Laser-plasma Instabilities Research Articles

Spatial-temporal modulation method of nanosecond laser for the double-cone ignition scheme

In order to improve the stability of the pulse, realize the high requirements of the direct drive ignition design for the uniformity of the target irradiation, reduce the interference of laser plasma instability, and improve the laser-target coupling efficiency, a nanosecond laser spatial-temporal modulation of high-power laser driver for double-cone ignition (DCI) research was proposed. Under the premise of satisfying the near-isentropic compression waveform of driving implosion, the time-power curves of all sub-beams in the facility are redistributed to reduce the waveform contrast ratio of each sub-beam. A fewer number of sub-beams are utilized to generate low-power foot pulses, which are focused on the target surface of the initial radius. And the remaining sub-beams are utilized to generate high-power driving main pulses, which are focused on a relatively small target surface. It is shown that the stability of the time-power curve of each sub-beam and the power balance control ability can be effectively improved by redistributing. At the same time, the variable focal spot control can be realized to reduce the influence of cross-beam energy transfer (CBET).

Mitigation of laser plasma filamentation by rotating beam smoothing scheme

The propagation of intense laser beams in plasma inevitably gives rise to laser plasma instabilities, which have a significant impact on the illumination uniformity of the focused spot on the target in inertial confinement fusion (ICF) facilities. Here we propose an ultrafast smoothing scheme using a rotating beam (RB) to mitigate the laser plasma filamentation. Using the propagation model of the rotating beam in plasma for the laser-plasma self-focusing (SF) and filamentation, the filamentation characteristics of laser spots were analyzed. The results indicate that the rotating beam smoothing scheme, operating at picosecond timescale, exhibits superior mitigation effect of laser plasma filamentation.

Measurements of laser-plasma instabilities in double-cone ignition experiments relevant to the direct-drive conditions at Shenguang-II Upgrade laser facility

Experiments have been performed to investigate laser-plasma instabilities (LPIs) relevant to the direct-drive inertial confinement fusion (ICF) conditions at the Shenguang-II Upgrade (SG-II UP) laser facility during the double-cone ignition (DCI) experimental campaigns, with the overlapped laser intensity ranging from 6×1014Wcm−2 to 1.8×1015Wcm−2 . An overall LPI scenario has been built from the collection and investigation of angularly distributed scattered light. Across broad ranges of laser and plasma parameters, relevant to the direct-drive ICF conditions, the dominance of the stimulated Raman side scattering (SRSS) was confirmed, and its coexistence with the two-plasmon decay (TPD) was also observed. Significant SRSS scattered light was observed across an extremely wide range of emission angles, concentrated at large angles, and demonstrated to be robust throughout the parameter space. Time-resolved spectral measurements show distinctly different SRSS behaviors along different angles and a slightly higher threshold compared to the TPD. The overall SRSS energy loss was measured, indicating a scattered light energy fraction of up to 6%. These results are of crucial importance for the precise assessment of the LPIs in the DCI as well as other laser directly driven ICF schemes.

Development of a full aperture backscatter system for the Orion laser.

A full aperture backscatter system (FABS) is currently in development on the Orion laser at AWE to measure scattered light from the stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) processes. The light is to be collected through the full aperture of the final optic assembly and traverse back down the beam path, with fractions of this light being directed to an optics table. By measuring the energy of this backscattered light, it is possible to gain insight into some of the laser-plasma instabilities that are present on the laser system and should give an indication of some of the scattered light losses due to the SBS and SRS processes. The uncontrolled scattered light can lead to hotter electrons, which then preheat the target causing a degradation in compression and can inhibit ignition in inertial confinement fusion experiments, as well as secondary instabilities whereby the scattered light may in itself cause further LPIs, such as two-ion decay or the Langmuir decay instability. The FABS diagnostic on Orion is planned to enhance the plasma diagnostics suite available and provide quantitative guidance on increasing the energy coupling. Current progress includes the characterization of filters and, hence, a broadband xenon lamp to be used in measuring the transmission efficiency of the optics chain, desktop alignment of the backscatter optics, and characterization of the streak cameras.

PM2D: A parallel GPU-based code for the kinetic simulation of laser plasma instabilities at large scales

Laser plasma instabilities (LPIs) have significant influences on the laser energy deposition efficiency and therefore are important processes in inertial confined fusion (ICF). Numerical simulations play important roles in revealing the complex physics of LPIs. Since LPIs are typically a three wave coupling process, the precise simulations of LPIs with kinetic effects require to resolve the laser period (around one femtosecond) and laser wavelength (less than one micron). In the typical ICF experiments, however, LPIs are involved in a spatial scale of several millimeters and a temporal scale of several nanoseconds. Therefore, the precise kinetic simulations of LPIs in such scales require huge computational resources and are hard to be carried out by present kinetic codes like particle-in-cell (PIC) codes. In this paper, a full wave fluid model of LPIs is constructed and numerically solved by the particle-mesh method, where the plasma is described by macro particles that can move across the mesh grids freely. Based upon this model, a two-dimensional (2D) GPU code named PM2D is developed. The PM2D code can simulate the kinetic effects of LPIs self-consistently as normal PIC codes. Moreover, as the physical model adopted in the PM2D code is specifically constructed for LPIs, the required macro particles per grid in the simulations can be largely reduced and thus overall simulation cost is considerably reduced comparing with PIC codes. More importantly, the numerical noise in the PM2D code is much lower, which makes it more robust than PIC codes in the simulation of LPIs for the long-time scale above 10 picoseconds. After the distributed computing is realized, our PM2D code is able to run on GPU clusters with a total mesh grids up to several billions, which meets the requirements for the simulations of LPIs at ICF experimental scale with reasonable cost. Program summaryProgram Title: PM2DCPC Library link to program files:https://doi.org/10.17632/xscj6vnkkw.1Licensing provisions: GNU General Public License v3.0.Programming language: C++, CUDA.Nature of problem: Although the large scale simulations of laser plasma instabilities (LPIs) is of great significance for the inertial confinement fusion (ICF), there is still no suitable code to simulate these problems. PM2D code based on a GPU platform provides an effective method to simulate these large scale problems in ICF.Solution method: A fluid model for LPIs is established firstly, which contains wave equations that describe the laser propagating process, electron and ion fluid equations that describe the plasma motions, and a Poisson's equation that describes the electrostatic field induced by charge separation. The wave equation is solved on a rectangular region using absorption boundary conditions on all of four boundaries. The absorption boundary condition on the left boundary is further extended to allow the incidence of driven lasers and absorption of scattering lasers simultaneously. The fluid equations in the physical model are solved by the particle-mesh method, in which the macro particles are driven to move by fluid forces. Since macro particles can move freely within the fixed fluid grids, the PM2D code can capture the kinetic effects self-consistently. The Poisson's equation for the electrostatic field is solved by a Fourier decomposition method in the y direction, which helps to decrease the simulation cost greatly. The PM2D code is developed on a GPU platform base on CUDA toolkit, which largely increase the computational speed.

Driver at 10 MJ and 1 shot/30 min for inertial confinement fusion at high gain: Efficient, compact, low-cost, low laser–plasma instabilities, beam color selectable from 2ω/3ω/4ω, applicable to multiple laser fusion schemes

Driver at 10 MJ and 1 shot/30 min for inertial confinement fusion at high gain: Efficient, compact, low-cost, low laser–plasma instabilities, beam color selectable from 2<i>ω</i>/3<i>ω</i>/4<i>ω</i>, applicable to multiple laser fusion schemes

What next: Further implosion space exploration on the path to NIF extended yield capability

We present quantitative motivations and assessments of various proposed and ongoing directions to further improving yields and target gain of igniting indirect-drive implosions at the National Ignition Facility (NIF). These include increasing compression and confinement time, improving hohlraum and ablator efficiency, and further increasing peak power and laser energy. 1D hydroscaled simulations, augmented by analytic 1D theory, have been used to project yield improvements for each of these implosion optimization tracks, normalized to the best current performing 4 MJ shot. At current NIF capabilities of 2.2 MJ, 450 TW, we project several paths could reach 15 MJ yield levels. We also expect several key implosion physics questions will be addressed in attempting to reach this yield level. These include demonstrating to what extent lower adiabat designs leading to higher compression will increase gain and efficiency, and whether we can reduce residual kinetic energy and ablator-fuel mix that is probably limiting the current burn-up fraction. For an envisaged NIF upgrade to EL = 3 MJ at fixed 450 TW peak power, scaling capsule size and fuel thicknesses faster than pure hydroscaling should allow for yields that could reach up to 60–80 MJ, depending on the efficiency gains realized in increasing deuterium-tritium fuel thickness, reducing hohlraum losses, and switching to lower Z ablators. The laser-plasma instability and beam transmission scaling in these larger hohlraums is shown to be favorable if the spot size is increased with hohlraum scale.

Spectral characteristics of laser-plasma instabilities with a broadband laser

Abstract Recent experimental progress regarding broadband laser-plasma instabilities (LPIs) showed that a 0.6% laser bandwidth can reduce backscatters of the stimulated Brillouin scattering (SBS) and the stimulated Raman scattering (SRS) at normal incidence [Phys. Rev. Lett., 132, 035102 (2024)]. In this paper, we present further discussion on the spectral distributions of the scatters developed by broadband LPIs, in addition to a brief validation of the effectiveness of bandwidth on LPIs mitigation at oblique incidence. SBS backscatter has a small redshift in the broadband case contrary to the blueshift with narrowband laser, which may be explained by the self-cross beam energy transfer between the various frequency components within the bandwidth. SRS backscatter spectrum presents a peak at a longer wavelength in the broadband case compared to the short one in the narrowband case, which is possibly attributed to the mitigation effect of bandwidth on filaments at underdense plasmas. The three-halves harmonic emission (3ω/2) has a one-peak spectral distribution under the broadband condition, which is different from the two-peak distribution under the narrowband condition, and that may be related to the spectral mixing of different frequency components within the bandwidth if the main sources of the two are both two-plasmon decay.

Ultrafast random polarization beam smoothing driven by counter-rotating wavefronts via the optical Kerr effect

We propose an ultrafast random polarization smoothing scheme to achieve ultrafast speckle movement and polarization randomization of the focal spot. In the scheme, each beamlet in a laser quad is driven by a rotating petal-like wavefront, giving rise to the ultrafast redistribution of the speckles within the focal spot. The rotating wavefront is induced by an optical Kerr medium pumped by a laser beam with rotating intensity distribution that is generated by the superposition of two Laguerre–Gaussian beams carrying conjugate vortex phase and frequency shift. In addition, by properly selecting the topological charges of the pump beams and polarization states of the beamlets, the beamlets in a quad can be divided into two sets with counter-rotating wavefronts and orthogonal polarizations, which further randomizes the polarization of the focal spot. Results indicate that the proposed scheme can reduce the contrast by more than 70% and the degree of polarization by more than 75% within several picoseconds, by utilizing the rotating phase pumped by two Laguerre-Gaussian beams with a peak intensity of 0.18GW/cm2 and a frequency shift of 1 THz. The ultrafast random polarization smoothing scheme is expected to suppress the growth of Laser Plasma Instabilities (LPIs) including the filamentation and backscatter in indirect-drive inertial confinement fusion (ICF) facilities.

Investigation of laser plasma instabilities driven by 527 nm laser pulses relevant for direct drive inertial confinement fusion

We report on a study of laser plasma instabilities with 527 nm laser pulses in an intensity range of 0.5×1013−1.1×1015 Wcm−2 and plasma parameters entering a regime that is relevant for direct drive inertial confinement fusion. Using the kilojoule high repetition rate L4n laser at the Extreme Light Infrastructure—Beamlines, more than 1300 shots were collected, and the onset and the growth of stimulated Brioullin scattering (SBS) and stimulated Raman scattering (SRS) were studied with a high confidence level. The measured onset intensities are 0.2×1014 Wcm−2 for SBS and 1.4×1014 Wcm−2 for SRS. At the maximum intensity, the total fraction of backscattered energy reaches 2.5% for SBS and 0.1% for SRS. These results are of high relevance for advanced concepts for inertial fusion energy, which rely on the use of 527 nm laser light to drive the implosion of the fuel target, and in particular, they can be used as a benchmark for advanced simulations.

Study on near forward scattering light of planar film target driven by broadband laser

Laser-plasma instability (LPI) is one of the key issues in the ignition process of inertial confinement fusion (ICF), and extensive theoretical, simulation, and experimental research has been conducted over the years. Broadband laser, due to its low temporal coherence, can reduce the effective electric field strength when interacting with plasma and disrupt the phase-matching conditions of LPI, thus considered an effective approach to solving LPI issues. Current extensive simulation studies indicate that broadband laser can suppress the generation of phenomena such as Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS), and Two-Plasmon Decay (TPD) to some extent. There are also a few backward scattering experimental studies, but more experimental research such as side-scattering is still needed. Therefore, based on the broadband second harmonic laser facility “Kunwu”, this paper designs experiments for the lateral scattering of critical density plasma driven by broadband and traditional narrowband lasers, as well as the production of hot electrons. The experimental results show that the side SBS and side SRS spectra and shares at different angles excited by broadband lasers with a power density of 1×10&lt;sup&gt;15&lt;/sup&gt;W·cm&lt;sup&gt;-2&lt;/sup&gt; have significant differences from those of narrowband lasers. Further analysis reveals that the overall share of hot electrons in the lateral direction is higher for broadband lasers compared to narrowband lasers. However, under broadband conditions, the share of SRS at small forward and backward angles is significantly lower than that of narrowband lasers. Preliminary qualitative analysis suggests that SRS may not be the primary mechanism for hot electron generation in this case, and that PDI might play a dominant role in the generation of hot electrons.

Low-temporal coherence light self-focusing effect by spatial resolved method

The low-temporal coherence light (LTCL) has received extensive attention in the research of inertial confinement fusion due to its physical properties of instantaneous broadband. Recent reports demonstrated that the LTCL has significant suppression effects on laser plasma instability. However, the temporal spike structures of the LTCL will not only induce the amplification of the self-focusing effect, but also make its small-scale self-focusing characteristics and corresponding damage mechanism more complicated. Exploring the self-focusing characteristics of the LTCL will provide an important information for improving the output power of the LTCL. In this work, we design a more accurate test method for comparing the nonlinear self-focusing effects of different lasers, and compare the self-focusing effect of LTCL with single longitudinal mode (SLM) pulse. In the experiments, fused silica is tightly focused by a short focal length lens to avoid damaging the input surface. A spatially resolved test method is designed to measure the nonlinear &lt;i&gt;I&lt;/i&gt;×&lt;i&gt;L&lt;/i&gt; value (where &lt;i&gt;I&lt;/i&gt; is the incident intensity, &lt;i&gt;L&lt;/i&gt; is the distance from the head of filamentation damage to the input surface), which is accumulated from the input surface to the head of filamentation damage. The results show that the nonlinear &lt;i&gt;I&lt;/i&gt;×&lt;i&gt;L&lt;/i&gt; value obtained by the spatially resolved method is lower than by the traditional test method, since the energy loss caused by incident surface damage and backward stimulated Brillouin scattering (SBS) has been resolved. Furthermore, the nonlinear &lt;i&gt;I&lt;/i&gt;×&lt;i&gt;L&lt;/i&gt; values of the SLM pulse and the LTCL are also compared by the traditional test method and spatially resolved method. The test results show that due to the temporal spike structure, the LTCL has a lower nonlinear &lt;i&gt;I&lt;/i&gt;×&lt;i&gt;L&lt;/i&gt; value than the SLM pulse. The SBS effect and the different damage characteristics of the input surface are also analyzed. This study provides a more accurate test method for better analyzing the self-focusing effect of LTCL and laser pulses with different characteristics, and hence presenting a reference for designing high-power devices of low-temporal coherence light.

Suppression of stimulated Raman scattering kinetic bursts by intensity-modulated broadband laser

Laser plasma instability is one of the difficulties that plague inertial confinement fusion. Broadband laser, as an effective tool for suppressing laser-plasma instabilities, has received a lot of attention in recent years. However, the nonlinear bursts of high-frequency instabilities, such as stimulated Raman scattering driven by broadband laser in the kinetic regime, make the suppression effect less than expected. In this study, a broadband laser model with intensity modulation is proposed. By choosing an appropriate intensity modulation envelope, it is possible to interrupt the amplification process of backscattered light in strong pulses, reduce the probability of high-intensity pulses inducing intense bursts, and drastically reduce the fraction of backscattered light and hot electron yield. Numerical simulations show that the intensity-modulated laser has a good ability to suppress stimulated Raman scattering. For a broadband laser with average power of &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ 1.0 \times {10}^{15}\;{\mathrm{W}}/{\mathrm{c}}{{\mathrm{m}}}^{2} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231679_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231679_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and a bandwidth of 0.6%, the reflectivity decreases by an order of magnitude and the fraction of hot electron energy above 20 keV decreases from 7.34% to 0.31% by using the intensity modulation technique. The above results confirm the feasibility of using the intensity-modulated broadband laser to suppress the high-frequency instability and are expected to provide a reference for designing the subsequent broadband laser-driven fusion experiments.

On the improvement of smoothing by spectral dispersion efficiency for laser–plasma interaction

Large energetic laser facilities provide an amazing tool for bringing matter into high energy density states but achieving a good energy conversion requires to optically smooth the high-power laser beams. Optical smoothing reduces the laser spatial and temporal coherences, allowing to mitigate the development of unwanted laser–plasma instabilities (LPI). Two schemes have been mainly developed: polarization smoothing and smoothing by spectral dispersion. Here, we focus on the latter. Smoothing by spectral dispersion consists in broadening the spectrum usually through a sinusoidal phase modulation and dispersing it with an optical grating. It is usually considered that the modulation frequency should be equal to the inverse of the time delay of the grating, because it maximizes the number of uncorrelated speckles patterns at a given bandwidth. However, current optical smoothing designs are still not sufficient for mitigating LPI. Because the optical smoothing system possesses degrees of freedom, we propose to improve the optical smoothing efficiency by a better tuning of those parameters. Considering the Laser Mégajoule optical system framework, we show that an increase in the modulation frequency allows a better efficiency of the smoothing while keeping the same bandwidth. We assess the efficiency by looking at a better mitigation of the stimulated Brillouin scattering that, due to its dangerousness in hohlraums developed for inertial confinement fusion applications in the indirect drive scheme, serves as a witness instability.

Backward stimulated Brillouin scattering spatial gain with polarization, spatial, and temporal beam smoothing techniques

A recent study [Ruyer et al., Phys. Rev. E 107, 035208 (2023)] modeling the influence of a random phase plate on the backward stimulated Brillouin scattering growth is here supplemented with the effect of temporal and polarization smoothing. Our analytical predictions are validated by a large number of three dimensional Hera paraxial simulations for various beam smoothing techniques and relevant to most high energy laser facilities. Neglecting all non-linear effects apart from the pump depletion, we then reconstruct the system of differential equations that the backward stimulated Brillouin scattering convective amplification of a smoothed beam propagating in a non-homogeneous plasma satisfies. Its resolution is successfully confronted with our simulation data and prepares the accurate modeling, in a ray tracing scheme, of the effect of laser smoothing techniques on laser plasma instabilities.

Point design of octahedral spherical Hohlraum with HDC–CH capsule for a predictable inertial confinement fusion at/beyond ignition

Fusion ignition has been successfully achieved at the National Ignition Facility, but the main obstacles of low-mode asymmetries, laser-plasma instabilities (LPIs), and hydrodynamic instabilities (HIs) still remain in the path toward a predictable yield for fusion ignition, especially at high gain. A recently proposed octahedral spherical Hohlraum, i.e., a spherical Hohlraum with six laser entrance holes of octahedral symmetry [Lan et al., Phys. Plasmas 21, 010704 (2014); Phys. Rev. Lett. 127, 245001 (2021)], was demonstrated to have the advantages of a naturally high radiation symmetry without any symmetry tuning technology and a high energy coupling efficiency from the drive laser to the capsule hotspot. In addition, a novel HDC–CH (here, HDC and CH refer to high density carbon and glow discharge plastic, respectively) capsule design was proposed to have the advantages in both low LPIs and low HIs by using two different ablators [Qiao and Lan, Phys. Rev. Lett. 126, 185001 (2021)]. For the first time, here we proposed a point design target composed of an octahedral spherical Hohlraum and an HDC–CH capsule to suppress the above-mentioned obstacles and presented the 2D simulation of the effect of symmetry and hydrodynamic instabilities on implosion performances. Our work provides a novel target design for a more predictable fusion ignition in experiment.

Control of laser-plasma instabilities by non-collinear polychromatic light

Normal broadband lasers with collinear polychromatic components have immense potential for mitigating laser plasma instabilities (LPIs). However, the projection complexity of collinear polychromatic light (CPL) is a significant challenge owing to the demand for a large bandwidth and beamlet number. Here, we propose a theoretical LPI model and optical design for non-collinear polychromatic light (NCPL), which has a small angle ∼4∘ and large frequency difference ∼1% between the double-color beamlets. LPI models of the NCPL demonstrate a decoupling threshold for the shared daughter waves under a multibeam configuration. Compared with the CPL, the wavevector couplings of LPIs are further reduced by the introduced angle. Therefore, both the growth rate and saturation level of LPIs are greatly mitigated by using the NCPL. The two- and three-dimensional simulation results indicate that the NCPL reduces the absolute and convective decoupling thresholds of the CPL and is sufficient to effectively mitigate the reflectivity, hot-electron generation, and intensity of cross-beam energy transfer. An optical design for the efficient generation of ultraviolet NCPL has been presented based on the unsaturated optical parametric amplification and non-collinear sum-frequency generation.

Investigation on the origin of hot electrons in laser plasma interaction at shock ignition intensities

Shock Ignition is a two-step scheme to reach Inertial Confinement Fusion, where the precompressed fuel capsule is ignited by a strong shock driven by a laser pulse at an intensity in the order of 10^{16} W/cm^2. In this report we describe the results of an experiment carried out at PALS laser facility designed to investigate the origin of hot electrons in laser-plasma interaction at intensities and plasma temperatures expected for Shock Ignition. A detailed time- and spectrally-resolved characterization of Stimulated Raman Scattering and Two Plasmon Decay instabilities, as well as of the generated hot electrons, suggest that Stimulated Raman Scattering is the dominant source of hot electrons via the damping of daughter plasma waves. The temperature dependence of laser plasma instabilities was also investigated, enabled by the use of different ablator materials, suggesting that Two Plasmon Decay is damped at earlier times for higher plasma temperatures, accompanied by an earlier ignition of SRS. The identification of the predominant hot electron source and the effect of plasma temperature on laser plasma interaction, here investigated, are extremely useful for developing the mitigation strategies for reducing the impact of hot electrons on the fuel ignition.

Full aperture backscatter diagnostics for characterization of laser plasma instabilities at the extreme light infrastructure (ELI) beamlines.

We report on the commissioning of a full aperture backscatter diagnostics station for the kilojoule, nanosecond high repetition rate L4n laser operating at a wavelength of 527nm at the Extreme Light Infrastructure (ELI) - Beamlines, Dolni Brezany, Czech Republic. Light scattered back from laser-plasma interaction into the cone of the final focusing lens is captured and split into different channels to measure the signatures of laser plasma instabilities from stimulated Brillouin scattering, stimulated Raman scattering, and two plasmon decay with respect to back scattered energy, its spectrum, and its temporal profile. The performance was confirmed in a commissioning experiment with more than 800 shots at laser intensities ranging from 0.5 × 1013 to 1.1 × 1015Wcm-2. These diagnostics are permanently installed at ELI Beamlines, and can be used to understand the details of laser-plasma interactions in experiments with kJ and 527nm light. The large number of shots that can be collected in an experimental campaign will allow us to study the details of the laser-plasma interaction with a high level of confidence.

Evolution and hot electron generation of laser–plasma instabilities in direct-drive inertial confinement fusion

A series of 2D in-plane plane wave particle-in-cell simulations find distinctive paths of laser-plasma instability evolution in OMEGA-scale implosions, depending on the initial electron temperature. At low temperatures, two-plasmon decay (TPD) dominates in both initial growth and the steady state. At high temperatures, the initial dominant modes switch to stimulated Raman scattering, but TPD still dominates a steady state characterized by cavitation and Langmuir turbulence. A hot electron scaling is also obtained from the simulations that, when combined with laser/plasma conditions from hydro simulations, can predict hot electron generation in implosions that do not employ smoothing-by-spectral-dispersion (SSD). It also shows that under the same laser/plasma conditions, SSD can reduce hot electron generation.