NuMI Horns and Targets MINOS-era operational challenges and NOVA-era expectations Labor day weekend: target installation ! 10/8/2013APT / NuMI Horns & targets / Jim Hylen1

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 10/8/2013APT / NuMI Horns & targets / Jim Hylen

yield versus target radius High E => narrow target For E ~ few GeV, optimum R target ~ 3 mm but fall-off at larger R not horribly fast Rod Fin NuMI Want small radius target so pions get out the sides Hence: small proton beam spot size large stress concentrated radiation damage 10/8/2013APT / NuMI Horns & targets / Jim Hylen

Protons to Neutrinos Jim Hylen July 22, 2013 Page 4 Parabolic Magnetic Horns -> Lens  focused by toroidal field between conductors Large toroidal magnetic field Requires large current, 200 kAmp Thin inner conductor, to minimize   absorption Water spray cooling on inner conductor Most challenging devices in beam design Prototype test to check design Focus   toward detector Outer Conductor Inner Conductor Stripline Drain Insulating Ring Water Spray Nozzle    Precision control of field - Achieved ~ 0.1 mm horn tolerance B  R -1 toroid dL  R 2 parabolic inner conductor Pt kick = BdL  R in thin lens approximation  must pass through inner conductor to get to field region Inner conductor as thin as possible: 2 mm Aluminum for horn 1

Horns connected in series with 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 10/8/2013APT / NuMI Horns & targets / Jim Hylen5

NuMI Operation summary May 1, 2005 (start of MINOS data) through April 29, 2012 (shutdown for ANU upgrades) : 7 years (2556 days)  /2 x POT at 120 GeV 1 MW-year of beam on target (to my knowledge, most of any accelerator neutrino beam) 10/8/2013APT / NuMI Horns & targets / Jim Hylen6 Days down Scheduled down or Accelerator Problem % Target1495.8% Horns1234.8% Tritium systems572.2% Total26.9%

NUMI horn operation summary 61 million pulses over 7 years to May 1, /8/2013APT / NuMI Horns & targets / Jim Hylen7 StartEndPulses (Million) Failure modeModification for subsequent horns HORN 1 PH1-013/20056/200824Suction line broke near electrical insulator Thicker steel at transition to insulator PH1-026/ OK HORN 2 PH2-013/200512/200828Strip-line fractured after high-strength steel washer broke due to hydrogen embrittlement Use lower strength stainless steel washers PH2-0212/200832OK

Horn 1 failure 2008 water line failed at ceramic transition (had repaired four such failures of different water lines) Horn was hot enough (75 R/hr) that decided to swap horn rather than repair 10/8/2013APT / NuMI Horns & targets / Jim Hylen8 Similar failure Switched from commercial unit to home-built Kovar brazed to ceramic Shrink fit 316L stainless steel on to AmAlOx 68 almina ceramic Much thicker material Zero failures with this new style

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 10/8/2013APT / NuMI Horns & targets / Jim Hylen9 In principle, can unbolt strip-line and replace it (bolt pattern deliberately unobstructed) But residual radiation 15 1 ft so would take quite a bit of remote setup and work

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) 10/8/2013APT / NuMI Horns & targets / Jim Hylen10 PH2-02 June 2012 D.S. end <- U.S. end ->

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 10/8/2013APT / NuMI Horns & targets / Jim Hylen11

Horn Strip-line modification for NOVA (700 kW) horn 1 10/8/2013APT / NuMI Horns & targets / Jim Hylen12 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 Temperature with Modified Geometry and added cooling at flange

NuMI graphite (older, MINOS style) target At center of Graphite, temperature jumps by 272 deg C in 10 microseconds, every couple seconds 10/8/2013APT / NuMI Horns & targets / Jim Hylen13 Graphite Fin Core 6.4 mm wide Water cooling tube Target fits 60 cm deep in the 200 kA focusing horn without touching. 95 cm long, 1.8 g/cm 3, segmented ( 1.1 mm RMS beam spot ) Helium containment IHEP Protvino design

NuMI Target operation summary 10/8/2013APT / NuMI Horns & targets / Jim Hylen14 7 targets over 7 years of operation (coincidentally, average matches CDR/TDR plan of 1 target per year) Total of  /2 x 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.

NuMI Target operation summary 10/8/2013APT / NuMI Horns & targets / Jim Hylen15 target Date of 1st POT Date of last POT (last - 1st) in weeks Integrated POT max beam power max POT/spillreason taken out of serviceModification from previous target design 400 kw4.0E+13 NT015/1/20058/13/ E kw3.0E+13 drive stuck in high energy position, experiment wanted low energy position (run at higher helium pressure after leak) NT029/11/20066/12/ E kw4.0E+13 graphite deteriorating, 10%-15% fewer nu/POT at peak restraining collar put on water pipe bellows and upstream water tubing NT039/11/20097/12/ E kw4.4E+13 break at ceramic tube-holder (probably water leak -> explosion) no water pipe bellows, helium pressure lowered NT048/22/20109/17/ E kw4.3E+13 water leak; explosion (blew off upstream beryllium window, no water leak during autopsy*) (* water leak only during beam hammering!) NT0510/29/20102/24/ E kw4.0E+13 water leak; eventual external water leak (water turnaround fell off at downstream laser weld) higher helium pressure to help keep water out of target tube NT064/7/20115/16/ E kw3.5E+13 water leak; eventual external water leak, leak was upstream, not at downstream turnaround different downstream water turnaround; tig weld instead of laser weld downstream NY01 '6/11/20117/8/ E kw2.6E+13 water leak; eventual high level of water in target; spray at downstream laser weld seen at autopsy (repaired motion mechanism; recycled target, so could not modify target core) NT02 '7/29/20119/15/ E kw3.8E+13 removed when NT07 was ready, still available as spare but with deteriorated graphite (recycled target, so could not modify) NT079/24/20114/29/ E kw4.0E+13 Still running, no leaksdownstream and upstream laser welds replaced by tig; water pipe ceramic moved outside tube

APT / NuMI Horns & targets / Jim Hylen ZXF5Q Graphite core degradation 10/8/ NT-02 NT-03 NT-07 helium NT-02 10% - 15% 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/ /22/2010) NT-07 No indication of degradation over 2.6e20 POT Why does later graphite appear more robust ? He added to DK

What joints can fail, to produce water leaks in helium volume? 10/8/2013APT / NuMI Horns & targets / Jim Hylen17 Weld sleeve Ceramic transitions Water turn-around This joint gets worst pounding by showering beam

What does water leak do? Water leak inside helium volume leads to unacceptable conditions in couple ways: 1)Beam ionization dissociates water to H and O; gas then explodes, causing misalignments or bursting windows 2)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. 10/8/2013APT / NuMI Horns & targets / Jim Hylen18

Outline of 2011 target problems NT-01, NT-02, NT-03 had all lasted reasonable amount of time NT-04, NT-05, NT 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 10/8/2013APT / NuMI Horns & targets / Jim Hylen19

NT-05 Autopsy 10/8/2013APT / NuMI Horns & targets / Jim Hylen20 Some damage of outer tube Cut off end of tube – see water-pipe welds had failed completely Not corrosion or pipe failure; just break of laser welds 1 st 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

NT-06 tip reworked, but water-line failed elsewhere After re-work Original TIG weld Autopsy, showing water flowing down from upstream end of target 10/8/2013APT / NuMI Horns & targets / Jim Hylen21

Re-did NT-07 welds with high Q.A. 10/8/2013APT / NuMI Horns & targets / Jim Hylen22 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 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.

NOVA target 10/8/2013APT / NuMI Horns & targets / Jim Hylen23 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 1 st one built by R.A.L. in U.K. Spares: one each by R.A.L. and F.N.A.L

NoVA target not nearly as problematic because: M.E. target is further upstream, does not have to fit in horn 10/8/2013APT / NuMI Horns & targets / Jim Hylen24 MINOS L.E. NOVA M.E. target target Proton Beam 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 Graphite target Comparison to scale: 3 cm

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 10/8/2013APT / NuMI Horns & targets / Jim Hylen25

LBNE Target for 700 kW 10/8/2013APT / NuMI Horns & targets / Jim Hylen26 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 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 Prototype Input from RAL

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 10/8/2013APT / NuMI Horns & targets / Jim Hylen27

ANSYS of most stressed Be fin, by Brian Hartsell 10/8/2013APT / NuMI Horns & targets / Jim Hylen28

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Proposal: Path to a Beryllium 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 1 st 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 10/8/2013APT / NuMI Horns & targets / Jim Hylen31

Backup 10/8/2013APT / NuMI Horns & targets / Jim Hylen32

Additional target monitoring: Target Vertical Position Thermometer Beryllium pins on upstream window of target to watch beam position Heat Sink Baffle hole 13 mm diameter Beryllium cylinders 1.6 mm diam. Beam profile, 1 sigma, 2 sigma (r = 1.3 mm, 2.6 mm) ThermocouplesNOVA Target 7.4 mm wide (not to scale; note baffle drawn behind target, although it is actually in front) 2 cm 12/19/201133Tgt. Vert. Pos. Therm. / Jim Hylen Support (but minimize thermal contact) 1.3 mm spacing Thermocouple

Horns for NuMI, NOvA and LBNE 10/8/2013APT / NuMI Horns & targets / Jim Hylen34 Horn 1 AssemblyHorn 2 Assembly

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