A 1D, steady-state model for Brillouin and Raman backscatter from an inhomogeneous plasma is presented. The daughter plasma waves are treated in the strong damping limit, and have amplitudes given by the (linear) kinetic response to the ponderomotive drive. Pump depletion, inverse-bremsstrahlung damping, bremsstrahlung emission, Thomson scattering off density fluctuations, and whole-beam focusing are included. The numerical code DEPLETE, which implements this model, is described. The model is compared with traditional linear gain calculations, as well as "plane-wave" simulations with the paraxial propagation code pF3D. Comparisons with Brillouin-scattering experiments at the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, p. 495 (1997)] show that laser speckles greatly enhance the reflectivity over the DEPLETE results. An approximate upper bound on this enhancement, motivated by phase conjugation, is given by doubling the DEPLETE coupling coefficient. Analysis with DEPLETE of an ignition design for the National Ignition Facility (NIF) [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, p. 755 (1994)], with a peak radiation temperature of 285 eV, shows encouragingly low reflectivity. Re-absorption of Raman light is seen to be significant in this design.
The Thomson scattering spectra by an electron moving in the laser-magnetic resonance acceleration regime are computed numerically and analytically. The dependence of fundamental frequency on the laser intensity and magnetic resonance parameter is examined carefully. By calculating the emission of a single electron in a circularly polarized plane-wave laser field and constant external magnetic field, the scale invariance of the radiation spectra is evident in terms of harmonic orders. The scaling law of backscattered spectra are exhibited remarkably for the laser intensity as well for the initi…
Stimulated Raman backscattering (RBS) of intense laser radiation confined by a single-mode plasma channel with a radial variation of plasma frequency greater than a homogeneous-plasma RBS bandwidth is characterized by a strong transverse localization of resonantly-driven electron plasma waves (EPW). The EPW localization reduces the peak growth rate of RBS and increases the amplification bandwidth. The continuum of non-bound modes of backscattered radiation shrinks the transverse field profile in a channel and increases the RBS growth rate. Solution of the initial-value problem shows that an el…
Raman backscattered radiation of intense laser pulses in plasma is investigated for a wide range of intensities relevant to laser wakefield acceleration. The weakly nonlinear dispersion relation for Raman backscattering predicts an intensity and density dependent frequency shift that is opposite to that suggested by a simple relativistic consideration. This observation has been benchmarked against experimental results, providing a novel diagnostic for laser-plasma interactions.
We show experimentally that XUV radiation is produced when a laser pulse is Thomson backscattered from sheets of relativistic electrons which are formed at the rear-surface of a foil irradiated on its front side by a high-intensity laser. An all-optical setup is realized using the Jena Titanium:Sapphire TW laser system (JETI). The main pulse is split into two pulses: one to accelerate electrons from thin aluminum foil targets to energies of the order of some MeV and the other, counterpropagating probe pulse is Thomson-backscattered off these electrons when they exit the target rear side. The p…
We develop a statistical theory of stimulated Brillouin backscatter (BSBS) of a spatially and temporally partially incoherent laser beam for laser fusion relevant plasma. We find a new collective regime of BSBS (CBSBS) with intensity threshold controlled by diffraction, an insensitive function of the laser coherence time, $T_c$, once light travel time during $T_c$ exceeds a laser speckle length. The BSBS spatial gain rate is approximately the sum of that due to CBSBS, and a part which is independent of diffraction and varies linearly with $T_c$. We find that the bandwidth of KrF-laser-based fu…
A new parameter regime of laser wakefield acceleration driven by sub-petawatt femotsecond lasers is proposed, which enables the generation of relativistic electron mirrors further accelerated by the plasma wave. Integrated particle-in-cell simulation including the mirror formation and Thomson scattering demonstrates that efficient coherent backscattering up to keV photon energy can be obtained with moderate driver laser intensities and high density gas targets.
Stimulated Raman backscatter (SRS) is used as a remote sensor to quantify the instantaneous laser power after transfer from outer to inner cones that cross in a National Ignition Facility (NIF) gas-filled hohlraum plasma. By matching SRS between a shot reducing outer vs a shot reducing inner power we infer that ~half of the incident outer-cone power is transferred to inner cones, for the specific time and wavelength configuration studied. This is the first instantaneous non-disruptive measure of power transfer in an indirect drive NIF experiment using optical measurements.
We develop the statistical theory of the stimulated Brillouin backscatter (BSBS) instability of a spatially and temporally partially incoherent laser beam for laser fusion relevant plasma. We find a new regime of BSBS which has a much larger threshold than the classical threshold of a coherent beam in long-scale-length laser fusion plasma. Instability is collective because it does not depend on the dynamics of isolated speckles of laser intensity, but rather depends on averaged beam intensity. We identify convective and absolute instability regimes. Well above the incoherent threshold the cohe…
When a laser passes through underdense plasmas, Raman and Brillouin Backscattering can reflect a substantial portion of the incident laser energy. This is a major loss mechanism, for example, in employing lasers in inertial confinement fusion. However, by slow rotation of the incident linear polarization, the overall reflectivity can be reduced significantly. Particle in cell simulations show that, for parameters similar to those of indirect drive fusion experiments, polarization rotation reduces the reflectivity by a factor of $5$. A general, fluid-model based, analytical estimation for the r…
Understanding magnetized laser-plasma interactions is important for controlling magneto-inertial fusion experiments and developing magnetically assisted radiation and particle sources. In the long-pulse regime, interactions are dominated by coherent three-wave interactions, whose nonlinear coupling coefficients become known only recently when waves propagate at oblique angles with the magnetic field. In this paper, backscattering coupling coefficients predicted by warm-fluid theory is benchmarked using particle-in-cell simulations in one spatial dimension, and excellent agreements are found fo…
On the relationship between the gain of Stimulated Raman Backscatter of a short-pulse laser in a plasma and the Pierce parameter for XFELs
State Key Laboratory of Nuclear Physics and Technology, and Key Laboratory of HEDP of the Ministry of Education, CAPT, School of Physics, Peking University（北京大学物理学院）；Beijing Laser Acceleration Innovation Center（北京激光创新加速中心）；Department of Physics and Astronomy, University of California, Los Angeles（加州大学洛杉矶分校物理与天文学系）；Department of Electrical and Computer Engineering, University of California, Los Angeles（加州大学洛杉矶分校电气与计算机工程系）
A number of theoretical calculations have studied the effect of radiation reaction forces on radiation distributions in strong field counter-propagating electron beam-laser interactions, but could these effects - including quantum corrections - be observed in interactions with realistic bunches and focusing fields, as is hoped in a number of soon to be proposed experiments? We present numerical calculations of the angularly resolved radiation spectrum from an electron bunch with parameters similar to those produced in laser wakefield acceleration experiments, interacting with an intense, ultra…
A new diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates is demonstrated to identify the presence of the high energy component beyond the CR-39's detection threshold limit. On irradiation of the CR-39 detector unit with a 25 MeV per nucleon He ion beam from conventional rf-accelerators, a large number of etch pits having elliptical opening shapes are observed on the rear surface of the CR-39. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This ion detection method …
Recent experimental results from the Trident laser confirm the importance of kinetic effects in determining laser reflectivities at high intensities. Examples observed include scattering from low frequency electron acoustic waves (EAWs), and the first few stages of a cascade towards turbulence through the Langmuir decay instability. Interpretive and predictive computational capability in this area is assisted by the development of Vlasov codes, which offer high velocity space resolution in high energy regions of particle phase space, and do not require analytical pre-processing of the fundamen…
A novel scheme is proposed to generate uniform relativistic electron layers for coherent Thomson backscattering. A few-cycle laser pulse is used to produce the electron layer from an ultra-thin solid foil. The key element of the new scheme is an additional foil that reflects the drive laser pulse, but lets the electrons pass almost unperturbed. It is shown by analytic theory and by 2D-PIC simulation that the electrons, after interacting with both drive and reflected laser pulse, form a very uniform flyer freely cruising with high relativistic gamma-factor exactly in drive laser direction (no t…
Propagation of intense laser beams is crucial for inertial confinement fusion, which requires precise beam control to achieve the compression and heating necessary to ignite the fusion reaction. The National Ignition Facility (NIF), where fusion will be attempted, is now under construction. Control of intense beam propagation may be ruined by laser beam self-focusing. We have identified the maximum laser beam power that can propagate through fusion plasma without significant self-focusing and have found excellent agreement with recent experimental data, and suggest a way to increase that maxim…
A proposal for a novel source of isolated attosecond XUV -- soft X-ray pulses with a well controlled carrier-envelope phase difference (CEP) is presented in the framework of nonlinear Thomson-backscattering. Based on the analytic solution of the Newton-Lorentz equations, the motion of a relativistic electron is calculated explicitly, for head-on collision with an intense fs laser pulse. By using the received formulae, the collective spectrum and the corresponding temporal shape of the radiation emitted by a mono-energetic electron bunch can be easily computed. For certain suitable and realisti…
We consider backscattering of laser pulses in strongly-magnetized plasma mediated by kinetic magnetohydrodynamic waves. Magnetized low-frequency scattering, which can occur when the external magnetic field is neither perpendicular nor parallel to the laser propagation direction, provides an instability growth rate higher than Raman scattering and a frequency downshift comparable to Brillouin scattering. In addition to the high growth rate, which allows smaller plasmas, and the 0.1-2\% frequency downshift, which permits a wide range of pump sources, MLF scattering is an ideal candidate for ampl…
ELI ALPS, ELI-HU Non-Profit Ltd.（ELI ALPS，ELI-HU非营利有限公司）；HUN-REN Wigner Research Centre for Physics（匈牙利科学院维格纳物理研究中心）；Department of Optics and Quantum Electronics, University of Szeged（塞格德大学光学与量子电子学系）；Cyclotron Institute, Texas A&M University（德克萨斯农工大学回旋加速器研究所）；Laboratori Nazionali del Sud, INFN（意大利国家核物理研究所南部分实验室）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）；Department of Physics and Technology, University of Bergen（卑尔根大学物理与技术系）；National Laser-Initiated Transmutation Laboratory, University of Szeged（塞格德大学国家激光诱导嬗变实验室）；King's College London（伦敦国王学院）；Csernai Consult Bergen（Csernai咨询（卑尔根））；Frankfurt Institute for Advanced Studies（法兰克福高等研究院）
The range of stimulated Raman scattering (SRS) frequencies covers a domain which at the low end abuts half the laser frequency, omega_0 / 2, according to the simplest SRS theories, corresponding to scatter from electron densities near 1/4 critical. Experiments, on the other hand, clearly point to a frequency gap: SRS is not observed at frequencies close to and above omega_0 / 2, indicating a drastic disruption of scatter from Langmuir waves as electron densities approaches 1/4 critical from below. Several one-dimensional mechanisms, linear and nonlinear, have been proposed to explain this "Ram…
The advent of high-intensity pulsed laser technology enables the generation of extreme states of matter under conditions that are far from thermal equilibrium. This in turn could enable different approaches to generating energy from nuclear fusion. Relaxing the equilibrium requirement could widen the range of isotopes used in fusion fuels permitting cleaner and less hazardous reactions that do not produce high energy neutrons. Here we propose and implement a means to drive fusion reactions between protons and boron-11 nuclei, by colliding a laser-accelerated proton beam with a laser-generated …
We propose a laser-driven near-solid density nano-structured micro-reactor concept operating with mixed nuclear fusion fuels. The micro-reactor is capable of making use of a range of neutronic and aneutronic fuels. Its core parts consists of an embedded nanoscopic nuclear fuel based laser-driven nano-accelerator that is capable of producing non-thermal fuel distributions almost instantly.
Compared with the deuterium tritium (DT) fusion, the environmentally clean fusion of protons with 11B is extremely difficult. When instead of nanosecond laser pulses for thermal-ablating driven ignition, picosecond pulses are used, a drastic change by nonlinearity results in ultrahigh acceleration of plasma blocks. This radically changes to economic boron fusion by a measured new avalanche ignition.
We comment on Marvel Fusion's proposal to use ultra-short, intensive laser pulses impinging on nanostructured targets for the production of hot ions, with the ultimate aim of energy production through the p-11B fusion reaction. We show how a minimum requirement on the line density of the heated region arises also for such schemes aiming at ignition or just beam-energy amplification, which already for the D-T reaction are prohibitive if no pre-compression of the target is foreseen. We conclude that advanced ultra-short laser pulses can be of use for fusion applications only if the fusion reacti…
Plasmas may be used as gain media for amplifying intense lasers, and external magnetic fields may be applied to improve the performance. For mid-infrared lasers, the requisite magnetic field is on megagauss scale, which can already be provided by current technologies. Designing the laser amplifier requires knowing the magnetized three-wave coupling coefficient, which is mapped out systematically in this paper. By numerically evaluating its formula, we demonstrate how the coupling depends on angle of wave propagation, laser polarization, magnetic field strength, plasma temperature, and plasma d…
Fast ignition is an alternative concept of laser fusion in which the task of compressing the fusion pellet to supersolid densities is accomplished by the conventional high energy nanosecond glass lasers and the task of igniting the compressed pellet is given to a high intensity, moderate energy pico second source which can set the pellet ablaze (with DT fusion reactions) by creating an adequate size hot spot in it. In this letter, we present a conceptual method by which energy from carbon dioxide ($ CO_2 $) laser could be coupled to heat up ions produced in situ in the plasma, which in turn pr…
For developing a laser boron fusion reactor driven by picosecond laser pulses of more than 30 petawatts power, advances are reported about computations for the plasma block generation by the dielectric explosion of the interaction. Further results are about the direct drive ignition mechanism by a single laser pulse without the problems of spherical irradiation. For the sufficiently large stopping lengths of the generated alpha particles in the plasma results from other projects can be used.
Driver at 10 MJ and 1 shot/30min for inertial confinement fusion at high gain: efficient, compact, low-cost, low laser-plasma instabilities, beam-color selectable from 2 omega/3 omega/4 omega, applicable to multiple laser fusion schemes
We report a laser-driven neutron source with high yield ($>10^8$/J) and high peak flux ($>10^{25}$/cm$^2$/s) derived from high-temperature deuteron-deuteron fusion reactions. The neutron yield and the fusion temperature ($\sim 200$ keV) in our experiment are respectively two orders of magnitude and one order of magnitude higher than any previous laser-induced D-D fusion reaction. The high-temperature plasma is generated from thin ($\sim 2\,μ$m), solid-density deuterium targets, produced by a cryogenic jet, irradiated by a 140 fs, 130 J petawatt laser with an F/3 off-axis parabola and a plasma …
In contrast to the broad stream of sustainable developments on fusion energy, new aspects are developed now by applying ultra-short, ultra-powerful laser pulses in a plasma-block ignition scheme by avoiding the well known difficulties of thermal-pressure instabilities and losses through using electro-dynamic non-thermal energy conversion. A further advantage is given by the new 10 kilo-Tesla magnetic fields for fusion of uncompressed proton-boron fuel which avoids problems of dangerous nuclear radiation.
Fusion energy from reacting hydrogen (protons) with the boron isotope 11 (HB11) resulting in three stable helium nuclei, is without problem of nuclear radiation in contrast to DT fusion. But the HB11 reaction driven by nanosecond laser pulses with thermal compression and ignition by lasers is extremely difficult. This changed radically when irradiation with picosecond laser pulses produces a non-thermal plasma block ignition with ultrahigh acceleration. This uses the nonlinear (ponderomotive) force to surprisingly resulting in same thresholds as DT fusion even under pessimistic assumption of b…
The declared aim of Marvel Fusion is the realization of a reactor based on the aneutronic fusion of proton and boron-11 nuclei in the near future, making use of latest-day laser technology and nano-structured materials. The aim of the preprint quoted above is to demonstrate the feasibility of fusion energy gain from the irradiation of an initially uncompressed target consisting of an array of nano-wires, by a femto-second laser. This proposal is in apparent contrast to text-book wisdom, which postulates - even for the fast-ignitor concept, and a DT fuel mix - a target density about 1000 times …
In this paper, a six-cylinder-port hohlraum is proposed to provide high symmetry flux on capsule. It is designed to ignite a capsule with 1.2 mm radius in indirect-drive inertial confinement fusion (ICF) . Flux symmetry and laser energy are calculated by using three dimensional view factor method and laser energy balance in hohlraums. Plasma conditions are analyzed based on the two dimensional radiation-hydrodynamic simulations. There is no Ylm (l<=4) asymmetry in the six-cylinder-port hohlraum when the influences of laser entrance holes (LEHs) and laser spots cancel each other out with suitab…
In the present Letter, we investigate a spherical hohlraums with octahedral six laser entrance holes (LEHs) for inertial fusion, which has advantages over the conventional hohlraums of cylindrical geometry since it contains only one cone at each LEH and the problems caused by the beam overlap and crossed-beam energy transfer can be eliminated and the backscattering can be reduced. In particular, our study indicates that at a specific hohlraum-to-capsule radius ratio, i.e., the golden ratio, the flux asymmetry on capsule can be significantly reduced. From our study, this golden octahedral hohlr…
An investigation of the possible inflation of stimulated Brillouin backscattering (SBS) due to ion kinetic effects is presented using electromagnetic particle simulations and integrations of three-wave coupled-mode equations with linear and nonlinear models of the nonlinear ion physics. Electrostatic simulations of linear ion Landau damping in an ion acoustic wave, nonlinear reduction of damping due to ion trapping, and nonlinear frequency shifts due to ion trapping establish a baseline for modeling the electromagnetic SBS simulations. Systematic scans of the laser intensity have been undertak…
A three dimensional molecular dynamic code is used to study the generation of fusion neutrons from Coulomb explosion of Deuterium clusters driven by intense near infra-red (NIR) laser ($λ=800nm$) of femtosecond pulse duration ($τ=50 fs$) under beam-target interaction scheme. We have considered various clusters of average sizes ($\langle R_0\rangle$=80,140,200Å) which are irradiated by a laser of peak spatial-temporal intensity of 1$\times10^{18} W/cm^{2}$. The effects of cluster size and spatial laser intensity distribution on ion energies due to the Coulomb explosion of the cluster are includ…
Extreme laser pulses driving non-equilibrium processes in high density plasmas permit an increase of the fusion of hydrogen with the boron isotope 11 by nine orders of magnitude of the energy gains above the classical values. This is the result of initiating the reaction by non-thermal ultrahigh acceleration of plasma blocks by the nonlinear (ponderomotive) force of the laser field, in addition to the avalanche reaction that has now been experimentally and theoretically manifested. The design of a very compact fusion power reactor is scheduled to produce then environmentally fully clean and in…
The fission-fusion reaction mechanism was proposed in order to generate extremely neutron-rich nuclei close to the waiting point N = 126 of the rapid neutron capture nucleosynthesis process (r-process). The production of such isotopes and the measurement of their nuclear properties would fundamentally help to increase the understanding of the nucleosynthesis of the heaviest elements in the universe. Major prerequisite for the realization of this new reaction scheme is the development of laser-based acceleration of ultra-dense heavy ion bunches in the mass range of A = 200 and above. In this pa…
We discuss scaling laws of fusion yields generated by laser-plasma interactions. The yields are found to scale as a function of the laser power. The origin of the scaling law in the laser driven fusion yield is derived in terms of hydrodynamic scaling. We point out that the scaling properties can be attributed to the laser power dependence of three terms: the reaction rate, the density of the plasma and the projected range of the plasma particle in the target medium. The resulting scaling relations have a predictive power that enables estimating the fusion yield for a nuclear reaction which ha…
In the present paper we introduce a new accelerator concept for ions. The accelerator is nano-structured and can consist of a range of materials. It is capable of generating large ionic currents at moderate ion energies. The nano-structures can be tailored towards the accelerator thus being capable of driving ion beams with very high efficiency. The accelerator is powered by laser arrays consisting of many repetitive and efficient lasers in the $100 \, \text{J}$ range with ultra-short intense laser pulses. Combining nano-structures and the proposed ultra-short pulse lasers can lead to new leve…
The effects of laser-plasma interactions (LPI) on the dynamics of inertial confinement fusion hohlraums is investigated via a new approach that self-consistently couples reduced LPI models into radiation-hydrodynamics numerical codes. The interplay between hydrodynamics and LPI -- specifically stimulated Raman scatter (SRS) and crossed-beam energy transfer (CBET) -- mostly occurs via momentum and energy deposition into Langmuir and ion acoustic waves. This spatially redistributes energy coupling to the target, which affects the background plasma conditions and thus modifies laser propagation. …
Two different methods have been employed to determine the plasma temperature in a laser-cluster fusion experiment on the Texas Petawatt laser. In the first, the temperature was derived from time-of-flight data of deuterium ions ejected from exploding D2 or CD4 clusters. In the second, the temperature was measured from the ratio of the rates of two different nuclear fusion reactions occurring in the plasma at the same time: D(d, 3He)n and 3He(d, p)4He. The temperatures determined by these two methods agree well, which indicates that: i) The ion energy distribution is not significantly distorted…
The results of numerical and theoretical studies of the gain of direct-drive inertial confinement fusion (ICF) target, which includes a kinetic description of energy transfer by laser-accelerated fast electrons, are presented. The range of initial temperature of fast electrons and fraction of laser energy contained in these particles were chosen based on the results of recent experiments at the National Ignition Facility (NIF).The effect of 'wandering' of fast electrons is taken into account. It is due to a remoteness of the region of fast electron generation from the ablation surface of implo…
After the very long consideration of the ideal energy source by fusion of the protons of light hydrogen with the boron isotope 11 (boron fusion HB11) the very first two independent measurements of very high reaction gains by lasers basically opens a fundamental breakthrough. The non-thermal plasma block ignition with extremely high power laser pulses above petawatt of picosecond duration in combination with up to ten kilotesla magnetic fields for trapping has to be combined to use the measured high gains as proof of an avalanche reaction for an environmentally clean, low cost and lasting energ…
Two-dimensional simulations of ion beam driven fast ignition are presented. Ignition energies of protons with Maxwellian spectrum and carbon ions with quasimonoenergetic and Maxwellian energy distributions are evaluated. The effect of the coronal plasma surrounding the compressed deuterium-tritium is studied for three different fuel density distributions. It is found that quasi- monoenergetic ions have better coupling with the compressed deuterium-tritium and substantially lower ignition energies. Comparison of quasimonoenergetic carbon ions and relativistic electrons as ignitor beams shows si…
Comment to the paper J. Yan et al. Experimental confirmation of driving pressure boosting and smoothing for hybrid-drive inertial fusion at the 100-kJ laser facility [Nature Communications (2023) 14:5782]
本文评论指出，由于缺乏关键实验数据，J. Yan 等人关于混合驱动惯性聚变驱动压力提升与平滑的实验验证结论不可信。
