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[en] We describe applications of the electrostatic plasma lens for manipulating and focusing moderate energy, high current, broad, heavy ion beams. Use of a plasma lens in this way has been successfully demonstrated in a series of experiments carried out collaboratively between IP NASU (Kiev) and LBNL (Berkeley) in recent years. Here we briefly review the plasma lens fundamentals, peculiarities of focusing heavy ion beams, and summarize some recent developments (experiments, computer simulations, theory). We show that there is a very narrow range of low magnetic field for which the optical properties of the lens improve markedly. This opens up some attractive possibilities for the development of a new-generation compact lens based on permanent magnets. Preliminary experimental results obtained at Kiev and Berkeley on the operation of a permanent magnet plasma lens for manipulating wide aperture high-current heavy ion beams are presented and summarized
[en] The Cygnus radiographic machine is a relatively compact low-energy (<3 MV) x-ray source with some extremely desirable features for radiographic applications. These features include small spot size critical for high-spatial resolution and high dose in a low energy range. The x-ray source is based on bremsstrahlung production in a small diameter (∼0.75 mm) tungsten rod by a high-current (∼60 kA) electron beam converging at the tip of the rod. For quantitative analysis of radiographic data, it is essential to determine the bremsstrahlung spectrum accurately. We have used the radiographic chain model that self-consistently models the diode with a two-dimensional particle-in-cell code (Merlin) which links to an electron-photon Monte Carlo code to obtain the spectrum under three different situations. These are: steady state spectrum using a voltage puise of 2.5 MV, time-integrated spectrum using a time-dependent experimental voltage pulse, and inclusion of reflexing electrons at the anode in our particle-in-cell simulation. Detailed electron dynamics have been obtained in our study. Our investigations conclude that the time integrated bremsstrahlung spectrum is significantly softer than that of the steady state. In our latest simulations, we have included the effects of reflexing electrons around the anode rod and found the spectrum to be in better agreement with experimental data.
[en] The vacuum arc ion source has evolved over the past twenty years into a standard laboratory tool for the production of high current beams of metal ions, and is now used in a number of different embodiments at many laboratories around the world. The primary application of this kind of source has evolved to be ion implantation for material surface modification. Another important use is for injection of high current beams of heavy metal ions into the front ends of particle accelerators, and much excellent work has been carried out in recent years in optimizing the source for reliable accelerator application. The source also provides a valuable tool for the investigation of the fundamental plasma physics of vacuum arc plasma discharges. As the use of the source has grown and diversified, at the same time the ion source performance and operational characteristics have been improved in a variety of different ways also. Here we review the growth and status of vacuum arc ion sources around the world, and summarize some of the applications for which the sources have been used
[en] Thallium arc plasma was investigated in a vacuum arc ion source. As expected from previous consideration of cathode materials in the Periodic Table of the Elements, thallium plasma shows lead-like behavior. Its mean ion charge state exceeds 2.0 immediately after arc triggering, reaches the predicted 1.60 and 1.45 after about 100 microsec and 150 microsec, respectively. The most likely ion velocity is initially8000 m/s and decays to 6500 m/s and 6200 m/s after 100 microsec and 150microsec, respectively. Both ion charge states and ion velocities decay further towards steady state values, which are not reached within the 300microsec pulses used here. It is argued that the exceptionally high vapor pressure and charge exchange reactions are associated with the establishment of steady state ion values
[en] Collective impact ionization has been used to explain lock-on in semi-insulating GaAs under high-voltage bias. The authors have used this theory to study some of the steady state properties of lock-on current filaments. In steady state, the heat gained from the field is exactly compensated by the cooling due to phonon scattering. In the simplest approximation, the carrier distribution approaches a quasi-equilibrium Maxwell-Boltzmann distribution. In this report they examine the validity of this approximation. They find that this approximation leads to a filament carrier density which is much lower than the high density needed to achieve a quasi-equilibrium distribution. Further work on this subject is in progress
[en] Repetitive pulses of voltage and current are applied in high power impulse magnetron sputtering. The current pulse usually lags the applied voltage by a significant time, which in some cases can reach many 10s of microseconds. The current time lag is generally highly reproducible and jitters less than 1percent of the delay time. This work investigates the time lag experimentally and theoretically. The experiments include several different target and gas combinations, voltage and current amplitudes, gas pressures, pulse repetition rates, and pulse durations. It is shown that in all cases the inverse delay is approximately proportional to the applied voltage, where the proportionality factor depends on the combination of materials and the conditions selected. The proportionality factor contains the parameters of ionization and secondary electron emission. The statistical time lag is negligible while the formative time lag is large and usually dominated by the ion motion (inertia), although, at low pressure, the long free path of magnetized electrons causing ionization contributes to the delay.
[en] The reflection of macroparticles, generated by a vacuum arc, from a substrate biased negatively with respect to the surrounding plasma is considered. Charging of macroparticle in the near-substrate sheath and its influence on the macroparticle motion were taken into account. It was found that macroparticles can be either reflected or attracted to the substrate depending strongly on the ion current density. The possibility of macroparticle reflection increases with negative bias voltage and saturates at about a few hundred volts
[en] The National Ignition Facility (NIF) Power Conditioning System provides the pulsed excitation required to drive flashlamps in the laser's optical amplifiers. Modular in design, each of the 192 Main Energy Storage Modules (MESMs) stores up to 2.2 MJ of electrical energy in its capacitor bank before delivering the energy to 20 pairs of flashlamps in a 400 (micro)s pulse (10% power points). The peak current of each MESM discharge is 0.5 MA. Production, installation, commissioning and operation of the NIF Power Conditioning continue to progress rapidly, with the goals of completing accelerated production and commissioning by early 2008, while maintaining an aggressive operation schedule. To date, more than 97% of the required modules have been assembled, shipped and installed in the facility, representing more that 380 MJ of stored energy available for driving NIF flashlamps. The MESMs have displayed outstanding reliability during daily, multiple-shift operations
[en] The authors have used a soft X-ray laser interferometer to study the collision and subsequent interaction of counter-streaming high-density plasmas. The measured density profiles show the evolution of the colliding plasmas from interpenetration, when the low-density edge of the plasmas first collide, to stagnation at the symmetry plane with density building at the symmetry plane
[en] Intense beams of light of heavy ions are being studied as inertial confinement fusion (ICF) drivers for high yield and energy. Heavy and light ions have common interests in beam transport, targets, and alternative accelerators. Self-pinched transport is being jointly studied. This article reviews the development of intense ion beams for ICF. Light-ion drivers are highlighted because they are compact, modular, efficient and low cost. Issues facing light ions are: (1) decreasing beam divergence; (2) increasing beam brightness; and (3) demonstrating self-pinched transport. Applied-B ion diodes are favored because of efficiency, beam brightness, perceived scalability, achievable focal intensity, and multistage capability. A light-ion concept addressing these issues uses: (1) an injector divergence of ≤ 24 mrad at 9 MeV; (2) two-stage acceleration to reduce divergence to ≤ 12 mrad at 35 MeV; and (3) self-pinched transport accepting divergences up to 12 mrad. Substantial progress in ion-driven target physics and repetitive ion diode technology is also presented. Z-pinch drivers are being pursued as the shortest pulsed power path to target physics experiments and high-yield fusion. However, light ions remain the pulsed power ICF driver of choice for high-yield fusion energy applications that require driver standoff and repetitive operation. 100 refs