S. L. Shope

Production of annular electron beams by foilless diodes

A number of important aspects of the production of annular electron beams by foilless diodes are examined, both theoretically and experimentally. The theories of Ott, Antonsen, and Lovelace (OAL) and Chen and Lovelace (CL) are compared, and the CL theory is extended to include the effect of an axial gap in an approximate fashion. For the case of finite magnetic field strengths, Larmor orbits are examined and radial oscillations of the beam profile are predicted from a beam envelope analysis. Experimental results obtained with both low‐ and high‐impedance sources have been compared with the theory, and based on such studies, the design and construction of an intense hollow beam generator are described. Experimental results obtained with the new diode compare favorably with both the analytic theory and the results of numerical simulations. The device currently produces 2‐MeV electrons at beam currents of 65–70 kA.

Multistage linear electron acceleration using pulsed transmission lines

A four‐stage linear electron accelerator is described which uses pulsed radial transmission lines as the basic accelerating units. An annular electron beam produced by a foilless diode is guided through the accelerator by a strong axial magnetic field. Synchronous firing of the injector and the acccelerating modules is accomplished with self‐breaking oil switches. The device has accelerated beam currents of 25 kA to kinetic energies of 9 MV, with 90% current transport efficiency. The average accelerating gradient is 3 MV/m.

Self-magnetic insulation in vacuum for coaxial geometry

Magnetic insulation obtained by employing the magnetic field of the line current in coaxial vacuum‐transmission lines is studied in experiments on two different relativistic electron‐beam accelerators, spanning the voltage range 0.4–10 MV. Effective magnetic insulation at fields up to 1.3 MV/cm is demonstrated. The self‐limiting impedance is measured and compared to a number of theories for magnetic insulation and it is found that none of the ’’standard’’ theories successfully describes the data. However, computer simulations using a self‐consistent two‐dimensional particle code give good agreement with the experimental data, as does a proposed modification of the parapotential flow model.

Matching beams from relativistic electron guns into solenoidal transport systems

In this paper we develop a new approach for controlling the electron trajectories in a relativistic electron beam diode which is based on appropriately contouring an externally generated, axial magnetic field. The technique provides a convenient method of matching a beam produced by a shielded source injector into a uniform solenoidal transport system of a linear induction accelerator. To illustrate the method, we analyze a simple diode geometry and compare the analytical results with trajectory code calculations.

High voltage high brightness electron accelerators with MITL voltage adder coupled to foilless diodes

Summary form only given. It has recently been experimetnally and theoretically demonstrated that foilless diodes can be successfully coupled to self-magnetically insulated transmission line voltage adders to produce very small high-brightness, high-definition (no halo) electron beams. The RADLAC/SMILE experience opened the path to a new approach in high-brightness, high-energy induction accelerators. There is no beam drifting through the device. The voltage addition occurs in a center conductor, and the beam is created at the high voltage end in an applied magnetic field diode. This work was motivated by the remarkable success of the HERMES-III accelerator and the need to produce small-radius, high-energy, high-current electron beams for air propagation studies and flash X-ray radiography. Design examples of devices that can produce multikiloamp electron beams of as high as 100 MV energies and with radii as small as 1 mm have been considered.