Time-resolved measurement of electron beam neutralization

Technical Report · Fri Dec 11 04:00:00 EST 2020

DOI:https://doi.org/10.2172/1735877· OSTI ID:1735877

Ekdahl, Jr., Carl August ^[1]; Schulz, Martin ^[1]

---

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

An intense relativistic electron beam (IREB) incident on a target generates positive ions by stimulated and thermal desorption of adsorbed gas, and subsequent electron impact ionization. These ions are accelerated upstream by the beam space-charge potential, thereby partially neutralizing the beam. If there is enough neutralization, the repulsive space-charge force can be overcome by the magnetic-pinch force due to the beam current. This so-called ion focusing is responsible for time dependent defocusing of the radiographic source spot. Since a single monolayer of adsorbed gas has a surface density of about 10¹⁵ /cm² and is formed in about one second in a one micro-Torr vacuum, there is always enough adsorbed gas to make this a concern in our accelerators. Therefore, time-resolved measurements of the degree of neutralization are valuable for better understanding of this process with an eye to mitigation for improvement of our radiography. Moreover, these measurements would aid quantification of uncertainties due to these effects when using invasive beam diagnostics, such as OTR imaging targets.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: 89233218CNA000001
• OSTI ID: 1735877
• Report Number(s): LA-UR--20-30186
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS