Nonlinear development of absolute Raman backscatter in ignition-scale direct-drive coronal conditions
Bibliographic record
Abstract
Motivated by a resurgence of interest in stimulated Raman scattering (SRS) in direct-drive inertial confinement fusion, we use Vlasov–Maxwell simulations to investigate the nonlinear saturation and associated hot electron production for absolute SRS backscatter near the quarter-critical density. The simulated plasma conditions are relevant to recent planar target experiments on the National Ignition Facility [Rosenberg et al., Phys. Rev. Lett. 120, 055001 (2018)]. It is discovered that wave–wave interactions dominate over kinetic effects in the nonlinear development of instability with clear signatures of the Langmuir decay instability (LDI) cascade and modulational instability of the primary electron plasma wave. Spectral broadening of the scattered light is shown to occur by two mechanisms: via a long wavelength modulation of the electron density—caused by the ponderomotive action of the near-turning point Airy-like structure of the SRS light—and by seeding of SRS by the LDI cascade. Hot electrons are produced at a level that is ≲1% of the incident laser energy by acceleration in the turbulent spectrum associated with the LDI cascade. Despite the high electron plasma temperature, collisions are shown to be important and have the effect of moderating the LDI cascade. The effect of collisions is shown to have a more dramatic effect on hot electron production than on the SRS reflectivity.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".