Secondary electron emission yield in the limit of low electron energy

Secondary electron emission (SEE) from solids plays an important role in many areas of science and technology.1 In recent years, there has been renewed interest in the experimental and theoretical studies of SEE. A recent study proposed that the reflectivity of very low energy electrons from solid surface approaches unity in the limit of zero electron energy2,3,4, If this was indeed the case, this effect would have profound implications on the formation of electron clouds in particle accelerators,2-4 plasma measurements with electrostatic Langmuir probes, and operation of Hall plasma thrusters for spacecraft propulsion5,6. It appears that, the proposed high electron reflectivity at low electron energies contradicts to numerous previous experimental studies of the secondary electron emission7. The goal of this note is to discuss possible causes of these contradictions.Comment: 3 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba, Ital

Controlling Charge and Current Neutralization of an Ion Beam Pulse in a Background Plasma by Application of a Solenoidal Magnetic Field I: Weak Magnetic Field Limit

Propagation of an intense charged particle beam pulse through a background plasma is a common problem in astrophysics and plasma applications. The plasma can effectively neutralize the charge and current of the beam pulse, and thus provides a convenient medium for beam transport. The application of a small solenoidal magnetic field can drastically change the self-magnetic and self- electric fields of the beam pulse, thus allowing effective control of the beam transport through the background plasma. An analytic model is developed to describe the self-magnetic field of a finite- length ion beam pulse propagating in a cold background plasma in a solenoidal magnetic field. The analytic studies show that the solenoidal magnetic field starts to infuence the self-electric and self-magnetic fields when ωce > ωpeβb, where ωce = eβ/mec is the electron gyrofrequency, ωpe is the electron plasma frequency, and βb = Vb/c is the ion beam velocity relative to the speed of light. This condition typically holds for relatively small magnetic fields (about 100G). Analytical formulas are derived for the effective radial force acting on the beam ions, which can be used to minimize beam pinching. The results of analytic theory have been verified by comparison with the simulation results obtained from two particle-in-cell codes, which show good agreement

Electromagnetic Weibel instability in intense charged particle beams with large energy anisotropy

In plasmas with strongly anisotropic distribution functions, collective instabilities may develop if there is sufficient coupling between the transverse and longitudinal degrees of freedom. Our previous numerical and theoretical studies of intense charged particle beams with large temperature anisotropy [E. A. Startsev, R. C. Davidson and H. Qin, PRSTAB, 6, 084401 (2003); Phys. Plasmas 9, 3138 (2002)] demonstrated that a fast, electrostatic, Harris-like instability develops, and saturates nonlinearly, for sufficiently large temperature anisotropy (T{sub {perpendicular}b}/T{sub {parallel}b} >> 1). The total distribution function after saturation, however, is still far from equipartitioned. In this paper the linearized Vlasov-Maxwell equations are used to investigate detailed properties of the transverse electromagnetic Weibel-type instability for a long charge bunch propagating through a cylindrical pipe of radius r{sub w}. The kinetic stability analysis is carried out for azimuthally symmetric perturbations about a two-temperature thermal equilibrium distribution in the smooth-focusing approximation. The most unstable modes are identified, and their eigenfrequencies, radial mode structure and instability thresholds are determined. The stability analysis shows that, although there is free energy available to drive the electromagnetic Weibel instability, the finite transverse geometry of the charged particle beam introduces a large threshold value for the temperature anisotropy ((T{sub {perpendicular}b}/T{sub {parallel}b}){sup Weibel} >> (T{sub {perpendicular}b}/T{sub {parallel}b}){sup Harris}) below which the instability is absent. Hence, unlike the case of an electrically neutral plasma, the Weibel instability is not expected to play as significant a role in the process of energy isotropization of intense unneutralized charged particle beams as the electrostatic Harris-type instability

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 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

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

Молекулярные детерминанты рецидива уротелиальной опухоли человека

Background. Urothelial carcinoma (UTC) is an aggressive disease with a known propensity for frequent recurrence. It is difficult to predict the velocity of the development of UTC recur using modern means of clinical diagnostics. Therefore, the development of the capabilities of histo-morphological study of tumor tissues is of particular relevance.Materials and methods. The materials of publications (PubMed, CrossRef) for 1990-2021, devoted to the choice of biomarkers for the diagnosis of UTC, the analysis of molecular pathways, progression and metastasis, were studied. The search was carried out for the key phrases "urothelial carcinoma", "recurrent UTK", "stem cells", "biomarkers of bladder cancer", "genetic changes in urothelium", "circulating tumor DNA".Results. Cancer stem cells serve as a source of UTC recurrence after removal from the primary focus, localizing in any areas of the urothelium, as well as outside the main tumor focus and are characterized by a common genotype, but different phenotypic manifestations. To predict the recurrence of the tumour is advisable to use gene expression signatures, since the subtypes of UTC are characterized by clear gene expression profiles. A larger sample and independent dataset is needed to confirm the clinical significance of the findings. Combined biomarkers predict UTC behavior, and FGFR3 and TP53 mutations can be components for a panel for predicting UTC recurrence. The use of the liquid biopsy method with the determination of the level of circulating tumor DNA is a promising diagnostic method that needs to evaluate the results of an initiated randomized trial.Conclusion. The accumulation of knowledge base about the molecular patterns of UTC will help bridge the gap between the results of molecular genetic and clinical diagnostics. Molecular changes in the transitional cell UTC demonstrates a high potential for determining the timing of tumor recurrence, assessing disease-free survival of patients and for planning the resource base of the healthcare system.Введение. Уротелиальная карцинома (УТК) - агрессивное заболевание со склонностью к частому рецидивированию. Прогноз развития рецидивов УТК с помощью современных средств клинической диагностики затруднен, поэтому особую актуальность приобретает развитие возможностей патоморфологического исследования опухолевых тканей.Материалы и методы. Изучены материалы публикаций (PubMed, CrossRef) за 1990-2021 гг., посвященных вопросам выбора биомаркеров для диагностики УТК, анализу молекулярных путей прогрессирования и метастазирования. Поиск проводили по ключевым фразам «уротелиальная карцинома», «рецидив уротелиальной карциномы», «стволовые клетки», «биомаркеры рака мочевого пузыря», «генетические изменения уротелия», «циркулирующая опухолевая ДНК».Результаты. Раковые стволовые клетки служат источником рецидива УТК после удаления первичного очага, локализуясь в любых участках уротелия, а также вне основного очага опухоли, и характеризуются общим генотипом, но различными фенотипическими проявлениями. Для прогноза рецидива УТК целесообразно использование экспрессионных сигнатур генов, поскольку для подтипов УТК характерны четкие профили экспрессии генов. Для подтверждения клинического значения полученных данных необходимы большая выборка и независимый набор данных. Комбинированные биомаркеры обеспечивают прогнозирование поведения УТК, а мутации FGFR3 и TP53 могут служить компонентами для панели прогноза рецидива УТК. Использование метода жидкостной биопсии с определением уровня циркулирующей опухолевой ДНК - перспективный метод диагностики, нуждающийся в оценке результатов инициированного рандомизированного исследования.Заключение. Накопление знаний о молекулярных паттернах УТК позволит преодолеть разрыв между результатами молекулярно-генетической и клинической диагностики. Молекулярные изменения УТК демонстрируют высокий потенциал для определения сроков рецидива опухоли, оценки безрецидивной выживаемости пациентов и планирования ресурсной базы системы здравоохранения