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Fast-electron generation in long-scale-length plasmas
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Image of FIG. 1.
FIG. 1.

(Color online) SAGE simulation of typical long-scale-length plasma on OMEGA EP. (a) Density contours at the end of the laser pulse and the projection onto the (r, z) plane of a subset of laser rays for an 1100-μm-diam beam. (b) Incident laser power and trajectories of selected coronal density contours, nc indicating critical. The initial CH surface is at z = 4.015 mm. The density scale length reaches a maximum at ∼1 ns and then stays constant. The plasma temperature reaches a maximum at ∼0.5 ns and then stays constant.

Image of FIG. 2.
FIG. 2.

(Color online) SAGE-calculated x-ray fluence from a shot at an irradiance of 2.7 × 1014 W/cm2. No normalization of intensity was applied.

Image of FIG. 3.
FIG. 3.

(Color online) Experimental setup. Four UV beams irradiate a planar Mo foil, coated with CH on both sides. XRS3, TCS, and SPC are x-ray spectrometers measuring the Mo Kα line; XRS1 measures the plasma thermal emission; and HXRD measures the hard x-ray spectrum.

Image of FIG. 4.
FIG. 4.

(Color online) X-ray image of the irradiated focal spot at 5 × 1014 W/cm2 (in the photon-energy range of 2–7 keV). The lineout on the bottom is through the horizontal dashed line in the image.

Image of FIG. 5.
FIG. 5.

(Color online) An example of the Mo Kα spectra measured on a single shot by three detectors: (a) a planar LiF crystal spectrometer and a Cauchois-type quartz crystal spectrometer and (b) a single-hit CCD array. The three measurements of Kα energy are consistent.

Image of FIG. 6.
FIG. 6.

(Color online) Measured Kα energy and relative Kα energy as functions of incident laser intensity. The code-calculated η values are indicated above the figure.

Image of FIG. 7.
FIG. 7.

(Color online) Mo Kα and HXR intensities. Both signals rise quasi-exponentially with laser intensity.

Image of FIG. 8.
FIG. 8.

(Color online) Measured hot-electron temperature T H as a function of incident laser intensity.

Image of FIG. 9.
FIG. 9.

(Color online) Monte Carlo–calculated HXR spectra for 107 incident electrons. The slope of the HXR continuum (79 keV) is about equal to the fast-electron temperature assumed for the MC code run (80 keV). The smoothness of the curve is an indication of the good statistics obtained with 107 electrons.

Image of FIG. 10.
FIG. 10.

(Color online) Monte Carlo–calculated angular distribution of Mo Kα as function of polar angle θ (relative to the target normal), per unit solid angle. “Back” stands for the back of the target (forward emission).

Image of FIG. 11.
FIG. 11.

(Color online) Monte Carlo–calculated ratio of the total incident electron energy and the Kα emission per unit solid angle in the target normal direction, as a function of the fast-electron temperature. This curve is used to deduce the total energy in fast electrons from the measured Mo Kα energy.

Image of FIG. 12.
FIG. 12.

(Color online) Total energy in fast electrons and relative energy as functions of incident laser intensity.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Fast-electron generation in long-scale-length plasmas