The principle of the self-adaptive feed-forward (SAFF) control to improve the beam quality of linac is introduced. The analytical procedure for calculating the control signals

the structure of a practical control system

and applications of SAFF in klystron

RF gun

and linac are presented

especially the application in the thermionic gun whose response is non-linear

time-variant and of large time-delay. The described control system is operational and some primary experimental results have been obtained

including the control of amplitude and phase fluctuations of the klystron output

the microwave field in the gun cavity and linac.