Radiative losses in plasma accelerators

We investigate the dynamics of a relativistic electron in a strongly nonlinear plasma wave in terms of classical mechanics by taking into account the action of the radiative reaction force. The two limiting cases are considered. In the first case where the energy of the accelerated electrons is low, the electron makes many betatron oscillations during the acceleration. In the second case where the energy of the accelerated electrons is high, the betatron oscillation period is longer than the electron residence time in the accelerating phase. We show that the force of radiative friction can severely limit the rate of electron acceleration in a plasma accelerator.     

Adiabatic beam buncher for plasma accelerators

An adiabatic free-electron laser wiggler for electron beam bunching is described. A free-electron laser naturally bunches an electron beam. When the beam is trapped adiabatically, the emittance of the bunched beam is decreased significantly compared with abrupt trapping. For a 57-period two-meter buncher having poleface magnetic field of 2 T and 10 GW of 100 μm radiation, adiabatic trapping reduces the final emittance by a factor of three     

Cavitation occurring in capillary tubes

Surface etches caused by cavitation often occur behind the blade of a rapidly rotating propeller or on a vibrating surface where liquid is subjected to suddenly reduced or oscillating saturation pressure. This phenomenon has never been reported in a continuous capillary pipe in which flow pressure varied gently without injection of external radiation energy. On the other aspect, acoustically tinkling signals were recognized decades ago during operation of the oscillation capillary heat pipe, but lacking of vigorous scientific understanding of the root causes. In this article, we report cavitation and its surface etches in meandering capillary tubes with the inner diameter of 1.8 mm. Numerous etching pits were observed on the interior face at the heat rejection region after over 200 hours operation. Irregular copper debris, with sizes ranging from 20 to 500 μm, is found in the reclaimed operating fluid. Analysis of temperature and acoustic data indicates that, driven by spiking temperature difference, highly turbulent two-phase flow carries the saturated vapor bubbles from the evaporator to the subcooled condensation region in a very short time of oscillation, turning vapor phase into oversaturated status. Rapid condensation accelerated shrinkage of the vapor bubbles causing strong micro jet impingement to damage the pipe wall, radiating acoustical signals.     

Emergent reaction-diffusion phenomena in capillary tubes

Pattern formation in the Belousov-Zhabotinsky reaction experiments carried out by filling capillary glass tubes with catalyst-immobilized gel for the reaction is reported. Under unperturbed and oscillatory conditions, helicoidal waves appear spontaneously. Quantitative structural data of those helices are obtained by devising an optical tomography technique for extracting rotationally symmetric structures from time-lapse data. Space-time representation of the catalyst oxidation reveals wave transmission phenomenon that is studied further by numerical simulations of a reduced spatial model.     

Energy spectra of electrons in plasma accelerators

The acceleration of electrons in the fast (relativistic) plasma wave, generated, e.g., by intense laser pulse in an underdense plasma, is studied theoretically and numerically. The analytical method, developed to describe the energy spectrum of electrons accelerated in one-dimensional (1-D) plasma wave of an arbitrary form, predicts the “bunching” of electrons in the energy space for linear (harmonic) plasma wave in contrast to the nonlinear one. The results of one- and two-dimensional (2-D) numerical simulations of the resonant and nonresonant electron bunch acceleration are presented and discussed     

Model of ion beam guiding using a flat capillary

This work is devoted to the further development of the theoretical model of double guiding of an ion beam using a flat capillary, which has given greater insight into the structure of the charge distribution created on the capillary wall during ion transmission. It is established that in the improved model the shape of a beam trace, similar to the one obtained in an experiment, which varies with the change in the angle of the capillary rotation, is observed on a screen.     

Laser-plasma electron acceleration in dielectric capillary tubes

Electron beams and betatron X-ray radiation generated by laser wakefield acceleration in long plasma targets are studied. The targets consist of hydrogen filled dielectric capillary tubes of diameter 150 to 200 microns and length 6 to 20?mm. Electron beams are observed for peak laser intensities as low as 5×10¹⁷?W/cm². It is found that the capillary collects energy outside the main peak of the focal spot and contributes to keep the beam self-focused over a distance longer than in a gas jet of similar density. This enables the pulse to evolve enough to reach the threshold for wavebreaking, and thus trap and accelerate electrons. No electrons were observed for capillaries of large diameter (250???m), confirming that the capillary influences the interaction and does not have the same behaviour as a gas cell. Finally, X-rays are used as a diagnostic of the interaction and, in particular, to estimate the position of the electrons trapping point inside the capillary.     

Magnetic control of particle injection in plasma based accelerators

The use of an external transverse magnetic field to trigger and to control electron self-injection in laser- and particle-beam driven wakefield accelerators is examined analytically and through full-scale particle-in-cell simulations. A magnetic field can relax the injection threshold and can be used to control main output beam features such as charge, energy, and transverse dynamics in the ion channel associated with the plasma blowout. It is shown that this mechanism could be studied using state-of-the-art magnetic fields in next generation plasma accelerator experiments.     

Scaling laws of design parameters for plasma wakefield accelerators

Simple scaling laws for the design parameters of plasma wakefield accelerators were obtained using a theoretical model, which were confirmed via particle simulation studies. It was found that the acceleration length was given by Δx=0.804λp/(1−βg), where λp is the plasma wavelength and βgc the propagation velocity of the ion cavity. The acceleration energy can also be given by ΔE=(γm−1)mc²=2.645mc²/(1−βg), where m is the electron rest mass. As expected, the acceleration length and energy increase drastically as βg approached unity. These simple scaling laws can be very instrumental in the design of better-performing plasma wakefield accelerators.     

Structure and dynamics of the plasma armature of railgunmacroparticle accelerators

Results of the optical diagnostics of the plasma armature in railgun macroparticle accelerators are summarized. Determining the structure of the plasma armature and measuring its brightness and temperature at an initial stage of high-current discharge are the focus of attention. Experiments show that the plasma induced by the electric explosion of a copper foil undergoes complex variations that include plasma stratification. The plasma structure continuously changes, being of a complicated, irregular character. The lifetime of an individual stratum changes within 1 to 10 μs. In experiments on solid-body acceleration, the arc burns for a long time at the foil site, where a strong electrode erosion takes place. As the body passes through the railgun channel, the plasma armature continuously increases its length so that it gradually occupies the entire accelerator channel. the current is observed to redistribute itself from the front towards the end face of the plasma armature. The maximum brightness temperature measured in the experiments is 26000±2600 K. As is shown by the experiments, it is arguable that a magnetic-compressed discharge may be realized in a railgun solid-body accelerator with a plasma armature     

Effects of ion motion in intense beam-driven plasma wakefield accelerators

Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear collider have included intense electron beams with densities many times in excess of the plasma density. The beam's electric fields expel the plasma electrons from the beam path to many beam radii in this regime. We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA collider scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are presented. Implications of ion motion on the feasibility of the PWFA-based colliders are discussed.     

Open-type image tubes for plasma research

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 518–520, September, 1991.     

Optical guiding of laser beam in nonuniform plasma

A plasma channel produced by a short ionising laser pulse is axially nonuniform resulting from the self-defocusing. Through such preformed plasma channel, when a delayed pulse propagates, the phenomena of diffraction, refraction and self-phase modulation come into play. We have solved the nonlinear parabolic partial differential equation governing the propagation characteristics for an approximate analytical solution using variational approach. Results are compared with the theoretical model of Liu and Tripathi (Phys. Plasmas 1, 3100 (1994)) based on paraxial ray approximation. Particular emphasis is on both beam width and longitudinal phase delay which are crucial to many applications.     

MHD plasma physics in rail accelerators for hydrogen-pelletinjection in fusion reactors

The behavior of the electromagnetic and thermal quantities in a plasma arc placed between two conducting rails is analyzed. The plasma hydrogen drives the hydrogen pellets for the refueling of magnetic fusion reactors. Considering the general equations of electromagnetism and of plasma fluid dynamics and assuming steady-state conditions in a frame which is moving at the same rate as the plasma arc armature, a one-dimensional model is deduced. The effects of an applied magnetic field on the behavior of all flow variables are investigated. Results indicate that the adverse effects of plasma arc heating can be reduced by the application of a magnetic-induction field normal to the current path in the armature. At the maximum acceleration pressure (30 bar) applicable to the hydrogen pellet in the proposed one-dimensional model, the arc temperature at the pellet backend falls from 20000 to 14000 K when a magnetic induction of about 5 T is applied     

飞秒激光等离子体通道传导能量特性的研究进展

基于强飞秒激光诱导等离子体通道的基本性质,分析了等离子体通道在传导电能和射频电磁能时的一些基本问题。综述了飞秒激光等离子体通道传输电能和电磁能方面的新概念和新技术,重点描述了该领域近几年所取得的一些理论及应用的最新成果。最后,展望了飞秒激光等离子体通道在传导能量技术领域中的发展趋势。     

Radiation guiding in a plasma wave wiggler free-electron laser

The radiation guiding of a plasma wave wiggler free-electron laser (FEL) in the Compton regime was examined. It was found that a Langmuir wave supported by a plasma cylinder acts as a wiggler for the generation of high-frequency coherent radiation when an annular relativistic electron beam passes through it. The radiation mode in the Compton regime tends to be localized close to the radius of the beam. A normal-mode analysis of this process revealed that the growth rate of the instability increases as the square root of the beam current. The treatment presented is restricted to the case where the radial width of the FEL radiation mode is larger than the beam radius, but smaller than the waveguide radius     

Optical guiding of elliptical laser beam in nonuniform plasma

Guiding of laser beam in plasma channel formed by short ionizing laser pulse is studied in this paper. When a delayed pulse propagates through this channel diffraction, refraction and self-phase modulation phenomena results which are not balanced resulting in increase/decrease in beam width. These are studied using direct Variational Technique. In this paper cross-focussing phenomena is not observed. Parameters like beam width and longitudinal-phase delay of elliptical laser beam are also studied. It has been observed that the propagation of semi-major axis and semi-minor axis of elliptical beam are independent leading to oscillating guided beam.