Emittance Growth Caused by Current Variation in a Beam-Transport Channel
Time variation of space-charge forces in a beam-transport channel will lead to a time-averaged emittance growth of the beam. The Kapchinskii-Vladimirskii (K-V) equations have been used to follow the envelope of a round beam with effective beam current fluctuation i through a transport channel. The area of the ellipse that encloses the varying ellipses at the end has been used as the criterion for emittance growth. Simple formulae give the relation between i, initial emittance ¿, allowable fractional emittance growth ¿¿, effective average current I, average beam radius R, and transport length. For example, for a long transport channel a nominally compensated beam must have i <(ß¿¿2I0/R2)¿¿, where I0 = 4¿¿0Mc3/e, and ß¿ is the usual relativistic factor. Results for other conditions are presented. A comparison with a numerical calculation from the TRACE code for transport of a 100-keV, 100-mA beam is made.
Static theory of density and potential distribution in a beam-generated plasma.
An electron beam passing through a gas ionizes the gas, and the electrons and ions so produced collect in the vicinity of the beam to form a plasma with a number density that can be much greater than the density of the beam. A one‐dimensional static theory for such a system, with a beam either partially or completely filling the space between two parallel planes, gives the plasma density and potential distribution in the space. The theory requires only minor modifications of the Langmuir‐Tonks free‐fall theory of the positive column. A plasma filling the space occupied by the beam is separated by a low potential sheath from a somewhat lower density plasma that extends to the walls where a second higher potential sheath is formed. A comparison between the results of this theory and some density measurements on beam‐generated plasmas reported in the literature gives reasonable agreement.
Physical Chemistry for the Life Sciences
PART 1 - BIOCHEMICAL THERMODYNAMICS PART 2- THE KINETICS OF LIFE PROCESSES PART 3 - BIOMOLECULAR STRUCTURE PART 4 - BIOMOLECULAR SPECTROSCOPY