COMET Target Design COherent Muon to Electron Transition

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

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

COMET Experiment • Mu-e conversion search • COMET Target group – Charged lepton flavor

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

COMET Staging Approach • • Phase I – Beam background study and achieving an

COMET Staging Approach • • Phase I – Beam background study and achieving an intermediate sensitivity of <10 -14 • 8 Ge. V, ~3. 2 k. W, ~3 weeks of DAQ • 2016 -2017 Phase II – 8 Ge. V, ~56 k. W, 1 year DAQ to achieve the COMET final goal of < 10 -16 sensitivity Phase II • Starts around 2019 -2020 μ- μ+ Phase I 104 Me. V/c 0. 03 BG expected in 1. 5 x 106 sec running time 10/Sep/2013 Satoshi MIHARA, PSI 2013 3

Beam Power • Phase I – 8 Ge. V, 3. 2 k. W –

Beam Power • Phase I – 8 Ge. V, 3. 2 k. W – # of protons per MR bunch equivalent to that of 3. 2 x(30/8)x 2 = 24 k. W operation at 30 Ge. V • Phase II – 8 Ge. V, 56 k. W – Faster repetition cycle is necessary (1. 47 sec)

Production Target • Phase I (Radiation cooling) – Graphite • Refractory material and so

Production Target • Phase I (Radiation cooling) – Graphite • Refractory material and so is tolerant to high temperature operation • Experience in T 2 K – 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

Radiation cooled tungsten (Phase I) Values used in simulations (not necessarily COMET baseline) Beam

Radiation cooled tungsten (Phase I) Values used in simulations (not necessarily COMET baseline) Beam power 3. 2 k. W Target heat load 194 W Target radius 4 mm Beam radius rms 1 mm Tungsten emissivity 0. 3 Temperature Max = 1298°C Von Mises stress Max = 3. 56 MPa

Phase II: How about helium cooling? Values used in simulations (preliminary) Beam power 56

Phase II: How about helium cooling? Values used in simulations (preliminary) Beam power 56 k. W Target heat load 3. 4 k. W Target radius 4 mm Beam size rms 1 mm Helium annulus thickness 1 mm Helium inlet pressure 8 bar Helium mass flow 5 g/s NB effect of beam cycle not included: 1/3 duty factor -> x 3 higher stress! Temperature Max = 921°C Von Mises stress Max = 63 MPa

Tungsten yield strength CW operation

Tungsten yield strength CW operation

Outline layout for annular cooling of target Coolant streamlines

Outline layout for annular cooling of target Coolant streamlines

Effect of off-centre beam Temperature profile for beam displacement of 2σ Deformation from beam

Effect of off-centre beam Temperature profile for beam displacement of 2σ Deformation from beam displacement of 2σ Maximum displacement = 0. 07 mm