164 research outputs found
Nonlinear plasma waves excitation by intense ion beams in background plasma
Plasma neutralization of an intense ion pulse is of interest for many applications, including plasma lenses, heavy ion fusion, cosmic ray propagation, etc. An analytical electron fluid model has been developed to describe the plasma response to a propagating ion beam. The model predicts very good charge neutralization during quasi-steady-state propagation, provided the beam pulse duration {tau}{sub b} is much longer than the electron plasma period 2{pi}/{omega}{sub p}, where {omega}{sub p} = (4{pi}e{sup 2}n{sub p}/m){sup 1/2} is the electron plasma frequency and n{sub p} is the background plasma density. In the opposite limit, the beam pulse excites large-amplitude plasma waves. If the beam density is larger than the background plasma density, the plasma waves break. Theoretical predictions are compared with the results of calculations utilizing a particle-in-cell (PIC) code. The cold electron fluid results agree well with the PIC simulations for ion beam propagation through a background plasma. The reduced fluid description derived in this paper can provide an important benchmark for numerical codes and yield scaling relations for different beam and plasma parameters. The visualization of numerical simulation data shows complex collective phenomena during beam entry and exit from the plasma
Update on beam-plasma interaction research at PPPL
We have performed experimental and theoretical
studies of beam neutralization by background plasma.
Near-complete space-charge neutralization is
required for the transverse compression of highperveance
ion beams for ion-beam-driven warm
dense matter experiments and heavy ion fusion..
Proton polarizability and the Lamb shift in muonic hydrogen
The proton structure and proton polarizability corrections to the Lamb shift
of electronic hydrogen and muonic hydrogen were evaluated on the basis of
modern experimental data on deep inelastic structure functions. Numerical value
of proton polarizability contribution to (2P-2S) Lamb shift is equal to 4.4
GHz.Comment: 8 pages, LaTeX2.09, 2 figures, uses linedraw.st
Scaling and Formulary cross sections for ion-atom impact ionization
The values of ion-atom ionization cross sections are frequently needed for
many applications that utilize the propagation of fast ions through matter.
When experimental data and theoretical calculations are not available,
approximate formulas are frequently used. This paper briefly summarizes the
most important theoretical results and approaches to cross section calculations
in order to place the discussion in historical perspective and offer a concise
introduction to the topic. Based on experimental data and theoretical
predictions, a new fit for ionization cross sections is proposed. The range of
validity and accuracy of several frequently used approximations (classical
trajectory, the Born approximation, and so forth) are discussed using, as
examples, the ionization cross sections of hydrogen and helium atoms by various
fully stripped ions.Comment: 46 pages, 8 figure
Discrete analogues of the Liouville equation
The notion of Laplace invariants is transferred to the lattices and discrete
equations which are difference analogs of hyperbolic PDE's with two independent
variables. The sequence of Laplace invariants satisfy the discrete analog of
twodimensional Toda lattice. The terminating of this sequence by zeroes is
proved to be the necessary condition for existence of the integrals of the
equation under consideration. The formulae are presented for the higher
symmetries of the equations possessing integrals. The general theory is
illustrated by examples of difference analogs of Liouville equation.Comment: LaTeX, 15 pages, submitted to Teor. i Mat. Fi
Proton polarizability effect in the Lamb shift of the hydrogen atom
The proton polarizability correction to the Lamb shift of electronic and
muonic hydrogen is calculated on the basis of isobar model and experimental
data on the structure functions of deep inelastic lepton-nucleon scattering.
The contributions of the Born terms, vector-meson exchanges and nucleon
resonances are taken into account in the construction of the photoabsorption
cross sections for transversely and longitudinally polarized virtual photons
sigma_{T,L}.Comment: 11 pages, 3 figure
МОЛЕКУЛЯРНО-ГЕНЕТИЧЕСКИЕ ИССЛЕДОВАНИЯ ГЛИАЛЬНЫХ ОПУХОЛЕЙ У ДЕТЕЙ
Glioblastomas are the most frequent malignant neoplasm among primary brain tumors of childhood. Despite the advances in a multimodality treatment approach including neurosurgery, radiotherapy and chemotherapy, the overall survival of such patients remains poor and doesn’t exceed 14 months. The using of targeted agents such as gefitinib in unselected patient populations showed insufficient efficacy. Nowadays, the most perspective approach is a selection of patient populations potentially sensitive to targeted therapy based on predictive markers of response. We performed a comprehensive analysis of the mutational patterns in 30 glioblastomas of children. Data Analysis was based on the new method of mass spectrometry (OncoCarta v1.0, Sequenom) that enabled us to estimate 298 mutations in 19 genes and to identify 10 mutations in 9 tumors (30 %). Mutations were found in BRAF, CDK, HRAS, EGFR, FGFR, MET and PI3K. The most mutated pathway was EGFR – in 20 % of the samples (6/30). The obtained results seem to be very promising in terms of possibilities of using new targeted agents including BRAF inhibitors for treatment of children with glial brain tumors.Глиобластомы у детей представляют собой наиболее частые злокачественные новообразования среди первичных опухолей головного мозга. Несмотря на развитие комплексного лечебного подхода, включающего нейрохирургические, радиотерапевтические и химиотерапевтические методики, общая выживаемость больных с впервые выявленными опухолями остается крайне низкой, не превышая 14 месяцев. При использовании таргетных препаратов, в частности, гефитиниба, в общей популяции больных продемонстрирована низкая клиническая эффективность. Наиболее перспективным в настоящий момент является определение популяции больных, потенциально чувствительных к действию таргетных препаратов, с учетом определения предиктивных молекулярных маркеров. В данной работе определены мутационные изменения в тканях 30 детских глиобластом. Анализ данных, основанный на результатах массспектрометрического секвенирования (OncoCarta v1.0, Sequenom), позволил определить 298 мутаций в 19 генах и идентифицировать 10 мутаций в 9 опухолях (30 %). Изменения выявлены в генах BRAF, CDK, HRAS, EGFR, FGFR, MET и PI3K. Наиболее часто (6/30, 20 % опухолей) мутации выявлены у участников сигнального каскада EGFR. Полученные результаты позволяют говорить о потенциальных возможностях изучения новейших таргетных препаратов, включая ингибиторы BRAF, для лечения больных детского возраста с глиальными опухолями головного мозга
Effect of temperature anisotropy on various modes and instabilities for a magnetized non-relativistic bi-Maxwellian plasma
Using kinetic theory for homogeneous collisionless magnetized plasmas, we
present an extended review of the plasma waves and instabilities and discuss
the anisotropic response of generalized relativistic dielectric tensor and
Onsager symmetry properties for arbitrary distribution functions. In general,
we observe that for such plasmas only those electromagnetic modes whose
magnetic field perturbations are perpendicular to the ambient magneticeld,
i.e.,B1 \perp B0, are effected by the anisotropy. However, in oblique
propagation all modes do show such anisotropic effects. Considering the
non-relativistic bi-Maxwellian distribution and studying the relevant
components of the general dielectric tensor under appropriate conditions, we
derive the dispersion relations for various modes and instabilities. We show
that only the electromagnetic R- and L- waves, those derived from them and the
O-mode are affected by thermal anisotropies, since they satisfy the required
condition B1\perpB0. By contrast, the perpendicularly propagating X-mode and
the modes derived from it (the pure transverse X-mode and Bernstein mode) show
no such effect. In general, we note that the thermal anisotropy modifies the
parallel propagating modes via the parallel acoustic effect, while it modifies
the perpendicular propagating modes via the Larmor-radius effect. In oblique
propagation for kinetic Alfven waves, the thermal anisotropy affects the
kinetic regime more than it affects the inertial regime. The generalized fast
mode exhibits two distinct acoustic effects, one in the direction parallel to
the ambient magnetic field and the other in the direction perpendicular to it.
In the fast-mode instability, the magneto-sonic wave causes suppression of the
firehose instability. We discuss all these propagation characteristics and
present graphic illustrations
Recommended from our members
Advances in U.S. Heavy Ion Fusion Science
During the past two years, the US heavy ion fusion science program has made significant experimental and theoretical progress in simultaneous transverse and longitudinal beam compression, ion-beam-driven warm dense matter targets, high-brightness beam transport, advanced theory and numerical simulations, and heavy ion target physics for fusion. First experiments combining radial and longitudinal compression {pi} of intense ion beams propagating through background plasma resulted in on-axis beam densities increased by 700X at the focal plane. With further improvements planned in 2008, these results enable initial ion beam target experiments in warm dense matter to begin next year. They are assessing how these new techniques apply to higher-gain direct-drive targets for inertial fusion energy
Recommended from our members
Heavy ion fusion science research for high energy density physics and fusion applications
During the past two years, the U.S. heavy ion fusion science program has made significant experimental and theoretical progress in simultaneous transverse and longitudinal beam compression, ion-beam-driven warm dense matter targets, high brightness beam transport, advanced theory and numerical simulations, and heavy ion target designs for fusion. First experiments combining radial and longitudinal compression of intense ion beams propagating through background plasma resulted in on-axis beam densities increased by 700X at the focal plane. With further improvements planned in 2007, these results will enable initial ion beam target experiments in warm dense matter to begin next year at LBNL. We are assessing how these new techniques apply to low-cost modular fusion drivers and higher-gain direct-drive targets for inertial fusion energy
- …