The RMS envelope equation describing a charged particle beam has a focusing term, an emittance term, and a term for this effect.
The RMS envelope equation describing a charged particle beam has a focusing term, an emittance term, and a term for this effect. The magnitude of this effect is described by a parameter called the generalized perveance. This effect is modulated by the control grid of a Wehnelt cylinder, where it is present underneath the cap. The magnitude of this effect is proportional to voltage squared over length cubed; but by assuming ballistic transport, it is proportional to voltage to the three-halves power over length squared—those equations are the Mott-Gurney and Child-Langmuir laws. In electronic devices, it occurs because thermionic emission generates a cloud of electrons near the surface of a metal, which impedes current flow. The depletion region of a p-n junction is sometimes named after, for 10 points, what concept, where free electrons within a dielectric are treated as a continuum of charge?
The RMS envelope equation describing a charged particle beam has a focusing term, an emittance term, and a term for this effect.
space charge [accept space-charge limited current or SCLC; prompt on thermionic emission]