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Energy transfer between laser beams crossing in ignition hohlraums
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10.1063/1.3103788
/content/aip/journal/pop/16/4/10.1063/1.3103788
http://aip.metastore.ingenta.com/content/aip/journal/pop/16/4/10.1063/1.3103788

Figures

Image of FIG. 1.
FIG. 1.

-vector diagram for the crossed-beam energy transfer process.

Image of FIG. 2.
FIG. 2.

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)].

Image of FIG. 3.
FIG. 3.

Hydrodynamic conditions in NIF hohlraums at peak laser power from LASNEX simulations: (a) electron density and material composition and (b) electron temperature.

Image of FIG. 4.
FIG. 4.

(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.

Image of FIG. 5.
FIG. 5.

(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 .

Image of FIG. 6.
FIG. 6.

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).

Image of FIG. 7.
FIG. 7.

(a) Near-field 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.

Image of FIG. 8.
FIG. 8.

(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 intensity-weighted center of the inner and outer cones measured as a shift on the hohlraum wall ( toward the LEH) from the center position without transfer.

Image of FIG. 9.
FIG. 9.

Schematics of the effects of crossed-beam 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.

Image of FIG. 10.
FIG. 10.

Area-weighted 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 x-ray flux on the capsule (the hohlraum axis is horizontal).

Image of FIG. 11.
FIG. 11.

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

Generic image for table
Table I.

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 .

Generic image for table
Table II.

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.

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/content/aip/journal/pop/16/4/10.1063/1.3103788
2009-04-10
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Energy transfer between laser beams crossing in ignition hohlraums
http://aip.metastore.ingenta.com/content/aip/journal/pop/16/4/10.1063/1.3103788
10.1063/1.3103788
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