T2K Target status PASI Meeting Fermilab 11 th November Chris Densham STFC Rutherford Appleton Laboratory On behalf of the T2K beam collaboration

Breakthrough Prize in Fundamental Physics awarded to Professor Koichiro Nishikawa on behalf of the K2K and T2K Collaborations for the achievements of K2K and T2K $3M prize shared with Kamland, Daya-Bay, Super-Kamiokande and SNO experiments

Chris Densham HINT 15 October 20153

Pacific 30 GeV PS 3 GeV PS 400 MeV LINAC T2K neutrino facility T2K Target Station 295 km to Super-Kamiokande Near detector MLF Beam dump

T2K operational history

T2K Secondary Beam-line 110m Muon Monitor Target station Beam window Decay Volume Hadron absorber Target Station, Decay Volume and Beam Dump all enclosed in large water-cooled steel helium vessel. –He atmosphere prevents nitrogen oxide (NO x ) production / oxidization of apparatus. Beam dump and vessel walls cooled by water circuits. –Maintenance is not possible after beam operation due to activation. –Radiation shielding / cooling capacity were designed for ~4MW beam.

T2K Secondary Beam-line Baffle 1st horn Target 2nd horn 3rd horn BEAM Iron shield (2.2m) Concrete Blocks Helium Vessel Muon Monitor Target station Beam window Decay Volume Hadron absorber

Horn & target system in Target Station m 10.6m Baffle Graphite Collimator Horn-1 Horn-2 Horn-3 Beam window Ti-alloy DV collimator Large flange, sealed with Al plates, t= 120mm 1.0m Concrete blocks Water-cooled iron cast blocks 29pcs. total 470t Support Module 2.3m Horns / baffle supported within vessel by support modules. Apparatus in beam-line highly irradiated after beam. Remote maintenance required. Service Pit maintenance area OTR Target Beam

Horn transfer from beamline to remote maintenance area Handling machine for horns Horn and target Guide cell on the maintenance area Horn support module Guide cell on helium vessel

Target exchange system Target & horn Helium cooled graphite rod Design beam power: 750 kW Beam power so far: 330 kW 3% beam power deposited in target 1 st target & horn replaced after 4 years, 6.5e20 p.o.t. 2 nd target being repaired after 5 e20 p.o.t. π π p

Inspection of target/horn in Remote Maintenance Area Cracked ceramic break diagnosed Not a real technical problem (inside helium vessel) Currently working on pipe replacement Known issue with diffusion bonded ceramic-to-stainless joint has been fixed

Plan for remote replacement of helium pipe

Inlet pressure = 1.45 bar (gauge) Pressure drop = bar Need higher pressure helium for higher powers Helium cooling velocity streamlines Maximum velocity = 398 m/s Current target – helium cooled solid graphite rod Designed for old parameters of MR 750kW beam: cycle: 2.1s, PPP: 3.3x10 14 Present expected parameters: Doubled rep-rate, MR cycle: 1.3 s, PPP: 2.0x10 14 Stress wave amplitude decreased by 40% -> What is maximum beam power possible for this design?

Effect of pulsed beam on T2K target Inertial ‘violin modes’ P. Loveridge Stress distribution after off-centre beam spill Radial stress waves – on centre beam spill 8 MPa 0.5 µs beam spill p

Stress wave magnitude determined by t spill <t oscillation period

Fast neutron radiation damage data for graphite (IG 110, similar to IG 43) Max temperature 736ºC assuming reduction in thermal conductivity by 75%

Beam Window Separates He vessel from vacuum in primary line with pillow seals Double skin of 0.3mm thick Ti-6Al-4V, cooled by He gas (0.8g/s) 300  C/200MPa, Safety factor 2 for 750kW(3.3x10 14 ) ~ Safer for 750kW(2.0x10 14 ) Reduction of Ductility reported with 0.24DPA 6x10 20 pot≈1DPA?: Replacement cycle should be considered. Same window in front of Target, Same material with OTR, SSEM 17

Pulsed beam tolerance for candidate window materials where ‘Thermal stress resistance’, UTS – ultimate tensile strength α – coefficient of thermal expansion E – Young’s modulus ΔT – temperature jump EDD – energy deposition density Cp – specific heat capacity NOTE: ΔT depends on material density as well as specific heat capacity, so these are also important variables.

ANSYS static (time-averaged) stress UTS Ti-6Al-4V ≈ 1GPa NOTE: 100W/m 2 K heat transfer coefficient applied to internal wall

Effects of elevated temperature, fatigue and radiation damage on beam window U.T.S. Safety Factor N. Simos (BNL) 8.9x10 20 pot ~ 1.5 dpa 0.24 dpa Significant loss of ductility at 0.24 dpa Now likely to be entirely brittle at 1.5 dpa Does it matter? Low stress at moment 320 kW 750 kW

New collaboration led by P. Hurh on accelerator target materials as part of Proton Accelerators for Science & Innovation (PASI) initiative. Key objectives: Introduce materials scientists with expertise in radiation damage to accelerator targets community Apply expertise to target and beam window issues Co-ordinate in-beam experiments and post- irradiation examination 12 members signed MoU – more welcome 21