This study investigates the repeatability of a Sealed Microwave Induced Chemical Etching (SMICE) protocol for CR-39 solid-state nuclear track detectors. The approach utilizes a sealed PTFE digestion vessel that maintains the etchant in liquid phase above its atmospheric boiling point through elevated internal pressure. Five CR-39 samples irradiated with 5.49 MeV alpha particles from an 241Am source were etched to evaluate bulk etch rate consistency and track diameter uniformity. Each chip was mounted on a PEEK backplate to restrict etching to one surface for accurate gravimetric measurements. SMICE reduced processing time to 13 min (9 min microwave irradiation, 4 min cooling) while producing well-defined tracks. The method achieved a bulk etch rate of 42.2 +/- 2.4 mu m/h and track diameters of 13.5 +/- 1.8 mu m. High microwave field intensities can induce localized plasma discharges within the vessel, therefore, a water jacket moderator is essential to absorb excess microwave energy and ensure controlled etching conditions. The discharge phenomenon suggests potential pathways for plasma-assisted chemical etching that could further reduce processing times.

The complex structure of Inertial Electrostatic Confinement (IEC) plasmas creates difficulties in accurately modeling electric field geometries and charged particle motion within such systems. Additionally, current models of IEC physics have fallen short of fully explaining the formation of key plasma structures, such as ion microchannels and virtual electrodes, which are critical to the operation and scaling of these devices. In order to optimize IEC systems to achieve breakeven fusion conditions, refined models are needed to explain the dynamics of IEC plasmas on a first-principles basis. This study presents several computational models of a spherical IEC fusion device using COMSOL Multiphysics. Electrostatic simulations using the AC/DC module indicate that the high-voltage feedthrough stalk and cathode grid asymmetries significantly distort the intended potential structure, thus producing perturbations in the plasma. The effects of electrode geometry on the internal electrostatic field structure are compared for two stalk designs with different ceramic insulation thicknesses as well as two geodesic grid designs: symmetric and asymmetric. Lastly, single particle trajectories of various ion species are presented, which provide preliminary insights into ion dynamics under several IEC configurations. The results of these simulations reveal that the complex field generated by the stalk significantly alters ion trajectories, reducing ion recirculation and total confinement time for all simulated ion species.

Inertial electrostatic confinement (IEC) utilizes strong electric fields to generate and confine plasma. It has been extensively used to conduct nuclear fusion reactions and commercially as a neutron source for activation analysis. This study investigates the two distinct discharge modes, "jet" mode and "spray" mode of an IEC thruster. This paper compares the discharge characteristics of an IEC system for various preliminary design options, such as cathode grid design and cathode grid dimensions. High resolution images are used to conduct intensity analysis at multiple operating points. A basic Faraday probe is used to qualitatively record the change in plasma current density. Results show that biasing the cathode at more negative potentials leads to an increase in current drawn by the grid and the visible intensity of the visible plasma. The current and light intensity increase is gradual until a mode transition from "jet" to "spray" occurs. In other words, the "jet" mode always precedes the "spray" mode. Additionally, background pressure and applied cathode potential are shown to be the two main operating variables for an IEC device. Finally, higher current densities were recorded when the device operated in "spray" mode, however, the ejected plasma was more collimated during "jet" mode.

The new candidates for laser fusion energy with minimized radioactivity were presented. The possibility of side-on laser ignition of H–11B with negligible radioactivity encouraged to study the fusion of solid state H–7Li fuel which again turns out to be only about ten times more difficult than the side-on ignition of solid deuterium–tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included. In other words, the specific approach discussed here involves inducing a fusion burn wave without radioactivity by laser-driven impact of a relatively large block of plasma on the outside of a solid density H–11B and H–7Li targets.

The possibility of nuclear reactions within a low voltage DC deuterium discharge with palladium electrodes is addressed. The solid-state nuclear track detector known as CR-39 was chosen to investigate the emission of energetic charged particles from the electrodes. A partially automated imaging platform and feature classification process was developed to scan the CR-39 surface and detect tracks. Typical discharge parameters were 10 Torr deuterium, 5-7 mm electrode gap distance, 20-40 mA/cm$^2$ current density, and -500 $\pm$ 100 V cathode bias. After discharge treatments to varied ion-cathode fluences, tracks formed in CR-39 which consistently corresponded to 138 $\pm$ 21 keV alpha particles emitted from the palladium electrodes. The track densities for deuterium discharges were often $\sim$100 times above controls with hydrogen and helium. Currently, there are no known mechanisms to accelerate ions to these energies within the apparatus. The production of energetic alpha particles with no source of helium or a means to accelerate the ions to such high energies indicate a nuclear origin. From particle trajectory estimates based on track geometries, it was concluded the reactions originated at the Pd electrodes and not from external sources such as atmospheric radon or cosmic rays.

The Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is a space propulsion system developed at the University of Illinois Urbana-Champaign. The HIIPER couples a helicon tube with an inertial electrostatic confinement (IEC) fusion system. Its operating principle involves a helicon ionization stage followed by an electrostatic grid (IEC cathode grid) extraction stage. The helicon setup used in the HIIPER is modified to include a helicon bias grid at the upstream end of the tube. This grid is applied with a positive direct-current voltage to increase the plasma potential and the most probable ion energy of the plasma injected into the IEC fusion chamber. The IEC cathode grid in the HIIPER uses an innovative asymmetric design, graphically depicted through a computational model, that ejects a stream of electrons that accelerate the exhaust ions and simultaneously neutralize the exhaust jet. The model is also used to plot ion trajectories inside the HIIPER to identify any wall collision losses. A separate numerical study was undertaken to show augmentation of plasma kinetic energy on adding a magnetic nozzle as the final propulsion stage of the HIIPER. Experimental results were used to establish a relation between the input parameters and the ion density of the resulting plasma. Langmuir probe measurements were performed at two locations to validate corresponding computational results, indicating ion losses due to ion-wall collisions inside the helicon-IEC coupling. The results in this study add to the proof of concept of the HIIPER and allow for designing an upgrade of the propulsion system. Increasing thrust while maintaining plasma densities between 10(17) and 10(18) m(-3) throughout the system is the current aim of HIIPER research. This study summarizes the various performance parameters of the propulsion system, along with a discussion of ongoing research and future scope.

Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is a combination of a radio-frequency (rf) thruster and an electrostatic propulsion system. Its design is inspired by a cold plasma, aneutronic, nuclear fusion device involving helicon plasma injection inside an Inertial Electrostatic Confinement (IEC) fusion reactor. Operating the IEC in the “Halo” (or “jet”) mode enables a unidirectional plasma jet that can be used to propel a space vehicle. Multiple researchers have independently observed the exhaust jet through experiments and theorized explanation based on their results, but a conclusive explanation of the physics involved is yet to be accepted. An experimental study was conducted to diagnose the properties of the exhaust jet and characterize its nature. It was found that the visible jet from the IEC cathode grid contained ions that can be used for space propulsion. The maximum beam current density of the exhaust jet was measured to be 1.273 A/(m^2). It is expected that the actual beam current density will be much higher when the experiments are repeated with higher (more negative) electron repeller potentials. Contrary to the electron temperature of 100’s of eV in the core, the jet electron temperature remained less than 10 eV for all the studied cases. The measured exhaust velocity of the ion jet remained between 24 km/s and 55 km/s for various operating conditions. These exit velocities classify HIIPER as a high specific impulse propulsion system. A novel, plasma plume diagnostic technique using solid state nuclear track detector is also described in the paper.

The characterization of a high current, relativistic electron beam, designated the Super Pinch electron beam, has been performed using compact pulsed-power accelerators of various architectures with a novel diode geometry. The Thunderbird accelerator has an initial 1.5-mu s rise time and 150-kA peak current. The drive voltage is compressed to produce a 12-ns 500-kV voltage pulse generating a similar to 40-kA electron beam, which apparently exceeds the Alve ' n current limit although the useful current at small radius is an order of magnitude less. Using an insulated hollow cathode with a 0.5-cm anode-cathode gap, the large current is enabled by the evolution of plasma from the dielectric sleeve enveloping the cathode and a 0.5-mm wire anode. Post-shot recovery of the anode target and measurements of its deformation and damage allow an evaluation of the enhanced electron-beam focusing whereby significant beam energy is delivered to the record small, microscopic volume inside the anode target. The electron beam is seen to have conditions favorable to those needed to ignite compressed fuel in inertial confinement fusion. These results motivated a deeper insight using theoretical modeling with hybrid particle-in-cell codes. The modeling presented in this paper shows an electron beam radius of 10 mu m containing a current of 3-6 kA or 500 MA/cm2 current density. Scaling up the accelerator, such preferred focusing, target penetration, and affordability of the pulsed power generated electron beams open a new opportunity for the application of the mainstream pulsed power devices in the research and development of fusion energy.

A coordinated experimental-simulation study was carried out to explore the relationship between plasma conditions and ion angular energy distributions incident on a DC glow discharge cathode. Langmuir probe measurements of the Electron Energy Distribution Functions (EEDF) validated a COMSOL simulation’s accuracy which confirmed the proper methodology for reproducing discharge dynamics. 1 The simulation was a coupling between COMSOL’s Plasma module and Boltzmann Equation, Two-Term Approximation module allowing for accurate calculations of the Townsend coefficients. Proper Townsend coefficients are necessary to represent the kinetics of DC discharges with low ionization fractions and species mobility that are highly dependent on the electric field, e.g., ions transiting the plasma sheath. The EEDFs were measured along the cathode dark space and negative glow regions using the Druyvesteyn method. 2 After the trend of EEDFs were validated, the model was expanded to extract ion angular energy distributions in conditions where measuring plasma properties became no longer feasible.

Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is an innovative magnetoplasmadynamic (MPD) thruster developed at the University of Illinois UC. It is considered a stepping stone towards nuclear fusion space propulsion system. It comprises of a two-stage mechanism – helicon injection into an Inertial Electrostatic Confinement (IEC) fusion chamber and plasma extraction, and expulsion, using the IEC cathode grid. Two salient features of HIIPER are explained as follows. Firstly, IEC cathode grids generate a stream of electrons which neutralize the exhaust plume and prevent the space vehicle from getting charged. Secondly, the presence of a helicon bias grid at the upstream end of the quartz tube increases the most probable ion energies inside the system. Langmuir probe analysis was done at various locations inside the system to check for wall losses. Ion density trends are established by changing the axial magnetic field, IEC grid voltage and helicon bias grid voltage. Retarding Potential Analyzer (RPA) is used to measure the most probable ion energy with changing helicon bias grid voltage. A Mach probe is also used to measure ion velocity distribution with changing bias grid potential. Although it was assumed that the helicon bias grid will collimate the plasma beam and reduce wall losses, the observed trend showed only a weak effect. However, it was established that the helicon bias grid increased the most probable ion energy and flow velocity. These results provide the basis for the next experimental setup, with an optimized quartz tube, replacing the metal bellow coupling to minimize wall losses.

A simple deuterium DC glow discharge was employed to study the production of densely packed deuterium clusters with high binding energies in palladium. The incident ions create damage cascades leading to the production of defects such as vacancies, dislocations, and voids. These defects trap interstitial deuterons with binding energies dependent on the trap’s geometry and volume. 1 Varying fluences of incident ions were used (1E18 ions/cm 2 , 1E19 ions/cm 2 , and 1E20 ions/cm 2 ) and incident energies dependent on cathode bias (-0.75 kV, -0.875 kV, and -1.0 kV). Thermal Desorption Spectroscopy (TDS) was used to estimate the clusters’ trapping energies. 2 There appeared to be a deuterium trapping limit dependent on defect concentration where once a distinct defect density was met any further damage was counterproductive in deuterium trapping. The condition that produced the most trapped deuterium was -0.75 kV in 1 Torr deuterium with a fluence of 1E18 ions/cm 2 . Some samples were observed under SEM and TEM. The results showed surface pit and blister formations which grew in concentration as the fluence increased. Beneath the surface formations, cross-section images showed large voids and holes in the material with cracks at grain boundaries. TEM images displayed the resulting damage structure which extended ~250 nm into the cathode for a sample at 1.0 Torr and -1.0 kV. A proposal is that as the damage concentration increased, these voids grew to such an extent that they formed the blisters and eventually ruptured.