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K. V. Lotov

Publications and source records attributed to K. V. Lotov.

46 records · Page 3Linked to original sources
arXiv2015

Guiding femtosecond high-intensity high-contrast laser pulses by copper capillaries

Propagation of high-intensity, high-contrast ($<10^{-8}$), 50\,fs laser pulses through triangilar copper capillaries is experimentally studied. The relative transmission through 20-mm-long, about 50\,$μ$m wide capillaries is directly measured to be 70\% for input intensities up to $10^{17}\,\text{W/cm}^2$. The copper reflectivity in vacuum, helium, and air is measured in the intensity range of $10^{10}$--$10^{17}\,\text{W/cm}^2$. No reflectivity decrease in vacuum and helium is observed, which leads to the conclusion that copper capillary waveguides can efficiently guide laser pulses of intensities up to $10^{19}\,\text{W/cm}^2$ on the capillary axis (that corresponds to $10^{17}\,\text{W/cm}^2$ on the walls). The reduction of the transmission efficiency to zero after a number of transmitted pulses is observed, which is caused by plug formation inside the capillary. The dependence of the capillary lifetime on the pulse energy is measured.

physics.plasm-ph↗
arXiv2015

Physics of beam self-modulation in plasma wakefield accelerators

The self-modulation instability is a key effect that makes possible the usage of nowadays proton beams as drivers for plasma wakefield acceleration. Development of the instability in uniform plasmas and in plasmas with a small density up-step is numerically studied with the focus at nonlinear stages of beam evolution. The step parameters providing the strongest established wakefield are found, and the mechanism of stable bunch train formation is identified.

physics.plasm-ph↗
arXiv2014

Note on quantitatively correct simulations of the kinetic beam-plasma instability

A large number of model particles is shown necessary for quantitatively correct simulations of the kinetic beam-plasma instability with the clouds-in-cells method. The required number of particles scales inversely with the expected growth rate, as in the kinetic regime only a narrow interval of beam velocities is resonant with the wave.

physics.plasm-ph↗
arXiv2014

Electron trapping and acceleration by the plasma wakefield of a self-modulating proton beam

It is shown that co-linear injection of electrons or positrons into the wakefield of the self-modulating particle beam is possible and ensures high energy gain. The witness beam must co-propagate with the tail part of the driver, since the plasma wave phase velocity there can exceed the light velocity, which is necessary for efficient acceleration. If the witness beam is many wakefield periods long, then the trapped charge is limited by beam loading effects. The initial trapping is better for positrons, but at the acceleration stage a considerable fraction of positrons is lost from the wave. For efficient trapping of electrons, the plasma boundary must be sharp, with the density transition region shorter than several centimeters. Positrons are not susceptible to the initial plasma density gradient.

physics.plasm-ph↗
arXiv2014

Transition regime of the one-dimensional two-stream instability

The transition between kinetic and hydrodynamic regimes of the one-dimensional two-stream instability is numerically analyzed, and the correction coefficients to the well-known textbook formulae are calculated. The approximate expressions are shown to overestimate the growth rate several times in a wide parameter area.

physics.plasm-ph↗
arXiv2014

Parameter sensitivity of plasma wakefields driven by self-modulating proton beams

The dependence of wakefield amplitude and phase on beam and plasma parameters is studied in the parameter area of interest for self-modulating proton beam-driven plasma wakefield acceleration. The wakefield sensitivity to small parameter variations reveals the expected level of shot-to-shot jitter of experimental results. Of all the parameters, the plasma density stands out, as the wakefield phase is extremely sensitive to this parameter. The study of large variations determines the effects that limit the achievable accelerating field in different parts of the parameter space: nonlinear elongation of the wakefield period, insufficient charge of the drive beam, emittance-driven beam divergence, and motion of plasma ions.

physics.plasm-ph↗
arXiv2012

Effect of plasma inhomogeneity on plasma wakefield acceleration driven by long bunches

Effects of plasma inhomogeneity on self-modulating proton bunches and accelerated electrons were studied numerically. The main effect is the change of the wakefield wavelength which results in phase shifts and loss of accelerated particles. This effect imposes severe constraints on density uniformity in plasma wakefield accelerators driven by long particle bunches. The transverse two stream instability that transforms the long bunch into a train of micro-bunches is less sensitive to density inhomogeneity than are the accelerated particles. The bunch freely passes through increased density regions and interacts with reduced density regions.

physics.plasm-ph↗
arXiv2012

Natural noise and external wake field seeding in a proton-driven plasma accelerator

We discuss the level of natural shot noise in a proton bunch-driven plasma accelerator. The required seeding for the plasma wake field must be larger than the cumulative shot noise. This is the necessary condition for the axial symmetry of the generated wake and the acceleration quality. We develop an analytical theory of the noise field and compare it with multi-dimensional simulations. It appears that the natural noise wake field generated in plasma by the available at CERN super-protons-synchrotron (SPS) bunches is very low, at the level of a few 10 kV/m. This fortunate fact eases the requirements on the seed. Our three dimensional simulations show that even a few tens MeV electron bunch precursor of a very moderate intensity is sufficient to seed the proton bunch self-modulation in plasma.

physics.plasm-ph↗
arXiv2011

Analytical model of brittle destruction based on hypothesis of scale similarity

The size distribution of dust particles in nuclear fusion devices is close to the power function. A function of this kind can be the result of brittle destruction. From the similarity assumption it follows that the size distribution obeys the power law with the exponent between -4 and -1. The model of destruction has much in common with the fractal theory. The power exponent can be expressed in terms of the fractal dimension. Reasonable assumptions on the shape of fragments concretize the power exponent, and vice versa possible destruction laws can be inferred on the basis of measured size distributions.

physics.plasm-ph↗