Spherical Inertial Electrostatic Confinement Research Articles

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.

Evaluation of the neutron production rate using D–D and D–T fuel in an inertial electrostatic confinement fusion device

The correlation between the neutron production rate and fuel species in a spherical inertial electrostatic confinement fusion (IECF) device is investigated by solving the Poisson equation for various ion and electron distribution functions. The fuel ion energy distribution function is determined at each radial point. The fusion reaction rate is evaluated from the energy distribution function. The dependence of the neutron production rate (NPR) on some important parameters, like the ion convergence, the broadening of the distributions in the energy space, working pressure and fuel species, are also investigated. Compared with the IECF device with D–D, numerical calculations show that by increasing the percentage of tritium in the D–T mixture fuel the neutron production rate grows significantly.

Analysis of the radial potential structure and neutron production rate in the spherical inertial electrostatic confinement fusion devices

The radial dependent potential and neutron production rate in spherical inertial electrostatic confinement fusion (IECF) devices is investigated. The electrostatic potential is determined by solving the Poisson equation for various deuteron and electron distribution functions. The fusion reaction rates are determined using energy distribution function. Also, dependence of potential structure and neutron production rate on some important parameters as the ion and electron convergence, working pressure, kinetic energy of the secondary electrons emitted from the cathode and the fraction of secondary electrons drawn inside the cathode are studied. Total produced neutrons as a function of input power at different working conditions are also obtained.

Analytical investigation of neutron production rate in spherical IECF devices

The radial profile of the neutron production rate in spherical inertial electrostatic confinement fusion devices (IECF) is investigated. The electrostatic potential is determined by solving the Poisson equation, and by using the potential; the fuel ion energy distribution function is determined at each radial point. From the energy distribution function, the fusion reaction rate is evaluated. Dependence of beam-beam and beam-background reaction rate on some important parameters as the spreads in the normalized angular ion energies, working pressure, and grid transparency are investigated.

Prediction of potential well structure formed in spherical inertial electrostatic confinement fusion devices with various parameters

AbstractIn this paper, the theoretical analysis regarding potential structure on the inertial electrostatic confinement fusion devices has been carried out. Negatively biased grid as cathode placed at the center of the device surrounded by anode is assumed. The device is an ion-injection system and electrons may be emitted from the surface of the cathode. So the existence of both ion and electron currents inside the cathode is considered. Dependence of radial potential well structure on some important parameters as the spreads in the normalized total and angular electron and ion energies, the ratio of ion circulating current to electron circulating current, ion perveance, and grid transparency are investigated by solving Poisson equation.

Numerical Study of Ion Recirculation in an Improved Spherical Inertial Electrostatic Confinement Fusion Scheme by Use of a Multistage High Voltage Feedthrough

Design of a multistage feedthrough is presented, which aims to enhance fusion reaction rate in a low-pressure spherical inertial electrostatic confinement device. Numerical simulation suggested significant improvement in ion recirculation current by a factor of ~3, by modifying spherical symmetry of electric field.

Space Probe Application of IEC Thrusters

Earlier studies have described Inertial Electrostatic Confinement (IEC) fusion power concepts using either D-He3 or p-B11 fuels to provide a high-power density fusion propulsion system capable of aggressive deep space missions. However, this requires a large multi-GW thruster forcing a long term development program. As a first step, we examine here a progression of near-term IEC thrusters, stating with a 1-10 kWe electrically-driven IEC jet thruster for satellites followed by a small 50-100 kW IEC fusion thruster module for next generation large deep space spacecraft. The initial electrically-powered unit is a novel multi-jet plasma thruster based on spherical IEC technology using electrical input power from a solar panel. This type of unit is discussed and its advantages for next step electrically driven units are identified.

Ion flow convergence in spherical inertial electrostatic confinement devices

Data collected with automated double and single probes is used to evaluate the convergence of ion flow in a spherical inertial electrostatic confinement device operated in glow discharge mode. A novel method based on the invasive nature of electrostatic probes is used to evaluate the width of the ion density peak. Over much of the star mode discharge regime, it is found that Rc∕Rg∼0.125 to 0.167 where Rc is the ion core radius, and Rg is the radius of the cathode grid, which remains fixed for all discharge conditions considered here. Near the star-to-jet mode transition, the technique shows that Rc∕Rg∼0.250, in agreement with direct measurements of the ion density profile with the double probe. The influences of space charge accumulation and cathode grid deflection are evaluated with floating potential measurements and tangential electric field measurements, respectively. It is concluded that the observed core growth is a result of ion microchannel degradation caused by an increased frequency in inelastic and elastic molecular encounters, while the effects of space charge are negligible.

Potential well structures in spherical inertial electrostatic confinement devices

Inertial electrostatic confinement (IEC) devices are of interest as neutron generators for many applications. Experiments by Hirsch inspired further efforts to decipher the potential distribution within IEC devices. In this paper, previous analyzes of potential distributions in IEC devices are reviewed and extended. Three types of IEC systems are classified and analyzed according to the arrangement of electrodes and the species within the system. These systems are the unipolar cathode-anode (UCA) system, the bipolar cathode-anode (BCA) system, and the bipolar anode-cathode (BAC) system. Results of extensive parametric studies are reported through an efficient method for solving the Poisson's equation. The method is benchmarked against prior computations by Hirsch and Swanson. For BCA and BAC systems, it is concluded that the double well depth (DWD) increases as the relative focusing of the secondary particle to the primary particle increases, agreeing with prior work by Momota and Miley. Although collisions are neglected in this model, and unverified energy distributions are employed, the method generally agrees with experimental observations by Gu that the DWD will increase as the perveance of the system is increased. Thus, the computations performed here serve as a valuable benchmark.

Electron density and two-channel neutron emission measurements in steady-state spherical inertial-electrostatically confined plasmas, with review of the one-dimensional kinetic model

Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from ≈0.4 to 7×1010 cm−3, the density generally increasing with the neutral gas pressure. Numerical solutions of the one-dimensional Poisson equation for IEC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with nonfusing hydrogen-1. The deuterium rates are consistent with predictions from the model. 2004 American Institute of Physics.

Correlation between ion/electron distribution functions and neutron production rate in spherical inertial electrostatic confinement plasmas

Correlation between ion/electron distribution functions and device performance, i.e. potential structure, density profile and neutron production rate, in spherical inertial electrostatic confinement plasmas is studied by solving the Poisson equation for various deuteron and electron distribution functions. For several combinations of the ion and electron convergences, dependence of the total neutron production rate on discharged current is discussed. It is shown that when electrons have high convergence and energetic component compared with ions, the neutron production rate can increase in proportion to more than a power of the discharged current, even if the neutron production is sustained mainly by the fusion reactions between the beam (deuteron) and background (deuterium) gases.

Virtual Cathode in a Stationary Spherical Inertial Electrostatic Confinement

“Double-well” potential structure (virtual cathode formation) is studied in a stationary spherical inertial electrostatic confinement (SIEC) using the nonlinear Poisson’s equation and particle densities derived from kinetic theory. A novel method to obtain a spherically symmetric stationary distribution function is introduced and an integral-differential equation is simplified by applying a relevant approximated formula for an integral. Electron and ion beams are collision-free, and their velocities are roughly aligned toward the spherical center, but with a slight divergence. Analyses show that the angular momentum of ions and the smaller one of electrons create a virtual cathode, i.e., a double-well structure, of the electrostatic potential on a potential hill near the center. The density limit of an SIEC is exhibited, and the condition relevant to form a deep potential well is presented.

Radial Profile of Neutron Production Rate in Spherical Inertial Electrostatic Confinement Plasmas

The radial profile of the neutron production rate in spherical inertial electrostatic confinement (SIEC) plasmas is numerically investigated for various device parameters, i.e., grid cathode current, grid voltage, etc. The electrostatic potential is obtained by solving the Poisson equation; and using the potential, the fuel-ion velocity distribution function is determined at each radial point. From the space-dependent velocity distribution function, the radial profile of the neutron production rate is evaluated. The influence of the broadness of the electron angular momentum distribution on the radial profile of the neutron production rate is also examined. It is shown that the height of the peak of the neutron production rate and its radial position are strongly influenced by the device parameters and the electron distribution.

Virtual Cathode in a Spherical Inertial Electrostatic Confinement Device

“Double-well” potential structure (virtual cathode formation) is studied in a spherical inertial electrostatic confinement (SIEC) device using non-linear Poisson's equation. Particle densities are derived from a kinetic equation equivalent to Vlasov's equation. Velocities of collision-free electrons and ions at the edge of the configuration will be almost aligned towards the center, however, they have small divergences. Analyses show appearance of a virtual cathode potential well relevant to bum fusion fuels near the center of SIEC.

Experimental study of potential structure in a spherical IEC fusion device

The spherical inertial-electrostatic confinement (SIEC) concept is designed to focus and accelerate ions and electrons radially inward towards the center of a negatively biased, highly transparent spherical grid. The converging ions create a high-density plasma core where a high fusion rate occurs. In addition, under proper conditions, the ion and electron flows create a space-charge induced well (a negative potential well nested inside a positive potential well). This structure traps high-energy ions within the virtual anode created by the double potential, providing a high fusion density in the trap volume. The present experiment was designed to verify double potential well formation and trapping by a measurement of the radial birth profile of energetic (3-MeV) protons produced by D-D fusion reactions in a deuterium discharge. This experiment was designed to operate at high perveance (0.4 to 1.4 mA/kV/sup 3/2/), where formation of a double well is predicted theoretically. Additional steps to aid well formation included: use of the unique Star mode of operation to obtain ion beam focusing down to -1.6 H the ballistic limit and the incorporation of a second electrically floating grid (in addition to the focusing/accelerating cathode grid) to reduce the ion radial energy spread to 0.34 mA/kV/sup 3/2/. As the perveance increased, the depth of the double well also increased. At the maximum perveance studied, 1.38 mA/kV/sup 3/2/ (corresponding to 80 mA and 15 kV), the negative potential well depth, corresponding to the measured proton-rate density, was estimated to be 22%-27% of the applied cathode voltage. This represents the first conclusive demonstration of double well formation in an SIEC, since prior measurements by other researchers typically yielded marginal or negative results.

Pulsed Operation of Spherical Inertial-Electrostatic Confinement Device

Inertial electrostatic confinement (IEC) fusion confines high energy ions in potential wells, where their increased energy and density yields a high fusion rate. Studies of the IEC at the University of Illinois (UI) initially concentrated on steady-state operation where neutron yields of approx.10{sup 6} D-D n/s are routinely obtained. However, the development of a pulsed configuration has been undertaken to provide higher neutron yields. Preliminary experiments have demonstrated I{sup 2} scaling during pulsed operation when the perveance threshold of 2.2 mA/kV{sup 3/2} is exceeded. Based on these results, it appears that the present IEC could be operated with 3-A, 100-kV repetitive pulses with a 10% duty factor to produce neutron yields of approx.10{sup 10} neutrons/second. 6 refs., 7 figs.