ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
The space-charge compensation of electron beams by hot ions with a Boltzmann energy distribution has been investigated by solving Poisson's equation. A unique relation is obtained between the degree of central compensation and the ion temperature: At high temperatures (as compared to the potential depression inside the beam) the compensation is low and the ions stay inside the electron beam only to a minor part, while at low ion temperatures, the beam is almost fully compensated. The potential difference between the beam axis and the surrounding tube is reduced by compensation, but when measured in terms of the temperature of compensating ions, it increases. This shall better confine the ions to the electron beam, the more complete the compensation. Increasing with the square of their charge state, trapped ions are heated by the ionizing beam electrons through small angle Coulomb collisions. For different ions with different charge states, the almost compensated electron beam acts as an energy filter, where the hotter ions are lost radially or axially. Therefore highly charged ions, which became "hot'' by waiting for stepwise ionization, can be cooled by lower charged ones, which still are "cold.'' This phenomenon has been called "evaporative cooling'' in electron beam ion sources (EBIS) and traps (EBIT) and space-charge compensation of the electron beam is the driving physic for it.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1145063
