In the present paper, filamentous structure formation, associated turbulent spectrum, and density cavity formation phenomena have been investigated for low-β plasma $\left(\beta \ll m_e/m_i\right)$ applicable to the auroral region. A set of dimensionless equations governing the dynamics of three dimensionally propagating inertial Alfvén wave (3D-IAW) and perpendicularly propagating magnetosonic wave (PMSW) has been developed. Ponderomotive force due to 3D-IAW has been included in the dynamics of the PMSW. Numerical simulation has been performed to study the nonlinear coupling of these two waves. From the obtained results, we found that the field intensity localization takes place which may further lead to the additional dissipation/turbulence process for particle heating and acceleration in space plasma. The associated turbulent spectrum is obtained with scaling nearly k−4.28 at smaller scales (in the dissipation range). Relevance of the obtained results with the observations reported by various spacecrafts such as Hawkeye and Heos 2 has been discussed. Also, density fluctuations (depletion) of ∼0.10 n0 are calculated, which are consistent with the FAST spacecraft observation reported.

Shattercane is a problematic summer annual grass weed species in regions that produce grain sorghum. Three shattercane populations (DC8, GH4, and PL8) collected from sorghum fields from northwestern Kansas survived the field-use rate (52 g ha−1) of postemergence-applied imazamox. The main objectives of this research were to 1) confirm and characterize the level of resistance to imazamox in putative imazamox-resistant (IMI-R) shattercane populations, 2) investigate the underlying mechanism of resistance, and 3) determine the effectiveness of postemergence herbicides for controlling IMI-R populations. A previously known imazamox susceptible (SUS) shattercane population from Rooks County, KS, was used. All three putative populations exhibited a 4.1-fold to 6.0-fold resistance to imazamox compared with the SUS population. The ALS gene sequences from all IMI-R populations did not reveal any known target-site resistance mutations. A pretreatment with malathion, which inhibits cytochrome P450, followed by imazamox at various doses, reversed the resistance phenotype of the PL8 population. In a separate greenhouse study, postemergence treatments with nicosulfuron, quizalofop, clethodim, and glyphosate resulted in ≥96% injury to all IMI-R populations. The lack of known ALS target-site mutations and the reversal of resistance phenotype by malathion suggest the possibility of metabolism-based resistance to imazamox in PL8 shattercane population.

The growth response of annual sowthistle (Sonchus oleraceus L.) to anticipated future climate conditions is currently unknown, and thus two parallel studies were conducted dealing with glyphosate-resistant (GR) and glyphosate-susceptible (GS) biotypes of S. oleraceus. The glyphosate efficacy study was conducted using different doses of glyphosate (0 [control], 180, 360, 720 [recommended dose], and 1,440 g ae ha−1) at two different moisture levels (well-watered and water-stressed conditions). In the second study, the growth and seed production of these biotypes were studied under different atmospheric carbon dioxide (CO2) concentrations (450 and 750 ppm) and under well-watered (100% field capacity) and water-stressed (50% field capacity) conditions. Results showed that the GR biotype survived (>68%) at 1,440 g ha−1, but for the GS biotype, no plant survived, and both biotypes were slightly (<10%) affected by moisture regimes. In the elevated CO2 condition, the GS biotype plants were >38% taller and produced >44%, >18%, and >21% more leaves, buds, and seeds, respectively, compared with the ambient CO2 concentration under both moisture regimes. The biomass also increased by 27% in comparison with the ambient CO2 concentration. For the GR biotype, plants at the elevated CO2 level, while they also grew 38% taller in comparison with the ambient CO2 concentration, the numbers of leaves, buds, and seeds and biomass were not affected by this increase in CO2. Results showed that there were minimal changes in response to glyphosate for GR and GS biotypes of S. oleraceus with or without moisture stress. Our study suggests that future climate change with elevated CO2 levels can affect the response of S. oleraceus to glyphosate, and such knowledge will be helpful for weed management in the future.

Glyphosate-resistant junglerice [Echinochloa colona (L.) Link] is a problematic weed in mungbean [Vigna radiata (L.) R. Wilczek] crops in Australia. Due to limited herbicide options in mungbean, there is an increased interest in developing integrated management strategies for the sustainable control of E. colona. Pot experiments were conducted in a screenhouse in 2017 and 2018 by growing E. colona plants (glyphosate-resistant [GR] and glyphosate-susceptible [GS] biotypes) alone (1 plant pot−1) and in competition with 4 and 8 mungbean plants pot−1. Both biotypes were developed from a single population using the clone method. The growth and seed production of both GR and GS biotypes were similar in response to mungbean competition. Averaged over biotypes, there was a reduction in the growth and seed production of E. colona as crop plants increased. Compared with the weed plants grown alone, crop interference reduced E. colona height by 17% to 19%, tiller numbers by 69% to 82%, total shoot biomass by 85% to 91%, and inflorescence numbers by 74% to 91%. When E. colona was grown with 8 mungbean plants pot−1, leaf weight ratio increased by 42% compared with plants grown alone. Compared with weed plants grown alone, mungbean interference (4 and 8 plants pot−1) reduced weed seed production by 85% to 95%. These reductions were similar for both biotypes (GR and GS), suggesting that there was no fitness penalty associated with resistance. The results of this study suggest that mungbean interference can reduce E. colona growth and seed production, but it should not be considered as a stand-alone strategy to manage E. colona and similar species in mungbean. These results also highlight the need for integrating crop competition with other management strategies to achieve complete and sustainable management of this weed.

Effects of external static magnetic field (applied in $\hat y$-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser $({\rm \omega} _0,\;\vec k_{0z})$ is incident over the metal surface and exerts a ponderomotive force on the metal electrons in the skin layer. The ponderomotive force disturbs the quasi-neutrality of plasma which results into the excitation of space charge field at the frequency 2ω0. The electron density perturbation at frequency 2ω0 driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW $({\rm \omega}, \;\vec k_z)$ and produces nonlinear current to drive another counter propagating SPW $({\rm \omega} _1,\;\vec k_{1z})$ at the phase matching conditions of frequency ω = ω1 − 2ω0 and wavenumber $\vec k_z = \vec k_{1z} - 2\vec k{}_{0z}$ (by feedback mechanism). The parametric process becomes resonant at 2ω0 ≈ ωp and the maximum growth rate is achieved for an incidence angle of laser θ = 40°. The growth rate of the process reduces to half on increasing the magnetic field from 0.49 to 2.45 MG. The present study may be significant to the laser absorption experiments where surface rippling can strongly affect the laser energy absorption.

A high-frequency surface plasma wave (SPW) excited over metallic surface irradiated by a laser beam, can undergo stimulated Compton scattering if phase velocity of daughter plasma wave is equal to the Fermi velocity for metal. The pump SPW ${\rm (}{{\rm \omega} _0},{\vec k_{0{\rm z}}})$ parametrically excites a quasi-electrostatic plasma wave ${\rm (\omega}, {\vec k_{\rm z}})$ and a backscattered sideband SPW ${\rm (}{{\rm \omega} _1},{\vec k_{1{\rm z}}})$ at resonance ω0 = ω − ω1 and ${\vec k_{0{\rm z}}} = {\vec k_{\rm z}} - {\vec k_{1{\rm z}}}$. The growth rate of Compton process increases with the frequency of incident laser and turns out to be 5.425 × 1010 rad/s at laser frequency ω0 = 0.7595 × 1015 rad/s for incident laser amplitude A0L = 11 × 1011 V/m, laser spot size b = 1.38 × 10−5 m, and free electron density of metal n0 = 5.85 × 1028/m3. The excitation of highly damped quasi-electrostatic plasma wave in this parametric process provide a better nonlinear option for surface heating as compared with direct laser heating. The process can also be used for diagnostics purposes.

Electron acceleration is studied during the resonant interaction of launched electron beam with the surface plasma wave (SPW) in the presence of static magnetic field. A configuration of two parallel metal sheets separated by a vacuum region supports the SPW of amplitude maximum on the two parallel interfaces and minimum in the middle. Kretschmann geometry is used to excite surface plasma mode by shinning laser on a glass prism. Dispersion relation of SPW is established in the presence of magnetic field and smaller cut-off frequencies are observed as compared with that of without magnetic field. An electron beam launched in the middle region, experiences a longitudinal ponderomotive force due to SPWs and gets accelerated to the velocity of the order of phase velocity of the surface wave. The energy gained by electron is higher in the presence of magnetic field as compared with zero magnetic field. The electron energy and trajectory are also presented for varying parameters such as amplitude of SPW and magnetic field strength. In the present scheme, electron beams can achieve maximum 550 KeV energy for the SPW amplitude ESP = 1.2 × 1011 V/m, plasma frequency ωp = 1.3 × 1016 rad/s, and cyclotron frequency ωc/ωp = 0.05.

Resonant THz radiation generation is proposed by beating of two spatial-triangular laser pulses of different frequencies (ω1, ω2) and wave numbers $\lpar \vec k_1 \comma \; \vec k_2 \rpar $ in plasma having external static magnetic field. Laser pulses co-propagating perpendicular to a dc magnetic field exert a nonlinear ponderomotive force on plasma electrons, imparting them an oscillatory velocity with finite transverse and longitudinal components. Oscillatory plasma electrons couple with periodic density ripples n′ = nq0eiqz to produce a nonlinear current, i.e., responsible for resonantly driving terahertz radiation at $\lpar {\rm \omega} = {\rm \omega} _1 - {\rm \omega} _2 \comma \; \vec k = \vec k_1 - \vec k_2 + \vec q\rpar $. Effects of THz wave frequency, laser beam width, density ripples, and applied magnetic field are studied for the efficient THz radiation generation. The frequency and amplitude of THz radiation were observed to be better tuned by varying dc magnetic field strength and parameters of density ripples (amplitude and periodicity). An efficiency about 0.02 is achieved for laser intensity of 2 × 1015 W/cm2 in a plasma having density ripples about 30%, plasma frequency about 1 THz and magnetic field about 100 kG.

This paper presents an investigation of self-focusing of intense Gaussian rippled laser beam in collisionless plasma by including the nonlinearity associated with the relativistic mass and the ponderomotive force and its effects on the excitation of ion acoustic wave. The growth of ripple, riding on an intense Gaussian laser beam in plasma and its coupling with ion acoustic wave has also been studied. Modified coupled equations for main laser beam, growth of laser ripple in plasma, rippled laser beam, beam width, and density perturbation associated with ion acoustic wave are derived using Wentzel-Kramers-Brillouin and paraxial ray approximation. These coupled equations are solved analytically and numerically to study the laser intensity in plasma and the variation of amplitude of the ion acoustic wave for various established laser and plasma parameters. From numerical computation, it is observed that both nonlinearities significantly affected the dynamics of the growth of laser ripple in plasma, propagation of rippled laser beam as well as ion acoustic wave in plasma at high laser power flux. The growth of laser ripple increase with increase in the intensity of laser beam and due to the contribution of growth rate, intensity profile of rippled laser beam and ion acoustic wave modified accordingly.

Resonant excitation of terahertz (THz) radiation by nonlinear coupling of two filamented spatial-Gaussian laser beams of different frequencies and wave numbers is studied in plasma having transverse static electric field. The static ponderomotive force due to filamented lasers is balanced by the pressure gradient force which gives rise to transverse density ripple, while, the nonlinear ponderomotive force at frequency difference of beating lasers couples with density ripple giving rise to stronger transverse nonlinear current which results into the excitation of THz radiation at resonance. The coupling is further enhanced by the presence of static electric field and spatial-Gaussian nature of laser beams. An increase of six-fold in the normalized amplitude of THz is observed by applying a direct current field of about 50 KV. Effects of frequency, laser beam width, and periodicity factor of modulated laser amplitude are studied for the efficient THz radiation generation. These results can be utilized for generating controlled tunable THz sources for medical applications using low filament intensities (~ 1014 W/cm2) of beating lasers.

This article presents the resonant excitation of the upper hybrid wave (UHW) by cross focusing of two high power laser beams in a collisionless hot magnetoplasma; taking into account the relativistic nonlinearity. The electric vectors of the two beams are polarized along uniform static magnetic field and the beams propagate perpendicular to the static magnetic field. The resonant excitation of the UHW occurs when the frequency difference (FD) of the two laser beams and difference of their propagation vector satisfy the dispersion relation corresponding to the UHW. It has been observed that the power associated with the excited UHW, which depends on the background electron concentration, magnetic field and the intensity of the two laser beams, becomes drastically modified with the distance of propagation. The effect of the excited UHW at the FD on the acceleration of electrons has also been discussed. The amplitude of the UHW, excited by two high power laser beams and the electron energy are also calculated. This study is relevant in heating of plasma near the upper hybrid frequency as well as electron acceleration. The results are presented for typical laser plasma parameters.