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

1 7

13 19 25 31 37 43 49 55 61 67 73 79 85 91 97

103

109

115

121

127

133

139

145

151

157

163

169

175

181

187

193

199

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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