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We have developed a thin-film coating for neutron generator targets that can be loaded with deuterium or tritium at low temperatures (100 °C), and at gas/Ti ratios greater than 1.7. The key to this improvement is the addition of a thin palladium overcoat at the end of the titanium deposition. This overcoat prevents the oxidation of the titanium film, yet still allows loading to take place at low temperatures. A palladium overcoat of just 50–100 A is sufficient to protect the titanium, while presenting a minimal energy loss to incident ions. We have just begun producing targets using this method, and see the possibility of substantial improvement in neutron generator efficiencies.

In responding to a series of questions regarding qualitative research in sport and exercise psychology, we offer our reflections on the: (a) strengths/merits and weaknesses/limitations of qualitative research; (b) frustrations, joys, concerns and dilemmas associated with evaluating, teaching or reading qualitative research and (c) future of qualitative research. We identify numerous positive aspects of qualitative research in sport and exercise psychology, which are tempered only slightly by several negative aspects. We argue that qualitative methods hold considerable promise for future research in sport and exercise psychology.

Turbulence usually makes plasmas more homogeneous. But in an unusual device for which the confining field is generated by a levitated half-tonne superconducting magnet, a study finds that turbulent fluctuations can actually increase the density of a plasma by driving diffusion against a density gradient.

Most studies that report apologetic behavior by female athletes employ observation or in-depth interviews. Although these studies provide great insight, they do not enable us to systematically compare apologetic behavior across a wide variety of athletes, sports, geographical locations, and time periods. The authors developed a questionnaire for such comparative purposes. The authors then used this questionnaire to study apologetic behavior on three collegiate teams. Most respondents reported that they either engaged in numerous apologetic behaviors on an occasional basis or a few apologetic behaviors on a more regular basis. The most common apologetic behaviors involved efforts to look feminine, apologize for aggression, and mark themselves as heterosexual. Softball players engaged in more apologetic behavior than soccer and basketball players. The authors urge others to utilize this questionnaire for comparative purposes.

A multi-chord interferometer (center frequency 60 GHz) has been constructed to measure the electron density profiles of plasmas in the Levitated Dipole Experiment (LDX). Theoretical considerations suggest that the density of a dipole-confined plasma will vary with radius as 1/r 4. Measurements have been made for LDX plasmas, where the dipole-field was produced by a coil that was not levitating but rather suspended from a central column by thin supports. A ray-tracing code has been written to fit the chord data, which are line-integrated densities, to azimuthally-symmetric electron density profiles n e (r, t). Initial analysis has focused on the model $$n_e(r, t) = A(t)(r-r_0)^{-\alpha(t)}$$ , where A(t) and α(t) are free parameters; α(t) is referred to as the “steepness exponent.” The density profiles are observed to exhibit dynamics due to ECR heating and neutral-gas fueling. The model-fit, meant only to serve as a rough approximation, suggests that LDX plasmas have steepness exponents in the range of 1.5–4. The density at the location of the 2.45 GHz ECRH resonance is reconstructed and found to be of the same order of magnitude as the heating cut-off $$n_e \sim n_c =7.4\times10^{10}\,{\rm cm}^{-3}$$ .

Plasmas in the Levitated Dipole Experiment (LDX) are formed and sustained currently via two electron cyclotron resonance heating (ECRH) sources: 2.5 kW at 2.45 GHz and 2.5 kW at 6.4 GHz. An important topic being investigated is how varying the ECRH affects the confinement and stability of the plasma. We report the results of using different operational combinations of our RF sources, such as varying the power composition, changing the power levels, and sequencing of the onset time.

The Levitated Dipole Experiment (LDX) is an innovative confinement concept that uses an internal superconducting dipole field to confine plasma. Plasma equilibrium is calculated by a least-squares fit of an anisotropic pressure model to magnetic measurements constrained by X-ray images. Reconstructions have been done for different heating schemes using two-frequency electron cyclotron heating at 2.45 and 6.4 GHz. Results show that a maximum local β ∼ 20% has been achieved using two frequency heating at a combined full power of 5 kW. Analysis of the reconstruction results shows that the magnetic sensors are sensitive primarily to changes in the plasma dipole moment. This is partly due to the fact that the dipole current decreases as the plasma current increases (as required by flux conservation through the superconducting dipole) and the magnetic sensors detect the sum of these changes. This paper will present details of the reconstruction procedure and describe how new magnetic sensors will aid in resolving the pressure profile more accurately.

The Levitated Dipole Experiment (LDX) explores confinement and stability of plasma created within the dipole field of a strong superconducting magnet. During initial experiments, long-pulse, quasi-steady state discharges that last more than 10 s and have peak beta of more than 20% are studied. The plasma is created by multi-frequency electron cyclotron resonance heating (ECRH) at 2.45 and 6.4 GHz. A population of energetic electrons, with mean energies above 50 keV, dominates the plasma pressure. Creation of high pressure, high beta plasma is possible only when intense hot electron interchange (HEI) instabilities are stabilized by sufficient neutral gas fueling. The instabilities resonate with the magnetic drift motion of the energetic electrons and can cause rapid radial transport. Measurements of the electrostatic and magnetic fluctuations of the HEI instability are described along with observations of the instability’s spectral characteristics. Fluctuations of the outer poloidal field induced by the HEI show a rapid evolution of the perturbed pressure profile.

The levitated dipole experiment (LDX) explores the physics of high-temperature plasmas confined by a dipole magnetic field. Stable high-beta plasma has been created and confined by the magnetic field of a superconducting coil. Discharges containing trapped electrons form when microwaves cause strong perpendicular heating at cyclotron resonance. To eliminate the losses to the supports, the magnetic dipole (a superconducting solenoid) will be magnetically levitated for several hours. The dipole magnetic field is generated by a Nb3Sn floating coil (F-coil), a maximum field of 5.3 T, operating for up to 2 h. A NbTi charging coil (C-coil) surrounds a portion of the vacuum chamber and induces the current in the floating coil. After the F-coil is lifted to the center of the chamber, the levitation coil (L-coil), made from high-temperature superconductor, magnetically supports it. In the first year of operation, the device has been operated in a supported mode of operation while experience has been gained in the cryogenic performance of the F-coil and the integration of the F-coil and C-coil. Current work focuses on the integration of the F and L coils in preparation for first levitation tests. © 2006 Published by Elsevier B.V.

The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions from a ∼cm length interaction. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood. We are exploring the mechanisms behind these large accelerating gradients using fully kinetic simulations of a DPF Z-pinch and ion probe beam measurements. Our particle-in-cell simulations have successfully predicted ion beams and neutron yield from kJ-scale DPFs1, which past fluid simulations have not reproduced. To access the regime of MJ-scale devices within computational resources, we have developed a handoff simulation starting from a fluid calculation near the end of rundown and continuing fully kinetic through the pinch. To probe the accelerating fields in our tabletop experiment, we inject a 4 MeV deuteron beam along the z-axis. For the first time, we have directly measured the gradients in the DPF and the acceleration of an injected ion beam. We observe > 50 MV/m acceleration gradients during 800 J operation using a fast capacitive driver2. In addition, we have now experimentally measured and observed in simulations for the first time, electric field oscillations near the lower hybrid frequency. This is suggestive that the lower hybrid drift instability, long speculated to be the cause of the anomalous plasma resistivity that produces large DPF gradients, is playing an important role. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.

Dense-plasma-focus (DPF) Z-pinch devices are sources of copious high-energy electrons and ions, x rays, and neutrons. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood and past optimization efforts of these devices have been largely empirical. Previously we reported on fully kinetic simulations of a DPF and compared them with hybrid and fluid simulations of the same device. Here we present detailed comparisons between fully kinetic simulations and experimental data on a 1.2 kJ DPF with two electrode geometries, including neutron yield and ion beam energy distributions. A more intensive third calculation is presented which examines the effects of a fully detailed pulsed power driver model. We also compare simulated electromagnetic fluctuations with direct measurement of radiofrequency electromagnetic fluctuations in a DPF plasma. These comparisons indicate that the fully kinetic model captures the essential physics of these plasmas with high fidelity, and provide further evidence that anomalous resistivity in the plasma arises due to a kinetic instability near the lower hybrid frequency.

We are seeking to gain a better fundamental understanding of the ion beam acceleration and neutron production dense plasma focus (DPF) device. Experiments were performed on a kilojoule level, fast rise time DPF located at LLNL. Ion beam spectra and neutron yield were measured for deuterium pinches. Visible light images of the pinch are used to determine the pinch length. In addition, an RF probe was placed just outside the cathode to measure fluctuations in Ez up to 6 GHz, which is within the range of the lower hybrid frequencies. We find these oscillations arise at a characteristic frequency near 4 GHz during the pinch. Comparisons of the neutron yield and ion beam characteristics are presented. The neutron yield is also compared to scaling laws.

The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions in a ∼cm length. The mechanisms through which these physically simple devices generate such high energy beams in a relatively short distance are not fully understood. We are exploring the origins of these large gradients using measurements of an ion probe beam injected into a DPF during the pinch phase and the first kinetic simulations of a DPF Z-pinch. To probe the accelerating fields in our table top experiment, we inject a 4 MeV deuteron beam along the z-axis and then sample the beam energy distribution after it passes through the pinch region. Using this technique, we have directly measured for the first time the acceleration of an injected ion beam. Our particle-in-cell simulations have been benchmarked on both a kJ-scale DPF and a MJ-scale DPF. They have reproduced experimentally measured neutron yields as well as ion beams and EM oscillations which fluid simulations do not exhibit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.

We recently produced a milestone 500 nA of pulsed current using 40 Ir field ionizer electrodes in our ion source. In conclusion, we have produced the milestone pulsed current of 500 nA using 40 electrochemically etched iridium tips in a field ionization source. The pulsed current output is repeatable and scales as expected with gas fill pressure and bias voltage. We expect these current will be sufficient to produce neutral yields of 1∙107 DT n/s.

We present first experimental results on ion beam injection along the z-axis of a Z-pinch plasma with MV/cm gradients and the first fully kinetic simulations of such beam-plasma systems. Multi-MeV, kilo-Ampere ion beams have been produced by 100 kJ class, centimeter scale, Dense Plasma Focus (DPF) Z-pinches. We have now demonstrated > 50 MV/m acceleration gradients in an 800J DPF using a fast capacitive driver1. Understanding the mechanisms behind these high gradients is essential for optimizing the device for unique compact accelerator applications. We employ an RFQ accelerator to produce a 4 MeV deuteron beam to probe the DPF plasma. Using this beam we seek to directly measure the gradients and demonstrate acceleration of an injected ion beam for the first time. Our fully kinetic, particle-in-cell simulations have reproduced observed DPF ion beams2. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability. These are the first steps to enabling a technologically simple, compact, high-current, plasma-based accelerator.

A palm sized, portable neutron source would be useful for widespread implementation of detection systems for shielded, special nuclear material. We present progress towards the development of the components for an ultracompact neutron generator using a pulsed, meso-scale field ionization source, a deuterated (or tritiated) titanium target driven by a negative high voltage lithium tantalate crystal. Neutron production from integrated tests using an ion source with a single, biased tungsten tip and a 3×1 cm, vacuum insulated crystal with a plastic deuterated target are presented. Component testing of the ion source with a single tip produces up to 3 nA of current. Dielectric insulation of the lithium tantalate crystals appears to reduce flashover, which should improve the robustness. The field emission losses from a 3 cm diameter crystal with a plastic target and 6 cm diameter crystal with a metal target are compared.

Accelerator driven fusion gammas and fast neutrons could provide unique radiography capabilities due to their ability to produce both high and low energy mono-energetic gammas and neutrons compared with broadband bremsstrahlung based x-ray sources. The possibility of simultaneously obtaining both gamma and neutron radiographs using one source could allow complex objects composed of a large range of low to high Z materials to be imaged. In this paper we review a 4 MV RFQ accelerator driven radiography test-bed at LLNL designed to study the physics involved in applying these dual output fusion reactions for radiography applications. First experimental neutron images from a carbon target are presented.

Active interrogation using neutrons is an effective method for detecting shielded nuclear material. A lightweight, lunch-box-sized, battery-operated neutron source would enable new concepts of operation in the field. We have developed at-scale components for a highly portable, completely self-contained, pulsed Deuterium-Tritium (DT) neutron source producing 14 MeV neutrons with average yields of 107 n/s. A gated, field ionization ion source using etched electrodes has been developed that produces pulsed ion currents up to 500 nA. A compact Cockcroft-Walton high voltage source is used to accelerate deuterons into a metal hydride target for neutron production. The results of full scale DT tests using the field ionization source are presented.

Stored, cooled proton beams of 200 MeV with intensities up to 3 mA pass along the axis of a Penning-Malmberg trap containing a nonneutral plasma of 1010 electrons. The plasma is maintained in a warmed steady state by injecting energy and angular momentum; the elevated temperature giving weak ionization to replenish lost electrons. Comparing charge density wave velocity with diocotron mode frequency gives continual non-destructive monitoring of plasma radius and density. The beam is observed to cause an increase in plasma radius indicating a torquing mechanism not yet understood. The effect is weakly sensitive to shifts in beam position or angle. Monitoring power input shows either “cooling” (increased electron loss rate) or heating depending on regulation method. Extension of these studies to higher containment fields will be described.

We have designed and built a Dense Plasma Focus (DPF) Z-pinch device using a kJ-level capacitor bank and a hollow anode, and fueled by a cylindrically symmetric gas puff. Using this device, we have measured peak deuteron beam energies of up to 400 keV at 0.8 kJ capacitor bank energy and pinch lengths of ∼6 mm, indicating accelerating fields greater than 50 MV/m. Neutron yields of on the order of 10(7) per shot were measured during deuterium operation. The cylindrical gas puff system permitted simultaneous operation of DPF with a radiofrequency quadrupole accelerator for beam-into-plasma experiments. This paper describes the machine design, the diagnostic systems, and our first results.

The Levitated Dipole Experiment (LDX) is used to study high-temperature plasma confined by the magnetic field produced by a high-current superconducting ring. Multiple-frequency electron cyclotron resonance heating (ECRH) heats and sustains plasma discharges for long, quasi-steady periods, and conditions of high plasma beta are reached by adjusting the rate of neutral fueling. When the superconducting ring is levitated by attraction to a coil located above the vacuum chamber, cross-field transport becomes the main loss channel for plasma particles and energy. We find operation with a levitated dipole always leads to centrally peaked density profiles, even when the plasma ionization source occurs near the plasma edge. In recent experiments, we also observe the normalized gradient, or shape, of the density profile to be 'stationary' while the ECRH heating power and gas fueling rates are strongly modulated. Theoretically, stationary profiles result in an energy confinement time (of the thermal plasma) that greatly exceeds the particle confinement time. This condition, along with high-beta plasma stability, is a necessary condition for utilizing advanced fuels in a fusion power source.

We report the first production of high beta plasma confined in a fully levitated laboratory dipole using neutral gas fuelling and electron cyclotron resonance heating. As compared with previous studies in which the internal coil was supported, levitation results in improved confinement that allows higher-density, higher-beta discharges to be maintained at significantly reduced gas fuelling. Contrary to previous supported dipole plasma results which had the stored energy consisting in a hot electron population, a significant plasma stored energy is shown to reside in the bulk plasma. By eliminating supports used in previous studies, cross-field transport becomes the main loss channel for both the hot and the background species. This leads to a significant improvement in bulk plasma confinement and a dramatic peaking of the density profile. Improved particle confinement assures stability of the hot electron component at reduced neutral pressure.