QCS IR magnets
N. Ohuchi
Y. Arimoto, H. Yamaoka, Z. Zong, X. Wang, M. Kawai, R. Ueki, K. Aoki,
M. Masuzawa, Y. Ohsawa, T. Oki, S. Nakamura, K. Tsuchiya

2019/07/08

SuperKEKB Review 20191

Contents
1. QCS operation and quench
2. Magnetic field of QCS
3. R&D devices and improvement issues••••

Field vibration measurement sensor
Hall probe calibration measurement
Improvement of the cryogenic cooling margin
SC sextupole for IR straight section

4. Summary
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QCS SC magnet system
QCS-R Cryostat

QCS-L Cryostat

Helium Vessel

Helium Vessel
QC2LP
4 correctors(a1,b1,a2,b4)

ESR1 Solenoid

ESL solenoid

4 correctors

QC1LP
4 correctors

Leak field(a1,b1,a2,a3)

b3 corrector

cancel coils(b3,b4,b5,b6)

QC2RE

IP
(a1,b1,a2,b4)

QC1LE
4 correctors(a1,b1,a2,b4)

ESR2

QC1RE

(a1,b1,a2,b4)

QC2LE
4 correctors

Helium Vessel

4 correctors(a1,b1,a2,a3)

83 mradLeak fieldcancel coils(b3,b4,b5,b6)

QC1RP
5 correctors

b3 corrector(a1,b1,a2,a3,b4)

QC2RP
4 correctors

HER(a1,b1,a2,a3)

ESR3

Helium Vessel
4 SC main quadrupole magnets: 1 collared magnet, 3 yoked magnets
16 SC correctors: a1, b1, a2, b4
4 SC leak field cancel magnets: b3, b4, b5, b6
1 compensation solenoid
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LER

4 SC main quadrupole magnets: 1 collared magnet, 3 yoked magnets
19 SC correctors: a1, b1, a2, a3, b3, b4
4 SC leak field cancel magnets: b3, b4, b5, b6
3 compensation solenoid

SuperKEKB Review 20193

QCS operation and quench
Operation of QCS system for Phase2 (March 16, 2018 ~ July 17, 2018)• Operation of the QCSL and QCSR cryogenic systems− QCSL:••

Cool-down: 15:06 Feb. 9, 2018 – 4:18 Feb. 11, 2018: 37 h 10 min
Warm-up: 16:08 Jul. 20, 2018 – 14:40 Jul. 26, 2018: 142 h 32 min••

Cool-down: 10:06 Feb. 2, 2018 – 17:48 Feb. 4, 2018: 55 h 42 min
Warm-up: 15:50 Jul. 19, 2018 – 16:14 Jul. 25, 2018: 144 h 24 min− QCSR:•

During the operation, 26 magnet quench events––25 events: beam induced quench
1 event: ESL power supply failure

Operation of QCS system for Phase3 (March 11, 2019 ~ July 1, 2019)•

Operation of the cryogenic systems− QCSL:•

Cool-down: 9:43 Feb. 20, 2019 – 11:53 Feb. 22, 2018: 50 h 10 min•

Cool-down: 9:21 Feb. 25, 2018 – 00:44 Mar. 1, 2019: 87 h 23 min− QCSR:•

During the operation, 6 magnet quench events––3 events: beam induced quench
3 events: QC2LE power supply failure (IMP abnormal work)

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SuperKEKB Review 20194

QCS operation and quench
Phase-2

Phase-3
CollimatortuningVertical collimator
damagedLinac trouble

Quenched magnets by beams•••

The quenched magnets were concentrated in the QC1 magnets and the accompanying correctors.
Some magnet quenches were induced with the power supply trouble.
From Phase-3, in order to correlate the magnet quench and the beam operation, the kicker trigger signal
was added to the QCS logger data, and the logger system was upgraded with the sampling time of 1 µs.

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QCS operation and quench• Magnet quench data (May 28th, 2019)– The origin of the trouble was QC2LE power supply failure (IPM trouble).
– SVD had a serious damage.

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SuperKEKB Review 20196
From the report by Y. Arimoto

QCS operation and quench

Expanded in the right plots
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SuperKEKB Review 2019

From the report by Y. Arimoto
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QCS operation and quench• The countermeasure to the quenches of the QC1 magnets has
been proposed to assemble the W alloy shield on the incoming
beam pipes by the QCS group.
– The QCS group is waiting for the beam simulation results contained theseshields concerning for the effectivity of the magnet quench protection.

QCS-R

QCS-Le-e+

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8QCS operation and quench
Cool-down of the QCSL and QCS-R system
QCS-R

QCS-L

87 hours

50 hours

The required time for precooling the magnets to 4 K and immersing the magnets in
LHe is longer than the expected time.
•Especially, from 20 K to the operation of the magnets:−•

QCSL= 30 hours, QCSR=67 hours

The condition results in the slow recovery from the magnet quench (June 9, 2019).
−

2019/07/08

The cause would be an unexpected heat load in the system, etc.
1. Current leads
2. Vacuum condition of the thermal insulation spaces
3. Unoptimized operational procedure of the cryogenic system for the new QCS
SuperKEKB Review 20199

Magnetic field of QCS
All superconducting magnets have the hysteresis effect in the magnetic field.
−−

The exciting functions of the main quadrupole magnets are defined by the 5th polynomial
fitting with the data during up-ramping.
The functions of the correctors are defined by the linear fitting with the averaged data
between the up- and down-ramping.
Optics Error

QC1RE

QC1RE-a1corrector

Transfer function = G/I

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SuperKEKB Review 2019

The field difference between up- anddown-ramping = 1.8 ×10-3 T at R=15mm(3.5 % of the field strength at 60 A)

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Magnetic field of QCS
Magnetic field profiles along the beam lines:
1. The field profiles of all quadrupole magnets were reported with thedistance function from IP.
2. The field profiles of the correctors are ready to be reported to the optics
group.
QC1LP A1 corrector

QC1LE B2 field profile at R=15 mm

QC1LP B1 corrector

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R&D devices and improvement issues

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Field vibration measurement probe
22 Hz (Meas.) 29 Hz (Cal.)

Vertical amplitude(cal.)=35 nm
Vertical amplitude(meas.)=40 nm

Vibration characteristics of the cryostat vacuum vessel were measured by the acceleratorsensors.
•••

The measured integrated amplitude at 20 Hz was 40 nm (≅ the design beam size at IP).
By the measurement, vibration of each quadrupole magnet can not be measured.
The amplitude of 40 nm has a sufficient degrading effect on Luminosity.

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Field vibration measurement sensor
The measurement system of thefield vibration is being developedwith BNL under the US-Japan
research collaboration.
The vibrations of quadrupoles in
LER and HER are measured in thesame instance.
• Required key technology:
Vibration-free of the probe

QC2LP

QC1LE

QC2LE

QC2LP

QC1LP

QC1LE

Carbon fiber support arm

Vibration isolationtable

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QC2LE

Pick-up coil probe

KEK probe

SuperKEKB(2000
Reviewturn
2019coil X 2: V & H)

QC1LP

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Field vibration measurement sensor
Vibration measurements at BNL (Dec. 18 – 19, 2017)
KEK probe coil(2000 turns)

Vibration dumping support:

BNL Laser
vibrometer

Active anti-vibration table

The integrated amplitude of vibration at
10 Hz was reduced to 3 nm in horizontal
plane with the single active anti-vibrationtable.
G10 and CFRP
anti-vibrationsupport

Vibration of the frequency lessthan 100 Hz is reduced with thepiezo actuator.

The anti-vibration design concept
in the gravity wave detector isreferred in the design of thepassive anti-vibration stand.

The test room and the granite table were prepared by BNL.

Tra. func. = Vibration on the stage/Vibration of the floorCFRP verticalplate

Verticalvibration

G10 horizontal
plate
One active anti-vibration tablein two tables worked.

Doubletables

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Completed in June, 2019

SuperKEKB Review 2019

Two active antivibration tables

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Hall probe calibration measurement

Measured field profile along HER beam line

The test room and the granite table were prepared by BNL.

QCSR

QCSL

Lakeshore 3 axial-Hall probe•••

Field error for beam operation ＜10 Gauss
Field error for Belle-II detector ＜15 Gauss
Specification error of 3-axial Hall prove：0.25 % B < 2 T、0.5 % B > 2 T
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Requirement of Hallprobe calibration
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Hall probe calibration measurement

Assembly of Hall probe and FNALrotating mechanism

2-axis-rotating stage for Hall probe

KEK Hall probe was calibrated at
0.5 T, 1.0 T, 1.5 T, 2.0 T, 2.5 T and 3.0 T.

3-axis-Hall probe•Research collaboration with FNAL and ANL for the Hall probe calibration measurements– FNAL: Hall probe rotation mechanism in the solenoid field and the measurement software– ANL: 4 T MRI solenoid and the magnetic field mapping system– The first measurements were performed at Dec. 4 - 13, 2018.
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Hall probe calibration measurement
Calibration measurement results••

The 3-axis Hall probe wascalibrated with data of 14600
points for one absolute
magnetic field by the MRI
solenoid.
Measurement time = ~8 hours

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SuperKEKB Review 2019

Hall probe calibration measurement•

Field calibration points of the Hall probe in Dec. 4~Dec. 12, 2018

With the 24 magnetic field strengths, the KEK Hall probe was planted to be calibrated.
The calibrated magnetic fields by the ANL MRI solenoid were 6 points, which are shown in the red points inthe table.

––•

In Sept. or Oct. 2019, we plan to perform the measurement at 12 field points.
The field points are shown by the blue points in the table.
We would like to complete the measurements in 10 days.

––•

After the measurements in FNAL/ANL in Sept. or Oct. 2019.

The calibration measurements less than 1.5 T with the 1.5 T MRI solenoid in the KEK cryogenic science center.
The FNAL mover and driver will be used in the measurement with the kind cooperation of FNAL.

––No.

Magnetic field,
T1020.1

30.2

40.3

50.4

60.5

70.6

80.7

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@KEK-Cryogenic
centerNo.

Magnetic field,
T○

121.2○○

131.1○

○

141.3

○

151.4

○

161.5

○

171.75

○

18

2.0

○

19

2.250.8

○

20

2.5

100.9

○

21

2.75

111.0

○

22

3.0

2019/07/08@FNAL/ANL

2019
2018
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●

●

●

●

●

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@FNAL/ANL●@KEK-Cryogenic
center

○○

●

●
●

●

●
●

●

●
●

●

●

○

Improvement of the cryogenic cooling margin
After the QCSR quench and He compressor stop at 22:11 June 9th 2019, it took
about 60 hours to excite the QCSR magnets again.
QCSR magnets quench, interlock
shutdown of He compressor and He
refrigerator turbine

Pressure of He gas
reservoir tank

QC1RP Temp.

QC2RE Temp.

Pumping the vacuum chamberof the cryogenic tube

LHe Vessel Temp.
LHe Level
Re-cooling magnets did notproceed during almost oneday.

The cause of the delay of the re-cooling magnets to 4 K:
1.
2.

Relatively small margin of the cooling power of the He refrigerator w.r.t. the heat load,
Vacuum degradation in the thermal insulation spaces of the cryostat and the cryogenic transfer tube
due to outgassing by stopping the liquid helium flow.

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Improvement of the cryogenic cooling margin
The QCSL and QCSR cryogenic systems have the cooling margin of 20 W,
individually, to the total cooling power of 240 W @ 4.5 K.
Cooling power of the QCS cryogenic system

LHe level is controlled by
the heater input.
The input power is 20 W.

Margin of coolingpower = 20W

heaterActual operation point:
38 L/h for cooling C. L.
100 W for heat load

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Improvement of the cryogenic cooling margin
The countermeasure to this thermal conditions is the reduction of amount of LHe
for cooling the current leads.
HTS current lead

Present 2000 A
current lead(cooled withthe evaporatedhelium gas)He gasTerminal at
R. T.

Connected to PS

Using LN2 to reduce the helium gas flow
and confirm the temperature at thecold end of the normal conductor lead
less than 80 K.
• Target: half of helium gas flow forcooling the current leadNormalconductor
current lead

Cooled at 80 K by LN2Heat exchanger(Electricalconductor)

Connected toSC magnet

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HTS leads

Cold terminal at 4K
SuperKEKB Review 2019

Heat exchanger
with LN2
Connected to SC magnet
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Development of SC sextupole magnet
Sophisticate normal sextupole magnet system in the Tsukuba beam straight section−−

The system consists of three types of the sextupole magnets.
The required maximum GL=234 T/m

LER

The sextupole magnet has afunction of rotation.
GD = 340 T/m2, Leff = 300 mm
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HERHER

GD = 480 T/m2, Leff = 600 mm
SuperKEKB Review 2019

GD = 480 T/m2, Leff = 500 mm
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Development of SC sextupole magnet
The superconducting sextupole magnet is being studied for the system.
••••

GD = 800 T/m2Corrector magnets: a3, b2, a2
Small refrigerator cooling−The sextupole magnets are placed along the distance of 250 m including IP.

Superconductor: HTS (REBCO) or Nb3Sn for the sextupole, and Nb3Al for correctors
GM smallrefrigerator

Test cryostat
Nb3Sn sextupole magnet
Max. B in coil= 6.02 T
Din = 135 mm
G=890 T/m2 @ 500 A
Tc= 12 K
Current density=730 A/mm2

HTS (REBCO) sextupole magnet:•••

The magnet was tested in KEK.
Double pancake race track coils
G=213.08 T/m2 @ 4.2 K and 250 A

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The Nb3Sn and Nb3Al cables are thecandidates for the QCS upgrade.
24Summary• QCS operation in Phase-2 and Phase-3
1.
2.
3.
4.

•

32 events of QCS quench happened in 31 weeks.
The collimator and beam abort system were strengthened, and the number of thequench event was reduced.
The monitor and the data logger systems of the magnet quench are improved, and they
are well working for the quench diagnosis.
For the quick recovery from the magnet quench and shortening the cool-down timefrom room temperature, the cryogenic system should be studied in terms of the originof the heat load.

R&D devices and improvement issues

1.
2.
3.
4.

Magnetic field vibration measurement probe−

Anti-vibration mechanism is almost completed, and the performance will be confirmed in September
in BNL.

Hall probe calibration measurement for the solenoid field profiles−

The calibration measurement will be completed in 2019, and the up-date of the solenoid field will beavailable in the beam operation in 2020.

HTS current lead−

The development of the new HTS leads has started right now. The leads will reduce the heat load ofthe cryogenic system.

SC sextupole magnet in IR beam straight section−−

2019/07/08

HTS, Nb3Sn, Nb3Al materials are being studied for the sextupole magnet.
The magnet is designed to be cooled with the small refrigerator.
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Back up2019/07/08

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Quenched magnets by beams in Phase-3

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QCSR main cryogenic transfer tube: 24.3 deg. C
Bypass cryogenic transfer tube: 25.1 deg. C
QCSL main cryogenic transfer tube: 25.0 deg. C
Bypass cryogenic transfer tube: 25.4 deg. C

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SuperKEKB Review 2019

Pumping the residual gas in the vacuum
chamber of the tube.
At opening the cock of the chamber:
3.5×10-3 Pa → 5.9 ×10-3 Pa.

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