Cylindrical Inertial Electrostatic Confinement Research Articles

Characterization of a radially emitting spray jet in a cylindrical inertial electrostatic confinement plasma source based on particle in cell simulation

This paper investigates the outflow mechanism of a cylindrical inertial electrostatic confinement plasma source using Particle in Cell plasma simulations. Various phenomena such as ion-wall interactions, impact ionization, excitation, and secondary electron generation are considered. Together with a fine time and cell resolution to reveal relevant phenomena. The results indicate a high electron and ion density in front of the cathode at the widest grid opening, which suggests the formation of a cascade-like charge carrier emission, commonly referred to as the “spray jet”. Initially, a virtual anode is formed within the cathode grid and is shifted toward the grid opening as time elapsed. Ions are accelerated in the plasma sheath around the cathode and collide with the cathode grids or oscillate through the grid opening. Electrons are accelerated and ionize the background gas at the plasma sheath edge. While the electron flow is disordered within the cathode it forms a cascade-like quasi-neutral plasma at the outlet of the plasma source. Through the formation of a virtual anode the discharge becomes self-sustained. With this simulation results the working principle of the inertial electrostatic confinement plasma source can be derived.

Neutron imaging with an inertial electrostatic confinement fusion neutron source.

A compact inertial electrostatic confinement (IEC) fusion neutron source was developed. Imaging tests using the cylindrical IEC neutron source were conducted with the indirect imaging plate (IP) method using dysprosium foil and an imaging plate. An array of B4C powder contained in a stainless-steel blade and Cd pins was successfully imaged. To calculate thermal neutron flux of the device, we tested multiple types of IP and IP scanners with the indirect IP method to create a calibration curve, and it was confirmed that dental IP scanners, which are more widely used than industrial ones, can be applied to the indirect IP method.

Neutron and x-ray emission from a cylindrical inertial electrostatic confinement fusion device and their applications

Table-top neutron/x-ray sources are of great interest for uses in neutron activation analyses, in neutron/x-ray radiography, and also in medical applications. Inertial electrostatic confinement fusion (IECF) is a multiple neutron source that can emit neutrons, protons, x rays, etc., as basic products when operated in both continuous and pulsed modes. In this work, D-D neutrons are produced in the steady-state mode using a cylindrical IECF device. The neutron production rate has been optimized by using cathodes having different dimensions and geometrical transparencies. The maximum neutron production rate is found to be approaching 107n/s, using a cathode having eight grid wires and a diameter of 3 cm. The neutrons are successfully used for neutron activation analysis of materials containing explosive elements. X-ray spectrum having a wide range of photon energies (30–70 keV) has been detected from this device while operated in the continuous mode. X-ray radiography of high density objects has also been performed and reported for the first time using the cylindrical IECF source with negative polarity of the central grid in this paper.

Cylindrical inertial electrostatic confinement plasma source for surface treatment

The inertial electrostatic confinement (IEC) has been commonly researched in the scope of application for space propulsion and fusions reactors since many years. The utilization as thruster is possible due to a free emitting stream in a so-called jet mode of the IEC source. Depending on the setup, this jet can be operated as high energetic electron beam (tight jet) with electron energies of several keV or as low energetic plasma jet close to quasineutrality (spray jet). These modes are of high interest for thin film applications and plasma treatment. However, the IEC source is still not used in this field of application. Relevant application scopes can be electron substrate heating, surface plasma pretreatment, ionized physical vapor deposition and plasma enhanced chemical vapor deposition. In this paper, a cylindrical IEC source is presented that emits the plasma in both known jet modes, spray jet and tight jet. The jet emission occurs in radial outlet direction along the entire source height (“curtain-like” emission). Furthermore, an ignition test and operational behavior test is introduced. A stable spray jet operation region was examined and dependencies on pressure and voltage are investigated.

Variation of Plasma Properties in Cylindrical Inertial Electrostatic Confinement Device by Changing the Anode Transparency

Inertial electrostatic confinement (IEC) is investigated in terms of direct-current discharge in a cylindrical configuration using nitrogen gas in the pressure range between 0.028 and 0.09 Torr. Discharge characteristics are determined for different anode transparencies of 84%, 92%, and 96% corresponding to 24, 12, and 6 anode rods, respectively. I-V characteristic curves indicate that the electric discharge is in the abnormal glow discharge region. The discharge voltage has the highest values for the low anode transparency for the same value of the discharge current. A double electric probe has been used to measure electron temperature and ion density. The low anode transparency (24 anode rods) enhances field uniformity and aligns the motion of electrons into a chord so that better electrostatic confinement is achieved. This will raise the ion density and lead to thermalization of the plasma, which reduces the electron temperature. The behavior of the electron temperature and the ion density was studied as a function of the gas pressure at the center and near the edge. The variation of the density and temperature in both positions can confirm the plasma confinement. In the low-pressure regime, the confinement process is reinforced. Because of the longer mean free path, electrons cause ionization at the center, which raises the ion density to about 1.44 × 1015 m−3 and the electron temperature to about 2.9 eV.

CHARACTERIZATION AND COMPARSION OF NEUTRON GENERATORS OF IEC AND LINEAR D-T BY THE SPECTROMETRIC SYSTEM NGA-01

This article focuses on description of two different neutron fields from linear and cylindrical Inertial Electrostatic Confinement (IEC) neutron generators. Both of these generators are well defined and commonly used. They use a deuterium-tritium reaction that produces neutrons with energies in the range 13 – 16 MeV, depending on the direction and the energy of the incoming deuterium nucleus. Two-parametric spectrometric system for neutron/gamma mixed fields NGA-01 was used to characterize neutron spectra in the proximity of generators. The cylindrical 45x45 mm stilbene scintillator was connected to this device using an active voltage divider. This way, we were able to measure neutron energies in the range 1 - 15 MeV while filtering out gamma radiation, even when counts per second is high. For the neutron spectrum calculation recoil spectra using deconvolution through maximum likelihood estimation was used. Measured neutron spectra have been compared with simulations realized via MCNP6. According to the theoretical prediction, these two types of generators produce different neutron fields. In case of the linear generator the target is very close to point located tritium bombarded by deuterons. Thus the neutron spectrum varies depending on the angle between the detector axis and the axis of the generator. Both experimental results and simulation show a shift of the neutron energy peak in pulse height histogram. For IEC type generators the neutron spectrum is more complicated. The shape and the position of the neutron energy peak depend heavily on the position of the detector. The most prominent effect is in the position in the plane perpendicular to the generator axis. In this case, the peak splits into two peaks that can be measured and distinguished. These results were verified by the diamond detector which was also used for characterization of the IEC type generator.

Kinetic characteristics of ions in an inertial electrostatic confinement device.

The kinetic analyses are quite important when it comes to understanding the particle behavior in any device as they start to deviate from a continuum nature. In the present study, kinetic simulations are performed using the particle-in-cell method to analyze the behavior of ions inside a cylindrical inertial electrostatic confinement fusion (IECF) device which is being developed as a tabletop neutron source. Here, the lighter ions, like deuterium, are accelerated by applying an electrostatic field between the chamber wall (anode) and the cathode (cylindrical gridded wire), placed at the center of the device. The plasma potential profiles obtained from the simulated results indicate the formation of multiple potential well structures inside the cathode grid depending upon the applied cathode potential (from -1 to -5 kV). The ion density at the core region of the device is found to be of the order of 10^{16}m^{-3}, which closely resembles the experimental observations. Spatial variation of ion energy distribution function has been measured in order to observe the characteristics of ions at different cathode voltages. Finally, the simulated results are compared and found to be in good agreement with the experimental profiles. The present analysis can serve as a reference guide to optimize the technological parameters of the discharge process in IECF devices.

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.

A study on neutron emission from a cylindrical inertial electrostatic confinement device

The adaption of new generation portable neutron sources has been increasingly marked in a wide range of research fields compared to the large-scale neutron generators. In this context, we have successfully demonstrated some essential parameters required for the emission of 2.45 MeV DD fusion neutrons from a steady state portable linear neutron source based on inertial electrostatic confinement scheme. The parameters that control the production of neutrons are the working pressure of the fuel gas, applied voltage, measured current and cathode geometries. The neutrons emitted from the source are confirmed using neutron monitor, bubble dosimeters, nuclear track detectors, and He-3 proportional counter. Presently, the device produces neutrons up to the order of ∼ 106 n/sec at discharge voltage ranging from -60 kV to -80 kV, and discharge current of 20 mA to 30 mA.

Investigation of gas breakdown in cylindrical inertial electrostatic confinement device with inner cage anode

The gas breakdown in the Inertial Electrostatic Confinement (IEC) device has been studied by DC discharge of Nitrogen gas in the pressure range between 0.03 Torr and 0.7 Torr. Paschen curves and Townsend coefficients are obtained in a cylindrical system with inner anode in shape of rods and the outer grid cathode. The breakdown occurs and the plasma is formed at the center of the electrodes. Townsend coefficients are calculated for anode transparencies of 84%, 92%, and 96% (24, 12, and 6 rods respectively). On the left hand side of Paschen curves, the high transparency has a higher breakdown voltage. More electrons are allowed to pass the anode. So, the collisions increase, leading to a slight increment of the first Townsend coefficient (α) decreasing of the second Townsend coefficient (γ) while the ionization efficiency (η) is not affected. For high reduced electric field E/P, i.e. a high electric field with low pressure, the probability of ionizing collision events decreases. This causes a decrement of α while γ is raised because the ions' energy is not exhausted in collisions at the center. The coefficients α and γ are working in harmony to balance the rates of electrons generated in gas ionization so that the relation between the two coefficients is satisfied.

Study on discharge plasma in a cylindrical inertial electrostatic confinement fusion device

Deuterium plasma has been produced in a cylindrical inertial electrostatic confinement fusion device using hot and cold cathode discharges and the plasma parameters are determined by employing an electrostatic probe. The plasma temperature and density are estimated at optimum experimental conditions and it is noted that the plasma temperature is 3 eV in the case of hot cathode discharge whereas 10 eV in the case of the cold cathode discharge. The plasma density as determined is two orders more in the case of the hot cathode discharge than the other. The probe is also used to observe the ion oscillation in the negative potential well that is formed in between the cathode grid and chamber (anode). The observation of spontaneous oscillation along with the harmonics has been reported.

Fusion-Fission Hybrid Using a D-D Cylindrical Inertial Electrostatic Confinement (IEC) Driver

Recent progress in fusion development combined with the rebirth of nuclear fission power has regenerated interest in fusion-fission hybrid reactors. Such systems could be applied to both low power research reactors for use in University and industrial research assemblies and power reactors. However most attention has been directed at D-T fusion drivers using Tokamak, ICF or various alternate confinement systems like FRCs. However, the necessity to have large devices and breed tritium in the blanket complicates the concept. Here we propose the inertial electrostatic confinement (IEC) fusion approach since it offers the advantages of simple structural, high power density and a non-Maxwellian beam dominated plasma suited for burning advanced fuels to minimize tritium involvement. The cylindrical IEC allows a small compact unit which can be inserted into fuel element slots in the fission reactor core, thus providing a compact overall system and excellent neutronic coupling. The basic physics for the IEC has been demonstrated in small-scale laboratory experiments close to levels needed for driving a subcritical assembly for use in student teaching labs. However, for use in future high power hybrids significant scale-up in source strength is required. Scale up using an external ion source (e.g. a Helicon) so the background gas pressure is minimized in the reaction zone potentially offers a route to the required neutron source strength.

Cylindrical IEC Fusion Neutron Source for Broad Area NAA

The development of a unique long cylindrical neutron source for broad area neutron activation analysis (NAA) is presented. This source uses inertial electrostatic confinement (IEC) to produce 2.54 MeV D-D or 14.1 MeV D-T fusion neutrons. The IEC offers a variety of applications ranging from security inspection stations to driven-subcritical research assemblies. This IEC design uses a biased grid to initial in a unique “star” mode plasma discharge creating beam-background gas (target) fusion reactions. They routinely produce ∼108 2.54 MeV D-D neutrons/s at steady state. Pulsed operation has achieved upto 109n/s. (∼1011n/s if a deuterium mixture is used). Indeed, a version of the IEC has been commercially produced as a portable neutron source for industrial NAA applications. While that IEC source used spherical geometry, the present work uses a cylindrical version which provides a unique long “linelike” neutron source for use in the present broad area NAA system.

Driven Subcritical Assembly Using a Cylindrical Inertial Electrostatic Confinement (IEC) Neutron Source

The design basis for a possible near-term driven subcritical assembly for student labs using a cylindrical Inertial Electrostatic Confinement (IEC) fusion neutron source is described. The rebirth of nuclear fission power is going to require a new generation of training facilities for students. The IEC driven subcritical provides a very versatile facility for such training. The IEC source can provide various neutron wave forms (pulses, sinusoidal ramp, etc.) by varying the applied voltage. This opens up an important class of dynamic experiments for student lab study. Driven subcritical operation also eases regulatory requirements and limitations on core configuration changes needed in various student experiments while also introducing the student to the important fusion-fission reactor concept. The possibility of employing the IEC source for future fusion-fission reactors is also briefly discussed.

Study on Discharge Characteristics of a Cylindrical Inertial Electrostatic Confinement (IEC) Device for High-Yield Fusion Sources

Inertial electrostatic confinement (IEC) fusion device has been investigated as a compact fusion source to generate byproducts of fusion reactions for many applications. However, the IEC fusion device still has insufficient fusion reaction rate and stability issues in high power operation. In this work, a cylindrical IEC device is designed and discharge voltage and current at various pressures and geometries are studied to understand their effect on discharge. From this result, three key features is observed and discussed: 1) discharge voltage in IEC device increases with lower transparent cathode at the identical operating pressure, 2) high voltage and current discharge can be obtained with higher operating pressure at the identical pd value. 3) high voltage discharge without decrease of operating pressure can be obtained by considering limit length of cathode diameter in IEC device. Based on these results, it is supposed that transparency and size of cathode in an IEC device can be optimized for high voltage and current discharge with relatively high operating pressure to increase fusion reactions of beam-cathode surface and beam-background gas besides ion-ion fusion reaction in continuous IEC discharge. Consequently, these results can be reflected on design of a high-yield fusion sources.

Neutron Beam Generation by the Cylindrical Fusion Neutron Source

We have investigated the neutron generation characteristics of discharge-type fusion neutron source by experiments and computer simulations for several years. The cylindrical inertial electro-static confinement device used for these studies has been considered to be a point source where neutrons emitted isotropic. The aspect ratio (length divided by diameter) of the device is 1∼2. For neutron applications, a beam shape where neutrons are emitted in a specific direction may be more convenient.In this paper we describe recent results of neutronic calculations for making a beam-type neutron source by increasing aspect ratio of the device and by locating reflecting material around the device. It is found that the increase of aspect ratio of 2∼5 does not strongly affect the neutron flux distribution, but that neutron fluxes in the axial direction becomes 2∼3 times larger than those without reflectors and more than 1 order stronger than the radial direction by adding reflector.

Cylindrical IEC neutron source design for driven research reactor operation

A resurgence in nuclear power use is now underway worldwide. However, due many university research reactors shutdown, they must rely on using sub-critical assemblies which employs a cylindrical Inertial Electrostatic Confinement (IEC) device to provide a fusion neutron source. The source is inserted in a fuel element position, with its power input controlled externally at a control panel. This feature opens the way to use of the critical assembly for a number of transient experiments such as sub-critical pulsing and neutron wave propagation. That in turn adds important new insights and excitement for the student teaching laboratory.

Application of Doppler spectroscopy inH2to the prediction of experimentalD(d,n)3Hereaction rates in an inertial electrostatic confinement device

In our previous paper, we developed an optical measurement for absolute densities of fast (tens of keV) H ions in an abnormal hollow cathode discharge of hydrogen in the units to tens of mTorr pressure range. We apply this method to a cylindrically symmetric inertial electrostatic confinement (IEC) discharge of hydrogen using the Doppler spectrum of Halpha. We predict neutron production rates for an equivalent discharge of deuterium and compare these with experimental values under the separate conditions of constant deuterium gas pressure (approximately 6 mTorr) and voltage (30 kV). Our predictions capture the variation of production rates with dc current (10-50 mA) and agree with experiment to within an order of magnitude. The applicability of this diagnostic to the cylindrical IEC discharge is thus demonstrated, with our results supporting the theory that the discharge is dominated by energetic neutrals emerging from the cathode apertures.

An Integrated Broad Area Coverage Fusion Neutron/X-Ray Interrogation Unit

Homeland security has an urgent need for an advanced detecting system to accurately and quickly search for nuclear and explosive materials in a wide variety of situations. An integrated broad area coverage neutron/x-ray interrogation unit is proposed here to meet such needs. This system will use a unique cylindrical Inertial Electrostatic Confinement (IEC) device. This compact pulsed neutron/x-ray line source can produce ∼2x1010 n/s 14.1-MeV D-T neutrons, ∼108 n/s 2.45-MeV D-D neutrons and 80 kV x-rays.Unlike prior neutron activation systems, this unit can provide a long line-like emission source to obtain broad coverage, providing very fast scan time for even large objects. The use of combined multi-energy neutron and x-ray sources, along with a 3-D detector array and fuzzy logic analysis system, are expected to provide high elemental identification accuracy, greatly decreasing false signals so commonly encountered in prior systems. Analysis techniques will employ both thermal neutron analysis (TNA)and pulsed fast neutron analysis (PFNA), accompanied by broad area x-ray imaging techniques.