Lawrence Livermore National Laboratory



Platform Purpose

The examination of the behavior of matter at extreme conditions is of fundamental scientific interest and critical to advancements in fields as diverse as condensed matter physics, astrophysics, and inertial confinement fusion. To illustrate this, consider the change in the molecular and atomic structure of matter with increasing pressure. Pressures of ~1 Mbar (106 atmospheres = 100 GPa) produce an energy density comparable to that of chemical bonds, and thus the material chemistry changes.  Between 0.1 to 1 Gbar, the energy density is comparable to inner core electron orbitals, so the atoms themselves change.

Examples of compelling scientific questions in the materials science area include:

  • How does matter behave at extreme energy density?
  • What is a solid at 10 Mbar and above?
  • What chemistry takes place at and above 100 Mbar?
  • What is the nature of matter where the photon pressure is comparable to material pressure (i.e., Tbar shocks)?
  • Is hydrogen superconducting or superfluid when the interatomic spacing is comparable to less than the DeBroglie wavelength?

The ability of NIF to access extreme conditions of matter will enable the exploration of this new scientific frontier.

Several basic science experiments exploring matter at ultra-high densities have already revealed exotic and unexpected material properties.  For example, shock compressed helium, precompressed in a diamond anvil cell, shows helium transforms to a metal at ~2 g/cc.  Shock compressed diamond shows a nearly constant melting temperature from 6 to 11 Mbar.  Ramp wave compression, which now enables solid-state experiments at ~10 Mbar, has revealed that the diamond phase of carbon remains stable and strong to 8 Mbar.  Both dynamic diffraction and EXAFS techniques will be used to determine the crystalline structure and local order in solids at 10+ Mbar.  The platforms described below will allow scientists to explore the nature of solids at several 10’s of Mbar, complex chemistry into the Gbar regime and the nature of helium and hydrogen at an interatomic spacing comparable to their DeBroglie wavelength.

Ramp compression platform for exploring solids and low-temperature fluids

One standard technique to compress matter dynamically to high pressures is to launch a strong shock wave. A single strong shock wave results in a significant increase in the temperature with increasing shock pressure so that for materials at shock pressures above a few Mbar (6 Mbar in diamond, 2.6 Mbar in Fe), one can only explore the properties of the fluid phase. To avoid forming a shock wave, the pressure must be increased gradually in time, and the data are collected before a strong shock wave forms.  Therefore, the ramp experiments are usually designed to capture the data before the shock wave forms.  If there were no intrinsic material heating upon compression (i.e., from material strength) the ramp compression path would follow the isentrope.  This ramped compression wave is generated quite simply by ramping the laser intensity with time.  The laser geometry and pulseshape design for ramp compressing iron to 20 Mbars is shown below.  Figure 1 shows the hohlraum geometry and diagnostic layout.  Figure 2 shows a target sketch and laser pulseshape.


Diagnostic Configurations
Figure 1a: This plot shows the diagnostic configurations. TARPOS is the target positioner, TASPOS the target alignment sensor at the equator of the target chamber and at 147 degrees on the azimuth. SXI is the Static X-ray Imager to capture performance of the hohlraum. GXD is the Gated X-ray Imager to observe the hohlraum performance along the axis of the hohlraum. Dante is the instrument that measures the radiation temperature of the hohlraum.

Filled Hohlraum
Figure 1b: NIF hohlraum filled with .3 Atm. neopentane gas with typical stepped target and cone shield used for ramp compression experiments. The cone shields the sample from unconverted laser light.

Diag Location Priority Type Calib / Charact
VISAR Any equatorial DIM 1 2 180-740kJ/ 20-40 nsec
Dante-1 Fixed 1 3 Pre-shot
GXD Polar 0-0 2 2 Pre-shot
Dante-2 64-350 2 3 Pre-shot
SXI 18-123, 116-326 2 3 Pre-shot
FABS/NBI Q31B, Q36B 2 3 Pre-shot
FFLEX 90-110 2 3 Pre-shot

 

Platform Target # of beams Laser energy/Pulse width
Ramp Compression Hohlraum- 0.3 atm neopentane fill 128 180-740kJ/ 20-40 nsec
holhraum
Figure 2a: Sketch of hohlraum (laser to x-ray converter) and stepped target.

compression example
Figure 2b: Fe 20-Mbar ramp compression example. Diagram of hohlraum and 128-beam ramp laser pulse.

compression example
Figure 2c: Fe 20-Mbar ramp compression example. Predicted performance of experiment.

Diffraction platform for determining crystal structure at several tens of Mbar

To determine the crystalline structure of solids at several tens of Mbar, a pulsed x-ray diffraction platform is being developed.  This platform uses nearly the same laser pulseshape as is used to ramp compress diamond.  The target consists of a diamond sandwich,  a thin slab of “target” material in between two diamond flats as sketched below.  This target is attached to half a hohlraum to allow for x-ray driving of the ramp compression wave.  The diamond sandwich and half hohlraum are attached to a detector box that contains x-ray detectors on the remaining 5 sides of the box to collect the diffracted signal.  Finally, separate NIF beams hit a backligher foil displaced from the main target to produce backlighter x-rays, which pass through the target and produce the diffraction signal. 


Platform Target # of beams Laser energy/Pulse width
Ramp Compression Hohlraum- 0.3 atm neopentane fill 68 90-380 kJ/ 20-40 nsec plus 20 kJ/ 10 ps -1 ns backligheter pulse

Mounted half-hohlraum
Figure 3: Half of a hohlraum mounted to a box containing image plates on four sides and the back plane to collect x-ray diffraction signals. The x-ray source is produced by separate beams hitting a backlighter foil. The x-ray backlighter beam passes through the half-hohlraum and then the target to produce the powder diffraction signal. Beams from the lower half of NIF illuminate the half-hohlraum to produce an x-ray ramped drive. The sample (right) consists of two diamond flats sandwiching several microns of polycrystalline iron.

Ramp and shock compression of precompressed fluids platform

Some materials are either very compressible or have low density at ambient conditions.  This limits the useful density range accessible by dynamic compression either with shock waves or ramp compression alone.  The NIF cryogenic target positioner has the capability  to reduce the sample temperature to a minimum temperature of ~14 K, and so can be used to solidify or liquefy materials like hydrogen and some of the rare gases.  An alternate technique for increasing the initial density is to precompress the sample in a diamond anvil cell and then launch a dynamic compression wave with NIF.  This gives significantly more flexibility for exploring matter at high densities and offers the ability to explore mixtures such as He and H2, which are immiscible at liquid densities and cryogenic temperatures.  Shock loading precompressed samples has been used to explore a number of materials at several high-energy laser facilities, and applied to NIF will allow us to potentially reach the core states of Jupiter, and determine if hydrogen becomes superfluid or superconducting at extreme densities and modest temperatures.  Figure 4 shows the sketch of the target and beam configuration.  One early experiment will be to ramp compress deuterium to over 5 g/cm3 starting at quite modest initial densities.  The pulseshape will be similar to that used for ramp compressing diamond to 30 Mbar (i.e., ramped pulse with 20-ns rise time and 440 kJ) and with the same diagnostic suite as used in the ramp compression stress-density experiments.

Laser and Target Configuration for precompressed shock or ramp wave experiment

Platform Target # of beams Laser energy/Pulse width
Ramp Compression Hohlraum- 0.3 atm neopentane fill 68 90-380 kJ/ 20-40 nsec plus 20 kJ/ 10 ps -1 ns backligheter pulse
Half hohlraum on a diamond anvil
Figure 4: Half of a hohlraum mounted to a diamond anvil cell used for precompressing H, He, Ne, LiD, etc. The diamond anvil cell will be mounted to the target positioner as shown in the upper right sketch. The target would be aligned using the target alignment system as used in the ignition or ramp-compressed stress density experiments.

High-pressure shock wave platform

To explore materials at very high pressures and temperatures (from 10 Mbar to >10 Gbar) we are developing strong shock wave platforms for NIF. These experiments will be used in either planar geometry where a sample is mounted to the side of a hohlraum as in the ramp wave stress density experiments discussed above, or in convergent geometry similar to the inertial confinement fusion experiments.  Planar experiments will achieve pressures up to ~1 Gbar while convergent experiments will push to beyond the 10 Gbar regime.  The case described below shows just the planar shock wave example designed to produce a steady shock wave in SiO2.  Two diagnostics are shown.  First is the Velocity Interferometer System for Any Reflector (VISAR) and Streaked Optical Pyrometer (SOP) used in the ramp compression experiments.  This would either detect the in-flight shock velocity for initially transparent materials or shock breakout times to determine the average velocity for samples transiting a known thickness.  The second diagnostic uses either a 1- to 3-ns or 10- to 100-ps pulse to illuminate a backlighter foil to generate x-rays that pass through the shock-compressed sample to form a shadow image on an x-ray imager.  The x-ray radiograph will contain the density and potential shock velocity.  For the 1- to 3-ns pulse, the x-ray detector will be an x-ray streak or framing camera.  For the 2- to 10-ps pulse, the detector would be a framing camera, image plate, or charge-coupled device (CCD).  Potentially we could use multiple x-ray snapshots to determine shock front velocity from the short pulse backlighter.

Laser and target configuration for precompressed shock or ramp wave experiments

Platform Target # of beams Laser energy/Pulse width
Shock wave compression Ignition hohlraum- 0.3 atm neopentane fill 128-192

50-1800 kJ/ 2-10 shaped pulse

Shock wave platform
Figure 5a (left): The diagnostic layout for shock wave experiments. Figure 5b (right): Two target packages, one for impedance match experiments where SiO2 is measured relative to aluminum, and one for absolute compression measurements where the sample compression (i.e., for Fe in this example) is measured directly with radiography.

Shock wave platform
Figure 5c shows the laser power vs. time and the resultant radiation temperature vs. time in an ignition scale-1 hohlraum.

Laser power and pressure
Figure 5d shows the resultant pressure profile in the impedance match target at a single snapshot in time.

Diagnostic configuration

Standard diagnostics for this platform and their location (elevation, azimuth) are provided below. See Chamber Geometry and Diagnostics for additional information. Generally, the VISAR and SOP provide compressibility and equation of state (EOS) information, while x-ray diffraction measurements are used to determine phase, lattice behavior, and similar measurements.

Diagnostic Location
Dante-1 Fixed (143-274)
FFLEX 90-110
VISAR DIM 90-135
ARC Quad 35T (FY2011 and beyond)
SXD/GXD Polar 0-0, or DIM 90-45
SXI, Top/Bottom Fixed ((18-123), (161-326))

 

For further information on scientific opportunities at the NIF, please contact:
User Office
PHONE: (925) 422-2179
nifuseroffice@llnl.gov



More Information

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