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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. - PowerPoint PPT Presentation
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APT / NuMI Horns & targets / Jim Hylen 1
NuMI Horns and TargetsMINOS-era operational challenges and NOVA-era expectations
Labor day weekend: target installation !
10/8/2013
APT / NuMI Horns & targets / Jim Hylen
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
10/8/2013
APT / NuMI Horns & targets / Jim Hylen
n yield versus target radius
High En => narrow target
For En ~ few GeV,
optimum Rtarget ~ 3 mm
but fall-off at larger R not horribly fast
Rod
Rod
Fin
Fin
NuMI
Want small radius target so pions get out the sides
Hence: small proton beam spot size large stress concentrated radiation damage
10/8/2013
Protons to NeutrinosJim Hylen
July 22, 2013 Page 4
Parabolic Magnetic Horns -> Lensp focused by toroidal field between conductors
• 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
Focus p+ toward detector
Outer ConductorInner Conductor
Stripline
Drain
Insulating Ring
Water Spray Nozzlep+ B I
Precision control of field - Achieved ~ 0.1 mm horn tolerance
B a R-1 toroiddL a R2 parabolic inner conductorPt kick = BdL a R in thin lens approximation
p must pass through inner conductor to get to field region Inner conductor as thin as possible: 2 mm Aluminum for horn 1
APT / NuMI Horns & targets / Jim Hylen 5
Horns connected in serieswith power supply by strip-line
Peak current: 200 kA Pulse width: 2.3 m-sec half-sine waveCycle: 1.87 sec -> 1.33 second
Peak field: 3 Tesla pions need ~ 300 MeV Pt kick
10/8/2013
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)
10/8/2013
Days down
Scheduled down or Accelerator Problem 359 14.0%
Target 149 5.8%
Horns 123 4.8%
Tritium systems 57 2.2%
Total 26.9%
APT / NuMI Horns & targets / Jim Hylen 7
NUMI horn operation summary 61 million pulses over 7 years to May 1, 2012
10/8/2013
Start End Pulses(Million)
Failure mode Modification for subsequent horns
HORN 1
PH1-01 3/2005 6/2008 24 Suction line broke near electrical insulator
Thicker steel at transition to insulator
PH1-02 6/2008 36OK
HORN 2
PH2-01 3/2005 12/2008 28 Strip-line fractured after high-strength steel washer broke due to hydrogen embrittlement
Use lower strength stainless steel washers
PH2-02 12/2008 32 OK
APT / NuMI Horns & targets / Jim Hylen 8
Horn 1 failure 2008water 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
10/8/2013
Similar failure
Switched from commercial unit
to home-built
Kovar brazed to ceramic
Shrink fit 316L stainless steel on toAmAlOx 68 almina ceramic
Much thicker material
Zero failures with this new style
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
10/8/2013
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 radiationPrevent oxidation of Nickel coating
Inner conductor Nickel coatedMitigate erosion by water spray of softer Aluminum - systematic error control against non-uniform currentAlso 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)
10/8/2013
PH2-02 June 2012
D.S. end<-
U.S. end ->
APT / NuMI Horns & targets / Jim Hylen 11
Horn design for NuMI, NOvA and LBNENuMI/MINOS design:
400 kW beam; 1.87 seconds design cycle time, but ran 2 seconds200 kA horn current, 2.3 milli-second half-sin-wave pulse width
NUMI/MINOS -- > NuMI/NOVARepetition rate (0.5 Hz -> .75 Hz): more Joule heatingBeam power (400 kW -> 700 kW): increased heating of outer conductorTarget 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 700Same rate & beam powerTarget 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
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 12
Horn Strip-line modification for NOVA (700 kW) horn 1
10/8/2013
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
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
10/8/2013
Graphite Fin Core6.4 mm wide
Water cooling tube
Target fits 60 cm deep in the 200 kA focusing horn
without touching.
95 cm long, 1.8 g/cm3, segmented
( 1.1 mm RMS beam spot )
Helium containment
IHEP Protvino design
APT / NuMI Horns & targets / Jim Hylen 14
NuMI Target operation summary
10/8/2013
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
10/8/2013
targetDate of 1st POT
Date of last POT
(last - 1st) in weeks
Integrated POT
max beam power
max POT/spill reason taken out of service Modification from previous target
design 400 kw 4.0E+13
NT01 5/1/2005 8/13/2006 67 1.6E+20 270 kw 3.0E+13drive stuck in high energy position, experiment wanted low energy position
(run at higher helium pressure after leak)
NT02 9/11/2006 6/12/2009 144 6.1E+20 340 kw 4.0E+13graphite deteriorating, 10%-15% fewer nu/POT at peak
restraining collar put on water pipe bellows and upstream water tubing
NT03 9/11/2009 7/12/2010 44 3.1E+20 375 kw 4.4E+13break at ceramic tube-holder (probably water leak -> explosion)
no water pipe bellows, helium pressure lowered
NT04 8/22/2010 9/17/2010 4 2.0E+19 375 kw 4.3E+13water leak; explosion (blew off upstream beryllium window, no water leak during autopsy*)
(* water leak only during beam hammering!)
NT05 10/29/2010 2/24/2011 17 1.3E+20 337 kw 4.0E+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
NT06 4/7/2011 5/16/2011 6 2.0E+19 305 kw 3.5E+13water leak; eventual external water leak, leak was upstream, not at downstream turnaround
different downstream water turnaround; tig weld instead of laser weld downstream
NY01 ' 6/11/2011 7/8/2011 4 2.1E+19 228 kw 2.6E+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 ' 7/29/2011 9/15/2011 7 4.5E+19 330 kw 3.8E+13removed when NT07 was ready, still available as spare but with deteriorated graphite
(recycled target, so could not modify)
NT07 9/24/2011 4/29/2012 31 2.6E+20 345 kw 4.0E+13Still running, no leaks downstream and upstream laser
welds replaced by tig; water pipe ceramic moved outside tube
APT / NuMI Horns & targets / Jim Hylen 16
ZXF5Q Graphite core degradation
10/8/2013
NT-02
NT-03
NT-07
helium
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 ?
He added to DK
APT / NuMI Horns & targets / Jim Hylen 17
What joints can fail,to produce water leaks in helium volume?
10/8/2013
Weld sleeveCeramic transitions
Water turn-around
This joint gets worst pounding by showering beam
APT / NuMI Horns & targets / Jim Hylen 18
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.
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 19
Outline of 2011 target problemsNT-01, NT-02, NT-03 had all lasted reasonable amount of timeNT-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
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 20
NT-05 Autopsy
10/8/2013
Some damage of outer tubeCut off end of tube – see water-pipe welds had failed completely
Not corrosion or 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 aluminumSolder joint to graphite fineSteel cooling pipes look fineDownstream spacer ring walked several inches upstream
APT / NuMI Horns & targets / Jim Hylen 21
NT-06 tip reworked, but water-line failed elsewhere
After re-workOriginal
TIG weld
Autopsy, showing water flowing down from upstream end of target
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 22
Re-did NT-07 welds with high Q.A.
10/8/2013
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.
APT / NuMI Horns & targets / Jim Hylen 23
NOVA target
10/8/2013
Graphite finsHelium atmosphereBeryllium windowsWater cooled aluminum pressing platesWater 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. and F.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
10/8/2013
MINOS L.E. NOVA M.E. target target
Proton Beam
6 cmWater cooling
• Water cooling moved 8 times as far away - but only 1.2 x more proton per pulseso 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
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
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 26
LBNE Target for 700 kW
10/8/2013
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 graphiteOption remains for beryllium as target material if it can be validated
Prototype Input from RAL
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 failureSuccess 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
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 28
ANSYS of most stressed Be fin, by Brian Hartsell
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 2910/8/2013
APT / NuMI Horns & targets / Jim Hylen 3010/8/2013
APT / NuMI Horns & targets / Jim Hylen 31
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 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
10/8/2013
APT / NuMI Horns & targets / Jim Hylen 32
Backup
10/8/2013
Tgt. Vert. Pos. Therm. / Jim Hylen 33
Additional target monitoring: Target Vertical Position ThermometerBeryllium pins on upstream window of target to watch beam position
Heat Sink
Baffle hole13 mm diameter
Beryllium cylinders 1.6 mm diam.Beam profile, 1 sigma, 2 sigma (r = 1.3 mm, 2.6 mm)
ThermocouplesNOVATarget
7.4 mmwide
(not to scale; note baffle drawn behind target, although it is actually in front)
2 cm
12/19/2011
Support(but minimize thermal contact)
1.3 mmspacing
Thermocouple
APT / NuMI Horns & targets / Jim Hylen 34
Horns for NuMI, NOvA and LBNE
10/8/2013
• Horn 1 Assembly • Horn 2 Assembly
APT / NuMI Horns & targets / Jim Hylen 3510/8/2013