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NuMI Horns and Targets MINOS-era operational challenges and NOVA-era expectations

NuMI Horns and Targets MINOS-era operational challenges and NOVA-era expectations. Labor day weekend: target installation !. Pions produced in target, focused by horns, with long decay channel for pion -> neutrino decay. NuMI.

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NuMI Horns and Targets MINOS-era operational challenges and NOVA-era expectations

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  1. NuMI Horns and TargetsMINOS-era operational challenges and NOVA-era expectations Labor day weekend: target installation ! APT / NuMI Horns & targets / Jim Hylen

  2. Pions produced in target, focused by horns,with long decay channel for pion -> neutrino decay NuMI Focusing of pions increases neutrinos in peak energy range by ~ factor of 5 to 10 Time dilation of pions means decay space needs to be long in order to get good efficiency APT / NuMI Horns & targets / Jim Hylen

  3. n yield versus target radius NuMI High En => narrow target For En ~ few GeV, optimum Rtarget ~ 3 mm but fall-off at larger R not horribly fast Rod Fin Want small radius target so pions get out the sides Hence: small proton beam spot size large stress concentrated radiation damage Rod Fin APT / NuMI Horns & targets / Jim Hylen

  4. Parabolic Magnetic Horns -> Lensp focused by toroidal field between conductors p must pass through inner conductor to get to field region Inner conductor as thin as possible: 2 mm Aluminum for horn 1 Outer Conductor Stripline • Large toroidal magnetic field • Requires large current, 200 kAmp • Thin inner conductor, to minimize p+ absorption • Water spray cooling on inner conductor • Most challenging devices in beam design • Prototype test 1999-2000 to check design B Inner Conductor p+ I Water Spray Nozzle B a R-1 toroid dL a R2 parabolic inner conductor Pt kick = BdL a R in thin lens approximation Focus p+ toward detector Insulating Ring Drain Precision control of field - Achieved ~ 0.1 mm horn tolerance

  5. Horns connected in serieswith power supply by strip-line Peak current: 200 kA Pulse width: 2.3 m-sec half-sine wave Cycle: 1.87 sec -> 1.33 second Peak field: 3 Tesla pions need ~ 300 MeV Pt kick APT / NuMI Horns & targets / Jim Hylen

  6. NuMI Operation summary May 1, 2005 (start of MINOS data) through April 29, 2012 (shutdown for ANU upgrades) : 7 years (2556 days) p/2 x 1021 POT at 120 GeV 1 MW-year of beam on target (to my knowledge, most of any accelerator neutrino beam) APT / NuMI Horns & targets / Jim Hylen

  7. NUMI horn operation summary 61 million pulses over 7 years to May 1, 2012 APT / NuMI Horns & targets / Jim Hylen

  8. Horn 1 failure 2008water line failed at ceramic transition (had repaired foursuch failures of different water lines)Horn was hot enough (75 R/hr) that decided to swap horn rather than repair Similar failure Switched from commercial unit to home-built Shrink fit 316L stainless steel on to AmAlOx 68 almina ceramic Much thicker material Zero failures with this new style Kovar brazed to ceramic APT / NuMI Horns & targets / Jim Hylen

  9. Horn 2 failure 2008 high-strength steel washers broke due to nitric-acid induced hydrogen enbrittlement, unrestrained strip-line eventually cracked (horn itself was OK)No failures since switched to lower strength washers In principle, can unbolt strip-line and replace it (bolt pattern deliberately unobstructed) But residual radiation 15 R/hr @ 1 ft so would take quite a bit of remote setup and work APT / NuMI Horns & targets / Jim Hylen

  10. Argon gas purge through inside of horn – Prevent buildup of explosive mixture from dissociation of H2O by radiation Prevent oxidation of Nickel coating Inner conductor Nickel coated Mitigate erosion by water spray of softer Aluminum - systematic error control against non-uniform current Also reduces probability of crack propagation from surface of Aluminum Nickel on outside of inner conductor is corroded by the nasty target pile air, but believe inside is protected by Argon (don’t see nickel flakes in RAW system filters) PH2-02 June 2012 D.S. end <- U.S. end -> APT / NuMI Horns & targets / Jim Hylen

  11. Horn design for NuMI, NOvA and LBNE NuMI/MINOS design: 400 kW beam; 1.87 seconds design cycle time, but ran 2 seconds 200 kA horn current, 2.3 milli-second half-sin-wave pulse width NUMI/MINOS -- > NuMI/NOVA Repetition rate (0.5 Hz -> .75 Hz): more Joule heating Beam power (400 kW -> 700 kW): increased heating of outer conductor Target no longer inside horn, moderates inner conductor heating Modifications: Reduce outer conductor thickness to compensate beam heating ( 1” -> 5/8“) Add water cooling near strip-line connections Move strip-line flex section to larger radius to reduce beam heating Horn 1 “crosshair” changed from Aluminum to Beryllium Horn 2 moved, starts ( 10 m -> 19.2 m ) downstream of start of Horn 1 NuMI/NOVA -- > LBNE 700 Same rate & beam power Target moves back into horn, increasing inner conductor heating Reference design same as NOVA. Possible Modifications: Horn 2 starts ( 10 m -> 6.6 m ) downstream of start of Horn 1 Will explore going to higher current ( 230 kA looks possible ) Will investigate re-optimizing inner conductor water spray (done) Will investigate other variations if funding becomes available APT / NuMI Horns & targets / Jim Hylen

  12. Horn Strip-line modification for NOVA (700 kW) horn 1 Temperature with Modified Geometry and added cooling at flange Temperature with old NuMI design if used for NOVA With improved cooling & flared out stripline geometry the max. temp. is reduced to < 100C as desired APT / NuMI Horns & targets / Jim Hylen

  13. NuMI graphite (older, MINOS style) targetAt center of Graphite, temperature jumps by 272 deg C in 10 microseconds, every couple seconds 95 cm long, 1.8 g/cm3, segmented Graphite Fin Core 6.4 mm wide Water cooling tube ( 1.1 mm RMS beam spot ) Helium containment Target fits 60 cm deep in the 200 kA focusing horn without touching. IHEP Protvino design APT / NuMI Horns & targets / Jim Hylen

  14. NuMI Target operation summary 7 targets over 7 years of operation (coincidentally, average matches CDR/TDR plan of 1 target per year) Total of p/2 x 1021 POT at 120 GeV Integrated beam power = 0.97 MW-year 5 targets replaced due to failure of water-cooling line 1 target replaced due to gradual deterioration of graphite (changing neutrino spectrum) ( 1 target temporarily out of action due to frozen motion drive ) Target 7 is still in good shape. APT / NuMI Horns & targets / Jim Hylen

  15. NuMI Target operation summary APT / NuMI Horns & targets / Jim Hylen

  16. He added to DK ZXF5Q Graphite core degradation helium NT-02 NT-02 10% - 15% n decrease over 6.1e20 POT radiation damage ? (~ 1 DPA) or oxidation, or ... ? plan to autopsy next year NT-03 No indication of degradation over 1.8e20 POT (anti-nu 9/29/2009 - 3/22/2010) NT-07 No indication of degradation over 2.6e20 POT Why does later graphite appear more robust ? NT-03 NT-07 APT / NuMI Horns & targets / Jim Hylen

  17. What joints can fail,to produce water leaks in helium volume? This joint gets worst pounding by showering beam Water turn-around Weld sleeve Ceramic transitions APT / NuMI Horns & targets / Jim Hylen

  18. What does water leak do? Water leak inside helium volume leads to unacceptable conditions in couple ways: • Beam ionization dissociates water to H and O; gas then explodes, causing misalignmentsor bursting windows • Water partly fills helium volume; extra material would cause experimental systematic errors by changing beam spectrum, so target must be discarded If outer tube is breached, water may run out, and target may continue operation as long as reasonable helium over-pressure can be maintained. Each target was rather unique in how it limped through water and helium leaks. Sometimes, managed to keep water out by over-pressuring the helium. APT / NuMI Horns & targets / Jim Hylen

  19. Outline of 2011 target problems NT-01, NT-02, NT-03 had all lasted reasonable amount of time NT-04, NT-05, NT-06 - - rapid series of failures, all due to bad water line joints from vendor NT-04 infant mortality. NT-04 would not leak during autopsy, only with beam pounding on it NT-05 To get back on air, installed NT-05 with no hardware changes, but with high helium pressure to try to keep water from entering the helium volume. NT-05 water line failed almost immediately, but the helium strategy did keep NT-05 working long enough to pretty much get NT-06 ready NT-06 Autopsy of NT-05 showed water leak at welds at target tip, so FNAL redid target tip welds on NT-06 with high Q.A. NT-06 failed quickly as well, but autopsy showed it was upstream, not the tip welds Refurbished and ran NT-01 and NT-02 until NT-07 was ready NT-07 first target built after NT-04 failure, all water-pipe joints inside redone by FNAL with high Q.A. Ran well. Finally, no problems! Down total of 1/3 of the time over 13 months: spares not ready, 5 change-outs, 4 autopsies, 2 modifications based on autopsies, 2 refurbishments shortest downtime for target replacement: 9 days APT / NuMI Horns & targets / Jim Hylen

  20. NT-05 Autopsy Some damage of outer tube Cut off end of tube – see water-pipe welds had failed completely Not corrosionor pipe failure; just break of laser welds 1st direct view of graphite after running ! Visible graphite looks perfect after 1.25e20 POT ( NT02 took 6e20 POT ) No corrosion of aluminum Solder joint to graphite fine Steel cooling pipes look fine Downstream spacer ring walked several inches upstream APT / NuMI Horns & targets / Jim Hylen

  21. NT-06 tip reworked, but water-line failed elsewhere TIG weld Original After re-work Autopsy, showing water flowing down from upstream end of target APT / NuMI Horns & targets / Jim Hylen

  22. Re-did NT-07 welds with high Q.A. Original welds from target vendor showed tungsten inclusions Replaced these even though they passed pressure test. Re-did all welds internal to the hydrogen volume. CT Scan to Qualify Downstream Turnaround Ring Weld Integrity (Difficult Geometry for Conventional X-ray Inspection) Rework welding development and microstructure analysis was conducted by contracted material science engineering experts APT / NuMI Horns & targets / Jim Hylen

  23. NOVA target Graphite fins Helium atmosphere Beryllium windows Water cooled aluminum pressing plates Water cooled outer can Will NOT fit inside horn (Fins end 20 cm upstream of horn) NoVA requested target upstream to optimize neutrino spectrum 1st one built by R.A.L. in U.K. Spares: one each by R.A.L. andF.N.A.L APT / NuMI Horns & targets / Jim Hylen

  24. NoVA target not nearly as problematic because:M.E. target is further upstream, does not have to fit in horn MINOS L.E.NOVA M.E. target target Comparison to scale: Proton Beam 3 cm Graphite target 6 cm Water cooling • Water cooling moved 8 times as far away • - but only 1.2 x more proton per pulse • so water-line stress is very modest ! • Does not need to be electrically insulated • - no ceramic break in water line APT / NuMI Horns & targets / Jim Hylen

  25. Expectations for NOVA era? Horns • (+) All known issues have been addressed; fatigue lifetime longer than NOVA run • (-) Corrosive atm., high stress, nasty environment; water cooled, higher power • Are using 3 year lifetime as basis for spares production planning Targets • (+) water problem that caused 5/6 MINOS target failures substantially mitigated • (-) if radiation damage caused NT-02 failure, extrapolate to 2 targets/700kw-year • Are using 2 targets/year as basis for spares production planning • Want to test Beryllium as Graphite replacement to try to increase target lifetime APT / NuMI Horns & targets / Jim Hylen

  26. LBNE Target for 700 kW Key change 2: outer containment tube beryllium instead of aluminum • Beryllium stronger, take higher temperature • Eliminates Al-Be brazing joint to the downstream beam window (beryllium) • Reduces horn heating / pion absorption Partially prototyped already for NuMI Reference material: POCO ZXF5Q graphite Option remains for beryllium as target material if it can be validated Input from RAL Prototype Developed from the NuMI Low-Energy Target • Same overall geometry • Conservative approach to design • Flexible tune for neutrino energy Key change 1: Cooling lines made from continuous titanium tubing • Previous was stainless with welded junctions • Eliminates water joints • Stronger and more resistant to heating, water pressure • Less heat produced / pions absorbed APT / NuMI Horns & targets / Jim Hylen

  27. Proposal: Test of Beryllium target material for NOVA? • Be is order of magnitude more radiation resistant than graphite • Longer lifetime has advantages: • Slower deterioration, more stable neutrino flux to experiments • Save lots of money on construction, installation, storage, disposal of targets • Less downtime for replacement of targets • Be targets have run for extended periods (WANF, Mini-BOONE) • Replacement of NuMI graphite by Be pushes stress to yield limit • Believe Be will survive, but how to test? • Propose putting a couple Be fins in NOVA target, one in highest stress region, one in lower stress region • Loss of one fin out of 50 should not make a target non-functional So minimal impact in case of failure Success might save 8 targets during NOVA run & help LBNE design • NuMI prototype target test took pulses on Be calculated to be beyond yield point with no visible damage, but did not do sustained running – so want NOVA test APT / NuMI Horns & targets / Jim Hylen

  28. ANSYS of most stressed Be fin, by Brian Hartsell APT / NuMI Horns & targets / Jim Hylen

  29. APT / NuMI Horns & targets / Jim Hylen

  30. APT / NuMI Horns & targets / Jim Hylen

  31. Proposal: Path to aBeryllium target • Installed target is all-graphite - - run it till it dies (catastrophic or spectrum too bad) • Install few Be fins in next target, MET-02 (ready December). • Install when 1st target fails • Run it until it dies • Autopsy target, see how Be fins fair relative to graphite • We already have a graphite spare target (MET-03), which would then go in • Target after that (MET-04) could be all-Beryllium APT / NuMI Horns & targets / Jim Hylen

  32. Backup APT / NuMI Horns & targets / Jim Hylen

  33. Additional target monitoring: Target Vertical Position ThermometerBeryllium pins on upstream window of target to watch beam position (not to scale; note baffle drawn behind target, although it is actually in front) 2 cm Beam profile, 1 sigma, 2 sigma (r = 1.3 mm, 2.6 mm) Beryllium cylinders 1.6 mm diam. Thermocouple Heat Sink NOVA Target 7.4 mm wide Thermocouples 1.3 mm spacing Support (but minimize thermal contact) Baffle hole 13 mm diameter Tgt. Vert. Pos. Therm. / Jim Hylen

  34. Horns for NuMI, NOvA and LBNE • Horn 1 Assembly • Horn 2 Assembly APT / NuMI Horns & targets / Jim Hylen

  35. APT / NuMI Horns & targets / Jim Hylen

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