Vector Modulation of High Power RF Y. Kang J. Wilson, M. McCarthy, - - PowerPoint PPT Presentation

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Vector Modulation of High Power RF Y. Kang J. Wilson, M. McCarthy, - - PowerPoint PPT Presentation

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Vector Modulation of High Power RF Y. Kang J. Wilson, M. McCarthy, M. Champion and RF Group Spallation Neutron Source Oak Ridge National Laboratory LLRF05 Workshop, CERN 10-13 October, 2005 Y. Kang Accelerator Systems Division/SNS/ORNL 1

slide-1
SLIDE 1
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 1

Vector Modulation of High Power RF

  • Y. Kang
  • J. Wilson, M. McCarthy, M. Champion

and RF Group Spallation Neutron Source Oak Ridge National Laboratory LLRF05 Workshop, CERN 10-13 October, 2005

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SLIDE 2
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 2

  • For savings in construction and installation of a charged particle accelerator

– Fanning out a higher power amplifier output to many cavities with individual amplitude and phase controls is less expensive than using an amplifier/cavity. – Applicable to all types of particle accelerations; cab be more effective for SRF ion accelerators

  • Independent controls of amplitude and phase in high power RF transmission

– Use two high power phase shifters with a hybrid junction (or two) – Well known principle not used for high power – Development in HPRF hardware (and LLRF control interface)

  • Concept sought for possible application to the SNS linac; no time to implement
  • Many new accelerator projects may benefit employing the design
  • Phase shifters may be constructed using:

– Ferrimagnetic materials

  • Control orthogonal magnetic field bias in ferrite (or YIG) material to change

permeability – Ferroelectric materials (high frequency)

  • Control voltage bias on electro-optic material to change permittivity

– PIN or Varacter diodes (lower power, short pulse)

High Power RF Vector Modulation

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SLIDE 3
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 3

HP Vector Modulator Development and Related Work

  • ORNL, FNAL, CERN, and other institutions are now working on

development of VMs

  • HPSL 2005 Workshop, May 22-24, Naperville, IL

– Y. Kang, “ High Power RF Distribution and Control using Ferrite Phase Shifters” – I. Terechkine, “High Power Phase Shifter for Application in the RF Distribution System of Superconducting Proton Linac” – D. Valuch, “A Fast Phase and Amplitude Modulator for the SPL” – D. Sun, “325 MHz IQ Modulator for the Front End of Fermilab Proton Driver”

  • More

– V. P. Yakovlev, “Fast X-Band Phase Shifter,” Advanced Accelerator Concepts: 11th Workshop, 2004 – Y. Kang, “ Fast Ferrite Waveguide Phase Shifter,” PAC2001

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SLIDE 4
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 4

2.5 MeV 86.8 MeV 185.6 MeV

RFQ DTL CCL to SCL

1 4 3 2

from CCL

185.6 MeV

SCL, β = 0.61

391.4 MeV

SCL, β = 0.81

391.4MeV

SCL, β = 0.81

1 GeV

402.5 MHz, 2.5 MW klystron 805 MHz, 5 MW klystron 805 MHz, 0.55 MW klystron Modulator p.s.

SNS Linac RF

1 3 2 4 6 5 1 2 3 4 6 1 2 3 4 5 7 8 9 10 11 1 1 2 3 4 5 6 7 8 9 10 11 12

5 6 7 8 9

Baseline: 26 mA

10

1.4MW

11 12 13 14

SNS Linac HPRF Systems

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SLIDE 5
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 5

Comparison of Two Configurations

PS PS Cavities Klystrons RF Signals & Controllers Vector Modulators Cavities Klystron

One Klystron/ One Cavity Fanning out One Klystron

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SLIDE 6
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 6

Cost Savings ?

  • Example: a system similar to SNS 805 MHz SRF linac

– 25-40 mA beam current (8% duty) – Eacc ~ 10 ~ 16 MV/m – Qext ~ 7 x 105 – ±1% amplitude, ±1° phase – π-mode superconducting Nb cavities will need ~200-600 kW/m – Klystron power spec: 550-600 kW/cavity – Klystron power supply (converter modulator) already fanned out to drive many klystrons

  • Fan out configuration

– Can use klystrons with ~10 – 50 times higher RF power output – Savings in construction and installation: klystrons, waveguides, labor and buildings – Extra cost for the vector modulators and control components

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SLIDE 7
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 7

Linac RF Cost for a 805 MHz System

(non-official estimate for a linac with100 cavities)

Can be more Other items 19,650 27,950 47,600 Subtotal ($) 800 200 0.10 2,000 1,000 0.10 10,000 Labor for WG/Klystron 7,000 1,000 0.20 5,000 8,000 0.20 40,000 Gallery 3,350 1,250 250 5 4,600 46 100 Waveguide

  • 3,000

13,500 135 100 10,500 105 100 RF Controls 5,000 50 100 5,000 50 100 Circulator + Loads 3,500 700 5 3,500 700 5 Transmitter + Power Supply 11,500 3,500 700 5 15,000 150 100 Klystron ($k) Total ($k) Unit Price ($k) Quantity Total ($k) Unit Price ($k) Quantity Savings Fan out (1:20) One/one

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SLIDE 8
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 8

Vector Modulation

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + −

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − =

2 2 1 2 1 1 ,

2 1

2 sin ) , (

φ φ

φ φ φ φ

j

  • ut

e V V

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + −

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − =

2 2 1 2 1 2 ,

2 1

2 cos ) , (

φ φ

φ φ φ φ

j

  • ut

e V V

Hybrid 1 Hybrid 2 Driver Amplifier Driver Amplifier Low Level RF Control Matched Load Matched Load RF input RF ouput V1 V2 1

φ

2

φ

slide-9
SLIDE 9
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 9

Vector Modulators

1

φ

2

φ

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + −

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − =

2 j 2 1

  • 2

1

  • ut

2 1

e 2 cos V ) , ( V

φ φ

φ φ φ φ

180-degree hybrid 90-degree hybrid Hybrid 0/90 Hybrid 180/90

  • Transmissive
  • Reflective

– Standingwave is formed – Reflected wave must be trapped before the RF generator (klystron): circulator

  • V
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SLIDE 10
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 10

Mm Mp

VM Output Amplitude and Phase vs. φ1 and φ2

φ1(rads) π Amplitude Phase φ2(rads) φ1(rads) π

  • π
  • π

π

  • π
  • π

π φ2(rads)

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SLIDE 11
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 11

VM with Ferrite Phase Shifters

  • Phase shifter uses ferrimagnetic material (ferrite, YIG)

– Magnetic bias field is orthogonal to the RF magnetic field in the material – Magnetic field bias (usually high current, Hb ~ 10-50 kA/m) can change the permeability of the magnetic material – Waveguide type (FNAL and others) and coaxial type (ORNL) being demonstrated

  • Design optimization:

– High power handling – low RF loss – Dimensions

  • Waveguide design may be too bulky for SRF accelerator

frequencies (especially < 1000 MHz) – LLRF Control – Fast response time – Reliability – Cost

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SLIDE 12
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 12

Waveguide Vector Modulator (FNAL)

Input Output Short Short Magnetic Field Magnetic Field

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SLIDE 13
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 13

Operating Frequency vs. Bias Current

  • f a Phase Shifter (10” active length)

100 150 200 250 300 350 400 450 500 550 600 5 10 15 20 25 30

Bias Field (103 A/m) Frequency (MHz)

Square Coaxial Phase Shifter Measurement (ORNL)

B

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SLIDE 14
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 14

805 MHz Vector Modulator Construction

  • Prototype construction and

measurement – Square coaxial TEM transmission line design – For 402.5 MHz operation – 100-300 kW peak power – 10 kW average power – 10” active length

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SLIDE 15
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 15

Amplitude and Phase vs. Bias Fields

140 150 160 170 180 190 200 210 220

13 14 15 16 17 18 19 20 21 13 14 15 16 17 18 19 20 21

Bias Field 2 (10

3 Amps/m)

Bias Field 1 (10

3 Amps/m)

0.93 0.95 0.91 0.91 0.89 0.96 0.89 0.85 0.85 0.79 0.79 0.73 0.73 0.67 0.67 0.61 0.61 0.55 0.55

13 14 15 16 17 18 19 20 21 13 14 15 16 17 18 19 20 21

The lookup table

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SLIDE 16
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 16

VM RF Control (preliminary)

Hybrid Feedforward Phase Shifter 1 Phase Shifter 2 Set Amplitude & Phase RF from Klystron

X

To Cavity HPRF Modulator LLRF Adaptive Feedforward + Feedback Feedback Compensation Converter Detector

+

Driver 1 Driver 2

+

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SLIDE 17
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 17

Control Response Consideration

  • Bandwidth limitation due to conductive housing:

– Skin depth causes control field loss through the phase shifter housing => δ=1/(πfµσ)1/2 Ex) for copper wall t=δ=1mm, f=4.2kHz

  • Magnetic bias field control :

– Time constant of solenoid circuit => R=ωL Ex) for solenoid L=10 µH, R=1Ω: -3dB frequency = 15.9 kHz, Time constant τ=L/R=10 µsec

  • Time constant may be reduced:

– by control loop gain of the detector/driver – by putting a zero in loop to cancel pole – The conductor loss also be minimized by properly slitting or laminating the housing for elimination of Eddy current

R L Good conductor

B

slide-18
SLIDE 18
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 18

System Design with VMs

Amplitude/Phase Variable Range

  • Accelerators RF cavities

– SNS SCL like configuration uses only few cavity designs that match to few beam beta’s – Variable ranges of phase and amplitude have to be greater

  • Phase range requirement

– Broader range is always desirable – some wants full 360-deg phase scanning for flexibility – expensive – If accelerator operates with any disabled (and detuned) cavity, a greater phase tuning range is needed at a cavity to compensate the phase slippage – With the knowledge, the right cavity phases can be predetermined for each case

  • the range can be smaller
  • Amplitude range requirement (...)

– all adjoining cavities will require all predetermined field distribution – To control the beam energy, the klystron power can be controlled

  • Use additional slow phase shifters between the cavities

– A slower inexpensive phase shifter, either ferrite or motorized mechanical stub types can be used in each cavity for sustained phase settings

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SLIDE 19
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 19

VM RF Control Consideration

  • The steady state characteristics of the phase shifters and the vector modulator can

be measured and a lookup table can be provided

  • Current (or voltage) drivers selected and transfer functions characterized
  • LLRF development - adaptive feedforward with feedback control needed like in many
  • ther systems
  • Frequency responses of phase shifters, bias circuits, and current/voltage drivers
  • Other important factors:

– Accelerator beam specification and control system requirements – Pulsed or CW – Temperature regulation – Power supply regulation

  • Dynamic Range/Slew Rate/Linearity/Noise

– Driver amplifier/power supply performance – Control system performance

  • Optimization of bias circuits: Slow high current supply + Fast lower current supply
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SLIDE 20
  • Y. Kang

Accelerator Systems Division/SNS/ORNL 20

Summary

  • VM using YIG ferrite material

– 402.5 MHz square coaxial TEM phase shifter design prototyped for

  • Size and Integration
  • Manufacturing cost
  • Cooling

– Low power bench measurements performed – High power testing being prepared

  • Housing and solenoid designs optimized
  • Power supplies/audio amplifiers

– High power RF measurement and test to be completed

  • First goal is to demonstrate 100-300 kW pulsed system
  • Will be modified for higher power operation (> 500 kW)
  • SNS RFTF has been equipped and readied for the testing
  • LLRF Control

– Initial high power testing will have only simplest feedforward – Preliminary design and bench testing of the VM LLRF – Full LLRF controls to be demonstrated with cavity load – Needed for HPRF improvement