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A novel plasma state has been found in the presence of a uniform applied axial magnetic field in periodic cylindrical geometry. This state is driven electrostatically by helical electrodes, providing a driving field that depends on radius and $m\theta-n\zeta$, where $\theta$ is the poloidal angle and $\zeta=z/R$ is the toroidal angle. We focus on $m=n=1$. The radial magnetic field at the wall is taken to be zero. With weak driving, the resulting distortion is very small, but for stronger driving the mean field of the state has field line safety factor $q_0(r)$ just above the pitch of the electrodes $m/n=1$ except near the edge, where $q_0$ increases monotonically. This state is characterized as a single helicity Ohmic equilibrium with the helical symmetry of the applied field. The plasma appears to be close to force-free in the interior, but current density crosses the magnetic flux surfaces near the edge, where current must enter and exit through the helical electrodes. This perpendicular current density drives large helical plasma flows. Sensitivity of this state to flow boundary conditions, plasma resistivity profile, strength of the electrostatic driving, and parameters such as the loop voltage and the Lundquist number is explored. The magnetic helicity is calculated for both the transient period and time-asymptotic state. Possible applications to current drive in toroidal confinement devices and to electrical transformers are discussed.

A new plasma state has been investigated [C.~Akcay, J.~Finn, R.~Nebel and D.~Barnes, Phys.~Plasmas $\textbf{24}$, 052503 (2017)], with a uniform applied axial magnetic field in a periodic cylinder of length $L=2\pi R$, driven by helical electrodes. The drive is single helicity, depending on $m\theta+kz=m\theta-n\zeta$, where $\zeta=z/R$ and $k=-n/R$. For strong $(m,n)=(1,1)$ drive the state was found to have a strong axial mean current density, with a mean-field safety factor $q_0(r)$ just above the pitch of the electrodes $m/n=1$ in the interior. This state has possible applications to DC electrical transformers and tailoring of the current profile in tokamaks. We study two geometric issues of interest for these applications: (i) scaling of properties with the plasma length or aspect ratio; and (ii) behavior for different helicities, specifically $(m,n)=(1,n)$ for $n>1$ and $(m,n)=(2,1)$.

A novel plasma state has been found [C.~Ak\c{c}ay, J.~Finn, R.~Nebel and D.~Barnes, Phys.~Plasmas \textbf{24}, 052503 (2017)] in the presence of a uniform applied axial magnetic field in periodic cylindrical geometry. This state is driven by external electrostatic fields provided by helical electrodes, and depends on radius $r

A new method of operating an inertial electrostatic confinement (IEC) device is proposed, and its performance is evaluated. The scheme involves an oscillating thermal cloud of ions immersed in a ba...

Two different, complementary approaches were taken to determine the effects of an Inertial Electrostatic Confinement (IEC) grid`s design on the neutron production rate of the device. A semi-empirical formula developed from experimental data predicts the neutron yield of an IEC device, given the chamber size, grid radius and transparency, and operating voltage and current. Results from the IXL computer program support some of the scalings found in the semi-empirical formula. A second formula was also developed that predicts the neutron yield of an IEC device using grid design parameters and the ion core radius. The SIMION computer program was used to calculate the ion core radius. These formulas are useful tools for designing grids that will maximize the neutron yield for IEC devices. 7 refs., 9 figs.

Magnetic divertors have been proven successful in minimizing plasma/wall interactions and in leading to high-confinement regimes in tokamaks. This suggests that similar benefits may occur i...

A major issue for electron injected inertial electrostatic confinement (IEC) devices is space charge neutralization. A new formalism is developed that will allow this neutralization to occur for both oscillating and steady-state IEC plasmas. Results indicate that there are limits on the amount of compression that can be achieved by oscillating plasmas while simultaneously maintaining space charge neutralization and parabolic background potential. For steady-state plasmas, there are no such limits and space charge neutralization can be achieved even when the plasma becomes quasineutral.

Inertial electrostatic confinement (IEC) is one of the earliest plasma confinement concepts, having first been suggested by P.T. Farnsworth in the 1950s. The concept involves a simple apparatus of concentric spherical electrostatic grids or a combination of grids and magnetic fields. An electrostatic structure is formed from the confluence of electron or ion beams. Gridded IEC systems have demonstrated neutron yields as high as 2*10 neutrons/sec in steady state. These systems have considerable potential as small, inexpensive, portable neutron sources for assaying applications. Neutron tomography is also a potential application. This paper discusses the IEC concept and how it can be adapted to a steady-state assaying source and an intense pulsed neutron source. Theoretical modeling and experimental results are presented.

The commemoration of the “discovery,” conquest, colonisation and missionizing of the American continent by Europeans, beginning some 500 years ago, is a fitting time for pondering the themes of Christianization and the mixing of cultures and religions in that part of the world.

Theoretical works by Barnes and Nebel [D. C. Barnes and R. A. Nebel, Phys. Plasmas 5, 2498 (1998); R. A. Nebel and D. C. Barnes, Fusion Technol. 38, 28 (1998)] have suggested that a tiny oscillating ion cloud (referred to as the periodically oscillating plasma sphere or POPS) may undergo a self-similar collapse in a harmonic oscillator potential formed by a uniform electron background. A major uncertainty in this oscillating plasma scheme is the stability of the virtual cathode that forms the harmonic oscillator potential. The electron-electron two-stream stability of the virtual cathode has previously been studied with a fluid model, a slab kinetic model, a spherically symmetric kinetic model, and experimentally [R. A. Nebel and J. M. Finn, Phys. Plasmas 8, 1505 (2001); R. A. Nebel et al., Phys. Plasmas 12, 040501 (2005)]. Here the mode is studied with a two-dimensional particle-in-cell code. Results indicate stability limits near those of the previously spherically symmetric case.

The Reversed-Field Pinch (RFP) is presented as a driven nonlinear dynamical system that evolves on time scales long compared with the fastest normal modes of the system. Numerical methods for the simulation of these processes, and examples of their application to experimentally observable phenomena, are presented.

Magnetic perturbations caused by field errors may pose a threat to magnetic confinement. They can cause the formation of magnetic islands, which may increase transport. The response of a reversed-field pinch (RFP) plasma to field errors has been calculated numerically. A three-dimensional nonlinear magneto-hydrodynamic code was used, with field errors specified as boundary conditions. Two types of field errors were studied: those arising from current flowing in the toroidal field coil set and those arising from induced currents in the conducting shell flowing around holes. Design data from two RFPs at the Los Alamos National Laboratory - ZT-40 (currently operating) and ZT-H (being designed) - were used. Results on the effect of the plasma on the radial field perturbation and on island size are given. The effects of the chosen equilibrium current profile resistivity, and viscosity are discussed.

A crucial question for the feasibility of high-beta ohmically heated devices, such as the reversed field pinch (RFP) and the Spheromak, is whether such devices can be formed with a modest amount of field dissipation and energy loss. By means of a convective startup technique, a low-loss formation and burn scenario for the RFP reactor, which maintains effective stability to ideal and resistive magnetohydrodynamic modes, is simulated. Results indicate small aspect ratio machines have the best possibilities for stable startup.

Oscillating field current drive on the reversed‐field pinch is simulated by using a three‐dimensional nonlinear resistive magnetohydrodynamic model in conjunction with a one‐dimensional hyper‐resistive model. When input from the three‐dimensional model is used for fluctuating fields in the hyper‐resistive equations, the two models are found to give similar relaxed profiles. Comparisons are made with experiments on the Los Alamos National Laboratory ZT‐40M reversed‐field pinch device [Nucl. Fusion 25, 1321 (1985)]. Simulation results indicate that the oscillation period must be much less than the resistive decay time, but should not be much less than the hyper‐resistive relaxation time, in order to maintain reversal without a steady‐state driving field.