1. Target Issues General Liquid Mercury Pb-Bi eutectic Solids Conclusions

2. General Issues Mats Lindroos: 4-5MW target station ~ small nuclear plant Likely to require secure, isolated nuclear site cf SNS – Oak Ridge JSNS – Tokai MEGAPIE – PSI Could be a big problem for CERN Beneficial for us Difficulty of getting safety approval shouldn’t be underestimated!

3. Liquid Mercury Baseline for SNS, JSNS, etc Only use so far: at SNS with 10kW beam Main issue – cavitation - limit lifetime to 2 weeksat 1MW - not solved yet (I believe) Contained targets……… …..but so is the NF target Velocity of mercury droplets bigger

4. Liquid Mercury - Cavitation For B=0 Droplet velocities ~ 70m/s For B>0 Droplets may be surpressed. MERIT will tell us.

5. Liquid 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

6. Liquid Mercury – Radiation Safety Marco Silari (TIS) After 10 years operation: - >10 18 Bq = 27MCi - >10 6 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

7. Liquid Mercury – Radiochemistry Jacques Lettry Most important R&D for a mercury target! Why?

9. Liquid Mercury – Radiochemistry Jacques 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

10. Lead-Bismuth Eutectic Compared with mercury Melting point: 120 o C! 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 120 o C - it likes oxygen - source of polonium 210!

11. Lead-Bismuth - Temperature Everything must be kept above 120 o C

12. Lead-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 880 o C Concentrations must be avoided

13. Solids 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

14. Solids - 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

15. Solids - 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

16. John Back Solids – Re-absorption Being repeated for a liquid jet

17. Solids – Target Change 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: Split coils: - 1 st 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

18. Solids – 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)

19. Solids – 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

20. Material Current (A) ΔT (K) Max. T (K) Pulses to failure Eq. power Tantalum30006018000.2x10 6 Tungsten 490010020003.4x10 6 1.9/3.5 72002002200Few!4.5/8.2 Stuck to connector 64001701900>1.6x10 6 3.5/6.5 556013019004.2x10 6 2.7/5.0 Connector failed 58401402050>9.0x10 6 3.0/5.4 700019020001.3x10 6 4.3/7.8 6200160200010.1x10 6 3.3/6.1 800025518302.7x10 6 6.1/>13 Cable #6 failed 744023018300.5x10 6 5.2/11.4 Still running*** 65201801940>9.7x10 6 4.1/8.7

21. Solids – 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

22. Solids – 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

23. Case 2. Bent wire 21 wire length = 5 cmwire radius (r) = 0.25 mmbPeak current = 5 kAb/r = 2 C LS-DYNA Bending frequency: ~ 1 kHz See: vm_bent_wire.mpgvm_bent_wire.mpg

24. 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 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

25. Solids – 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

26. Solids – 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

27. Radiation Damage 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

28. Solids – 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

29. Conclusions 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