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

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


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


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%


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


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


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


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 ->


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


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


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


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.


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


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


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


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


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


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


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


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.


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


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


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


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


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


ANSYS of most stressed Be fin, by Brian Hartsell

10/8/2013

APT / NuMI Horns & targets / Jim Hylen 2910/8/2013



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


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


Horns for NuMI, NOvA and LBNE

10/8/2013

• Horn 1 Assembly • Horn 2 Assembly


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

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