safety Check By smearing. Analysis takes .5day Removed RV Smear Inspection Send RV to maker for calibration Cancel Management Area

29 CONCLUSION After initial troubles were solved, Nu cryogenic system has been stable since FY2012 autumn. It was not expected that volatilization of the ammonia from the magnet, but fortunately, molecular sieve in the 5th oil separator can adsorb a gross quantity. Tritium of 40 Bq/L has been detected in refrigerant. In spite of lower value than its allowable limit of 7000 Bq/L, Nu cryogenic operation and maintenance method were examined in radiation evaluation committee. Helium vent must be through authorized line and stack after radiation measurement. Fortunately vent line from RV and the vacuum pumps had been constructed. Gas monitor and metal filters were installed into the vent line additionally. Some maintenance works, RV and oil filter etc. exchange, need setting of temporal radiation management area and complicated procedures.

30 Backup Slied

31 Conceptual Flow Diagram @ excitation
A pair of cooling gas flow for the current leads is divided from the SHE supply line simply. SC cables directly enter the SHE line SHE pump outlet is connected with the inlet of JTV. The pressure in this connection line is kept at 0.4 MPa by the JTV. This control scheme spontaneously complements the current leads cooling gas which falls out from the pumped circulation.

32 Specifications of each component in the cryogenic plant(1).
Item Specification Compressor Type Oil injected two stage screws compression Manufacture / Model name MAYEKAWA/HE3225MSC-KLBM Discharge pressure 1.4 MPa Discharge stream 160 g/s Oil separation 5 stages, Demister , 2 stage Coalescer, Activated charcoal, Molecular sieve Refrigerator Claude cycle Manufacture/Model name LINDE/ TCF200S Refrigeration power without LN2 @ Supplied gas pressure of 1.4 MPa Return gas pressure of 0.12 Mpa 1500 W at 4.5 K for pumped SHE stream W at 80 K for radiation shields + 1.1 g/s from 4.5 K for current leads Turbine type Dynamic bearing expansion turbine Turbine and JT stream at steady state 70 g/s, 80 g/s Shield stream 70 g/s (equal with turbine stream ) Sub-cooler Manufacture JECC TORISHA Phase separator ( LHe reservoir) capacity 1600 ℓ Stored LHe volume at steady state 800 ℓ SHE pump manufacture Barber-Nichols SHE pump bearing type Ball bearing Nominal pumped flow rate 300 g/s Available pressure head at nominal flow 100 kPa

33 Specifications of each component in the cryogenic plant(2).
Item Specification LN2 cold evaporator Volumetric capacity Operation pressure 20000 ℓ (stored volume ℓ) 0.5 MPa Manufacture CRYO-ONE Dryer Moisture absorber Synthetic zeolite Amount of throughput 200 Nm3/h ×24 h Absorption ability Outlet impurity 1.2 ppm, dew point -75 ۫C Cryogenic purifier Impurity absorber Activated carbon Outlet impurity 1.2 ppm Pressure vessel Volume 100 m3 ×4, one for buffer, others for storage 1.5 MPa COP, FOM 0.0026, 16 % External set of a dryer and a cryogenic purifier is installed, because large amount of moisture and air from magnet electric insulator were predicted. The capacity of this purification unit is large enough for the 1000 ppm inventory. Impurities in helium gas was actually removed in two days before cooling down, so the rate of operation of the dryer and the purifier is very low.

34 Effort of Power Saving Mode
before after High (discharge) pressure control MPaG 1.3 1.1 Refrigerator cycle flow rate g/s 155 125 LHe level control heater W 900 400 Refrigerator capacity 1500 1000 Lower unloader posision % 100 95 Compressor power consumption kW 570 430 Power cost per month (\15/kwh) K YEN 6,156 4,644 CO2 emission per month (0.555kg/kWh)* ton(CO2) 228 172 SHE flow (just for information) 300 Saving 1.5 MYen/month, 55 ton CO2/month

35 Conceptual Flow Diagram @ pre-cooling
CB&SC pre-cooling Gas transport The cooling He gas circulation through the magnets is driven by the compressor. The pump circulation is bypassed for its pre-cooling. Magnets is cooled down for 8 days. The shield circulation is driven by the compressor, too. During cool-down and warm-up, the head pressure of the pump becomes so low, due to the lower viscosity of the warmer helium gas, that the refrigerant helium is directly circulated through the magnets. And large amount of helium gas is supplied/restored from/to the pressure vessels under than 10 K because of drastic density change. Three pressure vessels with a capacity of 100 m3 are built to confine the helium gas of 1.3 MP for an idle period as the inventory for 3900 ℓ liquid helium. Another same size vessels is built to work as a pressure absorber for the constant gas compression Magnet Pre-cooling Shield Pre-cooling

36 Conceptual Flow Diagram @ Quench
Liquefaction Pump Protection Gas Recovery C/L Cooling At quench, the pump circulation quickly switch to the bypass line and is isolated from the magnets. The quenched magnet pressure is released to the storage tanks through the exhaustion lines directly. Quench behavior is one of the important test items, because the cryogenic controller must operate valves with swiftness and precision to protect the plant elements from pressure shock after quench. To verify the behaviors protecting the cryogenic plant and the magnets, quench demonstration tests have been carried out by igniting quench protection heaters at the nominal current of 4400 A. When some magnets were quenched, the current was shut down within 10 seconds. While a pressure of 0.5 MPa was developed in the magnets for several minutes, a pressure at the pump increased up to 0.45 MPa was monitored for several seconds. The pressure at the magnets was released through the exhaustion lines to the storage tanks without discharging through the safety valves. So refilling from external container wasn’t necessary. When re-cooling started, the magnet temperature was distributed from 5 K at non-quenched magnets to about 6 K at quenched magnets. Since the magnet temperature was low enough for the pump to generate nominal flow rate, re-cooling operation was simply switched the pumped flow back to the magnet lines. The recovery period of the magnet temperature and LHe level was about 1 hour and 2 hours respectively CP 0.45MPa Quench Emergent Exhaustion Shield Cooling

37 Tritium Estimation at 1W/m beam Loss ( in case of All beam loss in the SC )
After 4000 h 1w/m loss Beam Tube Periphery 180 Bq/cc * 5 litter Cooling Hole 25 Bq/cc * 10 litter Press Shoulder etc 10 Bq/cc * 15 litter End Space 50 Bq/cc * 40litter 3He to tritium 7 Bq/cc* ( ) litter Total 54 Bq/cc

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