Microtron accelerator for a free electron laser.
01 January 1986
The electron beam parameters of an energy tunable (11-22 MeV) circular microtron accelerator are measured to be close to that required for free electron laser (FEL) operation in the far infrared. Average currents of 30 mA are measured at an energy of 17 MeV during the macropulse (14 microseconds duration and 50 Hz repetition rate) in the 25 orbit microtron. The 3 GHz rf electron beam peak current is expected to be 20-40 times the macropulse average value. The relative energy spread of the electron beam is inversely proportional to the number of the microtron orbits and is expected to be about 0.2%. The radial emittance of the electron beam is measured after extraction from the microtron and has a value of about picm millirad with the axial emittance one third this value. Electron beam extraction from the 25th orbit is nearly 100% efficient. The area of the electron beam is observed to be less than 1.0 cm(2) in 270 Gauss helical magnetic field of 20 cm periodicity and 10 meter length.