COMET Target Design(COherent Muon to Electron Transition)

Satoshi MIHARA

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 beamProductiontarget

πμMuon stopping target

Electron spectrometer

proton pulse

prompt background

muon decay

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+

104MeV/cPhase I0.03 BG expectedin 1.5x106 sec running time

10/Sep/2013 Satoshi MIHARA, PSI2013 3

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)

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

Radiation cooled tungsten (Phase I)

Values used in simulations

(not necessarily COMET baseline)

Beam power 3.2 kW

Target heat load 194 W

Target radius 4 mm

Beam radius rms 1 mm

Tungsten emissivity

0.3

TemperatureMax = 1298°C

Von Mises stressMax = 3.56 MPa

Phase II: How about helium cooling?Values used in simulations

(preliminary)

Beam power 56 kW

Target heat load 3.4 kW

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

TemperatureMax = 921°C

Von Mises stressMax = 63 MPa

NB effect of beam cycle not included:1/3 duty factor -> x3 higher stress!

Tungsten yield strength

CW operation

Outline layout for annular cooling of target

Coolant streamlines

Effect of off-centre beamTemperature profile for beam displacement of 2σ

Deformation from beam displacement of 2σ

Maximum displacement = 0.07 mm

温度分布（空冷）・銅の外周 (φ1200) ： 5 W/m2K@30℃・タングステンコアの外周 (φ700): 5 W/m2K@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？

許容できる！

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/m2K@35℃・タングステンコアの外周 (φ700): 250 W/m2K@35℃