sekundääriemissiokertoimelle

Sekundääriemissiokertoimelle, often denoted by the Greek letter gamma (γ), is a crucial parameter in vacuum electronics and plasma physics. It quantifies the phenomenon of secondary electron emission, where incident particles, typically electrons or ions, strike a surface and cause the ejection of additional electrons from that surface. The secondary emission coefficient is defined as the ratio of the number of emitted secondary electrons to the number of incident primary particles.

The value of the secondary emission coefficient is highly dependent on several factors. These include the energy of the incident particles, the material properties of the target surface (such as its work function and atomic composition), and the angle of incidence. For most materials, the secondary emission coefficient is less than one at low primary electron energies, meaning more electrons are leaving the surface than arriving. However, as the primary electron energy increases, the coefficient rises and typically peaks at energies around a few hundred electron volts. Beyond a certain energy threshold, the coefficient often decreases again.

In vacuum tubes, secondary emission can be a source of unwanted effects, such as positive feedback loops or beam instability, and is often suppressed using techniques like suppressor grids. In contrast, in devices like photomultiplier tubes and channel electron multipliers, secondary emission is intentionally utilized to amplify weak signals. Understanding and controlling the secondary emission coefficient is therefore essential for the design and operation of various electronic and plasma-based systems.