J ‐ PARC Symposium 2019 2019/9/23 ‐ 26 Present Status of Neutron Source at J ‐ PARC MLF Katsuhiro Haga On behalf of MLF team (Neutron Source Section)
1 ‐ MW spallation neutron source at J ‐ PARC Cryogenic hydrogen system Moderators Mercury target system Neutron beam lines (23) Proton beam 21: in operation 3 GeV, 1MW, 25 Hz 5m 2
History of target operation at J ‐ PARC Year 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 20 ~ 220 kW, 471 MWh #1 210 ~ 150 kW, 1048 MWh #2 120 ~ 310 kW, 2050 MWh #3 #4 330 ~ 513 kW, 670 MWh Failure in outer water shroud #5 #6 Max. 505 kW, 170 MWh Failure in inner water shroud #7 300 ~ 525 kW, 1812 MWh #8 Improved robust design 300 ~ 535 kW, 2120 MWh #9 6 times target replacements to date 3
Work plan in FY2019 • Neutron source operations for 8 run cycles (176 days) with an availability over 90% • Target operations with a beam power of 500 kW or higher. • Replacement to the target vessel of new design, termed as constrain ‐ free structure, which has minimum coupling between water shroud and mercury vessel during summer shutdown. ‐ > The replacement work is going on. • Completion of a new target vessel. • Completion of the transportation of a used target vessel from MLF building to another storage building (Radio ‐ Activated Materials Building). ‐ > finished on July 22 4
Beam Operations with #8 and #9 Targets • Stable and long term beam operation of more than 500kW was achieved with high average efficiency of more than 90%. • 1MW beam study at the end of user beam operations was successful. Average efficiency in the case of target #9 was over 98%! Average operational efficiency per run# 1000 100 900 90 Operational Efficiency [%] 1MW study 1MW study 800 80 Beam Power [kW] (10.5 hour) (1 hour) 700 70 Target #8 Target #9 600 60 500 50 Beam power 400 40 Summer 300 30 shutdown (target 200 20 replacement) 100 10 0 0 Oct Jan Jul Aug Oct Jan Feb Jun Jul Nov Dec Feb Mar Apr May Jun Sep Nov Dec Mar Apr May 5 2018 2019
1MW Target Study of Target #9 Study data of #9 target Study data of #8 target Mercury temperature Mercury Temperature rise of mercury, ℃ 30 25 1MW study Heat deposition of 50% 20 of beam power into mercury was assumed. 15 Temperature riser of 10 Analytical mercury showed good Proton prediction 5 agreement with the beam Temperature trend analytical prediction. 0 at 1MW study 0 200 400 600 800 1000 120 1000 Beam power, kW Beam power Mercury vessel temperature 800 100 Temperature [ º C] Beam power [kW] Mercury vessel 60 600 80 Analytical 50 Temperature rise of Temperature rise of Mercury at outlet mercury vessel, ℃ prediction 400 60 mercury vessel at 1 40 Mercury at inlet MW was a little bit less 200 1MW Study 30 40 than the analytical 20 0 prediction. 20 10 The effect of beam 11:00 13:00 15:00 17:00 19:00 21:00 0 Temperatures reached almost profile can be one of 0 200 400 600 800 1000 the reasons. stable values in two hours. Beam power, kW Facility data of steady state under 1 MW beam condition could be obtained for the first time.
Critical Issues of Target Vessel for High ‐ power Operation 1.Improvement of the target vessel design to have sufficient reliability and robustness. 2.Mitigation of pitting damage at the beam window of the target vessel. 7
8 Design improvements of target vessel 1st ～ 7th (previous) 8 th , 9 th (current) 10 th ,11 th ,12 th End plate 1050mm constraint ‐ free Hg vessel Water Bolts shroud Water Diffusion shroud bonding Water channels 3mm Water shroud Hg vessel Hg Monolithic No coupling between vessel structure of vessels. Monolithic structure water shroud Fabrication techniques Made with diffusion bonding of water shroud & were improved. and many welds which can be Hg vessel the cause of initial defects. Welds were drastically reduced. High robustness and reliability can be obtained. Constraints between vessels cause high thermal stress which limits beam power.
9 Fabrication of Constraint-free Type Target Fabricated with the combination of TIG He layer （ Gap:3mm ） welding and Electron Beam welding. Mercury vessel Back plate Suppression of welding deformation is the key issue. Water shroud Water shroud Reinforcement rib By the high accuracy fabrication and welding techniques with little deformation, the 3 mm gap of helium layer could be maintained. Dial gauges By the intensified non ‐ destructive inspection, tiny defects can be detected in the fabrication process to minimize the possibility of target failure during the beam operation. The constraint ‐ free type target is ready to be used from Back plate this November.
Pitting Damage by Pressure Wave Mercury vessel Actual pitting damages Abrupt heating Pulsed of mercury proton beam Thermal expansion Pressure wave Mercury Beam window #1 SNS target (Thickness : 3 mm) 3055 MWh (D. McClintock, Most vulnerable to Pitting damage of the wall by JNM 2012) pitting damage the cavitation Schematic images of pitting Cavitation bubble Max. pit depth : damage generation 0.25 mm Mercury Micro ‐ jet Nov. 2011 #1 J ‐ PARC Wall target 471 MWh Φ 50 mm Cavitation bubble Shrink energy concentrates Cavitation bubble inflates to one point and damage is shrinks rapidly. by the mercury negative formed. pressure.
Technologies for Pitting Damage Mitigation Micro ‐ bubble Proton injection into beam Mercury mercury A Outer wall Proton B beam Rapid flow in Bubbler narrow channel A:Center of thermal shock P Micro ‐ bubble Absorption of thermal expansion of injection mercury by bubble contraction 50 mm 2mm Inner wall Rapid mercury flow in narrow channel Laboratory experiment in JAEA B:Propagation path Stagnant Flow Attenuation of pressure waves by thermal dissipation of kinetic energy 250 μ m
Monitoring the Efficacy of Bubble Injection Displacement velocity, m/s 0.4 Vibration of target vessel #8 P: beam power Proton beam : 300 kW 0.3 Velocity amplitude, m/s 1 Q: heat density 0.2 w/o bubbles , : constant 0.8 Analytical 0.1 prediction 0 P, Q and vibration velocity 0.6 -0.1 Study data amplitude are related well 0.4 -0.2 in the past w/ bubbles by the parameter P Q . -0.3 1MW The parameter showed 0 2 4 6 8 10 12 14 0.2 study data Time, ms good agreement with the 0 Microphone analytical prediction. 0 20 40 60 80 100 Laser P Q Doppler Because of inadequate Vibrometer(LDV) Sound signal of target vessel welding, Mirror dropped 1.5 value of sound signal off the target #9 by Data of target #9 pressure wave vibration. Mirror Normalized peak Data of target #8 Efficacy of bubble injection 1 was monitored by sound signal recorded by a 0.5 microphone. The sound data showed good linearity and Target 0 0 200 400 600 800 1000 agreement between #8 and vessel Beam power [kW] #9 targets.
Cutting Specimens from Beam Window of Target Vessel Target No. 8 (Oct. 2017 — Jul. 2018) 70 mm Total energy : 1812 MWh Off ‐ center Center Av. beam power : 434 kW@25 Hz Total pulses : ca. 3.76×10 8 shots Cut two locations (center and off ‐ center) Water shroud Specimens were cut out at the center and off ‐ Hole saw center locations of the beam window of target #8. Mercury vessel Quantitative damage data on the bulk side of the inner wall protected by microbubble injection was 4 layers window (3+3+3+5 mm) obtained for the first time. 13
Cavitation Damage of Target #8 ① Outer wall inside ③ Inner wall inside ① Outer wall inside ② Inner wall outside (Bulk side) (Narrow channel) Beam Center ② Inner wall ③ Inner wall D max : ~250 µm D max : ~15 µm outside inside Off ‐ center Center φ 50 mm Dose rate: ~200 Sv/h Off ‐ center Damage on the narrow channel side was much less than that on the bulk side, which is advantageous to protect the outer wall, i.e. mercury boundary. No ‐ visible damages were observed on the off ‐ center specimens. Soundness of the inner wall is also important since damage penetration through the inner wall from the bulk side would hamper the damage mitigation effect in the narrow channel.
Experimental verification Cavitation bubble behaviors in flow and narrow gap Stagnant Flowing 1.7 m/s Gap : 10 mm Gap : 3 mm Flow Electrode diameter: 1 mm 200 kfps 200 kfps 200 kfps 200 kfps Cavitation Microjet Microjet bubble Microjet Stagnant Flowing Narrow gap Flow velocity and gap width dependency (confirmed) Damage is reduced as the flow velocity increases. Damage changes depending on gap width. Power dependency of cavitation damage in narrow channel has not clarified yet. Effect of wall boundary on cavitation growing and collapsing behavior Pressure gradient strongly affects in narrow gap, which should be verified through experiments and numerical simulation 15
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