1. Overview of the mu2e magnet system2. Collaboration mu2e-COMET

R. Ostojic

Based on presentation of M. Lamm in ASC2010.All credit goes to the members of the mu2e magnet design team.

Measure the Rare Process: m- + N e- + N→ It will be world class experiment in the “Intensity

Frontier”…• 4 orders of magnitude improvement over

existing measurements• Judged by the US Department of Energy and the

High Energy Physics Community to be a high priority for Fermilab

→ …either with or without a signal….• WITH: Indicate new physics beyond the “standard

model”• WITHOUT: Put severe limits on theories beyond the

standard model• It will compliment Large Hadron Collider (LHC)

Experiments

2

What is mu2e?

3

Plan View of Solenoid System8 GeV P

•Production Solenoid

• 8 GeV P hit target. Reflect and focus p/m’s into muon transport

• Strong Axial Gradient Solenoid Field

• Sign/momentum Selection• Negative Axial Gradient in S.S. to

suppress trapped particles

•Transport Solenoid

• Graded field to collect conv. e-

• Uniform field for e- Spectrometer

•Detector Solenoid

24 meters

4

Tentative schedule

Start of Magnet Construction 2013

CD-2/3 Mid-2012

CD-1 Review March 1, 2011

CDR complete Jan. 15, 2011

Final cost & schedule and associated documentation.

Jan. 15, 2011

Director’s Design Review Nov. 1, 2010

CD-0 Nov, 2009

Time

Fermilab will act as a “General Contractor”: PS and DS will likely be built in industry

Need to develop a strong conceptual design and technical specifications for vendors

Final engineering design done by industry Similar strategy for most detector solenoids

TS will likely be designed/built “in house” Cryostat, mechanical supports built by outside vendors Coils wound in-house or industry depending on technology

choice Final assemble and test at Fermilab

Solenoid task has co-responsibility for all interfaces Significant magnet coupling between PS-TS and TS-DS Tight mechanical interfaces Cryoplant, power supplies, instrumentation…

5

Procurement strategy

6

Detector solenoid

Two functions:1. Axial Gradient Field for particle collection (2T1T)

Uniformity of axial gradient along axis: 5%2. Uniform field for spectrometer and calorimeter

Most like a HEP detector magnet but stricter field specs! ~3 meter high uniform field 0.2% request

Significant Axial Forces between Iron, DS and TS7

DS Challenges

Coils wound on separate mandrels, bussed in series, Iop ~5kA

Cold mass in “single cryostat” Use Al stabilized NbTi conductor

More experience with detector solenoid vendors Considerably less weight

Two layer coils throughout Achieve axial gradient by effectively changing winding density

by introducing spacers and varying conductor thickness. 8

DS Design Concept

9

DS 5-Coil Design

MECO(blue) field is overlapped on the field of this design(red)

Unusual field requirements “S”-shaped to reduce line of sight

PS to DS; momentum selection negative axial gradient in SS to

prevent trapped/out of time particles

Effect of magnetic coupling between TSn and PS/DS and S shape:

significant non-axial excitation forces

complicated stresses during cooldown

Removable TS3 to service collimator and vacuum break

10

Transport Solenoid Challenges

11

TS Design Concept

150

150

200

200

200

TS2/4 assembled using 3-coil modules

•Conductor in copper channel•Sections welded or bolted together•Coils bussed in series•I op ~1000 Amperes

12

Production Solenoid

Axially Graded Field: 5 T2.5 T ~5.7 T on conductor

Wide aperture 1.5 m, 4 m long Large stored energy (~100MJ)

There’s a target in the aperture…

25 kW off target, 25-50W into coils…depending on absorber design and beam intensity

Heat load and Radiation issues on conductor, insulator and stabilizers

Strong Magnetically Coupled with Iron and TS

Unlike typical detector solenoid significant axial forces >100 T of axial force

13

PS Challenges

• Gradient made by 3 axial coils same turn density but increase # of layers (2,3,4 layers)• Wound on individual bobbins

• Aluminum stabilized NbTi • reduce weight and nuclear

heating• Indirect cooling

• High Current/low inductance• Efficient energy extraction• Less layers: simplify winding,

minimize thermal barriers from conductor to cooling channels.

• I operation ~10 kA

14

PS Design Decisions

15

Conductor and Coil Support

Doped Al

NbTi/Cu

Cable cross-section

Outer supportshell

Pure Al sheets (RRR>500)

Coil Configuration

•4 Layer Coil•“Hardway bend”•Epoxy impregnated

Parameter Unit MU2E PS

Strand diameter mm 1.200 Number of strands - 36 Cable bare width mm 30.00 Cable bare thickness mm 6.50 Strand Cu/non-Cu ratio - 1.0 Overall stabilizer/non-stabilizer ratio in bare cable - 8.58

5.7 T peak field in the coil; >5 T peak field on the axis; ~2.5 T at the TS interface; <1.5 T field in the yoke

body; <2.4 T in the yoke end caps.

16

Flux densities

17

Axial gradient

No heat load:Operating point is at

68% of the SSL along load line or at 25% of the SSL at the constant field;

Under heat load:The temperature

increment of 5.32 K-4.50 K = 0.82 K allows to operate at 80 % of the SSL along the load line or at 40 % of the SSL at the constant field.

18

Critical current

0 1 2 3 4 5 6 7 8 9 10 110

2

4

6

8

10

12

14

16

18

20SSL @4.50K (68%)SSL @5.32K (80%)SSL @6.18K (100%)Load lineOperating point

Peak field (T)

Curr

ent (

kA)

19

3D field distribution

The second end cap was added to the iron yoke (vs. MECO) to eliminate the net axial self-Lorentz force (TS=off);

When all magnets are powered, the net axial force is +116/-124 tons, depending of the current direction;

MECO axial force of 140 tons was used for the design of axial supports;

Due to the force directions, the coil to coil interfaces are always under compression.

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Axial forces22

.46

MN

10.6

5 M

N10

.65

MN

• The Lorentz forces are reacted by the outer shells made or Al 6061-T6;

• The shells are assembled around the coils with no prestress;

• All gaps are filled with epoxy.

Coil support concept

Dimensions are in [m]

Materials:8.35% NbTi8.35% Cu17.33% G1065.97% Al100% Al 6061-T6100% Stainless steel100% Low carbon steel

21

• The Lorentz forces are reacted by the outer shells made or Al 6061-T6;

• The shells are assembled around the coils with no prestress;

• All gaps are filled with epoxy.

22

Cryostat design

Thermal syphon cooling

Suspension system

8 GeV proton beam, Au target (r=0.3 cm, H20, Ti), 25 kW, I=2E13, σx= σy= 1 mm

23

Baseline absorber configuration

24

Neutron flux >100 keV and power deposition

Absorbed dose (Gy/s) = Power density (mW/g), i.e., peak in the coils ~ 100 kGy/yr

25

DPA (displacements/atom)

Peak DPA in Al ~2x10-5/yr

26

NbTi degradation (Al Zeller, 2003) http://supercon.lbl.gov/WAAM/

5% degr.

15-20 years to accumulate 5 % of Ic degradation (w/o annealing)

Under the expected dose of 2÷6·10-5 DPA/year, Al resistivity degrades by a factor of: 5÷10 at B = 0

T 2.5÷5 at B = 5

T

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Al resistivity degradation

1 10 7 1 10 6 1 10 5 1 10 4 1 10 3 0.011 10 11

1 10 10

1 10 9

1 10 8

1 10 7

1 10 6

0.2

0.4

0.6

0.8

Al rho inducedRRR=2450, B=0TRRR=500, B=0TRRR=500, B=5T

Aluminum at 4.5K

DPA

Irrad

iatio

n-in

duce

d re

sistiv

ity, r

ho_i

(Ohm

*cm

)

Res

istiv

ity d

egra

datio

n, rh

o/(rh

o_i+

rho)

Al resistivity recovers during the thermal cycle: by 60 % at 80

K; by 100 % at

300 K.

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Al resistivity recovery

29

Quench protection

0

10

20

30

40

50

60

70

80

90

100

0

2000

4000

6000

8000

10000

12000

0 20 40 60 80 100 120

Tem

pera

ture

(K)

Curr

ent (

A)

Time (s)

PS quench study

all_500_CURR(A)

10m_200_CURR(A)

10m_50_CURR(A)

all_500_TEMP(K)

10m_200_TEMP(K)

10m_50_TEMP(K)

Pion Capture Solenoid

Muon Transport Solenoid

Spectrometer Solenoid

Detector Solenoid

proton beam

pion productiontarget

radiation shield

iron yoke

CSMS1

MS2

COMET SC Magnets

R&D Program Model coils of Al-

stabilized superconductor with high yield strength Development of conductor Model coil in the COMET-

Mu2e collaboration Neutron irradiation test

Expect 1021 n/m2 for 30 day operation in COMET

Need to check degradation of high yield strength aluminum

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

0

100

200

300

400

500

10-7 10-6 10-5 0.0001 0.001 0.01

RRR degradation by DPA

Al DeltaRhoCu DeltaRho

Al RRR(500)Cu RRR(200)D

elta

Rho R

RR

DPA

“Isochronal recovery of fast neutron irradiated metals,” J.A. Horak and T.H. Blewitt, Journal of Nuclear Materials, Volume 49, Issue 2, December 1973, Pages 161-180

Neutron irradiation facility Check degradation of

stabilizer up to 1021 neutrons/m2

degradation of resistivity recovery by annealing to RT

Kyoto Univ. Research Reactor （ KUR ） 5MW at maximum Low temperature facility

available 10K-20K 9.8 x 1011 n/cm²/s

32

The design of the mu2e experiment and its magnet system is vigorously proceeding with the goal of obtaining the DOE CD-1 approval in Spring 2011.

The mu2e magnet design uses many of the features developed for the latest generation of detector magnets. Its specific issues are: high field gradient, tight field tolerances and high radiation level.

The magnets will be built in industry and at Fermilab and should be operational by 2016. Their construction could be regarded as a technological bridge between the solenoids built for ATLAS and CMS and those proposed for the LC experiments.

A collaboration has been established between mu2e and COMET in view of resolving joint concerns, in particular obtaining improved data on properties of superconductors and stabilizers after irradiation.33

Summary