Abstract
The full scale modeling of power transfer between laser beams crossing in plasmas is presented. A new model was developed, allowing calculations of the propagation and coupling of pairs of laser beams with their associated plasma wave in three dimensions. The complete set of laser beam smoothing techniques used in ignition experiments is modeled and their effects on crossedbeam energy transfer are investigated. A shift in wavelength between the beams can move the instability in or out of resonance and hence allows tuning of the energy transfer. The effects of energy transfer on the effective beam pointing and on symmetry have been investigated. Several ignition designs have been analyzed and compared, indicating that a wavelength shift of up to 2 Å between cones of beams should be sufficient to control energy transfer in ignition experiments.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DEAC5207NA27344.
I. INTRODUCTION
II. DESCRIPTION OF THE MODEL
III. ENERGY TRANSFER BETWEEN ONE PAIR OF BEAMS: 30° AND 50°
A. Coupling geometry
B. Effects of laser beam smoothing
IV. ENERGY TRANSFER BETWEEN CONES OF BEAMS IN NIF
A. Average energy transfer
B. Effects of the crossedbeam transfer on beam pointing
C. Symmetry analysis
D. Comparison of several target designs
V. CONCLUSION
Key Topics
 Energy transfer
 27.0
 Hohlraum
 22.0
 Laser beams
 19.0
 Laser beam effects
 15.0
 Plasma waves
 13.0
Figures
vector diagram for the crossedbeam energy transfer process.
vector diagram for the crossedbeam energy transfer process.
Frequency broadening of the effective frequency and wave vector of the laser (a) in the time domain due to SSD and (b) in the spatial domain due to the optics finite aperture (represented is the near field of two NIF beams). Our coupling coefficient is averaging over all possible weighted pairs of frequencies and wave vectors [Eq. (10)].
Frequency broadening of the effective frequency and wave vector of the laser (a) in the time domain due to SSD and (b) in the spatial domain due to the optics finite aperture (represented is the near field of two NIF beams). Our coupling coefficient is averaging over all possible weighted pairs of frequencies and wave vectors [Eq. (10)].
Hydrodynamic conditions in NIF hohlraums at peak laser power from LASNEX simulations: (a) electron density and material composition and (b) electron temperature.
Hydrodynamic conditions in NIF hohlraums at peak laser power from LASNEX simulations: (a) electron density and material composition and (b) electron temperature.
(a) Contour plot of a half NIF hohlraum electron density and flow velocity vector plot (black arrows). The black rectangle shows the location of the simulation box for the (30°, 50°) pair of beams. (b) Laser intensity in the plane. The dashed rhombus represents the crossing area between the two beams.
(a) Contour plot of a half NIF hohlraum electron density and flow velocity vector plot (black arrows). The black rectangle shows the location of the simulation box for the (30°, 50°) pair of beams. (b) Laser intensity in the plane. The dashed rhombus represents the crossing area between the two beams.
(a) Map of the coupling coefficient in the simulation plane with the flow vector plot (red arrows) for the (30°, 50°) pair of beams and ; the dashed rhombus represents the crossing area between the two beams. (b) Coupling coefficient along the axis (bisector line between and ) as a function of .
(a) Map of the coupling coefficient in the simulation plane with the flow vector plot (red arrows) for the (30°, 50°) pair of beams and ; the dashed rhombus represents the crossing area between the two beams. (b) Coupling coefficient along the axis (bisector line between and ) as a function of .
Power transfer from the 30° to the 50° beams defined as the relative power gain of the 50° beam ( since both beams have roughly the same power) with CPPs only (dashed green line), CPP with PS (dashed blue line), and CPP with PS and SSD (red line).
Power transfer from the 30° to the 50° beams defined as the relative power gain of the 50° beam ( since both beams have roughly the same power) with CPPs only (dashed green line), CPP with PS (dashed blue line), and CPP with PS and SSD (red line).
(a) Nearfield diagram of all the beams entering one LEH of a NIF hohlraum. The total transfer for each circled beam is the sum of the contributions from all its nearest neighbors represented by arrows (each circle represents one of the six possible nearest neighbor configurations). (b) Relative energy gain per beam as a function of . (c) Relative energy gain for the inner and outer cones.
(a) Nearfield diagram of all the beams entering one LEH of a NIF hohlraum. The total transfer for each circled beam is the sum of the contributions from all its nearest neighbors represented by arrows (each circle represents one of the six possible nearest neighbor configurations). (b) Relative energy gain per beam as a function of . (c) Relative energy gain for the inner and outer cones.
(a) Laser intensity in the transverse plane at for the 30° and 50° beams with coupling turned off (no transfer) and with coupling and . (b) Shift in the intensityweighted center of the inner and outer cones measured as a shift on the hohlraum wall ( toward the LEH) from the center position without transfer.
(a) Laser intensity in the transverse plane at for the 30° and 50° beams with coupling turned off (no transfer) and with coupling and . (b) Shift in the intensityweighted center of the inner and outer cones measured as a shift on the hohlraum wall ( toward the LEH) from the center position without transfer.
Schematics of the effects of crossedbeam transfer on the effective beam pointing (here for the 30°, 50° pair) to each of the two transfer zones; the beam on top (inner beam outside the LEH, outer beam inside the LEH) always transfers to the beam on the bottom, leading to a systematic shift toward the LEH regardless of the overall transfer.
Schematics of the effects of crossedbeam transfer on the effective beam pointing (here for the 30°, 50° pair) to each of the two transfer zones; the beam on top (inner beam outside the LEH, outer beam inside the LEH) always transfers to the beam on the bottom, leading to a systematic shift toward the LEH regardless of the overall transfer.
Areaweighted flux asymmetry (defined as the rms of the spherical harmonics ) on the ignition capsule for the nominal electron temperature at the LEH and for an arbitrary increase in by 50%. The color maps on top show the xray flux on the capsule (the hohlraum axis is horizontal).
Areaweighted flux asymmetry (defined as the rms of the spherical harmonics ) on the ignition capsule for the nominal electron temperature at the LEH and for an arbitrary increase in by 50%. The color maps on top show the xray flux on the capsule (the hohlraum axis is horizontal).
Relative energy transfer between the inner and outer cones for three ignition target designs (cf. Table II); the electron density maps of the designs at peak laser power are shown on the right.
Relative energy transfer between the inner and outer cones for three ignition target designs (cf. Table II); the electron density maps of the designs at peak laser power are shown on the right.
Tables
NIF laser parameters used for the “285 eV Be” design per quad: polar angle , spot dimensions at best focus and , power , and average intensity in units of .
NIF laser parameters used for the “285 eV Be” design per quad: polar angle , spot dimensions at best focus and , power , and average intensity in units of .
Radiation temperature, hohlraum and LEH diameters, and intensity and spot size scale factor for the three target designs studied here. The 1.0 scale for the spot size corresponds to ellipse dimensions of and for the inner (23.5°, 30°) and outer (44.5°, 50°) beams, respectively. The other spot sizes are simply obtained by multiplying these dimensions by the scaling factor.
Radiation temperature, hohlraum and LEH diameters, and intensity and spot size scale factor for the three target designs studied here. The 1.0 scale for the spot size corresponds to ellipse dimensions of and for the inner (23.5°, 30°) and outer (44.5°, 50°) beams, respectively. The other spot sizes are simply obtained by multiplying these dimensions by the scaling factor.
Article metrics loading...
Full text loading...
Most read this month
Most cited this month










Electron, photon, and ion beams from the relativistic interaction of Petawatt laser pulses with solid targets
Stephen P. Hatchett, Curtis G. Brown, Thomas E. Cowan, Eugene A. Henry, Joy S. Johnson, Michael H. Key, Jeffrey A. Koch, A. Bruce Langdon, Barbara F. Lasinski, Richard W. Lee, Andrew J. Mackinnon, Deanna M. Pennington, Michael D. Perry, Thomas W. Phillips, Markus Roth, T. Craig Sangster, Mike S. Singh, Richard A. Snavely, Mark A. Stoyer, Scott C. Wilks and Kazuhito Yasuike

Commenting has been disabled for this content