[en] We present two-dimensional simulations in (r-z) and r-theta) cylinderical geometries of imploding-liner-driven accelerators of rings of charged particles. We address issues of azimuthal and longitudinal stability of the rings. We discuss self-trapping designs in which beam injection and extraction is aided by means of external cusp fields. Our simulations are done with the 2-1/2-D particle-in-cell plasma simulation code CLINER, which combines collisionless, electromagnetic PIC capabilities with a quasi-MHD finite element package

[en] Simulations performed with a fluid MHD extension to the PIC plasma code CCUBE show that it is in principle possible to design liner-driven ring accelerators so that they generate their own trapping well. The liner elements are tapered in mass and respond in a predictable way to the driving acceleration. Currents arise as the liner moves through an imposed axial field, and if the liner shape is appropriate, a magnetic trapping well results. A cusp-injected electron ring is then introduced, trapped, and accelerated to high energies

[en] Analytical and numerical studies have been performed on the electron gun and initial transport section of PHERMEX to provide high current injection without significant loss of beam quality. The CCUBE code was bench marked against measured PHERMEX data. A high-perveance gun was designed that requires minimal modification of the standard PHERMEX gun. The initial transport section was examined with both envelope equations and full CCUBE simulation and was found to degrade at higher voltage (approx. 1 MeV) for a 1-μp perveance beam. Preliminary results are presented of electron ring accelerator studies that seem promising as a future flash radiography candidate. 16 references, 27 figures, 2 tables

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No abstract available

[en] In the concept known as Magnetized Target Fusion (MTF) in the US and Magnitnoye Obzhatiye (MAGO) in Russia, a preheated and magnetized target plasma is hydrodynamically compressed to fusion conditions. Because the magnetic field suppresses losses by electron thermal conduction in the fuel during the target implosion heating process, the implosion velocity may be much smaller than in traditional inertial confinement fusion. Hence liner-on-plasma compressions, magnetically driven using relatively inexpensive electrical pulsed power, may be practical. The relatively dense, hot target plasma, with starting conditions O(10¹⁸ cm^-3, 100 eV, 100 kG), may spend 10 or more microseconds in contact with a metal wall during formation and compression. Influx of a significant amount of high-Z wall material during this time could lead to excessive cooling by dilution and radiation that would prevent the desired near-adiabatic compression heating of the plasma to fusion conditions. Magnetohydrodynamic (MHD) calculations including detailed effects of radiation, heat conduction, and resistive field diffusion are being done, using several different computer codes, to investigate such plasma-wall interaction issues in ongoing MTF target plasma experiments and in proposed liner-on-plasma MTF experiments

[en] Simulations performed with a fluid MHD extension to the PIC plasma code CCUBE show that it is in principle possible to design liner-driven ring accelerators so that they generate their own trapping well. The liner elements are tapered in mass and respond in a predictable way to the driving acceleration. Currents arise as the liner moves through an imposed axial field, and if the liner shape is appropriate, a magnetic trapping well results. A cusp-injected electron ring is then introduced, trapped, and accelerated to high energies

[en] A model for generating high electric fields for charged particle acceleration in dense plasma focus (DPF) devices has been developed. The mechanism found to be responsible for the generation of high electric fields is a magnetic Rayleigh-Taylor instability seeded by major features in the electrode geometry of DPF devices. The model extends to DPF devices incorporating hollow as well as solid anodes. The magnetic Rayleigh-Taylor instability is responsible for the formation of a trapped magnetic flux cavity in the plasma sheath as it converges on axis. The cavity is formed in a roughly toroidal geometry with the major axis corresponding to the centerline of the DPF device. The cavity of trapped flux then undergoes a fast compression at the sheath implosion velocity. Rapid compression of magnetic field in this geometry sets up a strong transient electric field suitable for charged particle acceleration. The development of the magnetic cavity was calculated using a two-dimensional, resistive magnetohydrodynamic code. The transient electric field was calculated using a set of one-dimensional electromagnetic codes. Preliminary results produced electric fields of 0.2 MV/cm over accelerating lengths of 0.5 cm with a duration of a few nanoseconds. Results of charged particle acceleration in the unique electromagnetic field geometry will also be discussed

[en] Imploding liners can be used to accelerate rings of charged particles to high energies. Simulations of such ring accelerators have been done in both r-z and r-theta cylindrical geometries in order to study the axial and azimuthal stability of compressing charged particle rings. These simulations have been done with the 2D-3V particle-in-cell plasma code CCUBE, together with the quasi-MHD package LINER. The latter package treats the moving liner as a conducting fluid interacting with the particles and fields of CCUBE via MHD equations

[en] Los Alamos is extending the performance of the Friedman-type, high-current relativistic klystron amplifier (RKA) to the microsecond regime while attempting to achieve the gigawatt-level peak power capability that has been characteristic of the RKA at shorter pulse lengths. Currently the electron beam power into the device is about 1 GW in microsecond duration pulses, with an effort underway to increase the beam power to 2.5 GW. To data the device has yielded an rf modulated electron beam power of 350 MW, with up to 50 MW coupled into waveguide. Several aspects of RKA operation under investigation that affect RKA beam bunching efficiency and amplifier gain include cavity tuning, beam diameter, beam current, and input rf drive power, and the development of an output coupler that efficiently couples the microwave power from the low impedance beam into rectangular waveguide operating in the dominant mode. Current results from experimental testing and code modeling are presented