ON THE TRANSPORT AND HEATING OF PARTICULATE CONTAMINATION ENTRAPPED IN AN INTENSE CYLINDRICAL ION-BEAM

Utilizing a previously developed entrapment model, the equations of motion for a particle confined within an intense cylindrical ion beam are derived. Energy transfer from the beam to the particle is then calculated and an expression for the time rate of change of the particle's temperature determined. From the resulting model, trajectories and temperatures are calculated for micron and submicron-sized aluminum and tungsten particles placed in a 100 keV, 10 mA, 3-cm-diam BF2 ion beam. It is predicted that the Al particles undergo a phase transition in a time approximately 1 ms, during which they acquire a center-of-mass velocity approximately 1 m/s, and traverse an axial distance approximately 1 mm, ultimately reaching the vaporization temperature. In contrast, during a 50 ms flight, the denser W particles are expected to follow precessing orbits, travel axial distances approximately 0.1-1 m, and possess final axial velocities approximately 10-100 m/s, never attaining their vaporization temperature. Along trajectories crossing a beam of radially varying ion density (a Gaussian profile is assumed), heat transfer to the particle varies as a function of radial position. Thus, as the particle's radial position fluctuates, particle temperatures are predicted to oscillate about an equilibrium value that is independent of particle properties, varying solely with beam parameters.