arXiv subjects

Yuqiu Gu

Publications and source records attributed to Yuqiu Gu.

17 recordsLinked to original sources

arXiv2026

On the degradation of hot spot performance due to mid-to-high-mode hydrodynamic instabilities

In an ignited design of inertial confinement fusion, the role of mid-to-high-mode hydrodynamic instabilities in degrading hot-spot performance, beyond reducing temperature, remains unclear. To address this, we propose an isobaric criterion to assess the isobaric assumption that forms the theoretical basis of the hot spot. The most dangerous mode l = 12 is determined through a balance between perturbation growth and ablation stabilization induced by thermal conduction. Thermal conduction outperforms convection when the Peclet number is much less than 1. Therefore, for mid-to-high modes, thermal conduction makes the hot spot isobaric before the outer mass inflow restores the lost heat. Consequently, neglecting thermal conduction overestimates pressure and underestimates volume. These results enhance our understanding of mid-to-high modes in degrading hot-spot performance, and suggest that thermal conduction losses may reduce performance even if perturbations are nearly stabilized by ablation.

physics.flu-dyn↗

arXiv2026

Tunable high-charge relativistic electron beams via direct laser acceleration in hohlraum-preheated foam targets

Direct laser acceleration (DLA) in near-critical-density (NCD) plasmas can efficiently generate high-charge relativistic electron beams, yet beam parameters depend critically on precise plasma state manipulation. Solid-ablation NCD plasmas evolve rapidly, posing severe controllability challenges. We produce NCD plasma via indirectly heating foam targets with ns laser driven hohlraum soft X-ray. Electrons are generated through irradiating the plasma with another picosecond laser. Tuning the laser pulse delay $\tau$ enables control of plasma profiles and beam parameters. Experiments show that when the foam is heated ($\tau$ = 6 ns, 9 ns), the beam exhibits $T \sim 13$ MeV effective temperature, $E_k \sim 80$ MeV cutoff energy, and hundreds of nC/sr charge for $E_k > 7.5$ MeV. These values are significantly higher than those from solid-foil ($T$ $\sim$ 2.7 MeV, $E_k$ $\sim$ 20 MeV, $Q$ $\sim$ 9 nC/sr) and cold-foam ($T$ $\sim$ 12 MeV, $E_k$ $\sim$ 50 MeV, $Q$ $\sim$ 5 nC/sr) interactions. At a longer delay of $\tau$ = 15 ns, the charge increases further while the temperature decreases, and at a shorter delay of $\tau$ = 3 ns, both temperature and charge are lower. 3D PIC simulations link these observations to the interplay between the microstructure of the cold foam and the evolving plasma density profile at different delay times, which together determine the beam charge, effective temperature, and divergence. The finding provides a routine to generate and tailor the relativistic electron beams, which is essential for designing laser-driven electron sources for high energy density physics and photonuclear reaction applications.

physics.plasm-ph↗

arXiv2026

Observation of stopping power reduction at strong ion-plasma coupling

Ion stopping in dense plasma is crucial for stellar evolution and fusion ignition. However, its behavior in the strong ion-plasma coupling regime beyond the linear limit has long remained elusive, due to formidable experimental challenges. Here we report the first experimental investigation of ion stopping at an unprecedented coupling parameter exceeding unity, achieved by sending laser-accelerated short-pulse and intense quasi-monoenergetic carbon ions ($\sim$583 keV/u, C$^{5+}$) into a uniform, long-lived, well-characterized dense plasma target ($T_e$ $\approx$ 17 eV, $n_e$ $\approx$ 4$\times$10$^{20}$ cm$^{-3}$). By simultaneously measuring ion energy loss and charge-state evolution, we eliminated key experimental ambiguities arising from charge-state determination. Our results clearly show a reduction in stopping power compared with predictions from standard linear dielectric response or binary collision models, and they agree well with the hybrid calculation of molecular dynamics with quantum corrections. The importance of nonlinear screening effects arising from many-body interactions and quantum effects due to the wave nature of electrons was demonstrated at strong coupling. This work establishes a definitive high-fidelity experimental benchmark for collisional dynamics in the strong-coupling regime. It offers critical insight for accurate modeling of energy transport in inertial confinement fusion and astrophysical plasmas.

physics.plasm-ph↗

arXiv2026

Frequency downshifting stair for ultra-intense femtosecond lasers through a plasma-photonics structure

Wavelength-tunable ultra-intense femtosecond lasers may enable breakthroughs in diverse areas of science spanning attosecond science, particle acceleration and beyond. Conventional crystal-based methods are limited by gain bandwidth and damage thresholds, which restrict their wavelength tunability. Plasma-based frequency conversion, unconstrained by material damage, offers a promising alternative. Here, a novel scheme named Frequency Downshifting Stair (FDS) based on plasma bubble filling control is presented. The FDS enables arbitrary frequency down-conversion of ultra-intense femtosecond pulses and yields chirp-free laser pulses. It can achieve near-100% photon conversion efficiency, approaching the physical limit. This is attributed to the linear control by the FDS of laser chirp evolution during the photon deceleration in the plasma wake bubble. For a laser pulse with an arbitrary wavelength {\lambda}_0 (e.g., {\lambda}_0=800nm), proof-of-concept PIC simulations demonstrate that a single-stage FDS enables continuous wavelength tuning from {\lambda}_0 to {2{\lambda}}_0 (800-1600nm). Moreover, a three-stage cascaded FDS achieves more than tenfold frequency (10{\lambda}_0) downshifting to a central wavelength of 8.5{\mu}m. The FDS scheme thus provides a universal pathway for generating high-energy, few-cycle pulses across the broad infrared regime, offering a powerful new tool for wavelength-dependent ultrafast science.

physics.optics↗

arXiv2026

A theoretical model for quantifying the imprinting sensitivity of direct-drive inertial confinement fusion implosions

To quantify the sensitivity of diverse implosion designs to laser imprinting, we developed an equivalent perturbation model that maps laser imprinting as the initial target surface perturbation. By incorporating imperfections in target fabrication and thermal smoothing in the plasma, the model shows a reduced implosion sensitivity to laser imprinting, extending the analysis beyond geometric irradiation. The imprinting sensitivity threshold is defined as $\frac{\delta h_{\text{proxy}}}{\delta h_{\text{tar}}(0)} = 0.1$, where $\delta h_{\text{proxy}}$ is the imprinting amplitude and $\delta h_{\text{tar}}(0)$ is the initial target perturbation amplitude. Radiation-hydrodynamics simulations confirm that when $\frac{\delta h_{\text{proxy}}}{\delta h_{\text{tar}(0)}} \leq 0.1$, variations in nonlinear onset time and adiabat remain within 12\% of that with $\delta h_{\text{tar}}(0)$ alone. Moreover, the imprinting sensitivity is supported by OMEGA experiments. Overall, for linear perturbations of medium-to-high modes in direct-drive, the model enhances our physical understanding of how laser and target perturbations evolve and serves as a simplified tool to optimize implosion performance.

physics.plasm-ph↗

arXiv2025

Efficiently Laser Driven Terahertz Surface Plasmon Polaritons on Long Metal Wire

We experimentally demonstrate a novel scheme for efficiently generating intense terahertz (THz) surface plasmon polaritons (SPPs) on a sub-wavelength-diameter meter-long metal wire. Driven by a subrelativistic femtosecond laser (a0=0.3, 3 mJ) focused at the wire's midpoint, single-cycle ten-megawatt THz SPPs are excited and propagating bidirectionally along it over 25 cm. The measured laser-to-SPPs energy conversion efficiency is reaching up to ~2.4%, which is the highest value at present. It is proved that the THz SPPs are excited by coherent transition radiation of the subrelativistic laser produced escaping electrons. Particle-in-cell together with CST simulations confirm the experimental observations. Our scheme of using readily available subrelativistic laser should thus be useful to applications requiring terawatt level single-cycle THz SPPs.

physics.optics↗

arXiv2024

Structure of weakly collisional shock waves of multicomponent plasmas inside hohlraums of indirect inertial confinement fusions

In laser-driven indirect inertial confinement fusion (ICF), a hohlraum--a cavity constructed from high-Z materials--serves the purpose of converting laser energy into thermal x-ray energy. This process involves the interaction of low-density ablated plasmas, which can give rise to weakly collisional shock waves characterized by a Knudsen number $K_n$ on the order of 1. The Knudsen number serves as a metric for assessing the relative importance of collisional interactions. Preliminary experimental investigations and computational simulations have demonstrated that the kinetic effects associated with weakly collisional shock waves significantly impact the efficiency of the implosion process. Therefore, a comprehensive understanding of the physics underlying weakly collisional shock waves is essential. This research aims to explore the formation and fundamental structural properties of weakly collisional shock waves within a hohlraum, as well as the phenomena of ion mixing and ion separation in multicomponent plasmas. Weakly collisional shocks occupy a transition regime between collisional shock waves ($K_n \ll 1$) and collisionless shock waves ($K_n \gg 1$), thereby exhibiting both kinetic effects and hydrodynamic behavior. These shock waves are primarily governed by an electrostatic field, which facilitates significant electrostatic sheath acceleration and ion reflection acceleration. The differentiation of ions occurs due to the varying charge-to-mass ratios of different ion species in the presence of electrostatic field, resulting in the separation of ion densities, velocities, temperatures and concentrations. The presence of weakly collisional shock waves within the hohlraum is expected to affect the transition of laser energy and the overall efficiency of the implosion process.

physics.plasm-ph↗

arXiv2024

First Proof of Principle Experiment for Muon Production with Ultrashort High Intensity Laser

Muons, which play a crucial role in both fundamental and applied physics, have traditionally been generated through proton accelerators or from cosmic rays. With the advent of ultra-short high-intensity lasers capable of accelerating electrons to GeV levels, it has become possible to generate muons in laser laboratories. In this work, we show the first proof of principle experiment for novel muon production with an ultra-short, high-intensity laser device through GeV electron beam bombardment on a lead converter target. The muon physical signal is confirmed by measuring its lifetime which is the first clear demonstration of laser-produced muons. Geant4 simulations were employed to investigate the photo-production, electro-production, and Bethe-Heitler processes response for muon generation and their subsequent detection. The results show that the dominant contributions of muons are attributed to the photo-production/electro-production and a significant yield of muons up to 0.01 $\mu$/$e^-$ out of the converter target could be achieved. This laser muon source features compact, ultra-short pulse and high flux. Moreover, its implementation in a small laser laboratory is relatively straightforward, significantly reducing the barriers to entry for research in areas such as muonic X-ray elemental analysis, muon spin spectroscopy and so on.

physics.acc-ph↗

arXiv2023

Charge equilibration of Laser-accelerated Carbon Ions in Foam Target

The charge equilibration of laser-accelerated carbon ion beams in 2 mg/cm3 foam target was investigated experimentally. The ions were generated through target normal sheath acceleration mechanism in laser-foil interaction scheme. This allows to get the equilibrium charge state in wide energy range near Bragg peak within a single shot. By using foam, the charge equilibration measurement in density regime between gas and solid state was firstly reached out experimentally. It was found that the theoretical predictions with tabulated cross section data for gas target greatly underestimated the charge states. The experimental data are in close agreement with both semi-empirical formula as well as rate equation predictions based on ion-solid interactions. The important role of target density effects that increase the ionization probability and decrease the electron capture probability through frequent multi-collisions in foam are demonstrated. The double electron processes are shown to have little influence on the average charge states. The findings are essential for high energy density physics research where the foams are widely used, and have impacts on a broad range of applications in medical, biological and material fields. The method also provides a new approach to investigate the interaction mechanism of swift heavy ions in matter by taking advantage of the laser-accelerated short-pulse wide-energy range ions.

physics.atom-ph↗

arXiv2023

Efficient production of nuclear isomer $^{93m}$Mo with laser-accelerated proton beam and an astrophysical implication on $^{92m}$Mo production

Nuclear isomers play a key role in the creation of the elements in the universe and have a number of fascinating potential applications related to the controlled release of nuclear energy on demand. Particularly, $^{93m}$Mo isomer is a good candidate for studying the depletion of nuclear isomer via nuclear excitation by electron capture. For such purposes, efficient approach for $^{93m}$Mo production needs to be explored. In the present work, we demonstrate experimentally an efficient production of $^{93m}$Mo through $^{93}$Nb(p, n) reaction induced by intense laser pulse. When a ps-duration, 100-J laser pulse is employed, the $^{93m}$Mo isomer at 2425 keV (21/2$^+$, $T_{1/2}$ = 6.85 h) are generated with a high yield of $1.8\times10^6$ particles/shot. The resulting peak efficiency is expected to be $10^{17}$ particles/s, which is at least five orders of magnitudes higher than using classical proton accelerator. The effects of production and destruction of $^{93m}$Mo on the controversial astrophysical p-isotope $^{92}$Mo are studied. It is found that the $^{93}$Nb(p, n)-$^{93m}$Mo reaction is an important production path for ^{93m}Mo seed nucleus, and the influence of ^{93m}Mo-^{92}Mo reaction flow on ^{92}Mo production cannot be ignored. In addition, we propose to directly measure the astrophysical rate of (p, n) reaction using laser-induced proton beam since the latter one fits the Maxwell-Boltzmann distribution well. We conclude that laser-induced proton beam opens a new path to produce nuclear isomers with high peak efficiency towards the understanding of p-nuclei nucleosythesis.

nucl-ex↗

arXiv2023

Energy loss enhancement of very intense proton beams in dense matter due to the beam-density effect

Thoroughly understanding the transport and energy loss of intense ion beams in dense matter is essential for high-energy-density physics and inertial confinement fusion. Here, we report a stopping power experiment with a high-intensity laser-driven proton beam in cold, dense matter. The measured energy loss is one order of magnitude higher than the expectation of individual particle stopping models. We attribute this finding to the proximity of beam ions to each other, which is usually insignificant for relatively-low-current beams from classical accelerators. The ionization of the cold target by the intense ion beam is important for the stopping power calculation and has been considered using proper ionization cross section data. Final theoretical values agree well with the experimental results. Additionally, we extend the stopping power calculation for intense ion beams to plasma scenario based on Ohm's law. Both the proximity- and the Ohmic effect can enhance the energy loss of intense beams in dense matter, which are also summarized as the beam-density effect. This finding is useful for the stopping power estimation of intense beams and significant to fast ignition fusion driven by intense ion beams.

physics.plasm-ph↗

arXiv2023

Diagnosis of Fast Electron Transport by Coherent Transition Radiation

Transport of fast electron in overdense plasmas is of key importance in high energy density physics. However, it is challenging to diagnose the fast electron transport in experiments. In this article, we study coherent transition radiation (CTR) generated by fast electrons on the back surface of the target by using 2D and 3D first-principle particle-in-cell (PIC) simulations. In our simulations, aluminium target of 2.7 g/cc is simulated in two different situations by using a newly developed high order implicit PIC code. Comparing realistic simulations containing collision and ionization effects, artificial simulations without taking collision and ionization effects into account significantly underestimate the energy loss of electron beam when transporting in the target, which fail to describe the complete characteristics of CTR produced by electron beam on the back surface of the target. Realistic simulations indicate the diameter of CTR increases when the thickness of the target is increased. This is attributed to synergetic energy losses of high flux fast electrons due to Ohm heatings and colliding drags, which appear quite significant even when the thickness of the solid target only differs by micrometers. Especially, when the diagnosing position is fixed, we find that the intensity distribution of the CTR is also a function of time, with the diameter increased with time. As the diameter of CTR is related to the speed of electrons passing through the back surface of the target, our finding may be used as a new tool to diagnose the electron energy spectra near the surface of solid density plasmas.

physics.plasm-ph↗

arXiv2022

Vortex $\gamma$ photon generation via spin-to-orbital angular momentum transfer in nonlinear Compton scattering

Vortex $\gamma$ photons with intrinsic orbital angular momenta (OAM) possess a wealth of applications in various fields, e.g.-strong-laser physics, nuclear physics, particle physics and astrophysics-yet their generation remains unsettled. In this work, we investigate the generation of vortex $\gamma$ photons via nonlinear Compton scattering of ultrarelativistic electrons in a circularly polarized laser pulse. We develop a quantum electrodynamics scattering theory that explicitly addresses the multiphoton absorption and the angular momentum transfer mechanism. In pulsed laser fields, we unveil the vortex phase structure of the scattering matrix element, discuss how the vortex phase could be transferred to the radiated photon, and derive the radiation rate of the vortex $\gamma$ photon. We numerically examine the energy spectra and beam characteristics of the radiation, while also investigating the influence of finite laser pulses on the angular momentum and energy distribution of the emitted vortex $\gamma$ photons.

hep-ph↗

arXiv2022

Target density effects on charge tansfer of laser-accelerated carbon ions in dense plasma

We report on charge state measurements of laser-accelerated carbon ions in the energy range of several MeV penetrating a dense partially ionized plasma. The plasma was generated by irradiation of a foam target with laser-induced hohlraum radiation in the soft X-ray regime. We used the tri-cellulose acetate (C$_{9}$H$_{16}$O$_{8}$) foam of 2 mg/cm$^{-3}$ density, and $1$-mm interaction length as target material. This kind of plasma is advantageous for high-precision measurements, due to good uniformity and long lifetime compared to the ion pulse length and the interaction duration. The plasma parameters were diagnosed to be T$_{e}$=17 eV and n$_{e}$=4 $\times$ 10$^{20}$ cm$^{-3}$. The average charge states passing through the plasma were observed to be higher than those predicted by the commonly-used semiempirical formula. Through solving the rate equations, we attribute the enhancement to the target density effects which will increase the ionization rates on one hand and reduce the electron capture rates on the other hand. In previsous measurement with partially ionized plasma from gas discharge and z-pinch to laser direct irradiation, no target density effects were ever demonstrated. For the first time, we were able to experimentally prove that target density effects start to play a significant role in plasma near the critical density of Nd-Glass laser radiation. The finding is important for heavy ion beam driven high energy density physics and fast ignitions.

physics.plasm-ph↗

arXiv2020

Region-of-interest micro-focus CT based on an all-optical inverse Compton scattering source

Micro-focus computed tomography (CT), enabling the reconstruction of hyperfine structure within objects, is a powerful nondestructive testing tool in many fields. Current X-ray sources for micro-focus CT are typically limited by their relatively low photon energy and low flux. An all-optical inverse Compton scattering source (AOCS) based on laser wakefield accelerator (LWFA) can generate intense quasi-monoenergetic X/gamma-ray pulses in the keV-MeV range with micron-level source size, and its potential application for micro-focus CT has become very attractive in recent years due to the fast pace progress made in LWFA. Here we report the first experimental demonstration of high-fidelity micro-focus CT using AOCS (~70 keV) by imaging and reconstructing a test object with complex inner structures. A region-of-interest (ROI) CT method is adopted to utilize the relatively small field-of-view (FOV) of AOCS to obtain high-resolution reconstruction. This demonstration of the ROI micro-focus CT based on AOCS is a key step for its application in the field of hyperfine nondestructive testing.

physics.app-ph↗

arXiv2020

Varied fusion reaction probability induced by ion stopping modification in laser-driven plasma with different temperature

The dynamics of nuclear reaction in plasma is a fundamental issue in many high energy density researches, such as the astrophysical reactions and the inertial confinement fusion. The effective reaction cross-sections and ion stopping power in plasma need to be taken into account to analyze the reactivity. In this research, we have experimentally investigated the from D-D reactions from interactions between deuteron beams and deuterated polystyrene (CD) plasma, driven by two laser pulses respectively. The neutron yields, plasma density and deuteron energy loss in plasma have been measured, and the plasma temperature and deuteron stopping power have been analyzed from simulations. It is shown that, compared with a cold target, the reaction probability in plasma conditions can be enhanced or suppressed, which is ascribed to the deuteron stopping power modifications in plasma. In hotter CD plasma, the energy loss of moderate energetic deuterons reduces, which leads to higher D-D reaction probability, while the contrary happens in colder plasma. This work provides new understanding of fusion reactions in plasma environment.

physics.plasm-ph↗

arXiv2020

Anomalous stopping of laser-accelerated intense proton beam in dense ionized matter

Ultrahigh-intensity lasers (10$^{18}$-10$^{22}$W/cm$^{2}$) have opened up new perspectives in many fields of research and application [1-5]. By irradiating a thin foil, an ultrahigh accelerating field (10$^{12}$ V/m) can be formed and multi-MeV ions with unprecedentedly high intensity (10$^{10}$A/cm$^2$) in short time scale ($\sim$ps) are produced [6-14]. Such beams provide new options in radiography [15], high-yield neutron sources [16], high-energy-density-matter generation [17], and ion fast ignition [18,19]. An accurate understanding of the nonlinear behavior of beam transport in matter is crucial for all these applications. We report here the first experimental evidence of anomalous stopping of a laser-generated high-current proton beam in well-characterized dense ionized matter. The observed stopping power is one order of magnitude higher than single-particle slowing-down theory predictions. We attribute this phenomenon to collective effects where the intense beam drives an decelerating electric field approaching 1GV/m in the dense ionized matter. This finding will have considerable impact on the future path to inertial fusion energy.

physics.plasm-ph↗