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.
Electron‐suppression experiments in a small multicusp H− source
Several techniques for suppressing the electrons before they form part of the extracted beam have been studied in a small multicusp H− source. It is found that some schemes reduce both the electron and the H− output currents. Other approaches, such as the installation of a collar at the extraction aperture, the addition of xenon or cesium to the hydrogen discharge, or the reduction of the source plasma potential, not only can reduce the electron current substantially, but bring about an enhancement in the extracted H− current.
Test security in medicolegal cases: proposed guidelines for attorneys utilizing neuropsychology practice.
In the context of forensic neuropsychological assessments, the professional interaction of law and psychology is viewed primarily as one where the retaining attorney or court dictates its needs to psychologists when resolving legal disputes. While this perspective is conceptually accurate, the positive and practical collaboration of law and psychology also relies on attorneys adhering to basic protections of sensitive psychological assessment procedures and tests. Objective testing is undermined when a practitioner of law engages in actions prior to, during, or following a neuropsychological examination in a manner that threatens the test security. An appreciation among practitioners of law and psychology regarding the necessity of test security is essential. This article reviews attorney actions that can affect test security, proposes a distinction by psychology between appropriate and problematic client preparation for a neuropsychological examination, integrates the available legal precedent regarding test security, and suggests productive measures to protect test security in medicolegal settings.