Electrostatic Confinement Research Articles

Melting of strongly coupled, negatively charged, two‐dimensional dust cluster: The role of charge fluctuation amplitude

AbstractStructural and melting characteristics are investigated for negatively charged dust particles in the presence of a two‐dimensional electrostatic parabolic confinement potential. For a restricted number of dust particles that are subject to the permanent flow of electrons and ions, numerical simulation is conducted taking into account the random charge fluctuation. The amplitude of the charge fluctuation affects the ground‐state configuration and melting characteristics of a finite number of particles interacting through Coulomb potential. The melting temperature decreases when the amplitude of the charge fluctuation increases as a result of particles' strong repulsive interaction.

Physics and application of plasma diagnostics, electrostatic confinement and characterization by optical emission spectroscopy

Physics and application of plasma diagnostics, electrostatic confinement and characterization by optical emission spectroscopy

The dual advanced ion simultaneous implantation experiment (DAISIE) for testing plasma-facing materials

A new dual ion beam experimental facility, the Dual Advanced Ion Simultaneous Implantation Experiment (DAISIE), has been constructed at the University of Wisconsin-Madison Inertial Electrostatic Confinement laboratory for implanting candidate plasma-facing components of multiple ion species. DAISIE is capable of implanting ions at energies from 10 kV to 50 kV, ion currents of 10 µA–950 µA, corresponding to steady-state ion fluxes of 1 × 1014 cm−2 s−1 to 1 × 1016 cm−2 s−1, incidence angles of 55°, and surface temperatures of at least 1100 °C. Improvements to the sample current and sample temperature measurement and control systems over those used in prior UW-IEC experiments have been made. Optical measurements of the spot size of the beam on samples in DAISIE are in agreement with existing measurements of the ion beam and spot size in previous UW-IEC experiments. Dual-beam operation has been confirmed with helium-deuterium ion implantations in tungsten surfaces.

Surface Hardening of Massive Steel Products in the Low-pressure Glow Discharge Plasma

A process vacuum chamber is filled with a homogeneous plasma of glow discharge with electrostatic electron confinement, which is used for surface hardening of massive products. At the current of 2–20 A and the gas pressure ranging from 0.1 to 1 Pa the discharge voltage amounts to 350–500 V. When a bias voltage of 2 kV is applied to an immersed in the plasma hollow cylinder with a mass of 15 kg, electrical power spent on heating it by accelerated ions exceeds by an order of magnitude the power spent on the discharge maintenance. The massive cylinder is heated up to 700 °C for 15 min. When argon mixture with nitrogen (30%) is used, the nitriding for 3h results in an increase in the surface hardness from 400 up to 1000 HV50 and the nitrided layer thickness grows to ~100 μm. The nitriding rate is enhanced by a high degree of nitrogen dissociation due to decomposition by fast electrons and surface structural defects due to bombardment by high-energy ions.

Design and Operation of First Egyptian IEC Fusion Plasma Device

In this paper, Egyptian first inertial electrostatic confinement fusion (IECF) device, constructed at the Egyptian Atomic Energy Authority (EAEA-IEC), is introduced the characterization of IEC Plasma Device. It consists of 2.8 cm stainless steel cathode, 6.5 cm anode diameter with 10 cm diameter 30 cm height vacuum chamber. The discharge current and voltage of plasma discharge has been recorded using current probe and resistive voltage divider respectively. The X-ray emissions in IEC plasma device were investigated by employing time-resolved detector. The temporal distributions of detected x-rays emission are occurring during the initial 1 microsecond. The calculated rate of DD-neutron generation using the same electrode configuration about 106 – 108 neutrons/second.

Mode Structure of a Transparent Cathode Discharge

In this paper, we characterize a Transparent Cathode Discharge (TCD), a type of Inertial Electrostatic Confinement (IEC) plasma, operated in helium and argon in the pressure range of 1–100 Pa. The discharge was investigated using a combination of electrical and optical diagnostic techniques. The imaging of the discharge indicated distinct operating regimes related to the background gas pressure, with each mode being characterized by different patterns of optical emission. The spectroscopic analysis of the optical emission showed that this mode structure represented an electron-driven discharge at higher pressures, and a discharge sustained by the activity of energetic heavy particles at lower pressures. The high-pressure discharge is shown to be assisted by the hollow cathode effect toward its low-pressure limit, and the visible color of emission from the discharge in helium is found to provide a convenient diagnosis of active species. The identification of a stable discharge mode in which energetic heavy particles are responsible for collisional processes has the potential to lead to new industrial applications based on this novel heavy particle-driven reactive plasma source.

Preliminary results of a miniature cylindrical inertial electrostatic confinement fusion device equipped with inductively coupled plasma generator

In this paper a cylindrical neutron generator based on inertial electrostatic confinement is designed and constructed. This miniature sized linear neutron generator is equipped with an inductively coupled plasma generator as the pre-ionization system. The preliminary neutron counting results by a 3He detector indicated linear correlation between the discharge current and Neutron Production Rate (NPR) at fixed voltages. The pre-ionization helps to increase the discharge current at fixed pressures therefore the charge exchange reactions does not increase by this method. Primary results represent NPR of 105 n/s at −40 kV cathode voltage that could be increased between 107 to 108 n/s by increment of this voltage up to −80 kV and cathode cooling considerations.

Studies on virtual electrode and ion sheath characteristics in a cylindrical inertial electrostatic confinement fusion device

An experiment on the formation of virtual electrode and ion sheath characteristics has been carried out in a hot cathode discharge plasma produced inside a cylindrical inertial electrostatic confinement fusion device. The plasma parameters such as electron temperature and plasma density are evaluated by using a Langmuir probe. Transition from a single potential well to multiple potential wells, i.e., virtual electrodes inside the cathode grid, is observed when the bias voltage applied to the cathode is increased from –1000 to –5000 V. An emissive probe has been used for the measurement of plasma potential due to its greater accuracy than the conventional Langmuir probe. Ion sheath potential structures and presheath characteristics for different cathode potentials have been investigated using the emissive probe and are found to be consistent with the Debye sheath model. A detailed discussion on the obtained results has been presented in this paper.

Potential Profile Measurements Inside a Gridded Cathode at High Potential in a Spherical Inertial Electrostatic Confinement Device

This paper proposes a Langmuir probe–based diagnostics for plasma parameters inside gridded cathodes at high bias potentials in inertial electrostatic confinement devices. As the first step for the proof of concept, floating potential profiles were measured in deuterium and helium plasmas in a glow-discharge mode. The measurements with fusion-relevant cathode voltages up to 55 kV were carried out successfully. The results revealed that the positive potential buildup at the center ranges from 5% to 8% of the applied bias voltage to the gridded cathode, which is found to be much smaller than those in earlier works under cathode voltages lower than 5 kV. It was also shown that the floating potential profile is different significantly between deuterium and helium discharge plasmas.

Improvement of the Neutron Production Rate of IEC Fusion Device by the Fusion Reaction on the Inner Surface of the IEC Chamber

Neutrons are generated in the inertial electrostatic confinement (IEC) device through different types of fusion reactions of the fuel gas such as deuterium (D) and tritium (T). Fusion in the IEC device takes place via various kinds of collisions like beam-beam collision, beam–background gas collision, and beam-target collision on the electrode surfaces. Two identical anodes for the IEC chamber made from titanium (Ti) and SUS-316L stainless steel (SS) are used to study the effect of the anode material on the neutron production rate (NPR). The NPRs from the chambers are measured at different applied powers. The achieved NPRs, so far, for Ti and SS are 8.9 × 107 n/s at 5.25 kW (75 kV, 70 mA) and 2.8 × 107 n/s at 10.5 kW (70 kV, 150 mA), respectively. The normalized NPR (NPR rated to the cathode current) from the Ti chamber is three to four times higher than that from the SS chamber. We observed a better NPR for the Ti chamber compared with the SS chamber. This is explained by the fusion reaction occurring between the neutrals and D atoms adsorbed/embedded on the inner surface of the anode. Moreover, the Ti chamber shows an improvement of the NPR as a function of the operating time ranging from 1.5 to 1.75 after 25 h from the first discharge.

Discharge current enhancement in inertial electrostatic confinement fusion by impulse high magnetic field

Effect of strong pulsed magnetic field on the discharge behavior of a cylindrical inertial electrostatic (IEC) device has been investigated both theoretically and experimentally. By applying strong pulsed magnetic field in a new fabricated miniature cylindrical IEC device equipped with Inductively Coupled Plasma (ICP), discharge current amplifications were observed at ordinary pressures as well as low pressure ICP-assisted operational regime with deuterium gas. The obtained results indicate the evidence for significant amplification of discharge current up to more than one hundred times. Since the neutron production rate has been previously proven to be linearly dependent on the discharge current, then this study might open new investigations for probable increment of fusion reaction rates in IEC devices with additional strong magnetic field.

Zero‐Energy Vortices in Dirac Materials

In this brief review, the problem of electrostatic confinement of massless Dirac particles is surveyed via a number of exactly solvable one‐ and two‐body models. By considering bound states at zero energy, a route to obtain truly discrete states of massless Dirac particles in scalar potentials is presented, circumventing the celebrated Klein tunneling phenomenon. It is also shown how the coupling of two ultrarelativistic particles can arise, and its implications for cutting‐edge experiments with two‐dimensional Dirac materials are discussed. Finally, an analytic solution of the two‐body Dirac–Kepler problem is reported, which may be envisaged to bring about a deeper understanding of critical charge and atomic collapse in mesoscopic Dirac systems.

On the dispersion relation for the Buneman instability in spherically confined plasmas

In this paper an analytically derived dispersion relation for the Buneman instability in spherically confined plasmas is presented. The calculations are based on plasmas with spherical symmetry in which the dependence of the dispersion relation is, thus, only radial. This article is supposed to give a solution for said dispersion relation as this has not been done for such a peculiar geometry. On the other hand, new research on electrostatic confinement fusion schemes shows that there are physical effects that are strongly connected with such instabilities in spherical plasma devices and have, hence, to be taken into account in order to get a proper scientific understanding of the underlying mechanisms.

Development of an efficient pulsed magnet for improvement of inertial electrostatic confinement fusion

In this paper thin Aluminum strip has been used to construct a low resistance low inductance magnet. This new magnet has relatively high bore diameter designed for magnetization of plasma in small sized fusion neutron generators; e.g. electrostatic confinement devices. This magnet enables us to use 900 Volts/33 mFarad capacitor bank. The small sized and comparatively low voltage capacitors are able to produce more than 2400A current to produce more than 2 Tesla magnetic field inside the 11 cm diameter bore without any coolant. The maximum current density for this coil was measured as 12 kA/cm2 that lasts for about 60 ms (with rise time of 7.5 ms). This relatively low current density decreases the destructive magnetic stress. Analytical and simulation results of the magnetic field profile and the experimental performance of the magnet are described in the paper.

Time resolved x-ray emission from nanosecond vacuum discharge with virtual cathode

Design features and parameters of a modernized installation of inertial electrostatic confinement based on a low-energy nanosecond vacuum discharge (∼ 1 J) are described when operating in diode geometry in the virtual cathode formation mode and the corresponding potential well. The device is used to study the processes of collisional DD synthesis in the interelectrode space, the processes of x-ray generation in complex plasma at various stages of the discharge: from the very initial stage, when the beam of autoelectrons only begins to irradiate the nonideal anode surface, to oscillating plasma configurations in later stages of the discharge. Here, the first steps were done to introduce x-ray spectral diagnostics, as well as to obtain the integral x-ray spectra for visualizations of interelectrode complex plasmas.

On pulsating DD neutron yield under inertial electrostatic confinement of complex plasma at miniature vacuum discharge

We continue to analyze the effects of deuteron oscillations in potential well of a virtual cathode under inertial electrostatic confinement based on nanosecond vacuum discharge. The goal of this paper is to present and discuss in detail available experimental results on pulsating DD neutron yield at this scheme. Also, the results of simulations for virtual cathodes and potential wells for particular experimental regimes of neutron yields are shown and discussed, as well as comparison with available similar scheme of periodical oscillating plasmas spheres for fusion.

Axial Ring-Cusp Hybrid (ARCH) plasma discharge: an approach to highly efficient miniature-scale ion sources

The miniaturization of conventional direct-current ion sources is predominantly restricted by efficiency limitations associated with the increased surface area-to-volume ratio of smaller-scale discharge chambers—reducing the effective confinement length of the high-energy ‘primary’ electrons that is necessary for efficient plasma generation. The Axial Ring-Cusp Hybrid (ARCH) plasma discharge addresses this scaling limitation by using a new approach that combines magnetic and electrostatic confinement to decouple the primary and plasma electrons loss mechanisms. Simulated ion thruster performance measurements show that the ARCH discharge may be capable of achieving a discharge loss and a propellant mass utilization of 175 eV/ion and 0.87, respectively. These estimates are supported by full internal maps of the plasma properties, including the electron energy distribution function, inside the discharge chamber. The measurements show highly effective confinement of the primary electrons, high average plasma electron temperatures of ∼5 eV, and low plasma sheath potential relative to the anode—attributes generally found only in efficient conventional-scale discharges with good overall plasma confinement. As such, the new ARCH discharge design approach may allow miniature ion thrusters to achieve the performance and efficiency levels similar to those of highly efficient conventional ion thrusters.

Evidence for surface fusion in inertial electrostatic confinement devices

Inertial electrostatic confinement is a method of producing nuclear fusion in which concentric spherical electrodes are used to accelerate ions to fusion relevant energies. Fusion events are generally attributed to collisions between accelerated ions and neutral gas molecules in the centre of the device, with ion–grid collisions considered detrimental. In this paper, we present data that indicate that collisions between ions and neutral gas molecules adsorbed on the grid surface may, in fact, contribute significantly to the observed fusion rate in deuterium fuelled systems. When operating in the 1 × 10−4–1 × 10−3 Torr, V ≤ 40 kV regime, fusion on the grid surface is found to contribute up to 80% of the measured fusion rate, as determined from hysteresis effects between the fusion rate and system pressure. Surface fusion measurements were also carried out for a selection of cathode materials, with graphite found to produce a fusion rate that is an order of magnitude greater than the highest performing metal targets.

Magnetic confinement of diamagnetic objects for space utilization

Utilization of the space environment provides invaluable opportunities for researchers to fulfill challenging tasks that are impossible on Earth. Longtime sustainable containerless and simultaneously weightless condition is a desirable physical environment that can be easily obtained in outer space. However, in a space station, due to unpredictable disturbances, i.e., g-jitter, objects that are floating in containerless and weightless conditions may not be able to stay motionless at a specific location, making it difficult to conduct any investigation of the objects. In this study, we propose a method to confine objects without energy consumption using permanent magnets. Two types of confinement apparatuses made of permanent magnets were designed and manufactured. The apparatuses were used to demonstrate the capability of the magnetic field to confine diamagnetic objects without mechanical contact. We took confinement of a water droplet as an example and calculated the confinement performance of the two apparatuses. The results showed that the idea of using permanent magnets to confine diamagnetic objects without energy consumption in the space environment is feasible. Compared with other confinement methods, such as ultrasound and electrostatic confinement methods, the method proposed in this study is simple, efficient and inexpensive. Most importantly, the confined objects are restricted in a region with a low magnetic field. These advantages enable the method a potentially useful alternative for studying objects under containerless and weightless condition in space.

A capacitance spectroscopy-based platform for realizing gate-defined electronic lattices

Electrostatic confinement in semiconductors provides a flexible platform for the emulation of interacting electrons in a two-dimensional lattice, including in the presence of gauge fields. This combination offers the potential to realize a wide host of quantum phases. Capacitance spectroscopy provides a technique that allows one to directly probe the density of states of such two-dimensional electron systems. Here, we present a measurement and fabrication scheme that builds on capacitance spectroscopy and allows for the independent control of density and periodic potential strength imposed on a two-dimensional electron gas. We characterize disorder levels and (in)homogeneity and develop and optimize different gating strategies at length scales where interactions are expected to be strong. A continuation of these ideas might see to fruition the emulation of interaction-driven Mott transitions or Hofstadter butterfly physics.