A SENSITIVE AND NONPERTURBING ELECTRON DENSITY DIAGNOSTIC FOR RF SOURCES

THE MULTIPHASE OBJECTIVE OF THIS PROJECT IS TO DRAMATICALLY UPGRADE IN SENSITIVITY A RECENTLY DEMONSTRATED OPTICAL ELECTRON-DENSITY BUNCHING MEASUREMENT TECHNIQUE AND TO DEVELOP A BUNCHING DIAGNOSTIC SYSTEM THAT WILL BE USEFUL FORA NUMBER OF RADIO FREQUENCY (RF) LINEAR ACCELERATOR SOURCES. THE TECHNIQUE, CALLED HETERODYNE (OR HOMODYNE) SIDEBAND INTERFEROMETRY (HSI), IS HIGHLY NONPERTURBING BECAUSE ONLY A LASER BEAM INTERACTS WITH THE ELECTRON BEAM. BOTH THE AMPLITUDE AND THE PHASE OF RF FOURIER COMPONENTS OF ELECTRON DENSITY CAN BE MEASURED. RF PHASE-MODULATION SIDEBANDS ARE INDUCED ON THE LASER BEAM BY THE ELECTRON BUNCHES. THE SIGNALS ARE DOWNSHIFTED TO DIGITIZER BANDWIDTHS BY OPTICAL HETERODYNE (OR HOMODYNE). THE TECHNIQUE ACHIEVES HIGH SENSITIVITY IN THAT ITS NOISE BANDWIDTH IS THAT OF THE PULSE ENVELOPE, RATHER THAN THE RF BANDWIDTH, AND BECAUSE AN INTERFEROMETER IS USED TO FILTER OUT THE CARRIER POWER, WHICH CAN THEN BE RAISED TO HIGH LEVELS WITH CORRESPONDINGLY HIGHER SENSITIVITY. ANOTHER ADVANTAGE IS THAT, UNLIKE OTHER ELECTRON INDEX-OF-REFRACTIONMEASUREMENT TECHNIQUES, THE DEVICE BEING MEASURED IS NOT PLACED INSIDE THE INTERFEROMETER, OFTEN AN IMPOSING PRACTICAL LIMITATION. IN PHASE I, OPTIMUM METHODS OF DATA ANALYSIS ARE BEING DETERMINED, MEANS OF ACCESSING THE ELECTRON BEAM IN VARIOUS RF SOURCES TARGETED FOR PHASE II MEASUREMENT DEMONSTRATIONS ARE BEING IDENTIFIED, AND A COMPLETE HSI ELECTRON BUNCHING MEASUREMENT SYSTEM IS BEING DESIGNED.