Electromagnetic waves destabilized by runaway electrons in near-critical electric fields

Runaway electron distributions are strongly anisotropic in velocity space. This anisotropy is a source of free energy that may destabilize electromagnetic waves through a resonant interaction between the waves and the energetic electrons. In this work we investigate the high-frequency electromagnetic waves that are destabilized by runaway electron beams when the electric field is close to the critical field for runaway acceleration. Using a runaway electron distribution appropriate for the near-critical case we calculate the linear instability growth rate of these waves and conclude that the obliquely propagating whistler waves are most unstable. We show that the frequencies, wave numbers and propagation angles of the most unstable waves depend strongly on the magnetic field. Taking into account collisional and convective damping of the waves, we determine the number density of runaways that is required to destabilize the waves and show its parametric dependences.Comment: 22 pages, 11 figures, to be published in Physics of Plasma

Ecology of the Ráckeve-Sorokság Danube – a review

Present paper is a review on the Ráckeve-Soroksár Danube in ecological standpoint. The goal of this study is to collect and evaluate all of available publications in that conception, concerning this Danube arm. Phytoplankton, zooplankton, macroinvertebrates, vertebrates, macrophytes and also water chemistry, water management, geographical description are presented. The review comprises the main studies beginning with the earliest faunistic publications up to the recent ecological, multidisciplinary investigations. Spatial and temporal patterns likewise water quality are considered as important. Additionally checklist of aquatic invertebrate and vertebrate fauna are given based on data from literature

Compositions with superlinear deterministic top-down tree transformations

AbstractWe denote the class of deterministic top-down tree transformations by DT and the class of homomorphism tree transformations by HOM. The sign of a class with the prefix l- (sl-, nd-) denotes the linear (superlinear, nondeleting) subclass of that class. We fix the set M = HOM,sl-DT, l-DT, nd-DT, DT of tree transformation classes. Then consider the monoid [M] of all tree transformation classes of the form X1 O … OXm, where O is the operation composition, m ⩾ 0 and the Xi's are elements of M. As the main result of the paper, we give an effective description of the monoid [M] with respect to inclusion. This means that we present an algorithm which can decide, given arbitrary two elements of the monoid, whether some inclusion, equality or incomparability holds between them

Coulomb suppression of the stellar enhancement factor

It is commonly assumed that reaction measurements for astrophysics should be preferably performed in the direction of positive Q value to minimize the impact of the stellar enhancement factor, i.e. the difference between the laboratory rate and the actual stellar rate. We show that the stellar effects can be minimized in the charged particle channel, even when the reaction Q value is negative. As a demonstration, the cross section of the astrophysically relevant 85Rb(p,n)85Sr reaction has been measured by activation between 2.16 < Ec.m. < 3.96 MeV and the astrophysical reaction rate for (p,n) as well as (n,p) is directly inferred from the data. The presented arguments are also relevant for other alpha and proton-induced reactions in the p and rp processes. Additionally, our results confirm a previously derived modification of a global optical proton potential.Comment: submitted to PR

Synchrotron radiation from a runaway electron distribution in tokamaks

The synchrotron radiation emitted by runaway electrons in a fusion plasma provides information regarding the particle momenta and pitch-angles of the runaway electron population through the strong dependence of the synchrotron spectrum on these parameters. Information about the runaway density and its spatial distribution, as well as the time evolution of the above quantities, can also be deduced. In this paper we present the synchrotron radiation spectra for typical avalanching runaway electron distributions. Spectra obtained for a distribution of electrons are compared to the emission of mono-energetic electrons with a prescribed pitch-angle. We also examine the effects of magnetic field curvature and analyse the sensitivity of the resulting spectrum to perturbations to the runaway distribution. The implications for the deduced runaway electron parameters are discussed. We compare our calculations to experimental data from DIII-D and estimate the maximum observed runaway energy.Comment: 22 pages, 12 figures; updated author affiliations, fixed typos, added a sentence at the end of section I