1. COMET Target Design (COherent Muon to Electron Transition) Satoshi MIHARA

2. COMET Experiment Mu-e conversion search – Charged lepton flavor violation – GUT, ν mass origin COMET Target group – RAL Chris Densham Peter Loveridge Tristan Davenne – KEK Makoto Yoshida Satoshi Mihara Proton beam Production target Production target πμπμ Muon stopping target Electron spectrometer proton pulse prompt background muon decay

3. COMET Staging Approach Phase I Phase II Phase I – Beam background study and achieving an intermediate sensitivity of <10 -14 8GeV, ~3.2kW, ~3 weeks of DAQ 2016-2017 Phase II – 8GeV, ~56 kW, 1 year DAQ to achieve the COMET final goal of < 10 -16 sensitivity Starts around 2019-2020 μ-μ- μ+μ+ 104MeV/c Phase I 0.03 BG expected in 1.5x10 6 sec running time 10/Sep/2013Satoshi MIHARA, PSI20133

4. Beam Power Phase I – 8 GeV, 3.2 kW – # of protons per MR bunch equivalent to that of 3.2x(30/8)x2 = 24kW operation at 30GeV Phase II – 8 GeV, 56 kW – Faster repetition cycle is necessary (1.47 sec)

5. Production Target Phase I (Radiation cooling) – Graphite Refractory material and so is tolerant to high temperature operation Experience in T2K – Tungsten Larger muon yield Radiation cooling may be OK but need careful assessment Phase II (Active cooling) – Tungsten Bad chemistry between tungsten and water Helium cooling instead of water cooling

10. Radiation cooled tungsten (Phase I) Values used in simulations (not necessarily COMET baseline) Beam power3.2 kW Target heat load194 W Target radius4 mm Beam radius rms1 mm Tungsten emissivity 0.3 Temperature Max = 1298°C Von Mises stress Max = 3.56 MPa

11. Phase II: How about helium cooling? Values used in simulations (preliminary) Beam power56 kW Target heat load3.4 kW Target radius4 mm Beam size rms1 mm Helium annulus thickness 1 mm Helium inlet pressure8 bar Helium mass flow5 g/s Temperature Max = 921°C Von Mises stress Max = 63 MPa NB effect of beam cycle not included: 1/3 duty factor -> x3 higher stress!

12. Tungsten yield strength CW operation

13. Outline layout for annular cooling of target Coolant streamlines

14. Effect of off-centre beam Temperature profile for beam displacement of 2σ Deformation from beam displacement of 2σ Maximum displacement = 0.07 mm

18. 温度分布（空冷） ・銅の外周 (φ1200) ： 5 W/m 2 K@30 ℃ ・タングステンコアの外周 (φ700): 5 W/m 2 K@30 ℃ - 冷却配管は Phase-I で内蔵させる。 冷却管内を Blower で空気を循環させたら？ 冷却管内を Blower で空気を循環させたら？ 許容できる！

19. 温度分布（水冷、 Phase-II ） ・シールド中心部： 38000 ℃  75 ℃ ・シールド外周部： 34000 ℃  42 ℃ ・真空容器： 30000 ℃  42 ℃ 冷却なし水冷 許容できる ? ・銅の外周 (φ1200) ： 1000 W/m 2 K@35 ℃ ・タングステンコアの外周 (φ700): 250 W/m 2 K@35 ℃