Excitation of surface plasmons at the boundary of overdense plasma

The excitation of surface plasmons （SPs） with a strip grating at the boundary of an unmagnetized overdense plasma has been investigated theoretically and experimentally. An incident electromagnetic radiation was p-polarized at the frequency of 5 GHz. Experiments showed that when the plasma density was four times higher than the critical density with the grating present, and the SPs could be excited at the boundary of the overdense plasma. Contribution of the glass layer in the formation of the SP dispersion relation was examined. When the incident electromagnetic radiation was coupled into SPs the coupling order with the effective permittivity was simulated qualitatively. We find that the existence of SPs at the boundary of overdense plasma indicates that the reflection coefficient of the incident electromagnetic radiation reaches its minimum and even becomes total absorption. In this work the plasma density was diagnosed by a Langmuir double probe.

Generation of a single attosecond pulse from an overdense plasma surface driven by a laser pulse with time-dependent polarization

The influence of time-dependent polarization on attosecond pulse generation from an overdense plasma surface driven by laser pulse is discussed analytically and numerically. The results show that the frequency of controlling pulse controls the number and interval of the generated attosecond pulse, that the generation moment of the attosecond pulse is dominated by the phase difference between the controlling and driving pulses, and that the amplitude of the controlling pulse affects the intensity of the attosecond pulse. Using the method of time-dependent polarization, a ＂single＂ ultra-strong attosecond pulse with duration T ≈ 8.6 as and intensity I≈ 3.08 × 10^20 W.cm-2 can be generated.

Producing High Intense Attosecond Pulse Train by Interaction of Three-Color Pulse and Overdense Plasma

Amplifying the attosecond pulse by the chirp pulse amplification method is impossible. Furthermore, the intensity of attosecond pulse is low in the interaction of laser pulse and underdense plasma. This motivates us to propose using a multi-color pulse to produce the high intense attosecond pulse. In the present study, the relativistic interaction of a three-color linearly-polarized laser-pulse with highly overdense plasma is studied. We show that the combination of ω1, ω2 and ω3 frequencies decreases the instance full width at half maximum reflected attosecond pulse train from the overdense plasma surface. Moreover, we show that the three-color pulse increases the intensity of generated harmonics, which is explained by the relativistic oscillating mirror model. The obtained results demonstrate that if the three-color laser pulse interacts with overdense plasma, it will enhance two orders of magnitude of intensity of ultra short attosecond pulses in comparison with monochromatic pulse.

Relativistic Electromagnetic Solitary Wave in a Cylindrical Magnetized Plasma

In the presence of an applied static and uniform magnetic field, a cylindrical Kadomtsev-Petviashivili equation is derived for a relativistic electromagnetic solitary wave propagating in collisionless plasma consisting electrons, positrons, and ions in the case of weak relativistic limit. This equation is solved in a stationary frame to obtain explicit expression for the velocity, amplitude and width of solitons. The amplitude of the solitary wave has a maximum value at a critical αc of the ratio of the ion equilibrium density to the electron one, and it increases as the applied magnetic field becomes larger.

High Density Plasma Heating by EC-Waves Injected from the High-Field Side for Mode Conversion to Electron Bernstein Waves in LHD

To realize an excitation of electron Bernstein waves （EBW） via mode conversion from X-mode waves injected from the high magnetic field side （HFS）, new inner-vessel mirrors were installed close to a helicM coil in the large helicM device （LHD）. 77 GHz electron cyclotron （EC） wave beams injected from an existing EC-wave injection system toward the new mirror are reflected on the mirror so that the beams are injected to plasmas from HFS. Evident increases in the electron temperature at the plasma core region and the plasma stored energy were observed by the HFS beam injection to the plasmas with the line-average electron density of 7.5~ 1019 m-3, which is slightly higher than the plasma cut-off density of 77 GHz EC-waves, 7.35~ 1019 m-3. The heating efficiency evaluated from the changes in the time derivative of the plasma stored energy reached ,,~70%. Although so far it is not clear which is the main cause of the heating effect, the mode-converted EBW or the X-mode wave itself injected from the HFS, an effective heating of high-density plasma over the plasma cut-off of EC-wave was successfully demonstrated.

Steady-State Plasmas in KT5D Magnetized Torus

Steady-state plasma generated by electron cyclotron resonance （ECR） wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge patterns taken by the camera and the plasma parameters measured by the probes were very sensitive to the working gas pressure and the magnetic configuration of the torus both without and with vertical fields. There existed fast vertical motion of the plasma. Tentative discussion is presented about the observed phenomena such as the bright resonance layer at a high gas pressure and the wave absorption mechanism at a low pressure. Further explanations should be found.

Toward managing mixed-species stands： from parametrization to prescription

A better understanding and a more quantitative design of mixed-species stands will contribute to more integrative and goal-oriented research in mixed-species forests. Much recent work has indicated that the structure and growth of mixed species forests may fundamentally differ from monocultures. Here we suggest how to progress from the present accumulation of phenomenological findings to a design of mixed-species stands and advanced silvicultural prescriptions by means of modelling. First, the knowledge of mixing effects on the structure and growth at the stand, species, and individual tree level is reviewed, with a focus on those findings that are most essential for suitable modelling and silvicultural designs and the regulation of mixed stands as opposed to monocultures. Then, the key role of growth models, stand simulators, and scenario assessments for designing mixed species stands is discussed The next section illustrates that existing forest stand growth models require some fundamental modifications to become suitable for both monocultures and mixed-species stands. We then explore how silvicultural prescriptions derived from scenario runs would need to be both quantified and simplified for transfer to forest management and demonstrated in training plots. Finally, we address the main remaining knowledge gaps that could be remedied through empirical research.