Inexpensive Electron Beam Optics for Ultrafast Electron Microscopy

Unlike traditional Transmission Electron Microscopes (TEM) Ultrafast Electron Diffraction (UED) and Microscopy (UEM) operate at higher electron energies to preserve the high quality electron beam required for unprecedented temporal and spatial resolution. This however forces stringent requirements on electron- optical components. In particular a set of high field (2 Tesla) solenoids acting as condenser, objective and projection lens are needed. While superconducting solenoids are expensive and require cryogenics, normal conducting solenoids are incredibly bulky, weighing about 2 tons each. At present there is no compact UEM optics available to enable a marketable machine. The uniqueness of the Euclid’s proposal is its utilization of a flux concentrator, a pulsed technology adopted for the design of the ILC positron target collection solenoid. Duty cycle reduction allows for a significant reduction in the size of the magnet. Pulsed operation allows a high peak magnetic field (2 Tesla) at a reasonable heat load, which can be managed by conventional cooling. In Phase I we manufactured a flux concentrator prototype for an existing solenoid and tested pulsed operation. The field enhancement due to flux concentrator had been demonstrated at low current operation. We also designed a full imaging system to convert Brookhaven’s UED beamline into a UEM machine. Traditional flux concentrator is not cylindrically symmetric. We developed a pathway towards symmetrization of the flux concentrator insert and simulated several cases using high accuracy finite element method codes. Result of the simulation had been imported into beam dynamics simulation to monitor electron microscope aberrations. The ultimate goal of Phase II is a beamline ready pulsed solenoid with high current pulser. We will produce a high current pulser with and a solenoid coil with inductance matched to the pulse rise time. The solenoid will be fully tested with a 3 MeV beam either at UED facility of Brookhaven National Laboratory or Argonne Wakefield Accelerator Facility. The proposed approach will be a major step towards commercialization of the next generation ultrafast electron microscopes. These machines are emerging tools that enable revolutionary advances in the study of electron interactions with matter. Every university in US has at least one TEM machine, meaning that potential market for UEM is very large.