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Proto-I axial-focusing experiments
The time-integrated axial (z) focus of the 4.5-cm-radius Proto I (1.5 MV, 500 kA) radial proton diode is presently limited to approx. 3 mm FWHM. This result is obtained with current neutralized beam transport in a gas cell with 6 Torr argon. If the vertical local divergence were the same (1/sup 0/ or less) as the horizontal divergence, the local divergence alone would produce a 1.5 mm FWHM focus. The axial focal size is evidently limited by time-dependent effects. These are studied by observing the beam incident upon various targets with two time-resolved pinhole cameras. The first camera observes Rutherford-scattered protons from gold targets with an array of 11 siicon PIN detectors. The second camera observes K/sub ..cap alpha../-fluorescence from aluminum targets with 4 independently-gated microchannel plates imaging tubes
Hot dense capsule implosion cores produced by z-pinch dynamic hohlraum radiation
Hot dense capsule implosions driven by z-pinch x-rays have been measured for
the first time. A ~220 eV dynamic hohlraum imploded 1.7-2.1 mm diameter
gas-filled CH capsules which absorbed up to ~20 kJ of x-rays. Argon tracer atom
spectra were used to measure the Te~ 1keV electron temperature and the ne ~ 1-4
x10^23 cm-3 electron density. Spectra from multiple directions provide core
symmetry estimates. Computer simulations agree well with the peak compression
values of Te, ne, and symmetry, indicating reasonable understanding of the
hohlraum and implosion physics.Comment: submitted to Phys. Rev. Let
Exploring the parameter space of MagLIF implosions using similarity scaling. II. Current scaling
Magnetized Liner Inertial Fusion (MagLIF) is a magneto-inertial-fusion (MIF)
concept, which is presently being studied on the Z Pulsed Power Facility. The
MagLIF platform has achieved interesting plasma conditions at stagnation and
produced significant fusion yields in the laboratory. Given the relative
success of MagLIF, there is a strong interest to scale the platform to higher
peak currents. However, scaling MagLIF is not entirely straightforward due to
the large dimensionality of the experimental input parameter space and the
large number of distinct physical processes involved in MIF implosions. In this
work, we propose a novel method to scale MagLIF loads to higher currents. Our
method is based on similarity (or similitude) scaling and attempts to preserve
much of the physics regimes already known or being studied on today's Z
pulsed-power driver. By avoiding significant deviations into unexplored and/or
less well-understood regimes, the risk of unexpected outcomes on future
scaled-up experiments is reduced. Using arguments based on similarity scaling,
we derive the scaling rules for the experimental input parameters
characterizing a MagLIF load (as functions of the characteristic current
driving the implosion). We then test the estimated scaling laws for various
metrics measuring performance against results of 2D
radiation--magneto-hydrodynamic HYDRA simulations. Agreement is found between
the scaling theory and the simulation results.Comment: 19 pages, submitted to Physics of Plasma
Lawson criterion for ignition exceeded in an inertial fusion experiment
For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37Â MJ of fusion for 1.92Â MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion
I
Abstract: A recently developed method for estimating confidence intervals when simulating stochastic systems having a regenerative structure is reviewed. The paper is basically tutorial, but also considers the pragmatic issue of the simulation duration required to obtain valid estimates. The method is illustrated in terms of simulating the M/G / 1 queue. Analytic results for the M/G / 1 queue are used t
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