NuMI-NOvA Target & Window K. Ammigan 10 th International Workshop on Neutrino Beams and Instrumentation 20 September 2017
Outline § Introduction § Target design history § IHEP § FNAL & STFC/RAL § Target analysis, testing and QA § Target fins, windows, baffle § Operational experience § Protons on target & DPA § Window failure § Target autopsy and R&D 2 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
ME target for NOvA experiment Proton-graphite interactions to produce pions, which are focused before decaying to • produce neutrinos Long/narrow target to allow pions to escape out sides and reduce pion re-interactions • 50 graphite fins: 24 mm long and 7.4 mm wide • Beam sigma: 1.3 mm • Helium atmosphere enclosed by US/DS beryllium windows • • Heat removal: Al pressing plates and water cooled outer can Design parameters (**center of peak fin) Beam energy (per proton) 120 GeV POT/10 µs spill 4.9e13 Repetition time 1.33 sec Proton beam power 700 kW Peak max. Edep. per spill ** 310 J/g Peak max. power deposition ** 235 W/g J. Hylen (FNAL) Instantaneous power during spill ** 30 MW/g 3 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
IHEP target design I IHEP 2006 report Initial design and study of the Medium Energy Target (MET) was performed by • IHEP (Protvino, Russia) in 2006 Designed for 440 kW beam: 120 GeV beam, 4 x 10 13 ppp, repetition time: 1.9 s • 12 x 100 mm long, 3.2 mm wide graphite plates • 4 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
IHEP target design II IHEP 2008 report Design revised by IHEP in 2008 for higher proton beam power • Designed for 880 kW & 1440 kW beam: 120 GeV beam, 5.5 x 10 13 , 9.0 x 10 13 ppp • every 1.2 s Main changes • Target core with 48 graphite fins (24.5 mm L and 6.4 mm W): decrease quasi-static/dynamic stresses and improve fin manufacturability Charge read-out (Budal) target position monitoring fins added upstream of the target • Water cooling system developed for target casing to reduce heating from secondary particles • 5 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
FNAL/RAL target design tweaks Design finalized by FNAL (M. McGee) and STFC/RAL (C. Densham) target groups • Mainly to improve fabrication/operation of components • He filled target canister DS Be window 48 POCO ZXF-5Q fins Canister cooling water inlet/outlet Budal monitors US Be window Water cooled clamping plates Cooling water inlet/outlet 6 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
NOvA targets MET-01 manufactured by STFC/RAL (used until failure) MET-02 manufactured by Fermilab (currently installed) MET-03 manufactured by STFC/RAL, modifications, 1) internal welds of outer vessel removed, 2) outer vessel anodized MET-04 manufactured by Fermilab 7 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017 M. Fitton, (STFC/RAL)
Fins heat transfer performance M. Fitton (STFC/RAL) Experimental tests using thermal camera imaging confirmed consistent thermal contact across all • graphite fins • Cooling issue with horizontal Budal monitor fin was identified Horizontal Budal bracket 310 ° C 152 ° C redesigned by thickening material and shortening conduction path. Simulation shows operating temperature reduced by ~50% 8 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target temperature simulations T. Davenne (STFC/RAL) Estimate of target fin operating temperatures and heat to outer vessel ANSYS CFX simulations of natural convection and thermal radiation inside target vessel Beam Energy: 120 GeV Gaussian beam sigma: 1.3 mm in x & y Heat balance Position: 4mm from top of fins. Protons per bunch: 4.9e13 • Total heat load = 7482 W Rep rate: 1.33s Heat conduction from fins to • cooling rail = 6867 W • Heat radiation from fins to outer vessel = 476 W Convection and conduction • through helium from fins to outer vessel = 139 W 9 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target fin stress calculations T. Davenne (STFC/RAL) POCO ZXF-5Q steady state temperature and stress Peak stress = 4.7 MPa T peak = 672 ° C Largest temperature gradient near cooling block Peak dynamic stress during beam pulse: ~26 MPa ZXF-5Q tensile strength: 79 MPa 10 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Welding development STFC/RAL Water cooled vessel of NOvA target Design modified after MET-01 so there are no internal welds MET-03, only 2 external welds 11 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Welding development STFC/RAL High quality welds (NAS 1514 Class II or better) in Al 6061 proved very difficult to produce consistently for plug weld Weld looks very good by visual inspection Radiography reveals significant porosity Parameters explored to optimize weld § Cleaning (including etching) § Filler wire selection Pre-heating § AC current/balance § Gas (Helium/Argon blend) § 12 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Welding development STFC/RAL Remove as many of the Aluminum welds as possible from the water cooling circuit Original design – 9 Aluminum welds AL-SS roll bonded plate replaced with friction welded blanks Modified design – 3 Aluminum welds Blind gun drilled holes, Pipe stubs with single cross drill machined into rail 13 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Welding radiography QA STFC/RAL Achieved NAS-1514, Class 1 certification for cooling rail 14 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Hydrostatic pressure testing STFC/RAL Testing for leaks and weakness at much • higher pressures than operational pressure Cooling rail tested to 200 psig • Outer vessel tested to 90 psig • 15 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Helium leak check STFC/RAL All components and complete assembly helium leak checked Specification : total leak rate <1 x 10 -9 atm.cm 3 /s 16 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target windows M. McGee (FNAL) PF-60 Beryllium US and DS windows • • US window: Ø 44.45 mm x 0.254 mm thick • DS window: Ø 135 mm x 1.25 mm thick Designed to withstand 15 psig without beam and 3 psig with beam (during operation) • US window reaches thermal equilibrium after 30 s (23 pulses) with T max = 66 ° C (b) (a) US window Figure (a) US 0.25 mm thick window structural results with 15 psig load (max equiv. stress: 223 MPa) , (b) With 3 psig He (maximum operational) load (max equiv. stress: 87.8 MPa) 17 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target windows M. McGee (FNAL) DS window reaches thermal equilibrium after 380 s (286 pulses) with T max = 67.3 ° C (a) (b) DS window Figure (a) DS 1.25 mm thick window structural results with 15 psig load (max equiv. stress: 211 MPa) , (b) with 3 psig He (maximum operational) load (max equiv. stress: 100 MPa) • Both US and DS window maximum Von Mises stress occurs at the edge of the window, < 224.1 MPa defined by ½ the UTS (FS: 2) and fatigue limit (> 10 7 cycles) of 268 MPa. • Expected maximum load is 3 psig (not 15 psig), after considering fluctuations in external barometric pressure conditions, internal pressure control and gas heating from beam Max. Von Mises stress of 87.8 MPa and 100 MPa for US and DS window, respectively • Be yield strength ~250 MPa , tensile strength ~450 MPa • 18 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target baffle (IHEP design) IHEP technical design report (2002) Requirement: operate with continuous 3% beam scraping • Consisted of graphite slugs inserted in Al sleeve with clamped pin radiators • NuMI 400kW baffle design (IHEP) Thermal analysis with NOvA beam parameters Peak temperature of 190 ° C in Aluminum sleeve (3% beam scraping) • Need to keep below 160 ° C to avoid Al ageing • 19 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target baffle (new design) FNAL Re-designed Al tube with 4 mm thick wall with cooling fins machined into tube • Eliminate Grafoil interface and hose clamps • Shrink fit at 150 ° C with interference fit of 0.003” • Al ID: 57 mm, OD: 65 mm • 18 fins at 20 ° spacing • Fin height: 20 mm, fin width: 2 mm • • Graphite slug baffle hole diameter: 13 mm Temperature distribution in baffle with 3% beam scraping Very conservative analysis 3% beam scraping • Low air velocity over baffle and convective heat • coefficient assumed Graphite T max : 157 ° C • Aluminum T max : 141 ° C • T max : 157 ° C 20 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
Target baffle operation Target assemblies starting with K.E. Anderson (FNAL) TA-04 will use new fin-style baffle TA-02 baffle (IHEP design) thermocouple readings DS end of Al containment tube Beam power: ~680 kW • Al tube temperature: 60 – 65 ° C • Much lower than predicted temperatures • Beam scraping < 1%, higher convective cooling • 21 9/21/17 K. Ammigan | NuMI – NOvA Target and Window, NBI 2017
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