Cryostat performance
Zhanguo ZONG, Norihito OHUCHI, Masanori KAWAI, Yoshinari KONDOU,Hiroshi YAMAOKA, Yasushi ARIMOTO, Xudong WANG, Kiyosumi TSUCHIYA,SC Magnet Group, SuperKEKB, Accelerator Laboratory, High Energy Accelerator
Research Organization (KEK)The 21th KEKB Accelerator Review
2016-06-14 (Tues.)

Contents•

Cooling requirements of the SuperKEKB QCS SC magnets− Introduction to the magnet cryostats− Sub-cooled LHe for the SC magnet cryostats− Cryogenic systems, and their cooling powers.

•Cold tests of the QCS-L cryostat in the experimental laboratory− Set-up to cool the QCS-L cryostat with the 1000 L dewar− Thermal performance of the QCS-L cryostat− Some issues (support rods, measured heat leaks and working point of therefrigerators)

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SC magnets and cryostats of the SuperKEKB IR
QCS-L Cryostat

QCS-R Cryostat
IP

QCS-L

Cryostats

QCS-R

Rear

Front

Front

Rear

Main quadrupoles

QC2LE

QC1LP
QC2LP
QC1LE

QC1RP
QC2RP
QC1RE

QC2RE

Compensation solenoids

-ESL

ESR1

ES2/ES3

Correction/Cancel coils

416

194Cold mass at LHe (kg)

273.5

1460

1981.31152.1

Helium vessels

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Cryostat of the SC magnets•

Cooling the rear and front vessels in series by one LHe flow.

Front LHe vessel

LHe ReturnRear LHe vessel

LHe Supply•

Multi-layer insulation and LN2 shields applied to intercept heat leaks•

Support rods
− 8 rods/vessel (16 foreach cryostat)− Made of
Ti-6Al-4V(ELI)− Largest heat leaks tothe LHe vessels

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Service cryostats of the SuperKEKB IR SC magnets

Ring-out

Ring-inCryostats
Service cryostats
2016/06/14 (Tue.)

QCS-L

QCS-R

To access cryogenic multi-channel lines, and toaccommodate cryogenic control valves, signal wires, current
leads
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Cooling requirements of SC magnets•

Vapor cooled current leads for the SC magnets− Large lead number (111 leads) and total current(33.1 kA to/from): 51 leads for the left, 16.2 kA
and 60 for the right to transfer 16.9 kA.
− Rated at 2.0 kA, 1.8 kA, 1.35 kA, 1.0 kA, 450 A
and 60 A, for the main quadrupoles, compensation
solenoids and SC correction/cancel coils.
− The leads with large currents were commerciallysupplied. The compact units were developed at KEK.

•Lead performance− Designed with thevapor cooled type.
− Tested at the KEK labwith LHe before
delivery to the factory.
− Heat load for each side: <30 L/hour (LHe)

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Cooling requirements of the SC magnet cryostats•Cooled by sub-cooled single phase LHe at the normal operation− The magnet cryostats were designed under the stringent space constraints, especiallyin the radial direction, and the annular helium channels in the cryostats are slim.
− The cryostats are cooled by sub-cooled single-phase LHe, to avoid the instability of
two-phase flow, and to exclude the occurrence of the helium vapor bubble.
− Cryostat performance is very important because heats are absorbed by the sensible
heat of the liquid helium (0.5 W/g/s, ΔT=0.1 K).

at 1.6 bar and the sub-coolers cool the

4.7

flow to ~4.4 K along the isobaric line.
− In the cryostat, return from 4.4 K (PointC) to 4.74 K (Point B), (13.3–11.2) J/g*20 g/s= ~40 W, available for eachcryostat.
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4.6

regio

4.8

B

Liquid− The refrigerators supply a flow of 20 g/sn

4.9

The refrigerators and sub-coolers
Temperature (K)•1.6 bar•A•bar region
Two1.4phase(Liquid-vapor)

4.5

C
4.4
4.3
3.5

D•4E

1.2 bar•56
Entropy(kJ/kg-K)

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897/18Heat leak estimations of the left cryostats
Cold massRemarks

Support rod (Thermal anchor: 110 K)
Current lead pipe
Thermal radiation from beam pipes

Rear
1.76
1.1

Front
6.68
3.18

Thermal radiation from LN2 shields

0.3

0.9

0.5 W/m2

Instrument signal wire
Summary

0.01
3.17

0.01
10.77

Estimation
13.94 W

Ansys
Ansys
5 W/m2Main heat leaks are from the support rods (~8.4 W)•A source: thermal radiation from warm beam pipes (from ~300 K to LHe temperature)− Experimentally studied (total MLI layers vs. heat

0.6

9.36

0.231

8.19

0.198

7.02

0.5

0.165

5.85

0.4

0.132

4.68

0.3

0.099

3.51

0.066

2.34

0.2

2016/06/14 (Tue.)LHe boil-off
ΔΤ

0.7

0.264

ΔΤ (K)Heat leak per unit length (W/m)

flux in the narrow gaps (from 3.5 to 6 mm)

0.8

12

34

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56Layers

78

9102

•

Heat flux density (W/m )

Items

8/18

Cryogenic systems for the cryostats

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Cold box and sub-cooler for each cryostat
4.9

Temperature (K)4.8

1.6 bar

B •

4.7

A

•

1.4 bar

4.6
4.5

C
4.4
4.3
3.5

•

D•
4

•

E

1.2 bar

5
6
Entropy(kJ/kg-K)

7

•
8

9

To maintain SC magnets in the single phase LHe cooling− A: outlet from Coldbox: 1.6 bar (20 g/s, ~4.74 K, saturated LHe, two phase)− A->B->C: in the sub-cooler and multi-channel transfer lines− C->B: single liquid phase in the service cryostat and cryostat, a part to current leads− B->D: J-T valve in the service cryostat.
− D->E: in the multi-channel transfer lines and subcooler, return to coldbox at E point

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Cold tests of the QCS-L cryostat•

Cooling the SC magnets down to ~4.5 K in the experimental laboratory (Feb.~Jul.)− To see the temperature profile in the SC magnet cryostat− To measure heat leaks of the cryostat− To excite all the SC magnets in the independent or combined modes (main quadrupole+corr.
+ESL)− For magnetic field measurements (by harmonic coils, SSW, and Hall probe)

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Setting-up to cool the SC magnet cryostat

1000 LLHe dewar•

4.9

Saturated LHe (two phase-vapor and liquid)

4.8− LHe was transferred into the service cryostat
from the pressurized LHe dewar (1000 L,
1.4~1.6 bar). Helium gas vents through current

Temperature (K)instant of the single phase LHeleads or return line from the cryostat (~1.2 bar).
− Not higher temperatures in the cooling process
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B•

V•

4.7

1.6 barAt the l

4.6

4.4
4.3
3.5

•

•

•

aborat ory

4.5

CA

1.2 barW •ED
4

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56Entropy(kJ/kg-K)

7

•

8

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Cold tests of the QCS-L cryostat in the experimental laboratory•

The cryostat was pre-cooled with LN2 and was cooled with LHe on Feb. 12 2016 (Fri.)− With LN2 cooling the LN2 shields (~ 40 L/hour) and use 1000 LHe a day.

•A small current (0.05~0.5 A) to monitor the evolutions of the coils’ resistances with temp..
− To see the SC state of the magnets with the temperatures (on Feb. 16, 2016, Tue.)•Vacuum level of the cryostat:10-5 (~50 K, in the morning) ~ 10-6 Pa (at LHe temperature)

ESL
QC2LP
QC1LP
QC1LE
to SC

Rear/Front:
4.57 K/4.65 K

QC2LEto SC

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Cold tests of the QCS-L cryostat in the experimental laboratory•Cryogenic ready (Once an hour to check and have a log of the main parameters)− LHe level: LL1− Flows of current leads− Flows of by-pass line
− Temperatures at LHe− LN2 shield temperatures•

Flow meter interlock with current sources

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Unit: K, SLPM (Standard liter per minute), L/hr)

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A typical one-day for magnetic field measurement• Cool down from ~45 K and keep more than 10 hours (consuming >1000 L LHe a day)
− About 2 hours cooling down and have the LL1 of about 80%, and then energize the SC magnets− The SC magnets were sufficiently cooled and no quench happened due to the cooling conditions.

Dewar change

LHe level

Corr. Coil Current (±60A)

QC2LP: 1 kA

Flows of current
lead: 69.5 L/hr
Bypass: 18.8 L/hr

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Some issues – Higher temperatures of LN2 level• Higher temperatures of LN2 shields (110 K to 130 K)− Because of the temporary setting-up in the experimentallaboratory (counter usage of the inlet and outlet of theLN2 shields to fit the port types) (needs more analysis)− For the next step, use the design set-up.

• High temperatures of thermal anchors of support rods
− 110 K to 155 K ( design about 90~100 K),
increase the heat leak to LHe level− Because of the higher LN2 shield temperatures− Because of the thermal anchor cross-sections
Item
Dimensions (mm)Heat leaks(120/155K)
Heat leaks (110 K)

Rear
Front
Total
120*7.5 133.5*13.5 83.5*13.5 W
0.9/1.1

4.2

7.2

13.4

1.76

2.44

4.24

8.44

Unit: K

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Some issues – Higher temperatures of LN2 level• High temperatures of thermal anchors of support rods
− The cross-section areas are not sufficient to intercept
heat leaks from room temperatures.
− For the QCS-R cryostat, we will confirm the thermal
anchor design (cross-section areas and contact
surfaces between the copper braids and LN2 shields)
Rear
Front
Total
Item
Dimensions (mm) 120*7.5 133.5*13.5 83.5*13.5 Design
Thermal anchor
Φ72.5*25
Φ7Design
ΔT (K)
2345.641.6
Cal.

ΔT=41.6 K(~ 39.3 K, by formula)
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Summary of the QCS-L cryostat cold test
Cold mass

Items
Total heat leaks at the cryostat side

RearFront

11.5

23.6

Remarks
35.1 W (Measured)

Total heat leaks at the service cryostat (calculated)

13.25

Multi-Channel transfer line between sub-cooler and the service cryostat<10 W• Heat leak meas.
with temp.
increase from10 to 16 K

Temperature of
Rear cold mass18161414~11 W

12~23 W

1012
10

LTC2A
LTC4A

Temperature ofFront cold mass644

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200
KEKB
Left+right
Margin:~80W

150

CoolingPow
Meas2013
KEKB
SKEKB
SKEKB1100862
2016-02-15 22:00

SuperKEKB-QCSL
Est.: 58.35 W + 30 L/hr
Margin: ~90 W

20168

250

22Refrigeration (W)Temperature (K)22 𝐶↓𝑖​𝑄 =​∑↑▒​𝑚↓𝑖 ∫↑▒​20
𝑑𝑇 /𝑡𝑖𝑚𝑒
18

2500~ 58.35 W + 45 L/hour, margin:30 W(~ 1.5, flows for Current leads)

01020

30
4050
Liquefaction (L/hour)

6070• Estimated working point of the refrigerator (for the left side)• Summary: The left cryostat has successfully been cooled down at the KEK lab and thefield measurements have been performed. The heat leaks are higher than expected andstill affordable for the refrigerator. More analysis is needed for the next stage.
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