1. RF Sources and Combiners
Emma Wooldridge

2. Joint Accelerator Workshop
Outline
Very quick RF power overview
RF power sources
Triodes
Tetrodes
Klystrons
IOTs (Inductive Output Tubes)
RF power combining
Waveguides
Combining cavity
28th-29th April 2004
Joint Accelerator Workshop

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Coax or Waveguide
E Field
B Field
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Joint Accelerator Workshop

4. Standing and travelling waves
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Joint Accelerator Workshop

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Triodes
Invented in the early 1900s
Differs from a diode due to a grid added between the cathode and the plate
By applying an RF voltage across the grid it is possible to obtain bunches of electrons instead of a continuous stream of electrons
28th-29th April 2004
Joint Accelerator Workshop

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Tetrodes
This is the same as a triode but with an added screen grid
This grid protects the anode and control grid from being linked due to capacitance.
The screen grid is at ground so most electrons go past and continue to hit the anode
28th-29th April 2004
Joint Accelerator Workshop

7. IOTs (Inductive Output Tubes)
First designed by Haeff in the late 1930s
Electrons are bunched as in a tetrode
The power is obtained from the electron beam as it passes the cavity
28th-29th April 2004
Joint Accelerator Workshop

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Klystrons
Invented in the late 1930s by the Varian brothers
Extract energy in a similar way to an IOT
Produces electron bunches by velocity modulation
28th-29th April 2004
Joint Accelerator Workshop

9. RF Power combining – Why?
It is not always possible to get the perfect power source for each job
Klystrons
Expensive
Long lead time
High power
Higher gain
IOTs
Comparatively cheap
Shorter lead time
Lower power
Lower gain
28th-29th April 2004
Joint Accelerator Workshop

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Methods of Combining
Magic Tee
Large Structure.
Failure of 1 input results in loss of symmetry and failure of the system.
Combining Cavity
Small/Compact.
Failure of 1 or more components gives graceful degradation of power.
28th-29th April 2004
Joint Accelerator Workshop

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Magic Tees
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Joint Accelerator Workshop

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Combining Cavity
Magic Tees are the standard for RF power combining
H. Bohlen of CPI has modelled a combining cavity in 1D using 6 inputs
Thales have built a working model cavity using 5 inputs
28th-29th April 2004
Joint Accelerator Workshop

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Modelling the cavity
Modelled in CST Microwave Studio.
With either: 2,3 or 4 IOTs.
At 1.3 GHz.
1st step - modelling the cavity at the required frequency.
2nd step – Optimising the IOT inputs into the cavity by varying their width and length within the cavity.
28th-29th April 2004
Joint Accelerator Workshop

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Results
Efficiency of all models between 65%-99%.
Efficiency of 65% only seen in models with 3 inputs
Due to the analysis not converging to a single result
Reflection minimised to less 1% for most models
28th-29th April 2004
Joint Accelerator Workshop

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4 IOT plot
For the 2 and 4 IOT models the output for each IOT is identical.
Output Power 396%
Reflected power 1%
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Joint Accelerator Workshop

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3 IOT plot
Due to constraints on the way the ports are defined the asymmetry of the 3 IOT model led to it not being optimised fully.
Reflected power 12%
Output Power 208%
Reflected power 52%
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Joint Accelerator Workshop

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18. Technical Demonstrator
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Joint Accelerator Workshop

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Specifications
Main body is made of aluminium
Couplers are made from brass
Inner cavity radius 88.5mm
Outer cavity radius to be 150mm
Both input and output couplers can move in and out of the cavity by ±10mm
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Joint Accelerator Workshop

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Joint Accelerator Workshop

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Measurements
Symmetric placing of couplers to compare against Microwave Studio results
Asymmetric positioning of couplers
Rotate the couplers
Alter the length of coupler inside the cavity
28th-29th April 2004
Joint Accelerator Workshop

25. Joint Accelerator Workshop
Conclusions
Power from RF sources can be combined efficiently
The combining cavity could be a new way of doing this
Modelling suggests that an efficient IOT combining cavity can be created
Prototype will be ready this week
Measurements to be taken in the next few weeks
28th-29th April 2004
Joint Accelerator Workshop

26. Any Questions?