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RF Sourced and Modulator

(mainly for Linac)

S. Fukuda KEK: High Energy accelerator Research

Organization

For School for Accelerator Technology

And APplication

2012/2/1 S. Fukuda Schooi for Accelerator Technology and

Application 1

Introduction

RF Source Importance

• Modern Accelerator is so called “RF accelerator”, and RF Is the key technology.

• Accelerator frequency is ruled by the existence of the rf source of matched frequency.

• RF system is expensive and large fraction of total cost is shared in RF source. Therefore choice of RF is very important.

• RF source is the source of failure (arcing etc.) and careful availability consideration and constant effort of maintenance are required.

2012/2/1 S. Fukuda Schooi for Accelerator

Technology and Application 2

Index

1.Introduction 2.Introduction : Accelerator and RF 3.RF Source suitable to accelerator 4.Klystron Theory 5.Klystron parameters 6.RF Source other than Klystron 7.Modulator General 8.Modulator- Line Type Modulator 9.Modulator- Other than Line Type Modulator



Introduction(1) Circular Accelerator

Lorentz Force Equation

F=e・E+e・v x B

F

v

B

Cyclotron

Electron has a circular orbit

In the magnetic field.

Revolution time is constant if B=const.

RF field is repeadedly used.



History of the Linac(1)

Ising(1924)

Wiedroe’s Linac

(1928)

Alvarez Linac

(1946)

Acceleration

Acceleration

Drift (constant velocity)

Drift (constant velocity)



Introduction(2) Linear Accelerator (Linac)

Charged particles are accelerated linearly.

High frequency electromagnetic wave (micro-

Wave) is used for the acceleration.

Principle:



History of the Linac(1)

• Linac was developed after the World War II. → Due to the Radar Technology for military purpose Short pulse high power microwave source. Klystron was invented by Varian Brothers, in 1939. (a few microsecond, 10 MW 10cm microwave) Related high-power power supply

(300kV,300A pulsed source) RF Technology is the key technology for linear accelerator

Reflection



History of Linac(2) • Stanford University Electron Linac(1950-)

Linac=Very big electron microscope

R. Hofstadter studied nuclear structure by electron

scattering(1954-57) and was awarded a Nobel prize (1961). Nuclear surface

(~10-13 cm）

Smooth Density

Change

Comparing with Dr. R. L. Moessbauer, Nobel

Winner In 1961, he was called the son of

Big Science.

• 2 mile accelerator was constructed in SLAC

(Stanford Linear Accelerator Center, CA, USA) (1966-)

• SLC(SLAC linear Collider) was constructed (1983-)

• Both cases, RF source (Klystron) was developed in SLAC



Variant of Linac - Electron Linac

• Since the electron mass is light, it is easy to be accelerated up to the light velocity (velocity is constant).

→overall structures are the same

• Longest Linac is SLAC 2-mile Linac (3.2km and 20GeV)

• Second longest linac is KEK linac (500m and 8 GeV)

• Small linac was developed for medical use (2-3m and 30 MeV)

• Short pulse linac of which pulse duration of a few to 20 microsec.

-----wavelength of 10cm (S-band), 5cm (C-band) and X-band (2.5cm)

• Long pulse linac of which pulse duration of a millisecond

------wavelength of 20cm class (L-band, ex., 1.3GHz)



Variant of Linac - Proton Linac • Since the proton mass is 2000 times heavier than electron, it is

hard to be accelerated up to the light velocity and depending on the b(=v/c), several structures are used in proton linac and each structure has a suitable frequency. – RFQ structures-----VHF band such as 201MHz-432MHz – Alvarez structures/DTL(Drift Tube Linac)-----same as RFQ – ACS(Anular Coupled Structure), SCS(Single Coupled-cell Structure) etc------

-Harmonics of low b section (0.8-1GHz)



RFQ Structure DTL Structure Element of ACS

RF Sources suitable for accelerator

• Factors required to accelerator rf source 1. Frequency range - higher than 0.3 GHz, klystron is best rf source. Less

than 0.3 GHz, Solid state amplifier, IOT and Tetrode are used.

2. Peak power capability-related with energy gain, short linac, and cost benefit. How to minimize the discharge rate in tube and structures.

3. Average power capability – related with duty cycle or repetition rate. Cw accelerator.

4. Gain – relate with driver amplifier. High gain is preferable; Generally klystron is high gain such as 50 dB. IOT is around 20 dB. Power tetrode is poor gain.

5. Phase stability – klystron is voltage driven device and if applied voltage is stable, phase property is excellent.

6. Simplicity, Availability and Long life – klystron is much matured device and satisfy these requirements.



Available RF Sources –states of art now

Average power vs frequency plot Peak power vs frequency plot

Frequency range

Suitable for accelerator

Most available rf source for

accelerator use, klystron is

a best device for

average and peak power

capability.

Efficiency (%) Bandwidth (%)

Gain (dB)

Relative Operating

Voltage

Relative Complexity of

Operation

Gridded Tube 10-50 1-10 6-15 Low 1

Klystron 30-70 1-5 40-60 High 2

Magnetron 40-80 High 3

Helix TWT 20-40 30-120 30-50 High 3

Coupled Cavity TWT 20-40 5-40 30-50 High 3

Gyrotron 10-40 1 30-40 High 5

IOT 10―70 １－５ 20－25 High 3

Comparison of various RF sources



Klystron Theory



Klystron Structure and Mechanism

Key Component of Klystron • Electron Gun

• RF Cavity

• Drift Tube

• RF Window

• Beam Collector

• Focusing Magnet

• Cooing System

Basic Mechanism of Klystron

• Electron is velocity-modulated in an input cavity.

• Then, electrons form bunch; density modulation

• Bunches are de-accelerated in an output cavity

---> beam energy to rf power

See: Inverse process of accelerator

Accelerator ----> rf power to beam energy



Important parameter; Perveance

Simon's formula Definition of Perveance

Low perveance klystron has

high efficiency but applied

voltage is high.

Accelerator Laboratory, KEK

It characterize the space charge

force and deeply related with the

bunching formation and therefore

with efficiency.



Beam Bunching Theory

Basic Mechanism of Klystron(Linear theory) • Electron is velocity-modulated in an input cavity.

• Then, electrons form bunch; density modulation

• For this bunching mechanism, a simple linear theory is educative. There are two

approaches:

- Ballistic theory: electron which has a modulated velocity propagate without any

interaction with other electrons.

- Space-charge wave theory: entire electrons behave like a wave which is

ruled by space charge force, and automatically it contains the space charge force

effect.

More Realistic Analysis (large Signal Analysis) • For the interaction region near to output cavity, linear theory is not applicable and non

linear large signal analysis are required.

• One dimensional analysis: Disc model

• 2.5 dimensional analysis: Particle in cell Analysis including magnetic interaction

• 3 dimensional analysis: MAFIA / MAGIC code



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Klystron: Ballistic Theory (1) Treatment of individual electrons without interaction

Inititial electron energy:

Electron Energy gain in the input cavity:

Assume V1<<V0 : Linearization The arrival time t2 in the second cavity depends on the departure time t1 in the first cavity with the assumption of an infinite thin gap:

or with

and called bunching parameter

0

2

2

1eVmu

teVmumu sin2

1

2

11

2

0

2

2

1

0

1

0 )sin1( tV

Vmuu

)sin2

1(0

1

0 tV

Vmuu

1

00

1

0

11

1

0

10

112 tsinV2u

mV

2u

1t

)tsin2V

mV(1u

lt

u

ltt

0

0u

1

10

V2

mVX

1012 tsintt X


Technology and Application

17

Klystron: Ballistic Theory (2) Because of charge conservation: Charge in the input cavity between time t1 and t1+dt1 equals the charge in the output cavity between time t2 and t2+dt2

then

0

1,57

3,14

4,71

6,28

0 1,57 3,14 4,71 6,28

Input Gap Departure Phase

Ou

tpu

t G

ap

Arr

iva

l P

ha

se

X=0

X=0.5

X=1

X=1.5

1

2121

1

22211

t

ttcos1

t

ttt

d

dIIandX

d

dwithdIdI

1

12

tcos1 X

II

Fourier transformation of the current in the output gap I2

)]sin()(cos[ 0202

1

02

tbtnaII nn

n

)()(cos)/1( 2022

0

0

tdtnIan

)()sin(cos)/( 1110 tdtXtnIan

0)()sin(sin)/( 1110

tdtXtnIbn

with Jn Besselfunction of the n- th order

)()(sin)/1( 2022

0

0

tdtnIbn

)(cos)(2 011002

tnnXJIII n

)cos()(2 010 tXJII

PVIVIP Beam58.0)2/)(2/(58.02 00

2012/2/1 S. Fukuda Schooi for Accelerator Technology and Application

18

Klystron: Space-Charge Waves Theory • Space charge forces counteract the bunching • Any perturbation in an electron beam excites an oscillation with the plasma

frequency • Therefore we have 2 waves with the Phase constants

• And therefore • The group velocity is • The density modulations appear at a distance of

0

0

0

m

ep

)/1(1

bb pee )/1(

2bb pee

uee/b

)/1/(1 pee uu )/1/(2 pee uu

uddu eeg b /

pep u /2

This means that the drift space or the distance between cavities is determined by the plasma frequency (klystron current) and the electron velocity (klystron voltage)

and is given by . 4/ p

More realistic approach: Space charge of electrons in the metallic tube is

reduced due to the mirror effect. Therefore plasma frequency reduced factor is

Introduced, and reduced plasma frequency (wavelength) determines optimum

length of klystron.



19

Comparison of the beam trace among

two approach

Ballistic Analysis Approach

No space charge interaction

Space-charge wave approach

Space charge repulsion is included



More Realistic Analysis of Klystron

One dimensional disc model • Constant diameter beam is expressed as series of disc and moving as ballistic manner. • Space charge among discs is considered

• Cavity-beam interaction is properly considered.

2.5 dimensional PIC program • Electron particle in 3D • Solving under axial symmetric condition • Space-charge and magnetic field effect are included. • Realistic approach and fairly good agreement between simulation and test



Klystron Parfameters



Klystron Efficiency Issues

•Klystron efficiency is important for high duty machine and cw accelerator use •There are two approches to raise the klystron efficiency

- Low pervence beam klystron High voltage, low current way and arcing in the gun area is concerned for high power application Multi-beam Approch to decrease voltage

- Using Higher order harmonics cavity • From the basic fact that saw-tooth like voltage

modulation gives the high efficiency • Most popular way is using 2nd harmonics

cavity in the bunching cavity region • More complicated structure to introduce

multiple harmonics cavities - By using computer simulation,a wide band tuning

klystron and a very high efficiency klystron such as 80% are realized.

Concept for high efficiency tube

Using the harmonics

Another way is using long distant

drift tube to mixing second

Harmonics component by split

Orbit due to space charge.



Multibeam Klystron Idea • Klystron with low perveance: => High efficiency but high voltage • Klystron with low perveance and low high voltage : =>low high voltage but low power

Solution • Klystron with many low perveance beams: • => low perveance per beam thus high efficiency • low voltage compared to klystron with single low perveance beam Measured performance

Operation Frequency: 1.3GHz

Cathode Voltage: 117kV

Beam Current: 131A

mperveance: 3.27

Number of Beams: 7

Cathode loading: 5.5A/cm2

Max. RF Peak Power: 10MW

RF Pulse Duration: 1.5ms

Repetition Rate: 10Hz

RF Average Power: 150kW

Efficiency: 65%

Gain: 48.2dB

Solenoid Power: 6kW

Length: 2.5m

Lifetime (goal): ~40000h THALES TH1801

2012/2/1 S. Fukuda Schooi for Accelerator Technology and Application 24

Klystron Characteristics

• Child’s Law- In space charge limit current, emission current is as follows.

where is perveance, and I is current, and V is applied voltage. • Then, power is Power’s variation

• Klystron’s Impedance

Therefore, klystron’s impedance varies with applied voltage.

2/3VPI m

2/5VPVIP m

VPVP

V

I

VZ

mm

12/3

V

V

VP

VVP

P

P

m

m

2

55.2

2/5

2/3

mP



25

Phase Variation of RF from Klystron • For linac, phase stability of RF is extreamly important

because variation dirctly reduces to energy variaion DE • Since klystron is voltage driven device and votage determine the electron

velocity, rf phase strongly depends on the voltage variation. and

– Usual S-band tube operating at 300kV range, this phase variation Is roughly 6-8 deg./(dV/V%). If you want to get DE /E=0.1%, then 0.025% of voltage flatness is required.

• Water cooling variation of tube body also causes rf phase variation. This happens since water temeperature changes the gain cavitiy‘s detuning frequency and bunch center changes from original position.

– this phase variation Is roughly 0.5-1 deg.phase/1 deg water temp.

-8

-6

-4

-2

0

2

4

6

8

10

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Ratio of applied voltage @300kV (%)

Ph

ase (d

eg

ree)

simulation

measured

-25

-15

-5

5

15

25

-10 -5 0 5 10Dwater temperature [degree]

Do

utp

ut

ph

as

e [

de

gre

e]

free (ANSYS)

rigid (ANSYS)

Experiment

2

2

0

0

0

0

)1(

11

22

mc

eVc

L

u

L

D)

%deg

(86)( VVV DD

D



26

Other issues for Klystron

• Other issues important to handle klystron are omitted here ad only lising up below.

• Beam focusing of klystron :Brillouin focussing or confined flow:

• Electron gun issues and arcing problem there

• RF window and its failure or protection from break-downer.

• Multipactoring in the window / drift-tube

• Cathode emission property and observation of emission history.

• Instability by various reasons



27

RF Source other than Klystron

• Klystron comprises of several cavities and their sizes are proportional to wavelength. Therefore, lower is the frequency, larger is the klystron size and actual lower limit of klystron is around 300MHz.

Tetrode

• Proton linac low beta section such as 200 MHz, Tetrode (or Triode) is used. RF system is complicated because each grid requires rf circuit.

Final stage ( a few MW) has a poor gain such as 6dB, and multi-stage

amplifier system is employed.

IOT(Klystrode)

• For 100-1300 MHz Range and up to 100kW (peak or cw), IOT is used, High efficiency such as 60% is achievable. No saturation nature and even under LLRF control, high efficiency is achievable. Low gain nature requires relatively large driver amplifier.

Solid – state amplifier

• For the same frequency range as IOT, promising device



RF Source other than Klystron (2)

Magnetron

• Magnetron is an oscillator and its oscillation frequency varies. Feedback to stabilize or tracking the frequency variation is inevitable. Crossfield amplifier is not so popular. On the other hand since magnetron is cheap, this rf source is used for small accelerator application

Gyroklystron

• Since gyrotron is oscillator, gyroklystron was intensively studied for NLC (X-band or more higher frequency ILC). Higher the frequency more suitable this device is, while now intense study is not reported. Around 30-50MW output level was reported. Expensive and difficult handling then klystron.



30kW IOT 1.3GHz for ERL Use

30ｋW IOT（CPI)

Specification



High Efficiency but low gain device Electron

bunch

Electron bunch is modulated in cathode-grid region, and no higher frequency device. UHF band there are lots of broadcast transmitter Application of around 100kW cw..

Progress of Recent Solid State Amplifier



For CW use, solid-state amplifiers replace to Klystron. High efficiency is achievable. In KEK, 20-30 kW cw solid-sate amplifier (1.3GHz)is more likely candidate than IOT or Klystron for cERL.

Modulator



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Requirement to RF source from

accelerator specification

• Energy Gain E

» It depends on the accelerator final energy, and it is the SQRT of P (proportional to electric field)

• Energy width E/E should be as small as possible

» this corresponds to minimize ΔP/P and Δθ/θ.

• In order to achieve these requirements, good quality of

modulator (good stability of output pulse) is required.



Various Modulator

• Modulator for short pulse ( microsecond order)

• Line type modulator: most popular, low cost, simple – Pulse forming

» PFN (pulse forming network)

» Blum Line

• Hard tube pulser (Solid state amplifier) – Pulse amplifier

– Pulse generation by IGBT

• Magnetic compressor modulator

• Marx Generator

• Modulator for long pulse( a few hundred microseconds to a few milliseconds)

– IGBT modulator with bouncer circuits

– Marx generator



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Modulator(1)

Line-type Modulator



KEKB Klystron and Modulator

Max. Peak Output Power 108 MW

Max. Average Output Power 30 kW

Pulse Transformer Ratio 1:13 .5

Primary Output Voltage 22.5 kV

Primary Output Current 4.8 kA

Total PFN Capacitance 0.6 µF

Pulse Rise time(10-90%) 0.8 µs

Pulse Flatness(P-P) 0.3 %

Pulse Width 5.6 µs

Thyratron Anode Voltage 45 kV

Thyratron Anode Current 4.8 kA

Thyratron Average Anode Current 1.3 A

Repetition Rate 50 Hz

Modulator Specifications

Output Power 46 MW

RF Pulse Width 4.0 µs

Efficiency 45 %

Perveance 2.1 µA/V3/2

Beam Voltage 298 kV

Repetition Rate 50Hz

Klystron Specifications

Pulse Transformer Tank

Klystron

Pulse Modulator SLED



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Circuit Diagram of KEKB Modulator

Klystron voltage,

current

waveforms and rf

waveform

Accelerator Laboratory

37

• PFN-type modulator

• LC resonant charging

• De-Qing

• Single thyratorn switch

• All components are unit type



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Principle of Line Type Modulator

(Most popular modulator)

• Basic Circuit

• Pulse width is determined by the traveling time of the line

• Matching condition (Z0 is characteristic impedance of co-axial line)

lineoflengththeiswhereu

.2

RZ 0



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Line Type Modulator

(Most popular modulator)

DC power supply

Charging Circuit

Discharging Circuit

Pulse Transformer

Klystron

Inverter P/S



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Discharging Circuit

• Cable Equivalent circuit

• Analysis of N stage pulse forming network (PFN) 1st stage

r-th stage

n-th stage

Solving this exactly is difficult and using Laplace transformation with suitable approximation or computer simulation is frequently used.

EdiiC

tiRdt

tdiL

t

))()((1

)()(

210

1

1

Open end

0))()((1

))()((1)(

10

10

dii

Cdii

Cdt

tdiL

rr

t

rr

tr

0)(1

))()((1)(

01

0

di

Cdii

Cdt

tdiL

t

nnn

tn



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Analysis of PＦＮ

• Laplace transformation

– r-stage

– General solution

If R=0 (Open end condition)

If matching condition( )

0)(1

)()2

()(1

11

pI

CppI

CpLppI

Cprrr

2

2

2

22

22

2

11cosh

1

2

)1sinh(sinh)2(

)1cosh(

)1sinh(sinh)2(

)1sinh(

sinhcosh)(

p

LCL

bb

L

Ea

nnbp

naB

nnbp

naA

where

rBrABeAepI rr

r

nn

nCEpI

sinh)1sinh(

sinh)(

1

N

N

N

N

NN

N

N

n

N

CCLLwhere

CLppC

L

n

n

pCppI

VnpZ

11

1

)coth(1sinh

)1sinh(1

)(),(

CLCLRNN

)1(

2sinh)12

sinh2()1sinh(

sinh)(

2

1

N

N

C

Lp

N

N

N

ne

C

Lp

V

nn

nCEpI



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Characteristics of PFN

• For n-stage PFN

pulse width

Characteristic impedance of PFN

Requirement of PFN-Parameter

• Klystron’s operation point Vs, Is then Zs = Vs / Is

• Step up ratio of pulse transformer n, then primary impedance is ZS = ZS / n2

• From matching condition, PFN characteristic impedance ZPFN = ZS

• Pulse width is come from Klystron’s requirement or system design.

• Total capacitance of PFN is derived

by energy equation: energy stored in

PFN=energy supplied to the load

• stage number is determined by flat top condition

nCCCnLLLwhere

LCnCL

iNiN

NN

,

22

C

L

C

LZ

N

N

PFN

2

0

2

2

2

1

C

pp

T

ppCT

V

IVCor

dtIVVC



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PFN Simulation Example

L=1.3[mH] L2=0[H] C=0.015[mF] Stage number of PFN 1,3,5,10,20



PFN Issues (Pulse flat top)

• Since charging-discharging cycle is repeated in each PFN stage, flat top is folding shape of n charging waveforms. Ringing of flat top of the pulse is strongly depend on the stage number n of the PFN. For large n, smoother flat top, but cost is expensive.

• Usually, capacitors varies a few to ten % from nominal, and such variation should be checked by analysis. C -> C+ affects the variation of Z and current i, and then causes to V+ ,

• On the other hand, effect of the inductance variation is,

• Therefore, for the flat top adjustment, variation of capacitor is more serious (4 times larger effect). In order to compensate the droop come from pulse transformer, larger capacitor should be set at the first stage, and positioning with the capacitance value is recommended.

• Since capacitance is hard to change, introduction of variable inductance is often employed. Variable mechanism example: mechanical shorted structure, cylinder to using eddy current effect.

VDCD

04

1)

L

L

V

VL

DD

000

,,12

11)

3

2

4

1()))

C

C

C

C

C

C

V

V

V

V

V

VICZCC

DDDDDD



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ＰＦＮ Issues (Pulse flat top)-II

First modulator for PF injector linac

n=16

C=0.018mF

L=0.67mH

Problems: Capacitor’s lead inductance and

connecting wire inductance is comparable with

nominal inductance of 0.67mH.

Cylindrical capacitor to reduce lead inductance is

Introduced.

Second modulator for KEKB injector linac employs

Parallel connected PFN to overcome above problems.

n=16

C=0.015mF

L=1.3mH

N-parallel PFN is frequently used to achieve easy flat

top adjustment by variable inductance.

sZCCLn

CLZ

Tii

ii

m

5.322

6

sZCCLn

ZZZCLZ

Tii

iior

m

5.522

7.4//4.92121



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Capacitor Bank Consideration

W

v

1

2r0E

2

Energy Density of Capacitor

W：Stored Energy(J)

v：Area of Dielectric Material(m3)

：Dielectric constant

０： of vacuum(8.85x10-12F/m)

E：Field Gradient(V/m)

•No-Healing

•Self-Healing(SH)

50~100V/µm

~200V/µm Metal icon

Thin Film by Evaporation

A few of 100ｘ１０－８

Dielectric Film Dielectric Film

Metal icon

Metal Thickness~7µm

Dielectric Film

Dielectric Material：Capacitor Thin Film(εr~4.5), plastic Film(εr=2.0~2.3)、



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Capacitor

Down-sizing of capacitor

V 2W

E2

Case volume V of capacitor:

W : stored energy : dielectric constant : packing factor E : field strength( ~ 60 V/µm for no-healing capacitor)

Self-Healing Type Capacitor

Test Capacitor Breakdown Capacitor Element

ATF Modulator 0

50

100

150

200

250

300

105 106 107 108 109 1010

SH

NH

Ref(n=20.8)E

lectr

ic f

ield

str

en

gth

(V/µ

m)

Lifetime(Shots)

L

L0

V

V0

n

Accelerated Life Test Electric field strength vs Lifetime

50pps X 7,000H X 8 Years

Capacitor

Volume

1/4

Cross section of dielectric/electrode

Configulation(not to scale)



Switching Device

• Typical switching device for high power application

– Spark-gap: Trigatron such as Ignitron and Crossatron

– Thyratron: most popular high voltage switching device



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Switching Device

• Important feature of thyratron • Thyratron is switching the high voltage pulse and current of

10kA peak is switched off. If it is not properly controlled, pulse time jitter is seriously generated.

• A keep-alive circuit or pre-trigger circuit is very important to reduce the pulse jitter. Many thyratron has a hydrogen reservoir in side and inner pressure of hydrogen is kept proper level. Frequent watch and adjustment of reservoir voltage are very important.

• Ranging techniques to determine the proper operation voltage of reservoir of the thyratron:

Change the reservoir voltage during the operation and observe the upper limit in which continuous discharging start and the lower limit in which thyratron quits operation, and then operation voltage of reservoir is set in the middle.



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• Modulator failure distribution

Total operation time : 6322 Hours

Machine failure time : 114 Hours

Operation Statistics in FY2007

•Keep-alive current tuning

•Thyratron failure

•Air cooling fan

Modulator availability=0.997

Modulator failure time = 17.6 Hours

• Linac failure distribution

53% of RF failure

Reliabilty of an RF system is directly linked to

the linac availability.



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Long term evaluation of the thyratron used in KEK

Life distribution of thyratron : total=74

• Period(September 1998〜 February 2008） Failure causes

Established using way •Acceptance test (all delivered are tested and only accepted ones are used）

•Replacement before life (at important section, every 2 years (-14,000hrs), new tubes are used）

•Reuse (replaced tubes mentioned above are stored as stand-by and set in not-so-important section）

•Prediction of the life (judged by the failure mode of keep-alive)

•Maintenance in a year（reservoir voltage adjustment、check of jitter and pulse timing）

Revised CX2411

Quality varies with year lots and company

Life is longer to 33.4 khrs year by year. Maintenance aims for min. cost and max. life operation.

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80

CX2410KF241L4888B

Nu

mb

er o

f T

ub

es

Time(kHours)

Arcing etc

Reservoir failure

G1 arcing

Failure of keep-

alive: 25%



Status of Thyratron

Litton EEV ITT L4888B CX2410K F-241

• 45 kV, 5 kA, 6 µs, 50 Hz Switching

Operation period ( Sep. 1998〜 Feb.2008) : No. of Thyratrons=74

• Lifetime Profile • Failure Modes Distribution

Thyratron Quality ?

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80

CX2410KF241L4888B

Nu

mb

er o

f T

ub

es

Time(kHours)

Driver circuit

•Keep alive has ~250 mA dc current at 100 V

• Thyratron circuit

Keep alive Failure

G1 discharge

High voltage

Break Down

Reservoir Failure

Others



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Maintenance activity for Thyratrons

•Acceptance Test

Break down rate < 0.05/ 1 hour at 100 hours operating

Switching Jitter < 10 ns

Check anode delay time

•Exchange new thyratron in advance

Most important modulators ( such as Buncher section)

at intervals of two years(~14,000 hours) , Exchanged one is reused.

•Checking and Tunning

Reservoir voltage and keep-alive current, switching jitter

•Regular maintenance

Thyratron Ranging and exchange bad one at intervals of one year

Thyratron MTTF : 33,400 hours (as of Feb. 2008)

53

To maximum lifetime, and to minimize cost.



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Matching and mismatching

• For lossless transmission line, current transformation is

• And its inverse transformation,

• Therefore, depending on , waveform is different after t=2.

• matching condition and no reflection

• mismatch (positive mismatch)

extreme case :open end

lower operation point than normal

• mismatch (negative mismatch)

extreme case :short end

pp

p

g

p

p

gg

eRZ

RZe

RZ

RZ

RZp

eV

eRZ

RZ

e

RZp

V

pZRp

Vpi

42

0

02

0

0

0

2

2

0

0

2

00

)(1)(

)1(

1

1

)()coth()(

6,4,2),(

00)(01)(

)6()4()()4()2()4()2()2(1)( 2

0

0

0

0

0

0

0

0

nntt

tfortUandtfortUwhere

tUtURZ

RZtUtU

RZ

RZtUtU

RZ

RZtU

RZ

Vti

D

DDDD

R

0ZR

0ZR

0ZR

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Protection Circuit for load discharge etc. • If discharge occurred in klystron or pulse transformer circuit, pulse

reflection occurs due to the mismatching effects. Serious case, undesirable inverse voltage causes the failure of various devices. Therefore, protection circuit is employed in the system and it force to stop operation with a pulse or a few pulses later.

• Fast protection: End of line clipper (within a pulse response)

• Rather slow protection: reversed shunt circuit Average of inversed current due to the load discharge is sensed and stop operation by meter relay etc.

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스티커 노트

펄스 반사, 역전압->EOLC, 역 션트 회로 보호 부하 방전으로 인한 역 전류 평균이 감지되고 미터 릴레이로 동작 정지됨

Charging Circuit is replaced by Inverter P/S

• Charging Circuit can be replaced by rather small inverter P/S.

• It is possible to eliminate charging reactor, and therefore modulator becomes smaller.

• Stability depends on the inverter’s

stability. De-Qing circuit is

eliminated.

• Inverter’s failure rate is carefully evaluated.

• Charging is conducted linearly.



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스티커 노트

충전회로는 인버터 파워로 대체

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충전 리액터 삭제 가능, 안정도가 좋으면 De-qing회로가 제거됨 충전은 선형으로 실행됨

Compact Modulator (Charger is replace to Inverter P/S)

1.8ｍ

4.7ｍ

Compact Modulator

Present modulator

57

• Start the development for C-band scheme of SuperKEKB

• Decrease the modulator size to one-third that of the

existing modulator.

•Switching power supply is essential to reduce modulator size.

•Single unit for easy maintainability

• Output voltage 50 kV(max.)

• Output power 30 kJ/s

• Voltage regulation ±0.1%

• Efficiency >80%

• Power factor >85%

• Input voltage 420 V, 3 Phase, 50 Hz, AC

• Cooling Water 5 liters/min.

• Size 19” rack mount

< 530mm(H), 480mm(W),

< 700mm(D)

• Operation Single and Parallel operation

Specifications



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Discharging and Noise Problem

Discharging Circuit

True grounded position for

high power discharge current.

1 point earthing principle

Tri-axial cable is

desired

Multi-grounded with

filtering



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스티커 노트

필터링으로 다중 접지됨

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고전력 방전 전류에 대해 실제 접지 위치. 1 점 접지 원리

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동축 케이블이 필요함

Discharging and Noise Problem (II)

• Since pulse modulator produces a few microsecond high power pulse, it is a serious noise generator. Especially the cabinet which contains thyratron, high voltage switching device, generate large noises. Control signal (relay signal etc.) and analogue monitor cable from this cabinet should be completely filtered from high

frequency noise.

• For control signal for relay, signal is

come from discharge cabinet thru low

pass filter

• Analogue signal is come from discharge

cabinet thru co-axial choke, which

reject common noise.

Discharging Cabinet

Which generate serious

noise

Charging Cabinet De’Qing cabinet Control Cabinet

Filtering case EMI mesh contactor



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스티커 노트

노이즈 제거 -> 싸이러트론, 고압 스위칭 장치가 큰 소음을 생성함(방전 캐비넷)

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제어신호(릴레이 신호 등)와 아날로그 모니터 케이블이 고주파 노이즈로 부터 완전히 걸러진다.

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릴레이 제어 신호에 대해 신호는 로우 패스필터를 거쳐 방전 캐비넷으로 간다

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아날로그 신호는 공통 노이즈를 제거하는 동축 초크를 거쳐 방전 캐비넷으로 간다

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Modulator other than Line-Type


Application 60

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라인 타입 외의 모듈레이터

Pulse Modulator Using Multi-Series Switch(1)

Series Switch

• Series Switch Modularor

Storage Capacitor PS PS

Cell Modulator

• Marx Type Modulator

• Flexible Active waveform control • Pulse waveform • Pulse flatness



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직렬 스위치모듈레이터 - 싱글 스위치??

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막스 타입 모듈레이터

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스티커 노트

펄스 파형, 편평도 조절이 능동적임


Bypass-Diodes(Freewheeling diodes)

Energy Storage Capacitors 17.3µF

Cell-Modulator

IGBT Mitsubishi CM1200-66H(1200A,3.3kV)

Resister Load 10 Ω

10-Stage Test Modulator

Max. 20 kV




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10단 테스트 모듈레이터

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IGBT: CM1200HB-66H(1200A, 3.3kV) Applied Voltage: 2 kV/stage, Repetition rate: 2 Hz Storage Cap.=17.3 µF(film), Resistor Load=10 Ω

20 kV, 2.0 kA Output Pulse Operation

2.8 µs

-500

0

500

1000

1500

2000

0 1 2 3 4 5 6 7

Ou

tpu

t C

urr

en

t(A

)

Time(µs)

With compensation

Without compensation

1st stage(for compensation)

3rd-10th stage(Main trigger)

2nd stage(for compensation)

Trigger Timing Chart

Active Waveform Control

IGBT: CM1200HA-66H x 5 + CM1200HB-66H x 5 Applied Voltage : 1 kV/stage, Repetition rate: 2 Hz Storage Cap.=17.3 µF, Resistor Load=4.1 Ω




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Parameters K2-3 Unit

RF Peak Power 30- 60 [MW]

Pulse Voltage 280 - 450 [kV]

Pulse Current 230 - 450 [A]

Modulator Peak Power 160 [MW]

Modulator Average Power 0,5 - 100 [kW]

Mains: 1-phase / 3-phase 3

Cooling Water

RF POWER UP TO 60 MW MODULATOR PEAK POWER UP TO 160 MW

Commercial Solid-state Amplifier

(Scandinova)



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Series Switch Modulator

(Diversified Technologies, Inc. )

IGBT Series Switch

140kV, 500A switch shown at left in use at CPI

As a Phase II SBIR, DTI is building a 120 kV, 130 A version with a bouncer to be delivered to SLAC at the end of 2006

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SNS High Voltage Converter

Modulator (Unit installed at SLAC)

RECTIFIER TRANSFORMER

AND FILTERS SCR

REGULATOR SWITCHING

BOOST TRANS-

FORMER

HV RECTIFIER AND FILTER NETWORK

13.8KV

3Ø

INPUT

LINE CHOKE

5th

HARMONIC

TRAP

7th

HARMONIC

TRAP

50mH

AØ

BØ CØ

3Ø

(ON/OFF)

4mH

400A

4mH

400A

6 EACH

6 EACH

RTN AØ BØ CØ

-HV -HV -HV 10ohm 20mH

.03uF

.03uF

.05uF VMON

HV

OUTPUT

RECTIFIER TRANSFORMER

AND FILTERS

SCR REGULATOR

HVCM EQUIPMENT

CONTROL RACK

ENERGY STORAGE

Other Alternative Modulators

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Longer Pulse Modulator with sag

compensation with RC circuit


Application 67

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Long Pulse Modulator with Bouncer Circuit(1)

CR

t

eVV

0

Klystron Impedance

R=120kV/140A

=857Ω

C

Pulse width

C

R Dr

=1.7ms

Dr=1%

R=857Ω

Dr Droop

Secondary Capacitance C=198µF

E 1

2CVk

2

E=1.4MJ

Vk=120kV

If droop of 20% is allowed, then C

and E are 1/20

Save Capacitor bank and space

to1/20 24min run

of 1kW

heater

C=9.9µF (Secondary)

C=1426µF(Primary)

Switch



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10kV

-120kV

140A

1.7 ms

5Hz 1.7kA




C L ＋

SCR(Need to Adjust）

Protection SW for Safety

C Discharge SW for

Overvoltage

Characteristics

•Simple and Compact

•20% droop is compressed to1%

•Easy Adjustment

•Cheep Cost

Charging Diode

Specification

Voltage：+-1kV Current：

• Invented by FNAL Quentine

•Kerns




Actual Waveform by Bouncer Circuit

Es=20kV, Pw=1.7ms, fr=5pps Rise-time(10-90%)=33µs

Es=17kV, Pw=1.7ms, fr=5pps Flatness=0.8%(p-p)

•With Bouncer Circuit

-100

-95

-90

-85

-2 -1.5 -1 -0.5 0 0.5

Kly

stro

n V

olt

age(

kV

)Time(ms)

Es=17kVfr=5pps

0.3ms

0.7ms

0.52ms

0.4ms

0.6ms

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000 -140

-120

-100

-80

-60

-40

-20

0

20-3 -2 -1 0 1 2 3 4

Bounce

r V

oltag

e(V

)/C

urr

ent(

A)

Kly

stron V

oltag

e(kV

)

Time(ms)

Klystron Voltage

Bouncer Voltage

Bouncer Current



Protection of Klystron at Breakdown

Es=9.0 kV, Pw=1.7 ms, fr= 5 pps

W 100V Ik dt

Energy deposit in klystron

from gun spark

W=2.0 J < design value

Arc voltage＝100 V

72 2012/2/1 S. Fukuda Schooi for Accelerator


Pulse Transformer Modulator Status

• 10 units have been built, 3 by FNAL

and 7 by industry (PPT with

components from ABB, FUG,

Poynting).

• 8 modulators are in operation.

• 10 years operation experience.

• Working towards a more cost efficient

and compact design.

• FNAL building two more, one each for

ILC and HINS programs – SLAC has

bulit switching circuits.

HVPS and Pulse Forming Unit

IGCT Stack

Marx Modulator for ILC


Application 74




Application 76

SLAC’s New Type Marx Modulator : P2

Vendor Design Marx Modulator for ILC



Thomson Marx Modulator: Low voltage Marx and Pulse Transformers

DTI’s Marx Modulator: 120kV Direct Pulse Generation

Marx Modulator's Feature

• Good flat top pulse when pulse duration is long such as a few millisecond.

( timing adjustment of individual Marx cell enable to make a good flat top)

• Even a direct output pulse case, acring probability in the modulater is small due to comprise of the low voltage cell’s assembly

• Fast shutoff of the output when klystron fails.



Thanks for listening my lecture

For RF source, PDS (power distribution system such as waveguide components)

are also important but this time completely omitted.

