RF Sources and Combiners Emma Wooldridge

28th-29th April 2004Joint 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 2004Joint Accelerator Workshop Coax or Waveguide B Field E Field

28th-29th April 2004Joint Accelerator Workshop Standing and travelling waves

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

28th-29th April 2004Joint Accelerator Workshop 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 2004Joint Accelerator Workshop Magic Tees

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

28th-29th April 2004Joint Accelerator Workshop 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 2004Joint Accelerator Workshop 4 IOT plot For the 2 and 4 IOT models the output for each IOT is identical. Reflected power 1% Output Power 396%

28th-29th April 2004Joint Accelerator Workshop 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% Reflected power 52% Output Power 208%

28th-29th April 2004Joint Accelerator Workshop

28th-29th April 2004Joint Accelerator Workshop Technical Demonstrator

28th-29th April 2004Joint Accelerator Workshop 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

28th-29th April 2004Joint Accelerator Workshop

28th-29th April 2004Joint Accelerator Workshop

28th-29th April 2004Joint Accelerator Workshop

28th-29th April 2004Joint Accelerator Workshop

28th-29th April 2004Joint Accelerator Workshop 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 2004Joint 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

Any Questions?