COMETSuperconducting
MagnetMakoto YOSHIDA (KEK/JPARC Cryogenics Section)
Sep.09, 2022 OHO221

Contents◼ COMET experiment◼ Superconducting Magnet for COMET◼ Radiation effects in Magnet Materials

2Lepton Flavor Mixing
Neutrino Oscillation

Charged Lepton Mixing(No evidence so far)eW-nemMuon decay in Beyond SMnm
Muon decay in SMSearches for Charged
Lepton Mixing
Lepton flavor violation→ Beyond standard model◼ Muon plays importantrole in the searches◼

SINDRUMII(2006)

 Low mass → High statistics

MEG(2016)

 Long life → easy to handle

L.Calibbi and G. Signorelli (2017)m → e g<4.2x10-13(MEG2016)m N → e N
1/400 (Al) of m → e g
Awaiting searches for Br<10-16

Goal ofCOMET/Mu2e

The COMET
Experiment

nucleusnuclear muon capturem - + (A, Z) → n m + (A,Z - 1)

stopping m- → Muonicatom◼

(→ eN )) ((mmNN →nN  )mdecay in orbit

m - → e -nn

m→e conversion
m - + (A, Z) → e - + (A,Z )B m - N → e- N =Detect monoenergetic electronsfrom m-e conversion
Physics Reach: Br<10-16 （PhaseII)<10-14 （PhaseI)→ 2x1018 muon stops→ 1011 m-/sec5

COMET at J-PARC◼
◼

◼

Pulsedprotonbeam

J-PARC E21
Pulsed proton beam
at 8GeV from Main
Ring
New muon beamline
is under construction
at HadronExperimental Facility

6

Muon Source◼
◼

◼

Inject protons on target
Trap secondary particles bymagnetic field
Transport pions, muons inlong solenoidmTransport
SolenoidpCapture
Solenoid

Solenoid Focus•charged particles in gradedsolenoid field are focused forwardp𝑡p𝑙𝜋 − → 𝜇 − + 𝜈𝜇p𝑡p𝑙p2𝑡 ൗ𝐵 ∝ p𝑡 × R = const.

BrFgraded B field
7

High Intensity Muon Source◼

Large aperture and strong magnetic
field to capture p,mD-line(50mSr)

 Radiation from production target◼

Long solenoid to decay p, transport mradiation shield

MuSIC

f1300

DC muon source@RCNP
f900 Cryogen-free magnets

COMETpion production
targetMu2e◼400W proton beam (100W on target)~f1600◼pion capture system◼~3x108 m+/s, ~108 m-/sa Neutrino Factory
f2400

Normal conducting solenoidpulsed beam
SuperOmega 1MW(50kW(5%) on target)◼

U-line@J-PARC MLF
f380◼400mSr◼~4x108 m+/s, ~107 m-/s

Superconducting Curved Solenoid

H.K. Sayed, Nufact12

Goal: 1011 m-/sec
Requirements on COMET muon beamline
1. Large acceptance to collect pions from production target
・High field on pion production target
・Graded field to focus pions forward

2. Reduce pion contamination / high energy muons・Long solenoids from production to muon stopping target
・Curved solenoid to select momentum / charge
3. Large signal acceptance. Reduce decay-in-orbit BG
・Graded field on muon stopping target
・Curved solenoid to select 105MeV/c electrons
9COMET Magnet(Phase2)
◼

5T3T
1T

Pion Capture Solenoid 5T High field on Target

 Tungsten shield inside◼

Muon Transport Solenoid 3T curved solenoid
 Correction dipole 0.03T~0.06T◼

Stopping Target Solenoid 3T→1T graded field◼

SpectrometerSolenoid

DetectorSolenoid

radiation shieldpion productiontarget

Muon TransportSolenoid

Spectrometer Solenoid 1T curved solenoid◼

Detector Solenoid 1T curved solenoid

Pion Capture Solenoid

10COMET Superconducting Magnet System

Staging ApproachPhase-I••••

3.2kW proton beam (8GeVx0.4mA)
Sensitivity Br<10-14
Graphite target
Pion Capture Solenoid + 90deg curvedsolenoid• Cylindrical drift chamber + trigger
hodoscope• Physics run will be in FY2024

graphite target
Pion Capture
Solenoid

Muon Transport
Solenoid

Muon Stopping
TargetCDC

Detector
Solenoid

Phase-II
Muon Stopping
TargetTungsten alloy
targetSpectrometer
Solenoid

Pion Capture
Solenoid

Muon Transport
Solenoid
Detector
Solenoid••••

56kW proton beam (8GeVx7mA)
Sensitivity Br<10-16
Tungsten alloy target
Pion Capture Solenoid + 180deg curved
solenoid + Spectrometer Solenoid• Straw tracker + calorimeter

Straw tracker/ Calorimeter

11

COMET Magnet
System (Phase-I)
PowerSupply

CurrentLeadBox
TransferTube
to MTS

ColdBoxTransferTube
to PCS

Pion Capture
Solenoid (PCS)

Detector
Solenoid

Muon Transport
Solenoid (MTS)COMET Pion Capture Solenoid
Superconducting
Solenoid Coils of
Al-stabilized Conductor
Support Shell ofForged Aluminum Alloy

Production Target
Radiation
ShieldNuclear Heating : >100W
Peak dose rate in Al : ~1MGy
Neutron fluence : >1021 n/m2

Key Issues
on PCSMARS2010+nuc.lib.

◼ Radiation tolerance ofmagnet materials isimportant◼ Organic material
 Insulation, structure Strength Out gas

Peak: 3~5x1021 n/m2

◼ Metal Cooling path, stabilizer Electrical conduction
 Thermal conduction◼ Radioactivation of He1026

1024

1022

1020

1018

1016

1014

1012

1010
14n/m2

Aluminum-stabilized
Superconducting Cable◼

Developed for detector
solenoids needs transparency forparticles◼

◼

Small nuclear interaction
cross section→ Small internal heating

◼

◼

◼
◼
◼

Size: 4.7x15mm
Yield strength@4K: >85MPa
RRR@0T: >500
Al/Cu/SC: 7.3/0.9/1
14 SC strands: 1.15mm dia.

Low residual resistivity

COMET CS stabilizing
 quench protection◼

High-strength Doping additives
 Hardened by cold work

100K 150K
15

Coil Structure (PionCapture Solenoid)◼

Aluminum stabilized SC cable◼
◼

for less nuclear heating (max. 35mW/kg)

Radiation resistant insulator, resin
Pure aluminum strips in between layers
to cool down a coil inside

CS coil structure

Al stabilized SC cable◼
Size: 4.7x15mm◼
Offset yield point of Al@4K:>85MPa◼
RRR@0T: >500◼
Al/Cu/SC: 7.3/0.9/1◼
14 SC strands: 1.15mm dia.

16

Coldmass Fabrication Support shell of forged A5083

heat curing
Impregnation with BT+Expoxy

CS coldmass

Wet winding with BT+Epoxy resin

CS thermal shieldCoil Temperature during BeamOperation◼
◼

◼
◼

Coils in Pion Capture Solenoid will beheat up by irradiation (max. 35mW/kg)
Peak temperature in coils is estimatedassuming irradiation by 56kW beam
operation
Temperature will rise as thermal
conductivity degrades by irradiation
Irradiation damage in aluminum can berecovered perfectly by thermal cycling toroom temperature.

Y. Yang et al., IEEE Trans. App. Supercond., 28(3), 4001405 (2018).

Tcs

Effects of Stabilizer
Degradation◼ RRR of stabilizer

will

decrease byirradiation.
◼ Temperature atquench is estimatedwith MIITs
 adiabatic condition

19

Simulation of Temperature Rise at
QuenchY. Yang et al., IEEE Trans. App. Supercond., 28(3), 4001405 (2018).

Muon Transport Solenoid
dipole3m◼ 3T toroidal field◼ Solenoid + correction◼ Cu-stabilized SC wire
 1.5mm dia. (w/o insulation) Cu/NbTi=6phase LHe pipeDipole468◼ Indirect cooling with 2-200

SolenoidElement coil◼ Muon beam duct / radiation

shield at 60K

 t10mm of SUS
21

Muon TransportSolenoid◼ Curved solenoid withcorrection dipole

Magnet already delivered at J-PARC.

Design Parameters of Transport Solenoid
Conductor
Cable dimensions(Solenoids)
Cable dimensions(Dipole coils)
Cable insulation

Magnet length
Curvature Radius
Num. of solenoid coils
Num. of dipole coils
Operation current
Field on axis
Stored energy
Total inductance
Coil inner diameter
Refrigeration
Quench protection

NbTi/Cu monolith wire
Cu/NbTi = 6f1.5 mm (without insulation)
f1.56 mm (with insulation)
f1.2 mm (without insulation)
f1.3 mm (with insulation)
Polyamide-imide enamel (AIW),PVF (TS2-15,16, TS3)
~6 meters
3 meters
1816 pairs
210 A (solenoids)
175 A (dipole coils)~3 T (solenoid)~0.056 T (dipole)
5.6 MJ
254 H
468 mm (TS2a~TS2-16)
600 mm (TS3)conduction from forced flow 2-phase
LHe piping (7~10 g/s)
semi-active quench back heater22Trajectory in Curved
Solenoid

Rss/R : bending angle

D

Bs=3T
Curvature R

D=1 𝑠𝑞𝐵 𝑅𝑝
2

cos 𝜃 +

1cos 𝜃High B

Low B

Bcomp=0.04T
Bs=3T
1 𝑝
B𝑐𝑜𝑚𝑝 =𝑞𝑅 2

1cos 𝜃 +cos 𝜃DsBs
Bcomp =Bs x D/s

23

Detector Solenoid
for phase1

1800mm

3320mm
CDCmuonstoppingtarget

muon beam◼ 1 Tesla on the muon

stopping target◼ Large aperture for CDC
and trigger hodoscope◼ Cyogen-free magnet

Bridge Solenoid
Detector Solenoid

φ 2188

 Cooled by 3 cryocoolers

DS coil24

Irradiation Effects in MagnetgMaterials◼ Organic polymer

ionizing radiation

 Insulator
 GFRPn Adhesive Impregnation◼ Pure metal

nuclear interaction

 Stabilizer Thermal conductor
25

Insulator, Resin◼ Need radiation hardness

above 10 MGy epoxy degradation ~1MGy◼ Polyimide◼ Bismaleimide-Triazine◼ MGC BT3309T, BT2160, …
 Applied in J-PARC

accelerator magnet, SuperOmega, etc.

◼ Cyanate ester Applied in ETER

Fabian and Hooker et. al., presented at “HHH-AMT, Topical Meetingon Insulation and Impregnation Technologies for Magnets”

26

Irradiation Tests of GFRPs◼ BT-based GFRP

has excellent
performance.

Flexural strength test w/ G10 sample irradiated at
30 MGy. Delamination of glass sheets is observed.

A. Idesaki et al. / Fusion Engineering and Design 112 (2016) 418–424

27

Irradiation Test on Thermal
Conductivity of Insulation

Y. Yang et al., Cryogenics, 89, 107-112 (2018).

Superconductor◼

NbTi
 No degradation up to 1022n/m2

◼

ReBCO
 Discussed in the next talkAdv. Cryo. Eng., 32, p853 (1986)

29
J. Nucl. Materials, 108&109, p572 (1982)

Irradiation Effects
in Pure Metal◼

Stabilizer
◼

Thermal conductor◼

Aluminum alloy
CopperPure aluminum
CopperAluminum alloy◼

Fast-neutron irradiation induces
defects in metal.

◼

Defects could be accumulated at
Low temperature,and causes degradation ofelectrical/thermal conductivity◼

Thermo sensor
drift at high neutron fluence◼

Problems inQuench protection, Stability
Cooling

COMET CS

LHC Project Report 209

100K 150K

J.A. Horak and T.H. Blewitt, J. Nucl. Materials, Vol. 49 (1973) p161

Pure Metal
Degradation byReactor Neutrons◼

fast neutrons >~0.1MeV

Irradiation damage can berecovered by annealing.
◼

Aluminum

Electrical resistivity increase withreactor neutrons◼

Recovery after irradiation
2x1022 n/m2 (E>0.1MeV)

perfect recovery in Al

Effect of impurity and strain?
CopperM. Nakagawa, K. Boning, P. Rosner, and G. Vogl, Phys. Rev. B 16, pp. 5285-5302 (1977)31

Low Temperature
Irradiation Facility◼
◼
◼
◼

Kyoto Univ. Research Reactor
Institute
5MW max. thermal power
Cryostat close to reactor coreSample cool down by He gasloop
 10K – 20K◼

[2][2] M. Okada et al., NIM A463 (2001) pp213-219

reactorFast neutron flux(>0.1MeV)
 1.4x1015 n/m2/s@1MW thermal

powerCryogenics
0.1MeVKUR-TR287 (1987)

Irradiation Sample◼

EDM cut from aluminum-stabilized SC cable
1mmx1mmx70mm (45mm Vtap)
Al-CuMg
◼




OFHC

5N Al + 0.2%Y with 10% cold work (RRR~330-360)

Al-Ni
◼

5N Al + 0.1%Ni with 10% cold work (RRR~560)

Copper

OFHC for SC wire, provided by Hitachi Cable Ltd.
f1mm x 50mm (35mm Vtap)
RRR~300

5N aluminum◼

5N Al + Cu(20ppm) + Mg(40ppm) with 10% cold work (RRR~450)

Al-Y
◼

◼

Al-Y

Aluminum alloy◼

Wire EDM

provided by Sumitomo Chemical
f1mm x 50mm (32mm Vtap)
RRR~3000

Thermometer

CERNOX CX-1050-SD, CX-1070-SD
Thermocouple (AuFe+Chromel)

2014AprIrradiation / Annealing Effect inElectrical Resistance
0.18

0.16
0.14

Al-Y1
Al-Y2
Al-Ni
Cu

0.12
0.10
0.08
0.06
0.04

0.02

4.50E-06
Sample Resistance (Ohm)Resistivity at Cryogenic Temperature (nWm)

5.00E-06

4.00E-06

3.50E-06

3.00E-06

2.83mW2.78mW

2.50E-06

0.00

Before After Before After Before After Before After After2011 2011 2012 2012 2013 2013 2014 2014 2014
irrad. irrad. irrad. irrad. irrad. irrad. irrad. irrad. anneal

Y1-2012
Y2-2012
Cu-2012
Y1-2011
Y2-2011
Cu-2011
Y2-2013
Cu-2013

2.00E-06
8.0

2.61mW

13.0

18.0

23.0

28.0

AuFe Thermocouple Temp. (K)• Al: 0.03 nOhm.m for 1020 n/m2
• Cu: 0.01 nOhm.m for 1020 n/m2
• All Al samples show “full” recovery of electrical resistivity afterthermal cycle to RT.
“Repetitive Irradiation Tests at Cryogenic Temperature by Neutrons and Protons on Stabilizer
Materials of Superconductor,“ M. Yoshida et al., IEEE Trans. Appl. Supercond, 32(6), 7100405(2022); doi:10.1109/TASC.2022.3178944

Proton irradiation test at J-PARC
sample• 3GeV-30GeV proton
beam from MR•Newly installed in 2019

Material andLife Science
FacilityNeutrino
Facility

MR
LinacRCS
Abort Dump

• Pure metal wire cooled byGM cryocooler• Sample can be inserted tothe beam line on demand.
• remote handling35

3.7E-05

4.8E-05

ThermalshieldResistance Al (W)

低温照射実験

3.6E-05

4.7E-05Cu
1.31 mW

3.5E-05

4.6E-05Al
3.4E-05

0.38 mW

Cold head
3.3E-05

4.5E-05

Resistance Cu (W)Beam ON

4.4E-05

-20.0

0.0

20.0

40.0

60.0

80.0 100.0 120.0 140.0

Time (min)Aluminum
Extension
Rod1020 mm

CERNOX
sensorSampleVoltagesense wire

AlCuW

purity>99.99%99.995%99.95%

RRR
58030628

shapewireφ0.25mm
wireφ0.25mm
wireφ0.25mm◼
◼

◼

Pure aluminum and copper wasirradiated by 8GeV and 30GeV protons
Damage rate is reproduced bysimulation with extensive MolecularDynamics (arc-dpa model)
Recovery was observed
Could be perfect even in Cu in this high energy
range“Repetitive Irradiation Tests at Cryogenic Temperature by Neutrons and Protons on Stabilizer
Materials of Superconductor,“ M. Yoshida et al., IEEE Trans. Appl. Supercond, 32(6), 7100405(2022); doi:10.1109/TASC.2022.3178944

36

Summary◼ Superconducting muon beamline forCOMET phase1 is under construction◼ Radiation-tolerant superconducting
solenoid, Pion Capture Solenoid, isdeveloped and under fabrication.
◼ Radiation effects in magnet materials areinvestigated.
37