Cryogenics(Helium refrigerator for SRF)

K.Nakanishi, K.Hara, T.Honma, S.Kessoku, H.Nakai, H.Shimizu(refrigerator group)Same slide as last meeting

History of our refrigerator
TRISTAN without Superconducting cavities (SCC) 1986~
TRISTAN with SCC

1988~1995

KEKB with SCC

1998~

KEKB with SCC and Crab cavities

2007~2010

SuperKEKB with SCC

2016~

2

Same slide as last meeting

Cryogenic system forSuperconducting Cavities.

1988
4kW @ 4.4K
(Design)Compressor(C5,C6) wereadded.
Supercriticalturbine expander(T3) was added.

1989
6.5kW @ 4.4K
(Design)8.1kW @ 4.4K
(Achieved)Troubles
The total operation time
TRISTAN: 38,000 hours
KEKB: 62,000 hours
SuperKEKB: 28,000~ hours
Upgrading

KEKB

Year:
Hour of inhibition/ hour of operation

SuperKEKB

2016: 0 / 3343
2017: 0 / 0
2018: 0.1 / 4362
2019: 39.4/ 5334
2020: 4 / 5099
2021: 0 / 5292
2022: 3.7 / 3246
2023: 0 / 02024: 0 /1200~

In recent years, the number of troubles has been increasing.
However, by preparing spare parts and/or using alternative functions, the operating
rate of the refrigerator is maintained still high.
(Hour of inhibition is not hour of repair. If it is in operation even during repair, it is included in the operation time.)

Control system• Initially a control system EX-1000 which made by Hitachi
was adopted in 1988.
• The control system was updated to EX-7000 in 2002.
• EX-8000 was adopted in 2012.

• It’s time to update again.
But the candidate isso expensive,
working on Windows10,etc
Small parts are replaced from time to time, and sparecomponents are kept if they are used in large quantities.

Maintenance and Updating• The cryogenic systems were inspected every year by theprefectural government. The legal inspection is a good guideline formaintenance.
• Check and adjust the actuators of the controlled valves, pressuregauges and thermometers in the inspection cycle. And some onethat can not be adjusted is replaced.
• It is recommended to replace the input / output module of thecontrol system every 5 ~ 7 years. (However, the update cycle isoften extended.)• Compressor open inspections are performed at the manufacturer'srecommended operation hours or at least every 10 years.
• Since the manufacturer has withdrawn from the refrigerator
business, any spare parts are not distributed.→Three spareturbines (T1,T2 and T3)are kept.
How long can we operate after use the spare turbine?

Spare turbines• I asked the manufacturer if they could produce a new turbine.
→No. They will try to repair that. But they can’t make new one.
• In about 35 years of operation, the turbines have never beendamaged. Can't you think that the life of a turbine is morethan 35 years?
• If two turbines(T1 and T2) are working, it can be operated as a4kW refrigerator. And that is enough for SuperKEKB.

We have no choice but to use them carefully.

KEKB (1998~2010)
SuperKEKB (2016~)
Components
Cryostat

Heat loads
30 W/cryostat x 8

240 W

Transfer Lines (380m)

412.4 W

Cold Valves & Joints

147 W

RF Loss

100 W/cavity x 8Total• The heat load was smaller than TRISTAN’s.
• The RF loss is stable during beam operation.
• The compensation heaters are even used.
• The refrigerator is powerful enough.

~800W

800 W
~1600 W

Compensation heater power is includedSame slide as last meeting

Cryogenic system forSuperconducting Cavities.

1988
4kW @ 4.4K
(Design)Compressor(C5,C6) wereadded.
Supercriticalturbine expander(T3) was added.

1989
6.5kW @ 4.4K
(Design)8.1kW @ 4.4K
(Achieved)Compensation heater (1)The RF loss of TRISTAN cavities were not constant.
Beam Injection (~30W/cavity)
2minites
Top energy operation(90~120W/cavity)
Compensation heaters were working
to make the heat load constant.
Compensation heaters are notrequired for SuperKEKB operation.
But they are still working.

Same slide as last meeting

Compensation heater (2)A member of the Cavity Group told me thatthe high Vacc operation would deplete theliquefied helium, so the following rules
must be followed:① It should pass through quickly.
② High voltage operation should be
limited to no more than two cavities atthe same time.
→Controlled by Auto aging program.

(Cavity group gave us the Q-Eacc data.)

D11D
250.0
200.0

Loss[W]

However, Why did the refrigerator detect thatthe aging operation for cavities was done. The
compensation heater doesn’t work well.
We found that the RF loss on the cavity wall was
not properly evaluated.
Since the data was updated, it will be improved
from the next operation.

150.0
100.0
50.0
0.0
0.0

2.0

4.0

6.0

8.0

10.0

Eacc[MV/m]

12.0

14.0

16.0

Same slide as last meeting

Auto Aging program
The aging operation of the Superconducting
cavity in SuperKEKB is to pass through thespecified voltage range six times.
I made the auto aging program.

Cavity group members
improved the GUI.

Compensation heater (2)aging

If the total heat load exceeds
100 W, the compensation
heater couldn’t compensate
completely.
He level [%]The behaviors of control valves are
improved.

aging

Valve openingThe layout of the COI building
18.9m④2K refrigerator
FY2025~

Pump for 2K refrigerator
FY2023,FY2027③Liquid helium transfer line(TRT)（~100m)
FY2025~①Control system update for liquefierand 2K refrigerator
FY2024~
Helium purifier
FY2024②Helium refrigerator(LR280:exist)
Change HPGS category.
FY202628/Mar/2024

Cross section of the transfer line
Advisory Board on MEXT-ATD Program

We are cooling the superconducting cavities to 2K at STF and cERL.
Recently, we are participating in the ITN(ILC Technology network) project and building anew 2K test station.
Please rest assured, we have enough jobs.

14Summary• In SuperKEKB, superconducting cavities are operatedusing a cryogenic system constructed for TRISTAN in 1988.
• Periodic update is been doing.
• If a turbine breaks down, a new one cannot be made. But
spare turbines are prepared.