Presented at
KEKB REVIEW COMMITTEE

Monday, Feb.16, 2004

High Power UHF CW Klystrons for KEKBand
One of the Key Techniques
Shigeru Isagawa*Accel Lab, KEK
High Energy Accel Res. Org.
1-1 Oho, Tsukuba-shi, Ibaraki-ken,
305-0801 Japan*E-mail : shigeru.isagawa@kek.jp

Present Line-up of CW Klystrons for KEKB(24) and PF-AR(2).
Number of klystron in each LV age category.

V : 1MW tubes from Philips (VALVO).
T : 1.2MW tubes from Toshiba.
V tubes now only being used forhalf of SC cavities.
Both tubes have been developedand improved originally for TRISTAN
in close collaboration between KEK
and each industry.
Some tubes are very long life,
top runner exceeding 72,000 LVH.
Hatched tubes install M-type (cold) cathode for solving Ba related problems.

Klystron MTBF at KEK
Power Rating

Operation Power

Total LVH

(kW)

(kW)

(h)

V

800-1,000 CW

150 - 850

543,571.7(540,143.5)

38(30)

14,305(18,005)T

1,200 CW

350 - 900

1,177,631.8(1,172,920.4)

34(25)

34,636(46,917)

Failures

MTBF(h)Numbers in parentheses denote the data when initial failuresduring the period below 1,000 LVH are not included, considering
Infant Mortality.
Stable, reliable and long life performances have been assured,
which contributed much to KEKB’s success.
MTBF : Mean Time Between Failures

Operation of a T-tube at the World’s Highest Power Level(1.3 MW CW)
P0 1.3 MW

Klystron characteristics at KEKB frequency, 508.887 MHz.
Constant collector loss curves (in kW) are shown up to 1000
kW.
The highest rf output is 1.3 MW.

P0 1.3MW,
Vk 94.1kV,
Ib 21.2A
η 64.8%,VSWR of the load 1.07.
Max η 65.5% at V k 85.2kV for I b 18.3A.

Performance of T41 as a function of beam voltage.

Klystron Output Coupler
The output coupler of our klystron is completely all right at the power level over 1.3 MW CW.

Ti N

Key Techniques :① Hybrid Cooling System② Titanium Nitride Coating of Window Ceramics

Hybrid (Air & Water) Cooling System

Figure summarizes power balance of the system.
At P0 1.3 MW total power from window 1.63 kW, while body loss 19.4 kW.
About 26% of heat from window removed by air and 74% by water.
Ratio by air increases with rf power P0 .

Linear Heating (1)Temperature rise of (a) cooling air and (b) chiller cooling water containing
10% ethylene glycol as a function of klystron output power up to 1.3 MW.

Linear Heating (2)Temperature rise
(Dissipated power)

islinear.
No abnormal increase
Heating mainly caused byceramic dielectric loss.
Multipactoring effectively
suppressed by TiNcoating.

Suppression of Multipactoring : Most Important Key Factor toGet Higher RF Power.
◎ Structure & quality of film depend on
coating method,equipment usedandcoating conditions.
◎ In our case, DC Reactive Sputtering used.
O2 background highDeposition rate low (1~3 Å / min)TiNxOy rather than TiNx formed with island andcolumnar structure.
Many weak links and High Resistivity.

DC Reactive Sputtering Method

Chamber updated.
DP replaced by CP afterwards.

No quality changes, however, observed.
We checked and confirmed it.

To Optimize Coating Conditionsat KEK Before.

Test Bench Developed

KLYSTRON OUTPUT

Experiments performed with

DUMMY LOAD

Yasunao Takeuchi, KEK.
Klystron PO fed through Y
CIRCULATOR

shaped circulator and 100%
reflected by WG short.
Ceramic tube or quartz tube

WG SHORT

placed at antinode positionof WR1500 (R6) WG.
TMP

Small ceramic samples
exposed to rf field in aquartz vacuum tube.

One can observe the tube and measure T from the top.
One can also observe the inner view of the tube
from the side viewing port made of sapphire.

Temperature Increase Due to Multipactoring
Caused by Large δ of Al2O3.

Ceramic tube broken.

POUPT measurement andside view of plasma.

Suppression of Multipactoring by TiN Coating.

Right sample
Left sample
Al2O3
Al2O3with 120 Å TiN
without coating(NC)PO 50 kW、 P 3.2 x 10-6 Torr

Left
100 Å TiNvsRightNC

PO 25.7 kW

Inner View of The Quartz Tube from The Side Viewing Port
Made of Sapphire. Alumina Samples are Installed Inside.
KLYSTRON POWER PO INCREASEDPLASMA GROWS UP

MAX PO
PLASMA SHRINKS DOWN

PO DECREASEDOptimum Coating Method and Optimum Thickness Determinedby Bench Test.

In Parallel, Measurements Were Also Made on DC Resistanceof Standard Shaped Samples.

Oxygen intentionally added
during plating.

TiNx (more precisely speaking, TiNxOyCz)e.g. x : 1.1, y : 2.3, z : 1.9

SEM Photos of Microscopic Structure of Our TiNxOy Films
Coated on Al2O3 Substrates.

TiN grows up in island or columnar
Form.

Very high resistivity is ensured byoxygen rich grain boundary layersof TiNxOy.

Important Points about Anti-Multipactoring Coating :1) Quality of film depends on equipment as well as methodof coating. Samples made by DC reactive sputtering inHVac always superior to those by ion plating performedin oilless UHV system.
2) TiNxOy is one of the best materials. R is very high andeven increases with thickness and with exposure to rf
field. Pure TiN is rather worse because of its highmetallic conductivity.
3) Optimum thickness for UHF use is 50~300 Å. The thicker,
the better if it’s below 150 Å . 60 Å is adopted for input
couplers and T-tubes. 100 Å tried for V-tubes (KEK andLEP) and excellent results obtained, too.