Neutron Diffraction Investigation of Residual Stresses Induced in Niobium-Steel Bilayer Pipe Manufactured by Explosive Welding

Recently, reliable and hermetic joining of stainless steel to niobium pipes has been achieved with the explosive bonding technique. Joining of these two materials are essential to ensure production of a bimetallic transition element of pipe-type for its further use as a part of charged beam acceleration systems of the new generation. A non-destructive neutron diffraction investigation of the tri-axial strains along a radial cross-sectional line through the joint section has been performed. Residual stress results indicate inherently different natures in the residual stress values within the respective pipe sections. In the external stainless steel pipe the residual stresses are tensile, showing a sudden increase to 600 MPa as the interface is approached, whilst being compressive in the internal niobium pipe, not exceeding 650 MPa. A characteristic abrupt stress discontinuity exits at the interface region.

Advances in Remote Plasma Cleaning of Electron Microscopes and Charged Beam Instruments

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

LONG TIME SIMULATION OF A BEAM IN A PERIODIC FOCUSING CHANNEL VIA A TWO-SCALE PIC-METHOD

We study the two-scale asymptotics for a charged beam under the action of a rapidly oscillating external electric field. After proving the convergence to the correct asymptotic state, we develop a numerical method for solving the limit model involving two time scales and validate its efficiency for the simulation of long time beam evolution.

Kelvin Probe Microscopy of Localized Electric Potentials Induced in Insulating Materials by Electron Irradiation

Kelvin probe microscopy (KPM) is a specialized atomic force microscopy technique in which long-range Coulomb forces between a conductive atomic force probe and a specimen enable the electrical potential at the surface of a specimen to be characterized with high spatial resolution. KPM has been used to characterize nonconductive materials following their exposure to stationary electron beam irradiation in a scanning electron microscope (SEM). Charged beam irradiation of poorly conducting materials results in the trapping of charge at either preexisting or irradiation-induced defects. The reproducible characteristic surface potentials associated with the trapped charge have been mapped using KPM. Potential profiles are calculated and compared with observed potential profiles giving insight into the charging processes and residual trapped charge distributions.