JCT e2v presentation-June_08.ppt

Presentation Title Presentation Date Insert Copyright statement here. See notes page for Copyright Text. Linac MagnetronsPrinciples of operationChris ThwaitesDavid FoxJune 2008 Linac Magnetron Range Magnetrons Magnetrons generate the high power RF pulses by coupling energy from an intense electron stream into a resonant RF circuit. Cross Field Devices Magnetrons Creating conditions to allow magnetron operation. Components and Assembly Cathodes and electron emission The role of the heater Creating a vacuum Secondary electron emission and back bombardment. Heater turnback Cathode depletion and end of life. Barium Evaporation Sputtering Comparing MG5193 and MG6090 Magnetrons Section Through MG5193 Magnetron MG5193 Magnetron Cathode Electron Emission Cathodes and Electron Emission The cathode produces electrons Could be made from many materials. Workfunction (energy required for release of electrons is important) Cathodes and electron emission Linac Magnetron typically use Barium / Strontium Oxides Low workfunction allows for cool operation. For Magnetrons, primary emission allows pulse to start The Heater Made from tungsten (W) Heated by passing current through tungsten wire. Radiates heat to internal diameter of cathode. Heater turns are insulated from cathode wall through use of ceramic. Creating a vacuum A good vacuum is required: To allow electrons to leave cathode surface To allow free flow of electrons inside of the magnetron. To prevent oxidation of materials which operate at high temperature. To reduce ion damage to cathode during operation at high voltage. Negative pulse on cathode Magnetron OperationAchieving the right conditions Magnetron Operation: Achieving the right conditions- Magnetic Field Magnetron Diode Magnetron anode X-Band, 18 Cavity MagnetronElectron trajectories at start-up. Ideal Magnetron Output Spectrum Cathode performance during magnetron operation Standby Cathode is maintained at correct temperature through po