1. Solid Target Studies for NF Solid Target Studies for NF Rob Edgecock On behalf of: J.Back, R.Bennett, S.Gray, A.McFarland, P.Loveridge & G.Skoro Tungsten wire at 2000K

2. Reminder Reminder Solid means  tungsten bars, each ~2x20cm  150-200 bars  changed between beam pulses  cooled radiatively or possibly by helium/water Why?  lots of experience world-wide & safer  already have a license at RAL Issues for solids:  shock – original show-stopper  radiation damage  targ et change Focus has been on shock - b ut now moving on

3. Shock Shock Was solid show-stopper: one of main reasons for liquids Impossible to lifetime test with proton beam, so 60kV, 8kA PSU, 100ns rise time Aims:measure lifetime validate LSDyna model understand W behaviour

4. Lifetime/fatigue tests results I, II, III –> ‘chronology’. We have got better with the tests over time (better clamping of the wire; better understanding of ‘violin modes’ –> better alignment of the wire) SEM imaging BegbrokeNano, Oxford Materials Characterisation Services The aim to observe any surface damage which might indicate the presence of thermal fatigue Results: inconclusive More than sufficient lifetime demonstrated: > 10 years for 2cm diameter target > 20 years for 3cm diameter target Focus now: Measure stress; Confirm modelling. Better at lower temperature! 200 targets

5. Laser Doppler Vibrometer Laser Doppler Vibrometer VISAR  Mis-informed that VISAR required at high temp  Large irreducible noise in our frequency range  Took a long time to get any (poor) results LDV  Much, much, much,................. better than VISAR  Works to >2300K  Used to measure wire surface velocity  Frequency analysis used to extract results  Compared with LSDyna other measurements

6. Laser Doppler Vibrometer Laser Doppler Vibrometer Longitudinal  Bigger oscillations: ~μm; lower frequency: ~20kHz  But.....temperature variation along wire  Wire fixed at one end, constrained at other  Oscillations more difficult to understand Radial  Smaller oscillations: 50-100nm; higher frequency: ~12MHz  But......fixed temperature  Easier to model Wire Laser beam Longitudinal and radial mesurements possible

7. Longitudinal oscillations Longitudinal oscillations Longitudinal oscillations vs LSDyna Frequency analysis

8. Radial oscillations Radial oscillations Radial oscillations: frequency analysis vs LSDyna Radial oscillations vs LSDyna

9. Comparison with LSDyna Comparison with LSDyna Oscillations are complicated  wire partially fixed to frame  frame also moves  violin modes, etc  Have pretty good agreement but studies continuing Level of stress is correct  correct velocity is reproduced  wire is being stressed at above NF levels Lifetime results are valid

10. ‘Fit’ – will be used later for comparison Comparison with Measurements Comparison with Measurements J.W. Davis, ITER Material Properties Handbook, 1997, Volume AM01-2111, Number 2, Page 1-7, Figure 2 Concern: low strength from static measuremts at high temp

11. Measurement in Wire Tests Measurement in Wire Tests If we know the Poisson’s ratio , density , root of corresponding Bessel function , wire radius r and measure the frequency f as a function of temperature then: Wire Laser beam Illustration

12. Tungsten Young’s Modulus Tungsten Young’s Modulus

13. Young’s Modulus of Tungsten Young’s Modulus of Tungsten Results are very encouraging But……  E is not tensile strength  Tensile strength is what really matters Expectation is E would fall rapidly once plastic Can we check this? Difficult with tungsten....having a go with Ta (see GS talk)

14. Young’s Modulus Conclusions Young’s Modulus Conclusions Measurements ~ comparable with existing Details largely understood, but more work required Bottom line: Strength remains high at high temperature and at high stress! Reason why measured lifetime higher than some expected Plans:  Continue detailed studies  Repeat lifetime tests, but measure with LDV over time  Use beams and measure with LDV to cf LSDyna - request made to ISIS - use Ilias’s facility at CERN

15. Radiation Damage Radiation Damage ISIS:  used tantalum for > 10 years, tungsten ~5 years  targets changed after ~12dpa  ~2-5 years at NF, depending on # of targets  no signs of swelling or embrittlement  Ta examined in detail; W still to be done Still to be done  tensile strength after irradiation  hope to form consortium to measure 12dpa ISIS target  but……..

16. Radiation Damage Radiation Damage NB Static measurements.

17. Target Change Target Change Current option: a wheel – being investigated now Several already used, but most relevant: design study Horizontal for compatibility with baseline target station

18. Target Change Target Change For us, major issue is capture solenoid Helmholtz coil looks difficult due to forces Placing wheel up-stream of solenoids: ~60% of Study II muon capture rate

19. Target Change Target Change Arranging visit to discuss collaboration with ESS But.....problem being studied by ISIS TS2 engineers Given free reign, uninhibited by physicists Studying an idea with minimal impact on solenoids More if it works out

20. Conclusions Conclusions Shock:  We’ve done this to death!  Don’t believe it is a problem  Tests with beams to come Radiation damage:  Lots of local experience exists  Needs to be applied to our case  But existing data are encouraging Target change:  Wheel looks feasible – detailed study underway  Alternatives being investigated