1. Wir schaffen Wissen – heute für morgen muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut PSI, Paul Scherrer Institut Meson Production Targets Daniela Kiselev

2. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Injector 2 Ring cyclotron 590 MeV Target M Target E SINQ UCN Comet: 250 MeV Gantry 1 Gantry 2 at present: 1.5 MW (2.4 mA) PROSCAN OPTIS OPTIS 2 Injector 1 PSI Proton Accelerator Facilities Target E: World’s highest intensity surface muon beams > 10 µ/s Target E: World’s highest intensity surface muon beams > 10 8 µ/s

3. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut All beam line components are surrounded by iron shielding. Beam line from Target E to beam dump (side view) 2.5 m Concrete shielding Working platform Target E Collimators Diagnostics Beam dump 5 m movable slits inflatable seals to SINQ

4. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Meson Production Area Access to working platform after removing 3-4 m of concrete roof shielding Use of remotely controlled shielded exchange flasks to remove defective components. Repair work done in a hot cell.

5. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Design of Target station E p TARGET E: 6/4cm Beam losses: 18/12 % COLLIMATOR 2 & 3 Beam losses: 22/18 % INFLATABLE ALL-METAL SEALTARGET CHAMBER BACKWARD SHIELDING FORWARD SHIELDINGSHIELDING COLLIMATOR

6. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Target-E design p-beam Drive shaft BALL BEARINGS *) Silicon nitride balls, coated with MoS2 Rings and cage silver coated *) GMN, Nürnberg, Germany SPOKES To enable the thermal expansion of the target cone TARGET CONE Mean diameter: 450 mm Graphite density: 1.8 g/cm 3 Operating Temperature: 1700 K Irradiation damage rate: 0.1 dpa/Ah Rotational Speed: 1 Turn/s Target thickness: 60 / 40 mm 10 / 7 g/cm 2 Beam loss: 18 / 12 % Power deposition: 30 / 20 kW/mA wheel cooled by radiation motor

7. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Graphite = anisotropic material anisotropic material properties, particularly important: thermal expansion coefficient, dimensional changes under irradiation Bonal et al, MRS Bulletin34 (2009), p28 a-axis PSI-Target from the 80íes: Structure: pyrolytic graphite: 10 % swelling 100  A, 1 month life time,

8. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut 0 1 2 3 4 5 6 * 10 21 [n/cm 2 ] 1100 K 1650 K 1 dpa  10 22 p/cm 2  10 Ah Linear dimensional changes [%] Polycristalline graphite more isotropic material properties due to special treatment during fabrication (isostatic molting, graphitization at high temperature) material properties are highly dependent on the source of material and processing conditions used, e.g. small grain size improves isotropy swelling in c-axis suppressed by „thermal shrinkage cracks“ formed during fabrication = a large number of small single crystallites which are irregularly arranged in space Irradiation induced shrinkage of polycristalline graphite W. Delle, Juelich 1980 0 -0.5 -1.5 -2.0 -2.5 -3.0

9. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Lifetime of the rotating polycristalline graphite target cones due to irradiation-induced dimensional changes The design of the spokes constrains anisotropic shrinkage of the graphite. Anisotropic dimensional changes causes deformation of the shape and hence leads to a radial wobble. Radial deformation rates of the graphite cones as a function of proton current for different graphite grades *). *) SGL Carbon Mean proton current [mA] Radial deformation rate [mm/Ah] Limit: < 2 mm Mean proton current [mA] 0.5 1 1.5 1.8 segmented graphite wheel current integral [Ah] 0 5 10 15 20 25 30 Width of the rim: 6 mm Beam size:  ~ 1 mm Radial variation: < 2 mm

10. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut A new design of graphite wheel: 2003 - now Record: Integrated beam current: ~33.5 Ah Irradiation damage rate: ~3.4 dpa The gaps allow unconstrained dimensional changes of the irradiated part of the graphite. 12 segments: 1mm wide gaps at 1700 K: 0.5 mm gaps intensity variation: < 0.2%

11. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Life time of the ball bearings 240 250 260 270 days new bearing average Monitoring of the motor current peak 0 1 2 3 4 bad bearing current [A] interlock at 5 A = 40 Nm

12. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Maintenance of the target-insert in the hot-cell Exchange parts: horizontal drive shaft

13. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Target E93 in April 2012: 33.5 Ah (~ 3.5 years) Tilt of the segments observed!  Quantitative measurement of displacement planned in hot cell (ATEC)  Investigation using thermal stress calculations  improved design?  Search for other graphite grades A closer look to the target after irradiation

14. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Operational limits for target E Temperature (K) Safety factor  yp /  Evaporation rate (mg/g/year) Be C I(mA): Proton current D(m) : Mean target diameter  * : effective emissivity 3mA operation of Target E D = 0.45 m  * = 0.7 at 4mA: ~100 g loss/ year ! safety factor = yield stress / thermal induced stress

15. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut 3 mA Evaporation rate operation limit: 3 mA @ 2000 K due to evaporation: ~10 g mass loss/year Target E Measurement of evaporation for different graphite grades planned M.S. Avilov et al., NIM A618 (2010) 1

16. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Target-M design P-BEAM Target M: Mean diameter: 320 mm Target thickness: 5.2 mm Target width: 20 mm Graphite density:1.8 g/cm 3 Beam loss: 1.6 % Power deposition: 2.4 kW/mA Operating Temperature: 1100 K Irradiation damage rate:0.12 dpa/Ah Rotational Speed: 1 Turn/s Current limit: 5 mA Usual life time: 50000 h  44 Ah ~ 4 DPA.

17. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Target-M layout p Drive-motor

18. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Vacuum chamber

19. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Exchange of Target-M Operation of the remotely controlled shielded flask Dose rate ~ 1 mSv/h in working area (after 3 months cooling)

20. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut New design of the Target-M insert Ti-V steel cooled Cu-plate Reason: better vaccum connection at flange: seal can be exchanged/cleaned drive shaft: better heat protection for the bearings 1. part made from Ti-V ( instead of steel) to prevent heat conduction additonal cooled Cu- plate  better cooling and protection of bearings against radiated heat will be installed in Feb. 2012

21. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut TargetM63: 63 Ah in 7 years ~ 7.5 DPA Graphite loss on both sides: ~23 g  0.026 mm/month too much for evaporation at 800 o C Possible reason: Oxidation due to leaky flange Graphite loss at Target M

22. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut Summary Components in the beam line are taking out by exchange flasks Target E: - segmented graphite cone works up to 33 Ah - small tilts of the segments observed  needs more investigation - actual current limit: 3 mA due to evaporation (needs to be confirmed by tests) Ball bearings: - coated Si 3 N 4 balls, steel cage+ring from GMN, large scattering of life time: 4000 - 8000 h  less then graphite wheel !  fully ceramic bearings are ready for testing Target M: much less heat load/DPA  life time of bearings/target much longer ~ 50000 h, new insert: planned for shutdown 2012/13

23. muSR Workshop at FNAL Oct 17-19, 2012, Daniela Kiselev, Paul Scherrer Institut The meson production targets: Target E and Target M Graphite targets: rotating with 1 Hz Production of muons: Surface muons: produced from a pion at rest at the surface of the target (d < 300 nm)   almost 100% polarized (spin in opposite direction to momentum) almost monochromatic: max. at 28 MeV/c (= 3.7 MeV) World’s highest intensity surface muon beams > 10 µ/s World’s highest intensity surface muon beams > 10 8 µ/s 590 MeV 15-60 MeV Low energy muons (LEM): 0.5 -30 keV moderated by a cryogenic target