T2K Target and Beam Window Upgrades for 1.3 MW Operation Chris - PowerPoint PPT Presentation

T2K Target and Beam Window Upgrades for 1.3 MW Operation Chris Densham , Mike Fitton (STFC Rutherford Appleton Laboratory) T. Nakadaira, T. Ishida, M. Tada, T. Sekiguchi (KEK Beam Group) A.Wilkinson, J. Gong (Oxford University Materials Science) P.Hurh (Fermilab, RaDIATE collaboration) 1

T2K Target & horn Next target under construction Helium cooled graphite rod • Design beam power: 750 kW • Beam power so far: 435 kW • 3% beam power deposited in • target as heat 1 st target & horn replaced after • 4 years, 6.5e20 p.o.t. 2 nd target OK after 2.2 e21 p.o.t. •

Beam and Window Parameters 750 kW 1.3MW Design T2KII path Beam Energy [Gev] 30 30 Protons per spill [-] 3.30E+14 3.20E+14 Energy deposited per kg per [J/kg/proto 2.52E-10 2.52E-10 proton n] Energy deposited per kg per [J/kg/pulse] 83300 80640 pulse Cycle time [s] 2.1 1.16 Spill length [s] 4.13E-06 4.11E-06 Number of bunches [-] 8 8 Bunch length [ns] 58 40 Gap length [ns] 523 541 Peak Heat Generation [J/m^3/s] 8.15E+14 1.14E+15 Beam sigma [mm] 4.24 4.24 Heat load per spill [J/cc/pulse] 378.18 366.11 Heat load per sec [W/cc] 180.09 315.61 Peak Temp per bunch [C] 19.78 19.15 Thermal stress per bunch [MPa] 61.27 59.32 Peak Temp per pulse [C] 158.27 153.22 3

1.3 MW beam window and target studies • Q: Can we push existing beam window and target design from 0.75 -> 1.3 MW? • Q: If so, what changes are needed for target and beam window materials, design, manufacture, and helium plant (pressure/flow rate)? • What is expected lifetime for upgraded target and, more crucially, beam window? 4

Target upgrade status • The increase in beam power from 0.75  1.3MW will increase the integrated heat load on the target (approx. 23kW  41kW). • Just increasing the flowrate will lead to very high velocities and pressure drops (current velocities already exceed 460m/s). • It is proposed that the helium cooling systems operating pressure is increased to reduce velocities and pressure drops. Increasing the pressure will increase the helium density and therefore • heat transfer coefficient. Higher operating pressure has the advantage of reduced pressure drop. • Running at higher pressure reduces the pressure drop and max velocity • Compressor will be cheaper to purchase and operate (less power • consumed).

CFX model heat inputs (MARS)

Potential solution for 1.3 MW operation → 5 bar helium 0.75 MW 1.3 MW Heat load 23.5 kW 40.8 kW Helium pressure 1.6 bar 5 bar Helium mass flow 32 g/s 60 g/s Pressure drop 0.83 bar 0.88 bar • Velocity contours ‐> max 400 m/s ( OK for helium ) 7

Conjugate Heat Transfer analysis Increased beam power, flow rate & pressure • 60g/s helium, 5barG outlet pressure – 1.3MW beam power Helium velocity flow lines

Thermal analysis for 1.3 MW operation Reduction in 0.75 MW 1.3 MW thermal Helium pressure 1.6 bar 5 bar conductivity(from US window temp 105 °C 157 °C fast neutrons) DS window temp 120°C 130°C 900 ° C It’s better Max graphite temp. 736°C 900°C 600 ° C hot (for 1/4 conductivity) 400 ° C Some iterating still to do Thermal analysis assuming x4 reduction in thermal conductivity 9

Pressure on upstream window (0.5 mm) • Pressure stress and deformation in current beam window (Ansys) • 5 bar pressure inside of target (proposed operating pressure) Stress in thin dome section agree with hand calculations (10.13MPa @ 1.6bar, 0.5mm) Max stress  75MPa

Reducing pressure stresses in upstream window at 5 bar • A parameterised model of the window has been optimized using a genetic algorithm. • Pressure stress can be halved from 75 -> 34 MPa by increasing outer plate thickness from 7 -> 10 mm • Window thickness remains unchanged at 0.5mm thick. Parameter ranges (limits) Current design (75MPa) Optimum found (34MPa) Plate thickness = 10mm External radius = 7mm Internal radius = 25mm

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

The ultimate destiny for all graphite targets? (T2K: c.2 x 10 21 p/cm 2 so far) NuMI target LAMPF fluence 10^22 p/cm2 PSI: fluence 10^22 p/cm2

Remote Target Exchange System Target exchanger and manipulator system 14

Helium cooling pipe ceramic development • New bolted design for ceramic isolator, metal seals – To make more resilient to thermal cycling Helium temperature cycle for 0 → 380 kW Ti brazed to ceramic

T2K beam window upgrade plans for - 1.3 MW Helium flow lines • Strong 1.3 MW beam • recirculation zones (steady state/CW driven by high simulation) speed jet Pressure drop 0.06bar @ 1.1g/s Max velocity 230 m/s 16

Through-thickness Stress Waves in Beam Window • Constructive interference of bunch structure (8 bunches) possible in existing 0.3 mm window. • For 0.3 mm window, the stress wave travels from one surface to the other and back in ~100 ns  10 MHz stress cycle • 0.32 mm  Peak stress in Z = ~20 MPa • 0.30 mm  Peak stress in Z = ~ 270 MPa 300 0.7 mm 0.5 mm 0.3 mm 200 100 SZ [MPa] 0 ‐100 ‐200 Comparison of stress in Z (through window stress) as function of time at window centre (max stress point) for 0.3, 0.5 and 0.7 mm thick windows @ 1.3 MW ‐300 0 1000 2000 3000 4000 5000 6000 Time [ns] 17

Beam Window Stress Wave Analysis 450 Equivalent Stress Z Stress X Stress 400 1.3 MW 350 300 Stress [MPa] 250 200 150 100 50 0 -50 -100 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 Window thickness [mm] NB. SZ = through-thickness stress SX = radial stress Current window Proposed upgrade 0.5 mm also good thickness window thickness - But more tolerance = 0.4 ± 0.05 mm activation, higher - too tight - much better heat load c. 0.01 mm tolerance for - Good for target manufacture window upgrade 18

Next beam window (update) 100 MPa Stress at end of 8 th bunch Stress increasing from thermal expansion Reflected radial wave from free (conduction) surface (simplified geometry) 10MHz through thickness oscillation, approx. 2.7MPa Bunch-to-bunch stress amplitude ~20MPa 750kW, 0.5mm thick Ti-6Al-4V window, long duration transient analysis

Transient Analysis – 750kW • New proposed beam parameters: • 2.0 x 10 14 ppp @ 1.28 s rep rate (750 kW) • HTC = 886 W/m 2 .K@ 300 K • Results summary: Quasi-static Peak Peak ± stress Thickness average temp stress limits [mm] stress [K] [MPa] [MPa] [MPa] 0.3 418.7 56.1 32.2 23.9 0.4 436.8 71.2 44.8 26.4 0.5 442.2 79.5 50.9 28.6 0.7 463.5 95.2 65.5 29.7 20

Effects of elevated temperature, fatigue and radiation damage on beam window 0.24 dpa Current window 22.4x10 20 pot  4.5 dpa (c/o T.Davenne) N. Simos (BNL) 1.3 MW, 0.5 mm 0.75 MW, 0.3 mm Significant loss of ductility at 0.24 DPA Existing window entirely brittle? Does it matter? Low stress at moment. Time to ask the materials scientists… RaDIATE 21

Next (or not) beam windows • Domes made from Ti-6Al-4V ELI (Grade 23) • Plate used instead of bar – maybe better properties at centre (or not?) • Spare material used for material characterisation.

Electron Back‐Scatter Diffraction Characterises microstructure of crystalline materials NB Following figures show grain orientations in through-thickness direction (of beam window)

• Plate: fine grains but large EBSD: 2” thick grade 23 plate macrozones (= regions with similar crystal orientations inherited from large prior beta grains). • Microstructure not as refined as it first appears. • The effective structural unit size may be much larger than it initially appears • Could impact badly on fatigue 100 µm properties. • Larger grains but less texture, EBSD: Centre of 8” dia. bar macrozones less evident in the bar • Current window (from bar) has performed well so far • Recommend staying with bar • Irradiation samples taken from 200 mm (8”) diameter bar Department of Materials 100 µm University of Oxford AJW 2016

Centre ‘pip’ taken for SEM, EBSD • 6 x 0.3 mm thick discs machined from same 8” Ti-6Al-4V bar purchased for next T2K window domes • 2 x sample foils polished to 0.25 mm and laser cut using very fine scanning laser • Foils installed at BNL/BLIP for 10 weeks irradiation at c.180 MeV, c.1 DPA Irradiation starting tomorrow

Measurement of deflection during resonant vibration (Oxford Univ. materials) Need to operate near but not on resonant frequency (c.20kHz) to Movement of generate stress range beam due to ‐> need to measure amplitude deflection Input laser beam 160 mm Specular Reflection ~0.65 ° Tresca stress 3 mm Plan to reproduce test Department of Materials equipment at Culham lab. for University of Oxford active samples testing Chris Densham AJW 2016

Ti-6Al-4V Fatigue Life Data from Lutjering & Gysler Titanium Science and Technology Department of Materials University of Oxford AJW 2016