[en] The evolution of small initial perturbations of the uniform equilibrium of the ''classical'' Pierce diode is studied using particle simulations. These simulations have been performed with the new bounded-plasma code PDW1 and cover the parameter range 0 < α < 3 π, where α = ω/sub p/L/v₀. In the linear regime, three stages (initial-transit, adjustment, and dominant-eigenmode) are distinguished; oscillation frequencies, growth/damping rates, and potential profiles of the dominant eigenmode as well as oscillation frequencies of the next-to-dominant eigenmode are recovered and shown to agree quantitatively with recent analytical results. In the linearly unstable cases, the system evolves nonlinearly to a final state which may be either a new, nonuniform dc equilibrium, or a state of large-amplitude oscillations. In particular, for α = 1.5π the character of the final state is found to depend on the details of the initial conditions

[en] The volume presents material illustrating European environmental policy and the situation in the various countries, and is intended among others for use as a teaching aid at school or in adult courses. A documentation of newspaper articles and other material is the center piece of the volume, arranged by environmental problems and cases, covering also basic text parts from the fields of law and politics. The six main subjects dealt with include: Pollution of the Rhine river, the Sandoz accident; - Nuclear power, Chernobyl and Cattenom; - Forest decline, acid rain and motor vehicle off-gas; - Toxic waste, Seveso and no end to be seen; - Agriculture and ecology; - Environmental impact statement, an EC Directive. The documentation has been selected so as to reflect a broad spectrum of political opinions. (orig./HSCH)

[en] Using simple analyses and 1d3v (one space and three velocity dimension) particle-in-cell simulations we show that the properties of the plasma-wall transition change when the angle α between the wall and the magnetic field is of the order of, or smaller than, certain values α₁, α₂. These values depend on the ion mass and collisionality, and on the ion-to-electron temperature ratio in the magnetic presheath. In this range of α, no significant decrease in the particle and heat fluxes to the wall is expected with decreasing α

[en] The behavior in time of a plasma bounded by a plane emitter and cold collector is observed in a movie showing simultaneous plots of electron and ion phase spaces (v/sub x/ vs x), potential phi(x), charge density rho(x) and current density J(t). Using T/sub i//T/sub e/ = 1 at the emitter, m/sub i//m/sub e/ = 40, eight sequences were made for various emission ratios (α = n/sub i/₀⁺/n/sub e/₀⁺ = 0.1, 1.0 and 4.0). With floating bias (open circuit), the plasma has fluctuations which are small compared with average values. With ion rich emission and virtual anode, an electron hole is expected but is found to be filled. With moderate positive bias, violent instabilities are observed in great detail for both electron and ion-rich emission, associated with formation of potential minima, ejecting electrons, then repeating. The new information is the detail, allowing more complete understanding. The script provides the model, the parameters of the movie, and brief descriptions of the sequences. 23 refs., 11 figs., 2 tabs

No abstract available

No abstract available

[en] The plane-diode model is used to study the equilibrium properties of a collisionless single-ended Q-machine over the most relevant parameter regions. A method is given for determining parameter points, or points of operation, which enables straightforward application of the theoretical results to specific experimental situations. A new disruptive effect is predicted which manifests itself in discontinuous changes in the equilibrium properties with a continuous variation of the neutral flux. As an example of application, a simplified analysis of the strong instability occurring at positive cold-plate biases is presented. (author)

[en] While our ultimate goal is a complete three-dimensional picture of the nucleon in terms of its fundamental constituents, there are still important lessons to be learned about its ''one-dimensional'' collinear parton distribution functions (PDFs) like f1(x) and g1(x). There are rigorous proofs for factorization and universality (process independence) which make these PDFs fundamental. They also appear as limits of Generalized Parton Distributions (GPD) and as integrals of transverse momentum-dependent (TMD) parton distribution functions. Experimentally, the unpolarized structure functions F1(x,Q2), F2(x,Q2) have been studied over a huge kinematic range in both variables. Information on the polarized structure functions g1(x,Q2), g2(x,Q2) is somewhat more limited, both in kinematics and in statistical precision. In both cases, much less is known about the neutron than the proton, due to the absence of a free neutron target. Accessing these structure functions at large x (where valence quarks dominate) has been challenging due to the high luminosity and the high resolution required. Finally, much information can be extracted from studying higher twist contributions to these structure functions and the connection between the DIS limit and the region where nucleon resonance excitation dominates. In my talk, I will present an overview of recent experimental results (with special emphasis on the valence region and the transition from quark to hadronic degrees of freedom). I will also give an outlook on the next round of experiments coming online with the energy-upgraded Jefferson Lab electron beam, and future projects like the Electron Ion Collider

[en] A method is presented which permits to reliably determine axial steady-state potential distributions in collisionless single-ended Q-machine plasmas. The method requires standard measurements of plasma parameters at negative cold-plate biases, whence the steady-state conditions at positive biases can be predicted by means of a simple theoretical extrapolation. In contrast to some models used in the literature, only two types of potential distributions are found to be possible at large positive cold-plate biases, viz. monotone increasing distributions and non-monotone distributions with a potential minimum in front of the hot plate and a positive plasma potential. They occur according to whether the plasma density at large negative biases is greater or smaller than a certain critical density, which depends on both hot-plate and ionic properties. A qualitative discussion of grid effects leads to the conclusion that a grid is equivalent to a massive cold plate only in the saturation regime of its current-voltage characteristics, whereas for smaller grid biases significant differences may be expected which render diode theory inappropriate. Applications of the theoretical results to real Q-machine experiments are given. (author)

[en] The plane-diode model is used to calculate steady-state parameters (plasma density, plasma potential, and potential extremum) for a strongly biased, collisionless single-ended Q-machine over a wide range of neutralization parameters. By solving the cold-beam dispersion relation in the long-wavelength limit, approximate expressions are obtained for the frequency and growth rate of the Buneman two-stream instability which occurs at sufficiently positive biases. All of these dependences exhibit a characteristic kink at the transition between monotone and non-monotone potential distributions. (Auth.)