Ronak Bhatt

Three-Dimensional Theory and Simulation of Non-Relativistic Elliptic Electron and Ion Beam Generation

A three-dimensional theory of nonrelativistic, laminar, space-charge-limited, ellipse-shaped, charged-particle beam formation has been developed recently. Charged particles (electrons or ions) are accelerated across a diode by a static voltage differential and focused transversely by Pierce-type external electrodes placed along analytically specified surfaces. The theory is presented here along with design examples for a 6:1 elliptic electron beam diode and a 3:2 heavy ion beam diode. OMNITRAK simulations are performed to verify the theory and to explore beam tolerances with respect to perturbations of the diode geometry of the sort likely to be encountered in a realistic device: finite electrode extent, part misalignment, and allowances for thermal isolation.

Three-Dimensional Design of a Non-Axisymmetric Periodic Permanent Magnet Focusing System

A three-dimensional (3D) design is presented of a non-axisymmetric periodic permanent magnet (PPM) focusing system which will be used to focus a large-aspect-ratio, ellipse-shaped, space-charge-dominated electron beam. In this design, an analytic theory is used to specify the magnetic profile for beam transport. The OPERA3D code is used to compute and optimize a realizable magnet system. Good beam transport is simulated with the designed magnetic fields, using both 2D particle-in-cell (PIC) and 3D ray trajectory codes.

Cold-Fluid Equilibrium of a Large-Aspect-Ratio Ellipse-Shaped Charged-Particle Beam in a Non-Axisymmetric Periodic Permanent Magnet Focusing Field

A new class of equilibrium is discovered for a large-aspect-ratio ellipse-shaped charged-particle beam in a non-axisymmetric periodic permanent magnet focusing field. A paraxial cold-fluid model is employed to derive the equilibrium flow properties and generalized envelope equations with negligibly small emittance. A periodic beam equilibrium solution is obtained numerically from the generalized envelope equations. It is shown that the beam edges are well confined in both transverse directions, and that the equilibrium beam exhibits a periodic small-amplitude twist as it propagates. A two-dimensional particle-in-cell (PIC) code, PFB2D, is used to verify the theoretical predictions in the paraxial limit, and to establish validity under non-paraxial situations.

An ideal circular charged-particle beam system

A theory is presented for the design of an ideal non- relativistic circular beam system including a charged- particle emitting diode, a diode aperture, a circular beam tunnel, and a focusing magnetic field that matches the beam from the emitter to the beam tunnel. The magnetic field is determined by balancing the forces throughout the gun and transport sections of the beam system. OMNITRAK particle trajectory simulations are performed, validating theory. The ideal circular electron beam system has wide applications in space-charge- dominated accelerator research, high energy density physics (HEDP) research, vacuum electronics, and medical and industrial accelerators.

A high-brightness circular charged-particle beam system

A method is presented for the design of a high-brightness nonrelativistic circular beam system including a charged-particle emitting diode, a diode aperture, a circular beam tunnel, and a focusing magnetic field that matches the beam from the emitter to the beam tunnel. The applied magnetic field is determined by balancing the forces throughout the gun and transport sections of the beam system. The method is validated by three-dimensional simulations.

Equilibrium and Stability of a High-Intensity Periodically Twisted Ellipse-Shaped Charged-Particle Beam

Summary form only given. It is shown that there exists an exact paraxial cold-fluid equilibrium of a high-intensity, space-charge-dominated charged-particle beam with a periodically twisted elliptic cross section in a non-axisymmetric periodic magnetic field. Generalized envelope equations, which determine the beam envelopes, ellipse orientation, density, and internal flow velocity profiles, are derived. Effects of nonlinearities in the magnetic fields and instabilities at high vacuum phase advances are investigated. The parameter space for stable operation is identified. The beam equilibrium and stability properties are verified by two-dimensional self-consistent particle-in-cell (PIC) simulations using the MIT 2D periodic focused beam (PFB2D) code. The beam equilibrium is further verified by 3D simulations using the commercial code OmniTrak. As applications, a nonrelativistic elliptic electron beam is designed for the MIT ribbon-beam amplifier and a relativistic electron beam is designed for a high-power L-band klystron

Three Dimensional Theory and Simulation of an Ellipse Shaped Charged-Particle Beam Gun

A three-dimensional (3D) theory of non-relativistic, laminar, space-charge-limited, ellipse-shaped, charged-particle beam formation has been developed recently [1] whereby charged particles (electrons or ions) are accelerated across a diode by a static voltage differential and focused transversely by Pierce-type external electrodes placed along analytically specified surfaces. The treatment is extended to consider whether the diode geometry solutions thus obtained are robust to perturbations and limitations of the sort likely to be encountered in a realistic device: finite extent, part misalignment, tolerances for mechanical and thermal stresses, etc. Analytic and semi-analytic estimates are presented along with simulations utilizing the 3D trajectory code, OMNITRAK [2]. It is found that the elliptic-beam solution is quite stable and robust, and its desirable properties can be maintained in a realistic diode.