Status of High-power rf system
for MR and DR

High-power RF-G
Ken Watanabe (3rd division)

2018/3/15

KEKB review

1

Contents

1. Introduction
2. Summay at Phase1
3. Current situation for Phase2
4. Summary (In order to survive more than 10 years from now (for half century-long to work)

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2Introduction (1)Tsukuba: Test stations (5)The high-power rf system in MR and DR has therole of supplying rf power to the accelerating
cavities, to compensate an enormous
synchrotron radiation loss of electron / positron
beams.

Nikko (8+1)(SC cavity)

The operating frequency is 508.9 MHz and therequired maximum rf power from one klystron is~700 kW, it is a dependent on the cavity system.
Fuji (10)Many equipments that build high-power rf
systems used in SuperKEKB are still many
manufactured at TRISTAN where construction
was done in the early 1980s. There have beenused for more than 30 years since manufacturing,
and are used while continuing maintenance.

(ARES cavity)

Oho (12)(ARES cavity)

DR (1)(DR cavity)*Total 31 stations are used for Phase 2.
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3Introduction (2)2 cavity/ 1 Klystron

Schematic diagram of RF system
1 cavity/ 1 Klystron* Klystron: Toshiba E3732 and E3786
Operation frequency 508.9 MHz
Max RF output 1.2MW (CW)
Efficiency: ~65 % (at saturation)
Vapor cooling (for cooling collector)*Klystron Power supply (KPS)
DC power supply, 3.96 MVA
Cathode Voltage (Vk): 45-90 kV
Anode Voltage (Va): 0-65 kV
Beam current: ~20 A x 2, Max 40 A for 2 klystron* Waveguide system: WR-1500 (Circulator, Waveguide, Water and Dummy loads)
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4High-power rf stations* Photo of the high-power components in power supply building.
D4-A (1:2)

D5-F (1:1)
To a AREScavity

Klystron

1.2 MW water load
(Cir #3)

KPS

Magic-T

To two ARES
cavities

Klystron

30 kW dummy load
(Cir #4)

1.2 MW water load
(Magic-T #4)

1 MW UHF circulator
WR-1500

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WR-1500
30 kW dummy load
(Cir #4)

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400 kW water
Load (Cir #3)
1 MW UHF circulator

5

Future plan

Current situation

first

Future in 20XXWhen the commissioning advances, then more rf power is necessary,: OHO（D4,D5）: Add Two klystrons and one KPS <- First: Fuji（D7、D8）: Add Two klystrons, and update one KPS <- It is dependent on theprogress of commissioning.
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6Summay of operation at Phase1 (1)Many of the troubles that occurred during phase1 operation (about 2900 hours) were
failure and breakdown of equipments due to aging. The beam abort occurred by trouble ofhigh-power components was total 13 times.
Thermo-sensor trouble in coolingchannel of klystron (D11-A): 1
KPS: Crowbar work happened without notice forparticular KPSs. D7-AB (4), D7-CD (4) and D5-FE(2): total 10 times (it happens on from KEKB)
It occurred between PM 19:00 to AM 9:00. It did not occurred
during the day time. -> Why ?

Failure of water supply system for thecollector of klystron (D5-E, D8-A): 2
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7Summay of operation at Phase1 (2)Sight glass (10 of 66)

Cooling system for klystron (Vapor cooling)* Water leaks were happened from cooling systems for the collectorof klystron. The components were broken due to aging.
* Connection point of fin-tube in AFC (Air fin cooler) was also
happened water leak at D7 (1 of 6).
These water leaks were repaired on the maintenance day.
AFC at D7

Repaired by pipe expanding
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Bellows (5 of 30)
8Welding seam (2)Summay of operation at Phase1 (3)High-power components
The WR-1500 waveguide, the high-power dummy and water loads: There was no big trouble causing the beam abort during operation.

1 MW UHF circulator: Total 30 circulator were used for RF stations. 22 of 30
circulators, these are fabricated at 1984-1987. 11 of 22, thesecirculator were done the overhaul for repair the water leakfrom cooling channel.

Magnet: Small water leakage was detected from five circulators
before starting operation. <- it can operates while
supplying water to reserve tank of cooling system (1-4weeks).

: Two more water leak were happened at D7-C
(March 23, small) and D7-D (May 18, serious).
At D7-D, the water leak rate grew to inoperable
amount in a few days. It was disconnected formthe operation (May 24).
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D7-D

9
From ARES cavity

Current situation of high-power system (1)Current situation
Construction of DR for Phase2:
A high-power rf system of DR was constructed using by many spare parts of MR.
Required rf power is 450 kW (150 kW/ cavity) at three cavity scheme. The
conditioning of DR cavity was started from May 2017.
Klystron moved from D11-E
AFCDR cavities
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KPS moved from D4-C

To cavities

Waveguide system moved from MR.
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10Current situation of high-power system (2)Operating time of Toshiba Klystrons before
SuperKEKB Phase2: Water leak was happened on the cooling pipe
for two klystrons at Feb and Mar 2018. Now, theklystrons changed to spare.-> Now, planning
repair in house.
: Fabrication of one klystron using new ceramicfor RF window in output coupler (Manufacturers
have changed) is planning at 2019-2020 or later.
Currently used klystrons are of two types,
Toshiba E3786 and E3732 (late-model).
If the E3786 is broken, repair it to the E3732
specification.
The E3732 specification achieves high stability
and long life expectancy.

Number of Klystron

Klystron

41 for SKEKB
4 for PF-AR

Since 1986

Operating time (hours) x 10^5D11-B (T-40-C)

Operation time (E3786) since TRISTAN
Average : 5.6 x 10^5 hours
Maximum: 11 x 10^5 hours (since 1986)

D4-C (T-46)
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Operation time (E3732) since 2003.
Average: 1.8 x 10^5 hours
Maximum: 7 x 10^5 hours

11

Current situation of high-power system (3)2018/3/15

Klystron 1

Cathode and Heater-Anodepower supply

Klystron 2

KPS (DC power supply): The control cabinet, thecommunication system of crowbarcircuit and the smoothing capacitor
were already updated.
The concern at this time is thefailure of the rectifier on highvoltage section. In the analysis ofinsulating oil in rectifier, noabnormality is found in electricalcharacteristics, but ethane, which isone of the items showing aged
deterioration, is increasing.
Frequent inspection for the highvoltage section is necessary to checkthe inside rectifier.

Crowbar-circuit
Smoothing capacitor

AC 3Φ 6.6kV

AC 3Φ 200 V

12 phase full-wave rectifier：0°(Δ→Y、Δ)、15°(Δ→Y, Y)：50kV、65kV、80kV、90kV taps

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12 phase full-wave rectifier
12Current situation of high-power system (4)Cooling system: Updating the equipment and piping that caused problems as a result of aging advanced
considerably. We were able to replenish spare parts sufficiently this fiscal year, so we are readyto respond promptly when trouble happen.
Phase shifterHigh-power components•Waveguide: We are updating waveguidemanufactured at the early stage of constructionof TRISTAN. Currently there are only a few
remaining in the Fuji area (D7 and D8).
•Circulator：As time goes on, the number of cooling water
channel that cause leakage of circulator whichhave not overhauled is increasing due tocorrosion by aging.
For repair, there is a limit on the cuttable
range of cooling water channel. So, newproduction is desired.
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Magic-T

3dB coupler

Permanent magnet

FerriteCooling water channel
on Phase shifter13

Current situation of high-power system (5)Dummy load
: All of the dummy loads made at TRISTAN
were broken, so they were discarded.
All dummy loads were updated from direct
water cooling type to the indirect watercooling type for SuperKEKB.

Loss on the resister

Water-flow

Water load
: The water leakage due to corrosion of sealmaterial was detected for all Rectangular-typewater loads after the end of KEKB. The causeof corrosion is that tap water (~ 360 μS/cm)
was used as a microwave absorber.
For the long operation without corrosion,•Water quality changes to mixed water (~ 20μS/cm) and controls the conductivity in water.
• Gold coated on the surface of metal seal for
improving sealing performance and corrosionresistance.
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Indirect water cooling type

Water tank: 1.5m
Water tank: 2.5m

Water-loads
Top: Cylindrical-type
Bottom: Rectangular-type

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Water leak due to corrosionof metal seal
14

Summary
In order to survive more than 10 years from now,
(For half century-long to work),
Klystron: Need fabrication and test for klystron with new ceramics (Manufacturers have changed): Repair work to E3732 if previous model is broken.
KPS: Breakdown of high-voltage equipment is the primary concern.
It is exhaustive to do frequent inspections.
High-power components: Waveguide -> No problem: Water load -> No problem: Dummy Load -> No problem: Circulator -> Need fabrication new one and continue repair work for aging material.
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16Back-up slides

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17Number of each components for high-power rf system* Number of high-power rf components for SuperKEKB MR, DR and test stations.
Klystron

TypeNumber

Other

Toshiba E3786
E3732 (late-model)

22
19

1986-2002: 22
2003-2014: 19 (10)(E3876 -> repaired to E3732 )

158

1983-1986: 13, 2010-2013: 2
1983-1986: 8(* 1.2MW CW 508 MHz)

KPS

Type-A (for two klystrons)
Type-B (for one klystron)

Wave guideWR-1500

Circulator

UHF 1MW 4-ports-type

38

1984-1987: 30 (Repaired: 11)
2004-2012: 8DummyLoads

1.2 MW water-load
400 kW water-load
20-50 kW Dummy-load

31942

1998-2002: 19, 2012-2014: 12
2005-2010: 9
2008-2017: 42

1983-1989: Many components•It is divert to SuperKEKB
2010-2016: Manufactured the Shortfall* All of the dummy loads made at TRISTAN were broken, so they were discarded.
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Klystron
Operating time of Toshiba Klystrons afterSuperKEKB Phase1

operation periodProject
Number of Stations
DateMaximum RF power
TRISTAN36
1986 ~ 1995
~ 900 kW
KEKB
291999 ~ 2010
~ 600 kWSKEKB Phase1 30
2016 Feb. ~ June
~ 500 kWSKEKB Phase2 31
2018 Feb. ~ July
~ 700 kW

Reasons for klystron failures TRISTAN KEKB SKEKB incidence rate (%)
Power variation *1
95017.5
Vacuum leak *2
75015.0
Bad electrical strength of DC gun 2407.5
Hysteresis of RF output
1001.25
Breaking of heater wire in DC gun 1
001.25

Number of KlystronReasons for klystron failures from TRIATAN (Total time: 11 x 10^5 hours).
Failure (cause of repair, disposal) occurred at 34 of 80 deliveries.

41 for SKEKB
4 for PF-ARSince 1988

*1: Operating time < 6 x 10^5 hours (only E3786), like as surge*2: Cooling water channel in output coupler -> 6Collector : 3
Bazing point: 1
Melting ceramic window: 1
Unknown: 1・ Power variation: It does not occur in the E3732 specification.
There is a possibility of occurrence of unreformed E3786 type.
・ Vacuum leak ： Significant decrease due to initial improvement
Those with a long operation time are expected to occur.
・ Bad electrical strength of DC gun ： Greatly improved with E3732 specification
In future it is expected to occur in proportion to the driving time.
・ Hysteresisof RF output ： It has not occurred since the initial improvement
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The E3732 specification achieves high stability and long life expectancy.

Operating time (hours) x 10^5Average operation time (E3786) : 5.6 x 10^5 hours
Maximum operating time: about 11 x 10^5 hours
Average operation time (E3732) : 1.8 x 10^5 hours
Maximum operating time: about 7 x 10^5 hours
19

Klystron Power Supply (KPS)
12 phase full-wave rectifier：0°(Δ→Y、Δ)、15°(Δ→Y, Y)：50kV、65kV、80kV、90kV taps

Crowbar-circuit
Smoothing capacitor

AC 3Φ 6.6kV

Cathode and Heater-Anodepower supplyKlystron 1

Klystron 2

AC 3Φ 200 V* DC power supply (Type-A, 3.96 MW), Ripple < 0.5 %•Operation voltage
Vk= 88 kV, Ib = 5~20 A(at Va= 25~65 kV, dependent on the RF output power from klystron)
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20Broadband performance of the circulator
・1MW UHF circulator (SPC)
Frequency: 508±5 MHz
Input: 1.0 MW (CW) Through600 kW (CW) Reflection
Loss: < -0.2 dB
At 1.0MW input, Loss is <46 kW.
Isolation: > -25 dB

#2

#1
#3

#4
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Phase shifter+45°、-45°

3dB coupler
21

Circulator (1)•1MW UHF circulator
Troubles* Water-leak from cooling water channel in phaseshifter* Clack on the ferrite
The circulator continues to use it by repairing thecooling channel. However, the cuttable range ofthe cooling water channel has become low, someoverhauling has come up.

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Magic-T

3dB coupler
Phase shifter22

Circulator (2)Repair of the cooling water channel is done bymachining and then subjecting the surface toalodine treatment.
As a current situation, the circulators arerepairing (overhaul) at two pace per year using
two spare parts.
At present, there are 6 of 31 units with small
water leakage detected. We are trying tocontrol water pressure, water temperatureand keep it to the minimum.
We are planning to repair for two circulator,
and to production new for one circulator.

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The surface current distribution in water-loadRectangular-tank

Cylindrical-tank

RFRF

Full model

Max surface current (at 1.2 MW input): 600 A/m on water tank.

Half model

Max surface current (at 1.2 MW input): 1500 A/m on water tank.
: 2200 A/m on RF window.

Tank material is stainless steel (SUS 304)
Rs = 0.038 [Ω] at room temperature and 508.9 MHz.
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Wallloss ≒ 15 kW

24Water-load
RF window

1.2 MW water-load (Two type): Rectangular-waveguide type x 19 (1998-2010): Cylindrical-waveguide type x 12 (2012-2014)
Rectangular-waveguide type has been usedfrom 1998 to 2010 at Fuji and Nikko. For theSuperKEKB, Cylindrical-waveguide type wasfabricated for update and reinforce at Oho.

RF in
RF in

WDL-R06WC (C)Water tank: 1.5m
Water tank: 2.5m
WDL-R066D (R)The water leakage due to corrosion of sealmaterial was detected for all Rectangular-typewater loads after the end of KEKB. It is causedby using Tap water as microwave absorber. But,
Tap water is good microwave absorbercompared to pure water. Because of, thedielectric loss tangent of Tap water dose notdecrease even at high-temperature. However,it turned out not to be suitable when
considering to use for long-term.
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Water-load
Water quality of water was changed from tap
water (~ 360 μS/cm) to mixed water (~ 20 μS/cm)
in SuperKEKB considering prevention of corrosion
and VSRW performance.
Regarding the surface of the metal seal used forthe load, a conventional one plated is adopted forthe purpose of improving sealing performance andcorrosion resistance.
From now on, I will pursue aged deterioration.

Pure water (7 years)

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Tap water (12 years)
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Cross-section of the metal seal at D10-B
basic copper sulfate

Tap-water (absorber)CuO
basic copper carbonate
basic copper sulfate

RF in

Water-tank(SUS)

Al2O3
RF window

CopperAir

SUS, InconelAl

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AL: wageguide27Cross-section of the metal seal at D11-F：
Pure water（Operating time：2006 ~2013）

Water-tank side (SUS)

Amount of corrosion rate : 30~40um/year
Initial = 0.5mm -> ~0.3mm
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RF window side

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Rectangular-type water load

OutletInlet

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29Corrosion of the metal seal compare with tap-water and pure-water
D10-A Operating time：13 years (tap-water)

D11-F Operating time ：7 years, pure-waterWithout pitting corrosion

With pitting corrosion

シール面まで浸食していた箇所があり、そこ角とE面の外皮が剥がれた。H面は剥がれから微量の水漏れあり。緑青のみ。孔食には
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30
る割合が少ない。緑青の他に孔食あり。
至っていない。