Transcript Thus TH595 shall be used for first high power amplifier chain.

High Power Amplifiers
R.A. Yogi
ESS RF Group Unit Leader for Spoke Power and RF Distribution
FREIA Group Unit Leader
ESS: Superconducting 5 MW Linac
Frequency = 352.21 MHz
Number of spoke resonators = 28
Maximum power to beam = 240 kW
Maximum generator power = 300 kW
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High Power Test Stand at Uppsala
New design being
developed at IPN
Orsay
High power testing
needed !
Power Coupler
Two high power RF chains are
needed to test two spoke cavities at
Uppsala test stand !
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Baseline Design for ESS RF system
Generation and distribution of the RF power
from a single source to a single accelerating
cavity
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Importance of selection of RF source
The capital and running cost of an accelerator is strongly
affected by the RF power amplifiers:
Capital cost:
 cost of the amplifiers
 gain of the power amplifier (decides number of stages) and
hence size and weight of the amplifiers: (decides gallery
requirements)
Running cost:
 efficiency determines the electric power required and also
amount of cooling needed
 Life time: replacement, maintenance schedule
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RF Source Requirements
• Maximum RF power for a spoke resonator = 240 kW
• Considering LLRF overhead = 15% (Simulink model shows 12.5% power
overhead)
• RF loss in distribution system = 5%,
Power of RF source = 288 kW. Aim for 300 kW (4.0% extra, Why ? Will
be explained in next slides)
• Beam pulse width = 2.86 ms, repetition rate = 14 Hz,
fill time of the cavity:
Natural fill time = tf =
= 135 µs, (QL = 1.5 x 106 )
RF pulse width = 3.1 ms
Duty factor of the amplifier  4.28 %
• Spoke cavity band-width = 2.34 kHz
system band-width  100 times larger than spoke resonator band-width
for tuning and regulation delay.
3 dB bandwidth ≥ 250 kHz.
High Power RF Amplifier
Specifications of RF Amplifier:
Frequency = 352.21 MHz
Power
= 300 kW
3dB band-width ≥ 250 kW
Pulse width = 3.1 ms
Pulse repetition rate = 14 Hz
Compared all the possible RF
sources like Tetrode, Klystron, IOT,
Solid state amplifier and selected
Tetrode for the first high power RF
chain.
Simultaneously high power RF
amplifier using solid state technology
under development for the second
chain.
No RF source exists at
ESS specifications !
Hence development and
prototyping is important !
Supported by AIR and TB at
ESS
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Comparison of Tetrodes
TH781, TH391 and TH595 tetrodes can be used at ESS specifications.
Typ.
TH781
Performance
Maximum
250 MHz
Frequency
Frequency (as per 200 MHz
TH391
TH595
450 MHz
450 MHz
352 MHZ
380 MHz
380 MHz
Thales catalogue)
Power
200 kW
350 kW
200 kW
200 kW
Pulse width
cw
3.5 ms
100 s
100 s
gain
Efficiency
12.2 dB
68.9%
13 dB
55 %
(predicted)
15 dB
67 %
15 dB
67 %
TH18230B (200
kW, 380 MHz)
TH18528 (100
kW peak, 85-115
MHz)
Air, 12 kW
Water, 40 kW
Cavity (as per
Thales catalogue)
Type of anode
cooling & anode
dissipation
Water, 250 kW
TH595 is selected for first high power RF chain.
Output power of two tetrodes needs to be combined.
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Foot area:0.6m x 0.6m
Foot area:2.5m x 2.5m
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Schematic for first RF chain
Loss in the
connections are
not considered
due to the 4%
margin on the
generator power.
SG: Signal generator, : Phase shifter, A: Attenuator,
A1 & A2: Preamplifiers, PA1 & PA2: High power amplifiers.
Transmitted power and RF distribution systems are specified on top of
schematic.
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Tetrode TH595 and cavity Th18595 A at Thales
Amplifier cavity
TH 18595A
Tetrode TH595
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Schematic of RF station used at Thales
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Conclusion for High power RF Amplifier
Comparison of target ESS specifications and
achieved performance of TH595 and cavity
Parameters
ESS
specifications
Test results at
Thales
Frequency
352.21 MHz
352.21 MHz
Power
> 320 kW
> 400 kW
(> 300 kW)
3 dB Band-width > 250 kHz
7 MHz
Efficiency
> 50 %
67 %
Gain
> 10 dB
15 dB
Thus TH595 shall be used for first high power amplifier chain.
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Pre-amplifier
As gain of tetrode decreases due to aging, conservative gain of 13 dB
is considered while calculating specifications of solid state amplifier.
Thus output power of pre-driver = 8.7 kW. Aim for 10 kW.
Specifications of Predriver:
•
•
•
•
•
Frequency = 352.21 MHz
Output power = 10 kW
Gain = 70 dB
Total efficiency = 55 %
Class of operation: AB
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Selected solid state amplifier after comparing the available technologies.
• Gain 70 dB
• Efficiency > 50 - 55% (class AB)
• Good reliability: Built in redundancy
• Modular system, easy replacement possible
• Off-shelf available system
RF unit of 700W power
RF 5 kW power module
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Conclusion
TH595 with amplifier cavity TH18595A can be used
as high power amplifier
Solid state amplifier can be used as pre-driver.
Thank you !
Comments and suggestions are welcome
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10 kW 352MHz Pre-amplifier
• Solid state amplifier:
Gain 73 dB, so only one stage
Good Reliability: Built in redundancy
Efficiency > 50 - 55% (class AB)
Modular system, so easy replacement possible
• Triode:
Low Gain 10 dB, so consists of three amplifier stages. It
requires pre-predriver triode (1 kW), and solid state low
power amplifier (10 W)
Complex system. 3 amplifier stages, their power supplies,
protections, hence low reliability.
Efficiency: 70%
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Features RF Distribution

No pressurization

Use of Ferrite loads

Distribution at 3 levels
•
Half height WR2300: 350kW
•
6-1/8 inch, 50  coax: 175 kW
•
7/8 inch, 50  coax: 10 kW
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Typical power sources
used at 352 MHz are
tetrodes, klystrons, IOTs
and solid state amplifiers
Criteria of comparison:
Power distribution scheme
Lifetime
Efficiency
Gain
Availability
Costs
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Klystron
Too big for 350 kW power
Size: 1 m x 1 m, weight: few tons
Efficiency: 60 – 65%
Modulator needed for power-supply,100 kV
Gain: 37 dB
Predriver not needed
Life time: 40-50 khours
Circulator needed for handling reflection
Base line of one RF amplifier per cavity
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Solid state amplifier
RF unit of 700W power
RF 5kW power module
70 modules of 5 kW each that
are combined
High reliability due to use of
circulators and hybrid couplers.
Size: very big 10 m2
Efficiency: 65%
Few distributed power supply
50 V, 200 A (low voltage, high
current)
Gain: 37 dB
Predriver not needed
Life time: 50 khours
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