Investigation of an expanding copper plasma across a transverse magnetic field generated by strip-type electron-beam

The electron beam assisted thermal processes are well-established technique for various applications such melting, evaporation, isotope purification, ion-implantation etc. The processes are time average, wherein process is carried out over a larger duration so that real time dependent variations gets averaged out. During electron beam evaporation and atomic beam generation, ions also get generated inherently due to interaction of primary and back-scattered electrons with the atomic vapour along with other routes like Saha ionization, secondary electron ionization etc. The presence of ions has a bearing in the quality of deposited films and influence the ion implantation process. It also has strong effect on dilution factor in isotope purification. Thus the knowledge of ion content, its distribution and evolution in the freely expanding atomic beam in vacuum is important for any process optimisation in electron beam evaporation applications. The thermal ion content in atomic vapour for a given element as a function of aspect ratio (height/length) and source Knudsen number can be used as most inexpensive technique to characterized the evaporation on time average as well as teal time processes. With this intension, a series of experiments were carried out in a 100 kW strip beam evaporator with 130mm strip electron gun with copper as target material. A wedge shaped copper atomic beam is generated from a two dimensional evaporating source (120mm × 6mm) by impingement of the electron beam up to 90kW power. Disk type Langmuir probe is used for measuring I-V characteristic plots for deriving the thermal ion flux. The measurements are carried out as a function source Knudsen number (depends on incident electron beam power), and the probe distance from source that defines the aspect ratio. Along with probe data, the atom flux is also simultaneously measured using quartz crystal thickness monitor. The evolution of ions and atoms with distance from source is compared.