Arthur Toor

Experimental configuration for isentropic compression of solids using pulsed magnetic loading

A capability to produce quasi-isentropic compression of solids using pulsed magnetic loading on the Z accelerator has recently been developed and demonstrated [C. A. Hall, Phys. Plasmas 7, 2069 (2000)]. This technique allows planar, continuous compression of materials to stresses approaching 1.5 Mbar. In initial stages of development, the experimental configuration used a magnetically loaded material cup or disk as the sample of interest pressed into a conductor. This installation caused distortions that limited the ability to attach interferometer windows or other materials to the rear of the sample. In addition, magnetic pressure was not completely uniform over sample dimensions of interest. A new modular configuration is described that improves the uniformity of loading over the sample surface, allows materials to be easily attached to the magnetically loaded sample, and improves the quality of data obtained. Electromagnetic simulations of the magnetic field uniformity for this new configuration will a...

High yield inertial confinement fusion target design for a z-pinch-driven hohlraum

Calculations are presented for a high yield inertial fusion design, employing indirect drive with a double-ended z-pinch-driven hohlraum radiation source. A high current (∼60 MA) accelerator implodes z pinches within an enclosing hohlraum. Radial spoke arrays and shine shields isolate the capsule from the pinch plasma, magnetic field, and direct x-ray shine. Our approach places minimal requirements on z-pinch uniformity and stability, usually problematic due to magneto-Rayleigh–Taylor instability. Large inhomogeneities of the pinch and spoke array may be present, but the hohlraum adequately smooths the radiation field at the capsule. Simultaneity and reproducibility of the pinch x-ray output to better than 7% are required, however, for good symmetry. Recent experiments suggest a pulse shaping technique, through implosion of a multishell z pinch. X-ray bursts are calculated and observed to occur at each shell collision. A capsule absorbing 1 MJ of x rays at a peak drive temperature of 210 eV is found to ha...

Magnetically driven isentropic compression experiments on the Z accelerator

Isentropic compression experiments (ICE) have been performed on the Z accelerator facility at Sandia National Laboratory. We describe the experimental design that used large magnetic fields to slowly compress samples to pressures in excess of 400 kbar. Velocity wave profile measurements were analyzed to yield isentropic compression equations of state (EOS). The method can also yield material strength properties. We describe magnetohydronamic simulations and results of experiments that used the “square short” configuration to compress copper and discuss ICE EOS experiments that have been performed with this method on tantalum, molybdenum, and beryllium.

Two‐dimensional radiation‐magnetohydrodynamic simulations of SATURN imploding Z pinches

Z‐pinch implosions driven by the SATURN device [D. D. Bloomquist et al., Proceedings of the 6th Institute of Electrical and Electronics Engineers (IEEE) Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] at Sandia National Laboratory are modeled with a two‐dimensional radiation magnetohydrodynamic (MHD) code, showing strong growth of the magneto‐Rayleigh–Taylor (MRT) instability. Modeling of the linear and nonlinear development of MRT modes predicts growth of bubble‐spike structures that increase the time span of stagnation and the resulting x‐ray pulse width. Radiation is important in the pinch dynamics, keeping the sheath relatively cool during the run‐in and releasing most of the stagnation energy. The calculations give x‐ray pulse widths and magnitudes in reasonable agreement with experiments, but predict a radiating region that is too dense and radially localized at stagnation. We also consider peaked initial density profiles with consta...

Calibrated ’’four‐color’’ x‐ray microscope for laser plasma diagnostics

Four quartz, orthogonal, cylindrical mirror pairs, two of which are coated with nickel, image the x‐ray emission from laser fusion targets on hard film with a magnification of 3. K‐edge filters used in conjunction with the mirror pairs permit us to take simultaneous pictures in four energy bands between 0.7 and 3.5 keV. We have measured microscope resolution, mirror reflection efficiency, and film sensitivity and used them to deduce the absolute emissivity and spectral characteristics of various laser fusion targets. This instrument is now used routinely for studying laser‐generated plasmas at Lawrence Livermore Laboratory.

Perspectives on micropole undulators in synchrotron radiation technology

Micropole undulators promise to advance synchrotron radiation (SR) technology in two distinct ways. The first is in the development of economical, low‐energy storage rings, or linacs, as soft x‐ray sources, and the second is in the opening up of gamma‐ray spectral ranges on high‐energy storage rings. In this paper the promise and current status of micropole undulator (MPU) technology are discussed, and a review of some practical obstacles to the implementation of MPU’s on present‐day storage rings is given. Some successful results of recent performance measurements of micropole undulators on the Lawrence Livermore National Laboratory linac are briefly summarized.

Growth of the Rayleigh–Taylor instability in an imploding Z-pinch

Rayleigh–Taylor (RT) instability of cylindrical, imploding plasma liners in a Z-pinch is analyzed. The reduction in total perturbation growth for multicascade systems (multiple imploding shells) is presented. This reduction is effective if the pressure produced by the impacting shell exceeds the magnetic pressure at the time of impact. Analytical and numerical solutions are also obtained for the RT instability of an imploding plasma liner accelerated into undisturbed plasma. The snowplow model is used in which the mass encountered by the imploding magnetic piston is swept into an infinitely thin sheath. A shock front launched ahead of the liner is shown to reduce the growth rate. It is also shown that accumulating the mass increases the growth rate. However, the total perturbation growth can be reduced if the liner accumulates the mass during the implosion compared to a liner with the same mass imploding into vacuum. Finally, it is shown that the final kinetic energy density for a given shell nonuniformit...

Operation of a normal‐incidence transmission grating monochromator at ALLADIN (invited)

A transmission grating (TrG) monochromator has been constructed and operated on the ALLADIN storage ring in Wisconsin in March–June of 1987. The x‐ray source was a recently installed 30‐period permanent magnet (PM) undulator with a 6.1‐cm period. The monochromator configuration employed a single‐bent focusing mirror between the source and the exit slit, with a gold transmission grating located between the mirror and the exit slit. The effective entrance slit was the circulating electron beam inside the ring. In this article, the performance of the monochromator in terms of its power loading capability is described.

Research and development for X-ray optics and diagnostics on the linac coherent light source (LCLS)

The Linac Coherent Light Source (LCLS) is a 1.5 to 15 {angstrom} wavelength Free-Electron Laser (PEL), under development at the Stanford Linear Accelerator Center (SLAC). The photon output consists of high brightness, transversely coherent pulses with duration < 300 fs, together with a broad spontaneous spectrum. The output energy density per unit area, pulse duration, repetition rate, and small FEL spot size pose special challenges for optical components and diagnostics downstream of the undulator. Planning for the photon beam transport, manipulation and diagnostics downstream of the undulator has begun.

Focusing Of Undulator Light At Spear with A Lacquer-Coated Mirror To Power Densities Of 10 9 watts/cm 2

A lacquer-coated, diamond turned Cu ellipsoid has been used to micro-focus undulator light from Beam Line V at SPEAR down to a half-power diameter of about 13 microns. This spot was source-size limited, as has been demonstrated with ray tracings of the optical system. The symmetry of the image, as well as its size and power density, clearly make this optic ideal for many soft x-ray applications, in particular for x-ray microscopy, microprobes, and for pumping soft x-ray transitions in various media.