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
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
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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.
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History of the Linac(1)
Ising(1924)
Wiedroe’s Linac
(1928)
Alvarez Linac
(1946)
Acceleration
Acceleration
Drift (constant velocity)
Drift (constant velocity)
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Introduction(2) Linear Accelerator (Linac)
Charged particles are accelerated linearly.
High frequency electromagnetic wave (micro-
Wave) is used for the acceleration.
Principle:
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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
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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
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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)
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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)
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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.
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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
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Klystron Theory
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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
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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.
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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
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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
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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.
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Comparison of the beam trace among
two approach
Ballistic Analysis Approach
No space charge interaction
Space-charge wave approach
Space charge repulsion is included
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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
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Klystron Parfameters
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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.
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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
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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
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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
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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
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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
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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.
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30kW IOT 1.3GHz for ERL Use
30kW IOT(CPI)
Specification
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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
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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.
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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
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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
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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)、
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 46
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)
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 47
Switching Device
• Typical switching device for high power application
– Spark-gap: Trigatron such as Ignitron and Crossatron
– Thyratron: most popular high voltage switching device
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 48
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.
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 49
• 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.
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 50
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%
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 51
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 52
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.
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 53
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
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.
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.
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 56
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 57
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 58
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 59
Modulator other than Line-Type
2012/2/1 S. Fukuda Schooi for Accelerator Technology and
Application 60
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 61
Accelerator Laboratory
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
Pulse Modulator Using Multi-Series Switch(2)
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 62
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
Pulse Modulator Using Multi-Series Switch(3)
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 63
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)
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 64
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
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
Longer Pulse Modulator with sag
compensation with RC circuit
2012/2/1 S. Fukuda Schooi for Accelerator Technology and
Application 67
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 68
Long Pulse Modulator with Bouncer Circuit(2)
10kV
-120kV
140A
1.7 ms
5Hz 1.7kA
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 69
Long Pulse Modulator with Bouncer Circuit(3)
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 70
Accelerator Laboratory
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
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 71
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
Technology and Application 72
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
2012/2/1 S. Fukuda Schooi for Accelerator Technology and
Application 74
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 75
2012/2/1 S. Fukuda Schooi for Accelerator Technology and
Application 76
SLAC’s New Type Marx Modulator : P2
Vendor Design Marx Modulator for ILC
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 77
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.
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 78
Thanks for listening my lecture
For RF source, PDS (power distribution system such as waveguide components)
are also important but this time completely omitted.
2012/2/1 S. Fukuda Schooi for Accelerator
Technology and Application 79