Status of High-power RF system
for MR and DR
High-power RF-GKen Watanabe (3rd division)

2024/3/26

The 27th KEKB Accelerator Review Committee

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Contents• Introduction•-Currents status and long-term operation plan forKlystron
Klystron power supply (KPS)
Waveguide system and Cooling system• Considering for energy saving in HPRF systems• Summary

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The 27th KEKB Accelerator Review Committee2Introduction
Many equipments, which compose high-power RF systems(including LLRF) used in SuperKEKB, were manufactured
for TRISTAN that was constructed in early 1980s.

Cooling system
for HPRF- Used for more than 35 years since manufacturing.
- Used while continuing maintenance systematicallywithin the approved budget.
The development of elemental technologies in the fieldclassified as high-power RF was almost completed by theKEKB.
- Target of research: Evaluation of the lifespanThe number of stations taken off from operation varies
depending on the location of the failure.
*Currently,- One KPS (D04E and D04F) is stopped due to failure ofaround rectifier, it occurred during startup for 2024ab run.
- One klystron (D07B) replaced in End of Feb 2024 due tobreakdown occurred in tube (trip rate gradually increased).
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Replace*Number of RF stations in SuperKEKB
Total 31 stations are operating in MR(30) and DR (1).
*In addition, we also have six stations for testing each component.
(508.9 MHz x4, 1018 MHz x1 and 1250 MHz x1)-> They also serve as spare part for RF stations of MR and DR.

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AFC (Air fin-cooler)

Introduction
High-power RF (HP RF) system is shown bellow,*Klystron (MR 30, DR 1) Toshiba E3876, E3732508.9 MHz, Max= 1.2 MW(CW)
Efficiency 40~60 % in operation*KPS (Klystron Power Supply): (MR 16, DR 1)
Vk ~90kV, Va ~80kV, Max 20A for a klystron(A-type for two klys and B-type for one kly)
*Waveguide system (MR 30, DR 1)-1.2 MW UHF Circulator (4-port)-Water load (1.2MW and 400kW)-Dummy load (30kW)-WR-1500 (Air filled) Total 1.6 km long.

Condensed water (~ 30 degC)
returns to reserve tank.

D4-A (1:2)

To ARES cavity in tunnel

KPS(DC power supply)

KlystronCollector loss~ 600kW/kly

Magic-TPump(For CIR)

1.2 MW water load(Magic-T #4)*Cooling system for HPRF (MR 6, DR 1)-AFC (vapor cooling) for klystron collector losses. WR-1500 (Air filled)
Cooling capacity ~ 8MW-Pumping system
30 kW dummy load (Cir #4)
for Circulator (2.2 kW pump)for Water loads (22 kW pump)2024/3/26

Vapor~0.1 MPa~102 degC

400 kW waterLoad (Cir #3)

1.2 MW UHF circulator

The 27th KEKB Accelerator Review Committee

Example: D5 power supply building Six klystrons (with cooling tower) arebuilt into one building.
 One AFC is placing at outside
4 of building.

Current status: Klystron
Klystron (Two model are used in MR and DR)- E3786 is first model. And E3732 is an improved version of E3786 with countermeasure of breakdown around electron gun.
- In total, more than 100 klystrons were manufactured from 1982-, including proto-types.
- The malfunctioning ones were discarded, and we currently have “38” of them for SuperKEKB and a test station of D1-AT.
E3786 -> 16 klystrons are working in MR (another one is used at D1-AT).
- Manufactured at 1986~1992 (have 20 klystrons).

Before starting 2024ab-- A possibility of breakdown (occurrence !!!)- Most long operation time is over 130,000 hours (D07B).
E3732 -> 15 klystrons are working in MR and DR.
- Total 18 klystrons have,- 10 klystrons modified to E3732 specification since 1993.
- 8 klystrons manufactured in 2003 to 2013

1987-2024
1993-- Information regarding lifetime is not yet available.
(because statistical data is not enough.)- Breakdown at electron gun has never occurred since
the specification changed to E3732.
Most long operation time is about 100,000 hours (D08C).
* Spare: Total 6 klystrons - E3786 x 3, E3732 x 3 (modified x 2)
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The 27th KEKB Accelerator Review Committee

5Long-term operation plan: Klystron2024-02-26 14:27 RF D07B trip

During a recent operation,a breakdown in tube with sudden increase of klystron output
occurred frequently in a short period time at D07B. Then, theklystron replaced to spare in one day.
(E3786 manufactured in 1987, just over 130,000 hours).

Klystron Input (Drive)-- Trip Rate: 8 times in 2 day (End of Feb 2024) --Cavity pickup- It is predicted that the number of such klystrons will gradually
increase within ~6 years.

Klystron output* It could not be used for operating at this trip rate. However, nodegrease in emissions from electron gun has been observed.

LLRF output

2~3 µsec

For future long-term operation,- Necessary to replace E3786 with “E3732-type”.
- Necessary to manufacture one klystron every 1~2 years,
if 5,000 hours operation time per year is assumed.
Currently, “new manufacturing” has the lowest cost for this issue.
Modification of old klystrons is no longer a good policy...

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The klystron output was responded first by breakdown aroundelectron gun. At this time, the instantaneous amount of change
in klystron output was more than double.
(Va is increased by breakdown, then Ib is also increased.)

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6Current status: KPS
Currently, we have total 21 power supplies.
- 19 power supplies manufactured in the 1980s(A-type x 12 + B-type x 7)
*Since then, it has been relocated as appropriate
depending on the configuration of the KEKB andSuperKEKB.

- 2 power supplies manufactured in 2011-2012 toreinforce RF power for SuperKEKBAAKPSAAAAKPS D5-CD
2011

AAA

A

A

A = for two KLYs

B = for one KLY

For DC part and Control Rack
- Completely updated from the original devices until 2012
(define as 2nd generation).
*PLC, control boards, small control power supply andinstruments with contacts etc..

- For the AC section, we have been updating the aging
components since 2020.
B

B A A
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KPS D4-EF2012* VCB (Vacuum circuit breaker) etc.. -> 40 years since installation.

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Long-term operation plan: KPS
AC section (Target item -> 40 years since installation)- VCB (Vacuum circuit breaker)
Total: 15 stations (12 stations updated in 2023).
Remaining three units will be updated in 2024.
- IVR and Rectifier
Performing continuous monitoring of insulation oil.
Insulation oil will change as necessary.
(Volume-> IVR: 560 L, Rectifier: 7850 L)

Other (Control rack and DC part)

Rectifier- PLC (more than 20 years since installation).
Total: 14 stations
Updating work will being in 2024.
- Smoothing capacitors (~100 pieces)
Completed. -> MR (2012) and DR (2023)- DC part
Necessary to update to 3rd generation,
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PLC
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VCB

Smoothing capacitors
8Trouble (D4-EF KPS manufactured in 2012)

3 phase AC 6.6 kV

2024/01/12 PM at D04EF-KPS- During startup of RF system for 2024ab run,
A discharge occurred around the bushing of the HV-cable connected
between the rectifier and cathode power supply while raising the rated
voltage to 88 kV DC (A discharge occurred at 85 kV).
**History of this KPS,- Manufacturing in 2012.
An inspection after manufacturing -> applied a high-voltage of 110 kV DC
for this line (no abnormalities).
- The rated voltage of 88 kV DC was applied every started up to confirm
that there were no abnormalities (worked w/o any problem until 2022ab).
- This failure occurred after 21,000 hours of operation since the manufacture.
Most of the time of this KPS was operated at around 75 kV.
(due to the storage beam current in HER is not maximum).

HV cablewith bushingRectifier- It is clear that, this is not an initial defect.
The cause of the discharge is currently under investigation.
The situation of rectifier cannot be decided until the disassembled.
**Future action (Note, currently under consideration with company)- Replace with spare (but, currently in use at the D1-AT) for this issue2024/3/26

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9Current status and plane: Waveguide and Cooling system for HPRF
Waveguide system- Worked well without serious failure.
Maintenance is caried out in a planned manner based on the aged deterioration of components.
Cooling system for HPRF
- The most serious problem was the aging of AFC (Air fin-cooler) for cooling the collector loss from klystrons.
There was in danger of collapsing due to corrosion of the steel materials used in structures (with poor water drainage).
- Reinforcing work over the past few years had put the situation out of the way.
- Ongoing of additional repair works:
Reinforcing work for the flames with painting work, updating the invertor-units and motor to drive the cooling fans.
- This will ensure that the cooling system for HPRF can withstand operation for more than 15 years.
Update base plate

More than half of the bolts broke

AFC in MR

Vaper move to AFCVapor

Corroded Base plateand flames

Adding support frame for fan-unit

Example: After reinforcing work for AFC
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Before reinforcing work

The 27th KEKB Accelerator Review Committee

Fan-units

Condensed Water
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Considering for energy saving in HPRF systems
Currently,

Vk= 91.5 kV (Beam Voltage)- Analog circuits use to control the klystron output by a slope of Va.
(Developed at TRISTAN)- They must be set on-site, and it is difficult to constantly make fineadjustments to all of them.

Limit (Va)

Loss= 520kW

For energy saving,- Modification of klystrons is not realistic in our case.
- Optimization of Va control is the most practical.
- Development of new module to control the parameters by remote(using FPGA and EPICS), stating from this year.
Expected reduction-> ~50 kW/KLY for the collector loss
In total, ~1.5 MW of electricity can save in intermediate output range .
** Electricity varies the range of 20~30 MW for HPRF dependingon the storage beam currents in both ring (from Idol to max currents).
Modulation Anode Voltage controller (Analog circuit)

RF out= 850kW

Currently-

Pd vs Po (E3786)

LinearSaturation (Limit for over dive)Collector loss (MW)Drive power (W)Va outDC power

Out power(KLY)

Parameter setting can only be done by Local (on-site).
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Turn up (Va)

Slope
(Pd vs Va)- Simple control method was applied to increase Va voltage
at an arbitrary slope relative to the drive power (KLY input).

The 27th KEKB Accelerator Review Committee

11Summary (For continues operation from 2024 to more than +15 years)
ItemRequire

Additional costfor +15 years

Maintenance cost
/ year

Klystron- Requires at least “seven” E3732 type klystrons.
It is necessary to purchase at least one klystronevery 1~2 years (during in 2024~2034)

600 million yen
for seven klystrons

15~20 million yen

KPS- Requires update again to 3rd generation for DC part. 500~600 million yen
50~60 million yen- Requires update of PLCs for 14 racks
for updating PLCs and otherKlystronand KPS
control- Requires new anode voltage control system for~50 million yenenergy saving. It is possibility that we can expect to for updating this controller
save ~150 million yen in electricity cost/year.
(31 stations)

Now estimating.

Waveguidesystem- Requires spare components for HPRF

100 million yen
for spare components

40~50 million yen

Coolingsystem- Requires additional repair work for AFCs.

100~150 million yen
for repair work for AFCs.

5~10 million yen~ 1.5 billion yen(divide in 10 years ?)~ 140 million yen

Total

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at least Circulator (2), Water load (4) and dummy load (10)The 27th KEKB Accelerator Review Committee(achieved every year)
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Backup2024/3/26

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Klystron

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Klystron
Pd vs Po (E3786)

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17Modification of klystron from E3786 to E3732 (509 MHz, CW 1.2MW)
1) Input/output hysteresis investigation and countermeasures- Presumed the multipacting around the gap of second cavity- Countermeasures -> A crown structure was machined on the gaps.

2) Breakdown around the electron gun with sudden increase of klystron output-

Estimated the creeping discharge of ceramics between the anode and the body.
Measures have been taken to prevent ceramic stains that can cause creeping discharge.

(A) Suppression of barium evaporation from electron guns-

When barium adheres to copper, the melting point of copper decreases and the firing
voltage decreases.
Countermeasure: Adopt a low-temperature cathode that prevents barium from scattering.

(B) Preventing copper sputtering on ceramics and suppressing direct discharge- Countermeasure: Coating high melting point chromium oxide on the anode surface(C) Suppression of direct discharge between the anode and body electrode-Countermeasure: Adopts tapered ceramic to increase the distance between theanode and body electrode*After taking the above measures (E3732), the klystron did not experience the breakdown.

See next slideIncreased distance between body and anode electrode- Countermeasures for the breakdown around electron gun

chrome oxide

BaDDM-type cathode(Low temp.-type)First model（E3786）

Improved（E3732-type）

Maximum electric field strength（Vk: 90kV、Va: 65kV) was shifted from 44 kV/cm (E3786) to 13 kV/cm (E3732)** Reference: Breakdown electric field strength of electrode with barium coating (evaporates from gun filament)= 100 kV/cm

1) Input/output hysteresis investigation and countermeasures

Crown structure* When changing the magnetic field of focusing coil near the second cavity, the characteristics of klystron changes.

List of klystrons- Time occurred breakdown(Specification of E3786)•

If the initial treatment of theelectron gun is done well, its
lifespan will be extended.

D07B
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The 27th KEKB Accelerator Review Committee

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