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High Power A mplifiers. 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 a mplifiers

High Power Amplifiers

R.A. Yogi

ESS RF Group Unit Leader for Spoke Power and RF Distribution

FREIA Group Unit Leader

slide2

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

high power test stand at uppsala
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 !

b aseline design for ess rf system
Baseline Design for ESS RF system
  • Generation and distribution of the RF power from a single source to a single accelerating cavity
slide5

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
rf source requirements
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= 2QL /  = 135 µs, (QL = 1.5 x 106 )RF pulse width = 3.1 msDuty 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. 3dB bandwidth ≥ 250 kHz.
slide7

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

No RF source exists at ESS specifications !

Hence development and prototyping is important !

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.

Supported by AIR and TB at ESS

comparison of tetrodes
Comparison of Tetrodes

TH781, TH391 and TH595 tetrodes can be used at ESS specifications.

TH595 is selected for first high power RF chain.

Output power of two tetrodes needs to be combined.

slide9

Foot area:0.6m x 0.6m

Foot area:2.5m x 2.5m

schematic for first rf chain
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.

slide11

Tetrode TH595 and cavity Th18595 A at Thales

Amplifier cavity

TH 18595A

Tetrode TH595

slide15

Conclusion for High power RF Amplifier

Comparison of target ESS specifications and achieved performance of TH595 and cavity

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

pre amplifier
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
slide17

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

slide18

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

10 kw 352mhz pre amplifier
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%
features rf distribution
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
slide21

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
slide22

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
slide23

Solid state amplifier

  • 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

RF unit of 700W power

RF 5kW power module