L. P. Mezhov-Deglin

Observation of an inverse energy cascade in developed acoustic turbulence in superfluid helium.

We report observation of an inverse energy cascade in second sound acoustic turbulence in He II. Its onset occurs above a critical driving energy and it is accompanied by giant waves that constitute an acoustic analogue of the rogue waves that occasionally appear on the surface of the ocean. The theory of the phenomenon is developed and shown to be in good agreement with the experiments.

Quasiadiabatic decay of capillary turbulence on the charged surface of liquid hydrogen.

We study the free decay of capillary turbulence on the charged surface of liquid hydrogen. We find that decay begins from the high frequency end of the spectral range, while most of the energy remains localized at low frequencies. The apparent discrepancy with the self-similar theory of nonstationary wave turbulent processes is accounted for in terms of a quasiadiabatic decay wherein fast nonlinear wave interactions redistribute energy between frequency scales in the presence of finite damping at all frequencies. Numerical calculations based on this idea agree well with experimental data.

A method to measure the resonance transitions between the gravitationally bound quantum states of neutrons in the GRANIT spectrometer

We present a method to measure the resonance transitions between the gravitationally bound quantum states of neutrons in the GRANIT spectrometer. The purpose of GRANIT is to improve the accuracy of measurement of the quantum states parameters by several orders of magnitude, taking advantage of long storage of ultracold neutrons at specular trajectories. The transitions could be excited using a periodic spatial variation of a magnetic field gradient. If the frequency of such a perturbation (in the frame of a moving neutron) coincides with a resonance frequency defined by the energy difference of two quantum states, the transition probability will sharply increase. The GRANIT experiment is motivated by searches for short-range interactions (in particular spin-dependent interactions), by studying the interaction of a quantum system with a gravitational field, by searches for extensions of the Standard model, by the unique possibility to check the equivalence principle for an object in a quantum state and by studying various quantum optics phenomena.

Excitation and Detection of Nonlinear Waves on a Charged Surface of Liquid Hydrogen

A new technique for exciting nonlinear waves on a charged surface of liquid hydrogen is described. Methods of optical detection of surface oscillations in experiments on capillary turbulence at frequencies of up to 10 kHz are discussed. The results of a study of capillary waves on the surface of liquid hydrogen are presented.

Measurement of the boundary frequency of the inertial interval of capillary wave turbulence at the surface of liquid hydrogen

The boundary frequency was experimentally measured for the upper edge of an inertial interval corresponding to the Kolmogorov spectrum for energy distribution over the oscillation frequencies at the surface of liquid hydrogen. It is shown that the dependence of boundary frequency ωb on the wave amplitude ηp at the pump frequency ωp is well described by the power law ωb∼ηp4/3ωp23/9.

Formation of a direct Kolmogorov-like cascade of second-sound waves in He II.

Based on measurements of nonlinear second-sound resonances in a high-quality resonator, we have observed a steady-state wave energy cascade in He II involving a flux of energy through the spectral range towards high frequencies. We show that the energy balance in the wave system is nonlocal in K space and that the frequency scales of energy pumping and dissipation are widely separated. The wave amplitude distribution follows a power law over a wide range of frequencies. Numerical computations yield results in agreement with the experimental observations. We suggest that second-sound cascades of this kind may be useful for model studies of acoustic turbulence.

Stationary soliton on a charged surface of liquid helium and hydrogen films

A change in the shape of a charged surface of liquid hydrogen and helium — the formation of a solitary wave (a positively charged hump for hydrogen and a negatively charged dimple for helium)-is observed in an electric field exceeding a critical value under conditions of total compensation of the applied field by the surface charge.

Static phenomena at the charged surface of liquid hydrogen

Evolution of the shape of the equipotentially charged surface of the liquid hydrogen layer covering the lower plate of a horizontally arranged flat diode in increasing external stretching electric fields has been studied experimentally for the first time. Reconstruction of a flat charged surface (formation of a stationary hump) at voltages higher than a certain critical value Uc1 is observed under conditions of total compensation of the electric field in the bulk of the liquid by a surface charge. It is shown that the transition of the flat charged surface to the reconstructed state is a phase transition close to a second-order transition. The height of the hump is found to increase with voltage, the reconstructed surface loses its ability at a voltage Uc2>1.2Uc1, and a streamed discharge is observed. Evolution of the shape of a charged droplet of constant volume suspended from the upper plate of a diode is studied with increasing electric field under the conditions when the forces of gravity and stretchi...

Negative charges in liquid hydrogen and deuterium

The temperature and pressure dependence of the mobilities of negative charges injected into liquid hydrogen and deuterium have been measured. We propose the existence of two types of charge carriers in liquid parahydrogen. One is a bubble with an electron inside while the other has higher mobility. Relaxation of the current through liquid hydrogen was observed. It is suggested that in liquid and solid hydrogen under β-irradiation neutral complexes are created which can trap the negative charges and have a lifetime of about 10 hours.

Structural transitions in ice samples at low temperatures and pressures

The structure of ice samples formed in the decay of a water impurity gel at temperatures above 4 K and atmospheric pressure has been examined. The X-ray diffraction analysis indicates that three phases coexist in the initial sample at temperatures of 85–110 K. These phases are amorphous ice occupying up to 30% of the sample volume, cubic-phase ice Ic metastable at low pressures (∼60%), and normal hexagonal ice Ih (≤6%). The characteristic sizes of crystals of the cubic and hexagonal phases are about 6 and 30 nm, respectively. The amorphous phase at annealing above 110 K is gradually transformed to the crystalline phase both cubic and hexagonal. This transition is accompanied by two processes, including a fast increase in the sizes of cubicphase nanocrystals and the partial transition of the cubic phase Ic to the hexagonal one Ih. Hexagonal ice Ih prevails in the bulk of the sample above 200 K.