It is proposed that if Imax
are the maximum and minimum noise currents in a noise standing wave on an electron stream, then the product of their magnitudes cannot be smaller than
.Various assumptions lead to a factor α ranging between 0.8 and 1. I0
is beam current, B
is band width, ω is frequency, ωq
is effective plasma frequency, Tc
is cathode temperature, and V0
is the voltage specifying the velocity of the electrons.