Energy from colliding phonon sheets in liquid 4He

When phonon sheets collide, they can produce a hot line in liquid 4He. The dependence of the energy in the hot line on the angle between two phonon sheets and the energy density in them was measured. It found that the magnitude of the maximum of the low-energy phonon signal of the hot line is directly proportional to the value of this angle at its small values and falls to zero at high angles. The dynamic equilibrium of the hot line was modeled by equating the energy gain from the consumption of the sheets with the energy loss due to the creation of high-energy phonons. At the same time, using theoretical values of the rate of formation of high-energy phonons from low-energy ones, good agreement with experimental results was obtained. We showed that the key factor in this process is the solid angle in the momentum space occupied by low-energy phonons, under the assumption that the magnitude of this solid angle is proportional to the initial energy density in a phonon system.