[i′lek‚trän ‚bēm ‚par·ə¦me·trik ′am·plə‚fī·ər] (electronics) A parametric amplifier in which energy is pumped from an electrostatic field into a beam of electrons traveling down the length of the tube, and electron couplers impress the input signal at one end of the tube and translate spiraling electron motion into electric output at the other.