october 30 th 2007 1 advances in heat transfer in high field accelerator magnet b. baudouy...

October 30th 2007 1

Advances in Heat Transfer in High Field Accelerator

Magnet

B. BaudouyCEA/Saclay - Dapnia/SACM

Annual meetingCARE07

29-31 October 2007

B. Baudouy CEA Saclay Advances in Heat Transfer in High Field Accelerator Magnet October 30th 2007 2

Outline

▫Heat transfer in superconducting magnets for accelerator

▫The NED Heat Transfer program◦Double-bath cryostat for NED

◦Test facilities

▫Experimental results◦Technical solution tests

◦Tests on NED electrical insulations−the classical insulation

−the innovative insulation

▫People in and around NED HT program◦J. Polinski, F. Rondeaux (CEA), S. Canfer (RAL)

◦N. Kimura (KEK)

◦D. Richter (CERN)

◦F. Michel (CEA – Grenoble)


Heat transfer in accelerator magnets (1/2)

▫“Wet” magnets with “heat exchanger”◦ Large internal losses and smaller stored energy

◦ Single phase coolant in contact with conductor

◦ Cooling Source: Internal tube flow heat exchanger

▫Heat transfer between the conductor and the cooling source determines the temperature margin

▫Electrical insulation constitutes the largest thermal barrier

▫LHC Electrical Insulation : All-polyimid◦10 mW/cm3 or 0.4 W/m (cable)

◦ΔT<0.3 K with permeable insulation or ΔT~4 K with monolithic insulation

◦He II + Conduction

0

0,05

0,1

0,15

0,2

0,25

0 0,05 0,1 0,15 0,2 0,25

Mesure

He II :

Conduction :

Calcul :

T i -

T b

(K

)

Q (W)

Qm

Q*

Qisol

QHeII

Qcalcul

QHeII

AL1 3

(T) dTTb

Ti

Q

isol + Q

HeII

Qisol

= ²T/R

Première couche

Seconde couche

Espacement

Vue en perspective Vue de dessus

(1)(1)


Heat transfer in accelerator magnets (2/2)

▫“Beam losses” of LHC upgrade with Nb3Sn Magnets

◦50 to 80 mW/cm3 or 2 to 3 W/m (cable) → ΔT~ K with polyimide insulation

◦Dry insulation for Nb3Sn Magnets !

▫Development of “innovative” ceramic insulation

◦Thermal treatment (insulation+Nb3Sn, easier and less costly construction)

◦Fiberglass + ceramic precursor (CEA patent)

◦Higher heat transfer rate, larger He volume in the insulation (Cp) and heat exchange surface increase (matrix participation)

Ceramic Classic (Polyimid) Full impregnation

Pore size d~100 µm (peak) 10 to 100 µm -Porosity ε 4.5 to 29 % ~1 % -Conductivity k≈4 10-2 W/Km kkapton≈10-2 W/Km @ 2 K - kepoxy≈10-2

W/Km

Courtesy of F. Rondeaux (CEA)


The NED heat transfer program

▫Characterization of the thermal performance of the magnet insulation◦Classical insulation and Innovative insulation

◦“real situation” (coil) and on the insulation itself

▫Construction of a pressurized He II double bath cryostat

▫The drum experiment◦Determination of the thermal conductivity and Kapitza resistance

▫The stack experiment◦Test on a stack of conductors closed to the coil mechanical, geometrical and

heat transfer configurations

▫Collaboration CEA-Saclay, KEK, CERN and RAL◦Tests in He II at CERN and Saclay, Tests in SHe at KEK (N. Kimura)

◦Construction of a Double bath Cryostat (WUT and CEA-Saclay) (J. Polinski)

◦Construction of molds by KEK (N. Kimura)

◦Collaboration with D. Richter at CERN


The NED Double bath Cryostat

T3

He IIp

He IIs

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

T5

T6T7

T0

T2

T1

He I

3

T

?TT

He II

T=1.7-2.2 K

He I

1 bar, T=4.2K5

1

2

4

CEA Saclay and WUT


11 mm

1.47 mm

CuNi strand wires

thermometer

Stycast

electrical insulation tapes

The Stack Experiment

▫Characterization of the thermal performance of the magnet insulation◦“real cable” geometry (CuNi cable)

◦Real electrical insulation

◦Mechanical constraints (compression)

◦Heat transfer configuration (Joule heating)


The Drum experiment

T i

T bCompressing flange

Sample holder flange

Support flange

Support b lind flange Feeding tube(Capillary)

Insulation materialsample

HeaterAB T emperature

Sensor

Scotch-W eld DP190Epoxy seal

80

Pressurised superfluidhelium bath

Inner helium volume

▫Heat transfer measurement perpendicular to the insulation (1 D)◦Determination of the thermal conductivity

◦Determination of the Kapitza resistances n 1

s K b

AΔT 2 eR

Q n h T λ


Technical solution tests (1/2)

▫Test with a “Saclay stack”

▫Central conductor heated

▫Insulation all polyimide (Kapton)◦1st layer : Kapton 200 HN 50 μm x 11

mm 2 wrappings (no overlap)

◦2nd layer Kapton 270 LCI 71 μ m x 11 mm 2 mm gap

▫60 MPa

SS conductor


Technical solution tests (2/2)

LHC beam Losses


Tests on the classical insulation

▫Glass-fibre epoxy insulation◦Developed by RAL

▫Determination of λ and RKapiza

◦To be published

Low temperature heat transfer properties of conventional electrical insulation for the Next European Dipole, J. Polinski et al., CEC 2007, Chattanooga, USA, 2007

Insulation Development for the Next European Dipole, S. Canfer et al., MT20, Philadelphia, USA, 2007

1,4 1,5 1,6 1,7 1,8 1,9 2,0 2,1

0,002

0,004

0,006

0,008

0,010

0,012

0,014

0,016

NED 0.073 mm Kapton 0.077 mm Kapton 0.014 mm

Rth

(K

.m2 /W

)

Temperature (K)1,5 1,6 1,7 1,8 1,9 2,0 2,1

0,01

0,02

0,03

0,04

NED Classical Kapton G10T

herm

al c

ondu

ctiv

ity

(W/m

2 K)

Temperature (K)


Tests on the Innovative insulation (1/2)

Courtesy of F. Rondeaux (CEA)

▫One wrapping with 50% overlap

▫Heat treatment of 100 h at 660 °C

▫10 MPa compression only !

▫5 conductors heated


0 10 20 30 40 50 60 700

5

10

15

20

25

30

1.8 K 1.9 K 2.0 K

T (

mK

)

Q (mW/cm3)

Tests on the Innovative insulation (2/2)

▫Very small ΔT, at least one order of magnitude smaller than for the LHC insulation tests

LHC beam Losses

LHC upgrade beam Losses

october 30 th 2007 1 advances in heat transfer in high field accelerator magnet b. baudouy...

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