Ian Bailey University of Liverpool / Cockcroft Institute ILC Baseline Target Collaborators STFC Daresbury Laboratory, STFC Rutherforord Appleton Laboratory, STFC ASTeC ANL, DESY, LLNL, SLAC POSIPOL 2007, LAL

ILC RDR Baseline Positron Source RDR Parameters  Centre of undulator to target: 500m  Active (K=0.92, period=1.21mm) undulator: 147m  Photon beam power: 131kW  Beam spot: >1.7 mm rms

Beam Spot on Target SPECTRA simulation Continuous undulator without misalignments, collimation or electron beam jitter mean: 1.9mm sd: 1.0mm power-weighted beam spot rms: 2.2mm

Baseline Target Design Wheel rim speed (100m/s) fixed by thermal load (~8% of photon beam power) Rotation reduces pulse energy density from ~900J/g to ~24J/g Cooled by internal water-cooling channel Wheel diameter (~1m) fixed by radiation damage and capture optics Materials fixed by thermal and mechanical properties and pair-production cross- section (Ti6%Al4%V) Wheel geometry (~30mm radial width) constrained by eddy currents. 20cm between target and rf cavity. T. Piggott, LLNL Drive motor and water union are mounted on opposite ends of through-shaft.

Baseline Target Activities Design underpinned by simulations –Thermal and structural –Vibrational and rotordynamics –Capture optics effects –Activation and radiation damage –(Polarisation transfer) Remote-handling solutions Alternative target materials Target prototyping

Thermal Studies W. Stein, LLNL TOPAZ-3D and DYNA-3D simulations  Rapid energy deposition generates a pressure shock wave  Maximum stress is experienced at the back surface of the target  For older beam parameters (small beam spot), peak stress was ~4x10 8 Pa  This is a factor of two below the yield stress  Simulation is being re- evaluated with updated parameters and target design.

4/rev 1/rev Primary Critical Speed = 500 RPM 1 st Secondary Critical Speed = 120 RPM 2 nd Secondary Critical Speed = 170 RPM Primary Critical Speed Secondary Criticals Cylindrical Whirl Mode Forward Tilt Whirl Mode Backward Tilt Whirl Mode Support Translational Stiffness = 100,000 lbf/inSupport Rotational Stiffness = 10,000 in-lb/rad 900 RPM Operating Speed UCRL-PRES Rotordynamics Studies This example is for older 4-spoke wheel design. L. Hagler, T. Piggott, LLNL

Eddy Current Modelling Capture optics induce eddy currents in the target wheel. Eddy current simulations have been carried out by Cornell, ANL(FEMLAB) and RAL (OPERA): –SLAC Cu disc experiment –2m diameter wheel (older design), s/c OMD field –1m diameter wheel, 1T field 2m results were presented at Beijing Positron Source meeting in Jan ’07 –Eddy current power losses of order 100kW –Difficult to compare but ~factor 4 difference in results –Studies began on 1m diameter wheel using standardised geometry and parameters.

1m Wheel Eddy Current Simulations Target wheel Coils J. Rochford, RAL For 1T field at 2000rpm RAL predicts ~6.6kW ANL predicts ~9.5kW Difference not yet understood…

Activation Simulations Extensive simulations have been carried out using FLUKA (interfaced to ASTRA for E field simulation) at DESY (Andriy Ushakov) collaborating with ANL, etc. Radiation damage evaluation using SPECTRE currently underway at DESY and LLNL. Data analysis from FLUKA activation benchmarking experiment (T-489) is underway. –Joint experiment by radiation protection groups at SLAC and CERN

A. Ushakov - DESY

c.f. 20mSv/year LHC manual worker limit.

Activation Simulations New target geometry (mostly) migrated to FLUKA Simulations will begin at DL shortly n/c rf cavity motor assembly target wheel (including water channel) flux concentrator L. Fernandez-Hernando, DL

Remote-Handling Design Large changes since POSIPOL 2006 Baseline uses a vertical remote-handling system Minimises target hall footprint (~100m 2 ) Estimated target change time is ~ 53 hours (not yet optimised)

M. Woodward, RAL Cryocooler (if required) + vacuum pump + water pump Details of vertical drive for target wheel not yet considered. Remote-Handling Module and Plug Module contains target, capture optics and first accelerating cavity.

Ceramics as Alternative Target Materials Reference MaterialsMachinable CeramicsNitrides Titanium Alloy Ti-6Al-4V Grade 5 Annealed Isotropic Graphite IG-43 “Macor” Machinable Glass- ceramic “Shapal-M” Machinable Aluminium Nitride AlN Aluminium Nitride Si 3 N 4 Silicon Nitride (Hot Pressed) “Sialon” Solid Solution BN Boron Nitride Heat Capacity J/kg. K – 2000 Expansion Coefficient /K x x x x x x –3.7 x – 36 x Density Kg/ m Radiation Length mm Thermal Conductivity W/m.K – 50 Electrical Resistivity Ohm.m 1.78 x x > x >10 11 >10 10 >10 9 Max. Use Temperature ºC Melting Point ~ – 1900 In non-oxidising atmosphere 1000 – 1800 In non-oxidising atmosphere Tensile Strength MPa Yield 880 UTS Compressive Strength MPaYield – 120 Elastic Modulus GPa P. Loveridge, RAL

Ceramics as Alternative Target Materials P. Loveridge, RAL CarbidesOxides B 4 C Boron Carbide (Hot Pressed) SiC Silicon Carbide (Reaction Bonded) SiC Silicon Carbide (Hot Pressed) WC 94 / Co 6 Tungsten Carbide / Cobalt BeO 99.5% Beryllia Al 2 O % Alumina ZrO 2 / MgO Zirconia (Magnesia stabilised) YO 99.9% Yttrium Oxide Heat Capacity J/kg. K Expansion Coefficient /K5.6 x –4.6 x x –5.0 x –9.0 x x – 10 x x DensityKg/m Radiation Length mm Thermal Conductivity W/m. K – – – Electrical Resistivity Ohm. m – x >10 12 See note10 12 Max. Use Temperatur e ºC Melts at ~2400 ºC Tensile Strength MPa >300 Compressive Strength MPa > Elastic Modulus GPa –

Prototype Target Wheel Experiment Aim to construct and test a prototype to establish the mechanical stability of the target wheel assembly in the field of a strong magnet (fixed field). Does not include internal water-cooling channels. Does not include vacuum vessel or vacuum conditions. Due to begin assembly of wheel at DL in Summer ’07. Commissioning and balancing of the prototype wheel should be complete September ’07. Experiment scheduled to finish May ’08. Will benchmark eddy current and rotordynamic simulations. Can we reduce the effective conductivity of the target rim? Envisaged as the first stage of a series of prototypes…depending on funding.

Prototype 1 Design Mechanical stability and eddy current tests Sectional view 1m diameter Ti6%Al4%V wheel with slightly simplified structure compared to current baseline target wheel. Prototype consistent with baseline vacuum feedthrough and water cooling designs. Motor being sized for angular velocities up to ~2000rpm. Construction at DL scheduled to be complete in August Expect eddy current power losses up to ~30kW in ~1.5T magnetic field.

Prototype Target Wheel with Belt Drive K. Davies, DL Shows vacuum feedthroughs replaced with cheaper (and stiffer) Plummer block assemblies. It has not yet been decided whether to use a direct-drive or belt-drive motor. Instrumentation includes: torque sensor, remote temperature gauges and accelerometers. Equilibrium temperature of wheel in air using 1.5T field at 2000rpm ~ 500K !

Summary and Future Activities Thermal + structural Updated studies underway at LLNL Larger beam spot may relax constraints on wheel speed Rotordynamics Ongoing studies for both prototype wheel and baseline design Capture optics effects / eddy currents Need to resolve mismatch between RAL and ANL results. Simulations of pulsed magnets and CARMEN simulation of spoke effects are expected soon. SIMULATIONS Activation and radiation damage Ongoing work at DESY, LLNL and DL. Need to know effective dose rates ~1 hour to ~1 day after beam shutdown. Analysis of T489 results expected in next few months.

Remote-handling design Current vertical r.h. design will be written up as a report Summer ‘07 Essential that remote-handling design evolves in parallel with target design. Little UK funding available to fund this activity at RAL for the coming financial year. Summary and Future Activities (2) Target Prototyping Design for prototype to measure eddy current effects in target rim is well-advanced. Solutions need to be found to keep the magnet cool when operating at high field (radiative and conductive heating of pole caps). Experiment should be taking data in Autumn ’07. Many tools have been developed for analysing the baseline target. An integrated approach to target development across the POSIPOL community would be welcome!