QFS2016 Book of Abstracts

Abstracts

P2.15 Exploding and Imaging Bubbles in Superfluid Helium Yadav Neha(1), Vadakumbatt Vaisakh(1), Maris Humphrey J.(2), Ghosh Ambarish(3) 1)Indian Institute of Science, Department of Physics, Bangalore, India 560012 2) Brown University, Department of Physics, Providence, Rhode Island 02912 3) Indian Institute of Science, Center For Nano Science And Engineering, Bangalore, India 560012 An electron bubble in liquid Helium-4 under saturated vapour pressure becomes hydrodynamically unstable at a pressure more negative than-1.9 bars, which can be easily achieved with focused sound waves. Here, we report on imaging the cavitation of an electron bubble at 30000 frames per second, which reveals that the bubbles can grow to as large as 1 mm within 2 ms of the cavitation event. As revealed from our numerical simulations, the inertia of the bubble wall during cavitation plays an important role in determining its maximum size. The dependence on temperature and static pressure within the experimental chamber will also be discussed. P2.16 NANO-SIZE INHOMOGENEITY SUBSTRATE ANALYSIS USING SURFACE ELECTRONS OVER SUPERFLUID HELIUM FILM Bezsmolnyy Yaroslav, Nikolaenko Viktor, Sokolov Svyatoslav B.Verkin Institute for Low Temperature Physics and Engineering of NAS of Ukraine, Department of Physics of Quantum Fluids and Crystals, Prospekt Nauky, 47, Kharkiv 61103, Ukraine The quality of the substrate is a crucial in building of a quantum system. The surface electrons (SEs) over helium film with thickness d on substrate can be a good tool to analyze the surface. The mobility of SEs is limited by interactions with the helium atoms in gas, with ripplons and by surface roughness: m − 1 = m − 1 c + m − 1 im ( m c and m im are mobilities of SE for ideal and real substrate). The variation potential from substrate is

1 / 2

e 2 4 π 0 Z

πξ A

A Z

e − 2 πZ A

δv ≈ − Q d

(0.1)

( Z is distance of SE from the substrate, ξ and A are effective amplitude and period of inhomogeneities). At A ≈ z ≈ d ≈ 10 − 5 cm (z is distance from liquid helium surface) δV ≈ 10 − 3 K and at z ≈ d ≈ A/ 2 the δV ≈ 1 K that leads to decreasing SEs conductivity. We suppose the activation energy can be applied instead of value δV . Here we propose innovation method providing a uniformity of d by accurate horizon of the cell and using electro-mechanic driver with plunger to adjust the liquid level.

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