Klystron

In the klystron, electrons are emitted from a hot filament cathode (the negative electrode in the tube) by thermionic emission. These electrons are accelerated toward a hollow anode (the positive electrode) by an external electric field. After the electrons pass through the anode, they are reflected back toward the anode by another negative reflector electrode. The velocity of electrons within the klystron is modulated by their interaction, and an oscillation develops that depends on the reflector voltage and the dimensions of a cavity that is part of the tube. An adjustment of the reflector voltage is used to tune the tube to resonant oscillation at a typical oscillation frequency $>1$ GHz, $10^{9}$ Hz, producing radio waves with a wavelength of a few cm. This energy is coupled out of the tube into a waveguide, and then to an antenna. In the device we use, the antenna is a simple horn that matches the waveguide to free space, and directs the radiated energy into a beam.