Cryogenics for arc and transfer line magnets

LER Workshop, CERN, October 11-12, 2006

Cryogenics for arc and transfer line magnets - Yuenian Huang

1

LHC Accelerator Research Programbnl-fnal-lbnl-slac

Outline:–LER cryogenic system design–LHC cryogenics infrastructure at CERN–LER arc magnet cryogenics–Current leads for arc magnets–LER transfer line magnet cryogenics–Current leads for fast switching magnets–Summary

Cryogenics for arc and transfer line magnets



2

LER cryogenic system design

• For any cryogenic system design, first thing we need to know is to identify the heat load Q, conduction, radiation, Joule heating, etc.

• Figure out at what temperature level T this heat load is introduced into the cryogenic system, 1.9 K, 4.5 K or 50 -75 K etc.

• Then we need to know where these cryogenic cooling powers coming from and how much the temperature difference between the conductor and coolant at heat load Q and temperature T

Q, Tsm, THe

Magnet

Thermal shield Cryostat



3

LHC cryogenic system layout

• 5 cryogenic islands• 8 refrigerators

• 2 at P4, 6 and 8• 1 at P1.8 and P2

• 1 refrigerator serves 1 sector, 3,300 m

• Each refrigerator is 18 kW @ 4.5K and 600 kW pre-cooler

• LER will use LHC existing cryogenic infrastructure as show below

P4 P6

P3 P7

P2 P8

P1

P1.8

P5



4

LHC helium refrigerator system setup

300 K 90 K 75 K 50 K 20 K 4.5 K

LHC supply

LHC return

Shield supply

Shield return

HP

MP

LP



5

LHC cryogenic distribution line (QRL)

Header B

4 K, 16 mbar

1.9 K pumping line

Header C

4.6 K, 3 bar

Cold mass, 1.9 K, intercept and beam screen

Header D

20 K, 1.3 bar

Beam screen cooling return line

Header E

50 K, 20 bar

Shield cooling supply within arc cryostats

Header F

75 K, 19 bar

Shield cooling return

Cryogenic Distribution Line (QRL)



6

Installed refrigeration capacity in the LHC sectors

Temperature level

High-load sector *

Low-load sector -

50 – 75 K [W]4.6 – 20 K [W]4.5 K [W]1.9 K LHe [W]4 K VLP [W]20 – 280 K [W]

330007700300240043041

310007600150210038027

* The high-load sectors are 1-2, 4-5, 5-6 and 8-1.

- The low-load sectors are 2-3, 3-4, 6-7 and 7-8.



7

Static heat in-leaks in standard cell arc, DS and LSS

Temperature level

50 – 75 K [W]

4.6 – 20 K [W]

Cell 482 14.0Are (23 cell)

11090 323

DS 1,2,4,5,6 & 8 *

788 28

DS 3 & 7 * 794 28LSS 1 & 5 *

658 15

LSS 2 & 8 *

791 14

LSS 3 & 7 *

130 3

LSS 4 * 508 5LSS 6 * 232 0Total 15,473 430



8

Static heat in-leaks in distribution system

Temperature level

50 – 75 K [W]

4.6 – 20 K [W]

Sector 1-2, QRL + Other

10325 + 500

245 + 190


9894 + 95 235 + 67


9853 + 156 237 + 93


10353 + 746

247 + 198


10300 + 586

245 + 183


9723 + 156 231 + 93


9740 + 156 232 + 93


10723 + 586

248 + 183

Other means Interconnection boxes, local transfer lines and vertical transfer lines



9

LER arc main dipole and LHC quads

- LER will use VLHC drive conductor design

- LER ring length 26658.9 m- LER arc magnet sector length ~ 3.3

km- Heat load at 4.5 K for each sector is

346 W- Cryogenic support for each LER arc

magnet ring: 18 g/s @ 3 bar, 4.6 K supply, outlet temperature <6.0 K

- He inventory for whole LER ring is 1700 kg

- LER magnets and current return line will share the same current leads which can carry a peak current of 72 kA



10

VLHC transmission line magnet cryogenics

Drive conducto

r

Current return

Shield

T in (K) 4.5 4.52 37P in (bar)

4 3.8 17

T out (K) 5.57 5.8 70P out (bar)

2.8 1.9 13

Heat loads (W/m)

0.044 0.024 1.534

Distance (m)

19400 19400 38800

Mass flow (g/s)

60 120 60



11

LER drive and return conductors

• Same design for LER drive conductor and return conductor•LER arc magnet length : 12m•Beam pipe gap: 30 mm•Peak current : 72 kA•Helium supply is 3 bar, 4.6K•Helium return is 2.5 bar, 6.0K•Helium flow : < 20 g/s for each sector conductors•Pressure drop for each sector is < 0.5 bar



12

LER arc magnet correctors

Every half-cell will have a set of corrector magnets. To place them, the drive conductor is moved up 230 mm, next to the return conductor thus creatinga field-free zone below.

Arc magnet correctors and their count (based on the VLHC design):

Dipole (Horiz. or Vert.) 0.8T 0.5 m 410 Quadrupole 20 T/m 0.5 m 410 Sextupole 1400 T/m2 0.8 m 410



13

Main parameters of three types of conductors

Drive

bus

Return bus

Bus in correction

spaceCu/Sc ratio in

strand1.8 1.8 1.3

Diameter (mm)

0.648

0.648 0.808

Conductor type

Braid

Braid 9 Rutherford

CablesNumber of

strands288 288 270

Cu wire diameter

(mm)

0.64 0.64 0.64

Number of wires

240 240 288

Inner pipe diameter

(mm)

25.4 25.4 36.8

Outer pipe diameter

(mm)

38.1 38.1 50.1

Max. working pressure

(bar)

40 40 40



14

LER driver conductor model



15

VLHC transmission line magnet calculated heat loads

4.5 K level 40 K levelMechanical supports (mW/m)

53 670

Superinsulation (mW/m)

15 864

Beam loss (mW/m)

2 1

Splice (mW/m) 7 -Total heat loads (mW/m)

77 1535

Mechanical support is provided by the pegs spaced at 0.5 m.40 layers of MLI wrapped on the 50 K thermal shield and 20 layers on the conductor outer pipe to reduce the heat load at lower temperature level.



16

LER arc magnet heat loads scaled from VLHC study

4.6 – 6.0 K level

50 - 75 K level

Mechanical supports (mW/m)

53 670

Super-insulation, MLI

(mW/m)

15 864

Beam loss (mW/m)

2 1

Splice (mW/m) 35 -Total heat loads

(mW/m)105 1535

Heat load per arc, 3300 m

(W)

346 5066

Since LER arc magnet will use the same design as VLHC model, the heat load should be the same level as VLHC design values.



17

LER arc magnet current ramping scheme

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200 1400 1600

Tim e (sec)

I (kA

)

The current ramping scheme for LER arc magnet is shown above.Since LER arc magnet is made of superconductor, the heat loadsduring current ramping will be the splice heating and heat load dueto current leads.



18

Current lead for LER arc magnet ring

• We have designed and made a pair of helium vapor cooled current leads (made of copper) for VLHC study, which optimized for a DC current up to 100 kA.

• During the demonstration test of superferric magnet program, the current was ramped up to 104 kA when magnet quenched.

• The helium consumption rate is within the design target – 5.6 g/s per lead and all quenches were in the superconductors located far away from the splice between the lead and superconductor.



19

Cryogenic system setup for VLHC study



20

Fast switching magnet design and cooling



21

Transfer line magnet list

Magnet size

[mm x mm]

LER beam

vertical lift

[mm]

Magnet

length

[m]

Field

[T]

Inductance

[μH]

Peak

Voltage

[kV]

Number of magnets

Number of supplies

40 x 40 0 – 5.5 1.6 1.46 1.3 40 4 4

40 x 50 5.5 – 16.2 1.4 1.46 1.5 43 3 3

40 x 60 16.2 – 27.6 1.3 1.46 1.6 46 2 2

40 x 70 27.6 – 36.6 0.9 1.46 1.3 40 2 2

40 x 80 36.6 – 46.2 0.8 1.46 1.3 40 2 2

30 x 30 75.0 – 170.0 2.0 1.95 - - 6 1

30 x 30 170.0 – 1350.0

1.5 8.00 - - 10 1



22

LER fast switching magnet (V1 - V5) cryogenics

0

10

20

30

40

50

60

0 200 400 600 800

t (sec)

I (kA

)

0

50

100

150

200

0 200 400 600 800

t (sec)

Hea

t lo

ad (

W)

• Fasting switching magnet ramp scheme and Joule heating curve are shown on the left for RRR=1000 Cu.

• The magnet is cooled by 4.6 – 15 K, 3 bar helium.

• The average heat load during current ramping is 30 W per meter long conductor.

• Heat transfer between conductor surface and helium is calculated and temperature difference between the two is less than 0.1 K.

• Required helium flow is 1.5 g/s per meter long conductor to carry the heat load away.



23

LER fast switching magnets (V1- V5) heat loads

Cu RRR 1000Cross sectional

area (cm^2)4.36

Calculated heat load (W/m)

30.44

Total length of conductor (m)

66.4

Total heat load for FSM set (W)

2020

Helium inlet temperature (K)

4.6

Helium outlet temperature (K)

15

Enthalpy difference (J/g)

20.33

Required helium flow per meter

(g/s)

1.5



24

LER transfer line magnet V6 heat load

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400

Time (sec)

Cu

rren

t (k

A)

0

20

40

60

80

100

120

140

0 200 400 600 800 1000 1200 1400

Time (sec)

Q (

W)

LER transfer line magnet current ramping curve, ramping rate is210 A/s, first flattop is 15 kA andSecond flattop is 55 kA and then there is a long ramping down tails.

Using RRR=1000 copper and cool the magnet with 4.6 K helium, the Jouleheating within the magnet conductorwill be ~ 42 W/m. Total length of conductor is 48 m, so total heat load is 2040 W.



25

LER transfer line magnets (V6) heat loads

Cu RRR 1000

Cross sectional area (cm^2) 4.36

Calculated heat load (W/m) 42.5

Total length of conductor (m)

24

Total heat load for FSM set (W)

2040

Helium inlet temperature (K)

4.6

Helium outlet temperature (K)

15

Enthalpy difference (J/g) 20.33

Required helium flow per m (g/s)

2



26

Current leads for fast switching magnets

Another heat load for fast switching magnet is caused by heat conductionfrom current leads. Since each fast switching magnet needs a powersupply to energize, the number of PS equals number of magnet.



27

Current lead heat loads scaled from LHC HTS leads

LHC 13 kA HTS current lead heat leak (W) *

< 1.5 W

LER FSM 55 kA HTS current lead heat leak (W)

6.0 W

Total number of leads per arc 52

Total heat leak at 4.6 K level 312 W* HTS at CERN & LHC Current Leads by Dr. Amalia Ballarino released at website.



28

Summary

• LER arc magnet will add additional heat load of 346 W for each sector at 4.6 K to 6.0 K level and 5,000 W at 50 – 75 K level.

• LER current lead can use the same design as for VLHC design study prototype current lead, which can be used for LER arc magnet ring.

• Each fast switching magnet set will add additional 2 kW heat loads at 4.6 K level to the LHC cryogenic system.

• Each transfer line magnet set (V6) will add additional 2 kW heat loads at 4.6 K level to the LHC cryogenic system.

• Current leads for fast switch magnet will add 312 W at 4.6 K level.

• The total cryogenic capacity of current LHC infrastructure is 7700 W at 4.6 K level and 33,000 W at 50 – 75 K level.

• Helium inventory for LER ring is only 0.5 L/m, or 1700 kg (or 13 m3).

• Helium inventory for fast switching magnets is 0.24 L/m.

Cryogenics for arc and transfer line magnets

Documents