QCSToshiyuki OKI
on behalf of the SuperKEKB QCS GroupThe 27th KEKB Accelerator Review Committee
2024/MAR/26thOutline• Main work carried out during LS1(1) Modifications of the head of QCS cryostat to reduce background(2) Repair of vacuum leakage at the QCSR service cryostat• Operational status (cooling, magnet power supply)• Plan for anti-ageing of old system(1) Overhaul of electric motor for helium compressor(2) Refrigeration control system renewal• Considerations(1) Additional heat exchanger(2) Cooling margin of refrigerator

Modification work around IR to reduce background• Before LS1, the beam background production points were evaluated by the Belle group.

K. Nakamura. Mar 4, 2021
SuperKEKB IR meeting
made by heavy metal• During LS1, modification work was carried out around the IR to reduce background: the Belle group
added several types of shields, and we, QCS group, together with the vacuum group, modified thefront part of the QCS cryostat.

QCSL cryostat: head plate replacement• The tungsten head plate at the front part of the QCSL cryostat was replaced with a stainless steelone.
• For this replacement work, the beam pipes had to be shaked across the beam axis, so that theflanges between the cryostat and beam pipes were removed. In preparation for that, the cryostat
front section was supported on a stand while the cryostat middle section was opened to allow
access to the beam pipe support screws and BPM cables. Displacement measurements werecarried out before and after the work.
head plate

QCSR cryostat: front cap with head plate replacement• For the QCSR, the tungsten head plate was also replaced with a stainless steel one.
• Furthermore, the front cap of the cryostat has been redesigned smaller along with the inner heatinsulating layers, so that the cable space for the VXD was enlarged.
• The QCSR cryostat has service ports from which the beam pipes can be accessed.

front capVacuum leak repair work on the QCSR service cryostat• Before LS1, a vacuum leak had been found in the upper and lower connection of the QCSR service
cryostat.
• During LS1, it was investigated for identification of the leakage part and repaired.

Milling stepServicecryostat

Fibrous material

Polished bywhetstoneQCSR leak rate and vacuum pressure after repair• The leakage rate of the QCSR cryostat was high before the repair work, but improved to the samelevel as the QCSL after the repair.

Leak rate (Pa*m3/s)• A cooling test in December 2023 confirmed that the vacuum pressure could be reached at thesame level as the QCSL both at room temperature and at low temperatures.
5E-05
1E-05
1E-06
1E-07

GHe toHe-traps

1E-08

2023/03 QCS-R
Service cryostat
O-ring40 min. GN2 toafter 18 min.
Remove GHe gas by GN22022/09 QCS-R
Service cryostatO-ring2022/10/14 QCS-L
Service cryostat O-ring
40 min. GN2
2023/03/16 QCS-L

1E-09
1E-10

01020

30

4050

Time since spraying GHe into GHe-trap (minutes)

Current status of QCS: cooling• According to the cooling characteristic curve at the start of cooling, the QCS has been cooled wellwithout any negative effects due to the cryostat modification work during LS1.

Current status of QCS: operation• From the start of 2024a run to the present, the QCS magnet power supply has operated stably
without failure with a current stability of a few ppm/week.
• As reported in the previous ARC, the QC1 magnet initialisation pattern for ramp-up is also used in2024a run to mitigate the flux creep in superconducting magnets.
Current stability for a week (5ppm/div)
QC1LP
QC1RP
QC2LP
QC2RP
QC1LE
QC1RE
QC2LE
QC2RE
ESL
ESR1
ESR23

5ppm
Ramp-up pattern for QC1P

Overhaul/renewal of deteriorated system: motors for He compressor• There are three electric motors for the helium compressor, one each for the QCSL/QCSR and onefor a spare. These are over 30 years old and beyond their usual lifetime, so an overhaul is planned.
• To allow overhauls to be carried out during short shutdown periods, the plan is to overhaul the threemotors in sequence, one each year; one was done last year and the other will be done this year.

Overhaul work for the QCSL He compressor motor in 2023 (1/2)• Overhaul of a motor for QCSL He compressor was carried out at a factory in 2023.
• An electrical test was carried out just before the overhaul work.
• The results showed that the worst-case remaining lifetime was only about one year. The need foroverhaul for the remaining motors is strongly recognised.

Overhaul work for the QCSL He compressor motor in 2023 (2/2)• At the factory, the bearings were replaced, coils were rewound, and various adjustments and tests
were carried out.
• The overhauled motor has been applied to the QCSL and is currently operating without problems.
Overhaul for QCSR motor is planned in summer 2024.

Overhaul/renewal of deteriorated system: refrigerator control system• The control system controls the refrigerator from Nikko
control room to Tsukuba area (consisting of more than 300
control loops).
• The system has been in use since the KEKB era and is nolonger supported by the fabrication maker. Some of them
have no replacement parts.
• The control system needs to be updated to operate for thenext 10 years or so.
• The most important thing to keep in mind is not to destroy theexisting refrigerator system (the refrigerator system cannot
be replaced. It is too expensive and impractical to renew
them.).

Nikko control room

Renewal Plan
• There are two main options for the update plan.
(A) Install successor system of the current system: All design (including sequence design) is
done by the manufacturer.
(B) Build a new system by ourselves: All design is done by ourselves, where the system will
be based on PLC. The cooling control scheme in the software is the same as the presentsystem.

Current system

PLC based home-made system

Pros. & Cons.
(A) Successor(B) Home-madeCost

790k USD(Belle+QCS)

Low(R&D cost isunknown)

Manpower

a few

Large

Compatibility(system,operation)

GoodPoor

Risk to destroy arefrigerator or stopsystem

Low

Need to debug withspare system

Coupled Belle & QCS system• Note: The QCS and Belle refrigeration control systems share information and infrastructure
facilities with each other. It is therefore preferable to renew them at the same time in the samesystem. In particular, Belle's cryogenic group has commented that they want to avoid theuncertainty risk from the development required to introduce a new environment.

Reducing the use of LN2: consideration of additional heat exchangers• To reduce the LN2 quantity consumed for the cryogenic system (ECO-system), we have started todiscuss about the installation of the additional heat exchanger.
• The amount of the LN2 quantity is 3500 L/day for the QCS-R and QCS-L helium cryogenic systems.
The cost of the LN2 per year is about 40 MJ¥ (267 kUS$).
• By the additional heat exchanger, the amount of the LN2 consumption can be reduced to be smaller
than the half.
• For the installation, the cost is estimated to be 17 MJ¥ × 2 units. The work period in the practicalsetting is about 2 months (and for construction of the heat exchanger, 9 months).
• There is no risk for the additional heat exchanger, and the exchanger enhance the stability of thehelium refrigerator.

Reducing the use of LN2: Thermal condition of QCS cryogenic system
He Refrigerator

Cold Box

Present thermal condition at the 1st H.X.
High
pressure
GHe 1.7 MPa
298 K
44.58 g/s

Low
pressureGHe
0.111 MPa282 K
43.4 g/s

Additional H.X.
1st-H.X.

2nd-H.X.

16.3 g/s

1st H.X.
1.7 MPa
86.2 K

0.111 MPa
79 K

Service Cryostat

0.12 MPa
GN2 274 K

0.12 MPa
82 K

By adding the Heat Exchanger,

3rd-H.X.

High
pressureGHe
1.7 MPa
298 K
44.58 g/s

LowpressureGHe0.111 MPa290 K
43.4 g/s

4th-H.X.

GN2 0.12 MPa
274 K

3.75 g/s

Additional H.X.
LHe: 4.35 K, 0.16 MPa

LHe Subcooler

1st H.X.

Magnets: 4.5 K

Magnet Cryostat

0.111 MPa
79 K

1.7 MPa
86.2 K

0.12 MPa
82 K

Reducing the use of LN2: Thermal condition of QCS cryogenic system
Location of the additional heat exchanger

Additional H.X.

1st Heat Exchanger between high and low-pressure
helium gases and nitrogen gas .
The additional heat exchanger is expected to be one
third of the 1st H.X..

QCS-R Helium refrigerator and sub-cooler

Cooling-power margin of the refrigerators• We have begun to investigate the margin of cooling capacity in preparation for future upgrade plans.
• How to estimate current cooling-power margin:– The liquid level in the receiver is controlled to prevent liquid helium from overflowing by using aheater to evaporate the extra helium produced.
Pheater = Pmargin– Heater power is as the refrigerator power margin.
Liquid Helium
from Liquefierto Magnets

Decrease
heater power

Liquid Helium
from Liquefierto Magnets

Increase
heater power

History of the heater power of QCSR ( margin of the refrigerator )• The heater power varied and exhibited 0 watt, sometimes. The variation caused by change ofoperation conditions such as the liquid nitrogen filling. A heater power of 0 W indicates that theheat load exceeds the liquid helium supply.
• Even if the control is well adjusted and the heater power can be smoothed, the margin is only
~20 W for a cooling power of 250 W.

Heater power (W)• We need careful consideration to maintain the margin of the cooling power.
80Heater power of QCSR, 7 days in June 2022

40
The average is ~20 W.
0Summary• During LS1, the head of QCSL/QCSR cryostats were modified to reduce background. Vacuum
leakage at the QCSR service cryostat was also repaired.
• QCS magnet power supply and cooling system have operated stably from the start of 2024a
run to the present.
• Plans to overhaul or update ageing systems: electric motors for helium compressors areplanned to be overhauled annually. Consideration has started to be given to renewing therefrigeration control system.
• Consideration for the additional heat exchangers to reduce liquid nitrogen and the coolingmargin of refrigerator has begun.

Backup

Control systems and operations of cryogenic systems

Operations (QCS-L&R+BelleII):

Central control room
for refrigerators
Nikko Exp. Hall

QCS-L cryogenicsystem
SuperKEKB IR
Tsukuba Exp. hall
Belle II cryogenicsystem

KEK staffs: on-call
3 operators/shift, 3 shifts/day
Same control room in the Nikko Hallwith cryogenic system of SuperKEKB
SRF cavities, STF and cERL.

SuperKEKB
Accelerator
central room

To display some
VIP parameters

QCS-R cryogenicsystem

cERL
KEKB SRF cavities
STFliquid phase

5.0From
to C subcooryo
stat ler

QCS-L
QCS-R

4.8

4.4

inside Cryo
stat

4.6

4.2
3CV601
Subcooler

40.161 MPa

CV413

Saturation
linevaporphase

From
cold box

Measured points inside
LHe vessels with ~20 g/s

CV602

0.120 MPa
Subcooler LHe container

QHeater

two-phase region

567150

54100
5000

640
6080
Liquefaction (LLHe/hour)

Commissioning
operation

QCS-L

30

QCS-R

2520

315

210120

QCS-L
QCS-R

35Total operation hours (×1000 hours)

200

7Operation per year (×1000 hours)

Refrigeration or heater power (W)

L:Coldbox+subcooler
L:Coldbox+subcooler+cryostat
L:Operation with accelerator
R:Coldbox+subcooler
R:Coldbox+subcooler+cryostat
R:Operation with accelerator

0For physics operation

2016 2017 2018 2019 2020 2021 2022

5048/66

89

Entropy (kJ/kg-K)

Mixed loads of refrigeration and liquefaction (250 W in total, to cool 51 leads in QCS-L and 59 in QCS-R, 40 L/hour)• Total operation time: ~ 30 khours• QCS quench events: 66 (48 due to beams), recently due to earthquake250

low pressure side of cold box5.2

Temperature (K)Subcooled cooling scheme (stable, temperatures lower than saturated LHe)

Current leads

QCS systems of SC magnets, cryostats and cryogenic systems

QCS systems of SC magnets, cryostats and cryogenic systems
Ground devices (compressors, helium tanks, liquid nitrogen tanks)

Underground devices (refrigerators, subcoolers, cryostats, instrumentations and quench detectors)