Target Issues Target Issues • General • Liquid Mercury • Pb-Bi eutectic • Solids • Conclusions
Jan 20, 2016
Target IssuesTarget Issues
• General
• Liquid Mercury
• Pb-Bi eutectic
• Solids
• Conclusions
General IssuesGeneral Issues
Mats Lindroos:Mats Lindroos:
• 4-5MW target station ~ small nuclear plant
• Likely to require secure, isolated nuclear site
• cfSNS – Oak RidgeJSNS – TokaiMEGAPIE – PSI
• Could be a big problem for CERN
• Beneficial for us
• Difficulty of getting safety approval shouldn’tbe underestimated!
Liquid MercuryLiquid Mercury
• Baseline for SNS, JSNS, etc
• Only use so far: at SNS with 10kW beam
• Main issue – cavitation- limit lifetime to 2 weeks at 1MW- not solved yet (I believe)
• Contained targets………
• …..but so is the NF target
• Velocity of mercury droplets bigger
Liquid Mercury - CavitationLiquid Mercury - Cavitation
For B=0
Droplet velocities ~ 70m/s
For B>0
Droplets may be surpressed.
MERIT will tell us.
Liquid Mercury - CavitationLiquid Mercury - Cavitation
Two main problem areas: (1) beam window
Identified by Nick Simos
Effect of charged droplets?
Two main problem areas: (2) beam dump!
50-100kg of Hg/s at 30 m/s
Target station will need some attention
Liquid Mercury – Radiation SafetyLiquid Mercury – Radiation Safety
Marco Silari (TIS)Marco Silari (TIS)
• After 10 years operation:- >1018Bq = 27MCi- >106 times more active
• Distillation gains a factor of 10
• >5000kg will need to be stored
• Will need to be solid for disposal
• A leak would be a huge problem
• Didn’t believe get safety approval at CERN
Liquid Mercury – RadiochemistryLiquid Mercury – Radiochemistry
Jacques LettryJacques Lettry
• Most important R&D for a mercury target!
• Why?
Liquid Mercury – RadiochemistryLiquid Mercury – Radiochemistry
Jacques LettryJacques Lettry
• Most important R&D for a mercury target!
• Why?
• Guenter Bauer: Corrosive chemical created
• Not checked for SNS
• Many unanswered questions
• Rod still exists
• Must be repeated
Lead-Bismuth EutecticLead-Bismuth Eutectic
Compared with mercuryCompared with mercury
• Melting point: 120oC!
• Now being used at PSI
• No irradiation problems seen in PSI tests
• Will have the same cavitation problems
• Two problems of its own:- melting point is 120oC- it likes oxygen- source of polonium 210!
Lead-Bismuth - TemperatureLead-Bismuth - Temperature
Everything must be kept above 120oC
Lead-Bismuth - OxygenLead-Bismuth - Oxygen
• Pb-Bi is corrosive – strips oxide layer off everything
• Used most often as reactor coolant
• Must have oxygen circulated through it uniformly
• Typically 10-5 % by weight
• None/less used at PSI?
• Slowly produces PbO – melting point 880oC
• Concentrations must be avoided
SolidsSolids
• They are solid!
• Huge amount of experience in use, handling, etc
• Much of it here
Advantages:
Issues
• Temperature changing target, station design
• Shock
• Radiation damage
Solids - TemperatureSolids - Temperature
• T ~ 100K per pulse 5000K per second
• Needs efficient cooling!
• Helium is not impossible
• Large volumes of radioactive gas should be avoided
• Must change target between pulses
• Two possibilities:- fluidised metal jet- change individual targets and radiation cool
• Need high Z, high emissitivity, high T, high MP
• Original idea, rotating tantalum band
Solids - TemperatureSolids - Temperature
rotating toroid
proton beam
solenoid magnet
toroid at 2300 K radiates heat to water-cooled surroundings
toroid magnetically levitated and driven by linear motors
Bad for many reasons!
Latest: re-absorption along beam
Split into blocks 2-3cm , 15-20cm long
John Back
Solids – Re-absorptionSolids – Re-absorption
Being repeated for a liquid jet
Solids – Target ChangeSolids – Target Change
proton beam 4 MWtarget 1 MW
beam dump
pion collector solenoids
to the muon front-end
3 MW
s/s
thick shield walls
proton beam 4 MWtarget 1 MW
beam dump
pion collector solenoids
to the muon front-end
3 MW
s/s
thick shield walls
Inject transverse to beam
Next target in solenoid
Support targets via chain or cable
Velocity ~ 3m/s
“Trivial” – Tim Broome
500 targets ~ 0.1Hz, 1800K
Issues:Issues:
• Split coils:- 1st look OK- detailed study proposed
• Chain/cable- prototype in proposal
• Effect of magnetic field - in proposal
• Radiation damage:- SS tested many times- need to test joints
• Target station- loop in target station
- remote handling - radiation safety
Solids – ShockSolids – Shock
• Reason why solid targets could not be used
• Needed: - to reduce stress- test rig
supported
Stress in real target
(4 MW, 50 Hz, 6 GeV)
Stress in tungsten wire
(7.5 kA, 800 ns long pulse)
Solids – Test FacilitySolids – Test Facility• Need to heat centre of target by ~100K << reaction time
• Can be done with pulse p/s: ~6kA, rise time<100ns
• ISIS kickers
• Needs thin wires: 0.5mm diameter
MaterialMaterial Current Current (A)(A)
ΔΔT T (K)(K)
Max. T Max. T (K)(K)
Pulses to Pulses to failurefailure
Eq. Eq. powerpower
Tantalum 3000 60 1800 0.2x106
Tungsten
4900 100 2000 3.4x106 1.9/3.5
7200 200 2200 Few! 4.5/8.2
Stuck to connector
6400 170 1900 >1.6x106 3.5/6.5
5560 130 1900 4.2x106 2.7/5.0
Connector failed 5840 140 2050 >9.0x106 3.0/5.4
7000 190 2000 1.3x106 4.3/7.8
6200 160 2000 10.1x106 3.3/6.1
8000 255 1830 2.7x106 6.1/>13
Cable #6 failed 7440 230 1830 0.5x106 5.2/11.4
Still running*** 6520 180 1940 >9.7x106 4.1/8.7
Solids – ShockSolids – Shock
• Must:- measure surface acceleration- check violin modes -
check size effects - check temperature dependence - get better understanding of annealing, etc
• Use a beam:- ISOLDE right shock, short time -
LANL right shock(?), longer time
• Try a laser – Nick Simos
• All in proposal
Solids – Violin ModesSolids – Violin Modes
• Due to beam off central axis or at an angle
• Lettry et al claim very important
• Goran: max around 20% increase in stress in NF
• But…….also looked at including in wire tests: - using parallel wires - by bending a single wire
Case 2. Bent wire
2 1
wire length = 5 cm
wire radius (r) = 0.25 mm
b
Peak current = 5 kAb/r = 2
b/r = 2
C
LS-DYNA
Bending frequency: ~ 1 kHz
See: vm_bent_wire.mpg
LS-DYNA
NAS
Additional stress as a function of the wire bending
Additional stress (AS) normalized to the straight wire stress (SWS) for 5 kA peak current
Case 2. Bent wire
SWS
ASNAS
b/r
12
1
2
Comparing this with Slide (8) one can see that both approach can be used for inducing violin modes of oscillation and putting additional stress into the wire, but ‘bent wire’ approach looks less complicated.
Relatively small bending gives similar results as ‘the 2 wire approach’.
~ constant
Solids – ShockSolids – Shock
• Must:- measure surface acceleration- check violin modes -
check size effects - check temperature dependence - get better understanding of annealing, etc
• Use a beam:- ISOLDE right shock, short time -
LANL right shock(?), longer time
• Try a laser – Nick Simos
• All in proposal
Solids – Radiation DamageSolids – Radiation Damage
• Usual effects:- embrittlement- swelling due to gas production
• ISIS has used:- tantalum for years- tungsten for >18 months
• Tungsten changed after 18 months, 12DPA- not yet cut up- but no sign of damage
• CF NF target:- rates ~ similar
Radiation Damage
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• Irradiation of tungsten
• Atomic displacements for 10 years operation
• Max ~20DPA
• ISIS now uses tungsten
• Target changed after 18 months operation
• 12DPA
• No signs of swelling or embrittlement
Solids – Radiation DamageSolids – Radiation Damage
• Usual effects:- embrittlement- swelling due to gas production
• ISIS has used:- tantalum for years- tungsten for >18 months
• Tungsten changed after 18 months, 12DPA- not yet cut up- but no sign of damage
• CF NF target:- rates ~ similar- lower temperature diffusion slower- but greater surface area
• Should irradiate NF size at PSI, ISIS, etc
ConclusionsConclusions
• No target technology proven for NF yet
• All three still require much work
• Getting safety approval should not be underestimated
• Simplicity will help
• For solids- lots of experience, so problems known -
doing everything we can with limited resources - no show-stoppers so far
• Ultimately, may require 4MW beam for target proof