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Motivation

Motivation. Investigating worst-case transients in the shorted stubs in E-H tuner B. Foster had concern about transient standing waves that could be generated in stubs, with possible large amplitudes Simulate E-H tuner behavior, investigate amplitude of generated standing wave

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Motivation

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  1. Motivation • Investigating worst-case transients in the shorted stubs in E-H tuner • B. Foster had concern about transient standing waves that could be generated in stubs, with possible large amplitudes • Simulate E-H tuner behavior, investigate amplitude of generated standing wave • Used PSpice 9.1, Student version (free): Available at http://www.orcad.com/downloads/demo/default.asp

  2. The components concerned Klystron Isolator Branchline Coupler Hybrid Shorted Stub Transmission Line Shorted Stub Resonant Cavity

  3. Klystron/Isolator Model • Simulate Klystron as sine-wave voltage source, with 50 Ω front-termination resistor for isolator SPICE Model

  4. Branchline Hybrid • Four quarter-wavelength transmission lines, with impedances as shown at left, with shorted stubs (coax, ferrite) off of ports 2 and 3 http://www.microwaves101.com/encyclopedia/Quadrature_couplers.cfm#branchline SPICE Model

  5. Preliminary Tests Performed • To test setup, ran tests with 0λ, λ/4, λ/2 difference in stub lengths, with 50 Ω to ground termination resistor – power split as expected • Added constant length to both stubs, gives pure phase-shifted output SPICE Model Port 4 • Assume that stub impedance • doesn’t change, only electrical length

  6. Electrical Length Difference=0 Red=Drive Signal, Blue=input, port 1, Green=output, port 4 2V 0V -2V After a few cycles, 100% of power goes to output port 4

  7. Electrical Length Difference=λ/4 Red=Drive Signal, Blue=input, port 1, Green=output, port 4 2V 0V After a few cycles, 0% of power goes to output port 4, and all power is reflected back to port 1 -2V

  8. Electrical Length Difference=λ/2 Red=Drive Signal, Blue=input, port 1, Green=output, port 4 2V 0V -2V After a few cycles, 100% of power goes to output port 4

  9. Resonant Circuit • On resonance, cavity acts like a 50Ω resistor, thus, lose 50% of voltage in front-termination resistor, no phase shift • Use this to tune LRC circuit (with Q=~100s to save simulation time, cavity step-up ratio is only about 5:1 for plotting convenience) to act like resonator so that output voltage at port 4 approaches half the driving voltage as cavity approaches resonance Node where cavity voltage is measured Drive point SPICE Model

  10. Cavity Resonance Test Green =2V driving voltage, Red =Voltage in Cavity Node, Blue= Voltage at Port 4 -Thus, the resonant circuit looks like a 50Ω resistance without phase-shift on resonance

  11. Monitoring standing waves in stubs • Divided shorted stub into two pieces, one fixed at length λ/4, the other variable • Reason: Monitor maximum of any possible standing wave (can place probe there) SPICE Model

  12. Investigation on Transients • Sine wave source that will turn on, turn off, or jump phase instantaneously • Look at turn-on and turn-off transients • Look for worst case conditions: jump klystron phase by 180o (might be caused by control problem?) • Timergali’s suggestion: Investigate effect of variable-length transmission line between hybrid and cavity

  13. Complete Circuit Diagram Used two sine sources to jump phase, etc. Adjustable electrical lengths on stubs Adjustable electrical length on cable to cavity SPICE Model

  14. Stub Transients during Cavity Filling Transient during filling of ~2x steady-state Stub voltages Drive and Cavity voltages Yellow = Voltage in resonant cavity, Green = Driving signal, Purple=output voltage (port 4), Red= Voltage in top stub Blue= Voltage in bottom stub

  15. Transients during Cavity shut-off Transient during shut-off not larger than steady-state Stub voltages Drive and Cavity voltages Yellow = Voltage in resonant cavity, Green = Driving signal, Purple=output voltage (port 4), Red= Voltage in top stub Blue= Voltage in bottom stub

  16. Transient following 180o phase-jump of Klystron Transient from phase-jump ~2.5x steady-state Stub voltages Drive and Cavity voltages Yellow = Voltage in resonant cavity, Green = Driving signal, Purple=output voltage (port 4), Red= Voltage in top stub Blue= Voltage in bottom stub

  17. Include Transmission Line to Cavity of length λ/4 (worst case) Stub voltages Transient during filling of ~3.3x steady-state Drive and Cavity voltages Yellow = Voltage in resonant cavity, Light Blue = Driving signal, Purple=output voltage (port 4), Red= Voltage in top stub Blue= Voltage in bottom stub

  18. Include Transmission Line to Cavity of length λ/2 (no effect on worst case) Transient during filling of ~2.5x steady-state Stub voltages Drive and Cavity voltages Purple= Voltage in resonant cavity, Green= Driving signal, Red=output voltage (port 4), Blue= Voltage in top stub Yellow= Voltage in bottom stub

  19. Conclusions • PSpice model correctly reproduces expected steady-state behavior of E-H tuner • Significant voltage transients observed in stubs • Worst case so far seems to be a 180o Klystron phase-jump with the λ/4 transmission line length between hybrid and cavity (factor of 3.3x steady-state voltage, factor of ~10 in peak power) • Transients are important for specifications for power-handling in stubs • Still need to do parameter sweep on transmission line length to see if there are worse cases

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