P. Skyba

Electrometric direct current I/V converter with wide bandwidth

A principle of operation and electrical characteristics of a high frequency current-to-voltage (I/V) converter are presented. The I/V converter measures the electric current with selectable gains of 10(5), 10(4), and 10(3) V/A in the frequency range from DC to 500 kHz, 1.2 MHz, and 2.4 MHz, respectively. These properties make this I/V converter suitable for wide range of applications such as tuning forks, torsion oscillators, ultrasound transducers measurements, detection of the piezoelectric transducers used in STM techniques, etc., in low temperature physics. The influence of the input impedance of a I/V converter on the precision of alternating current measurements is also discussed.

Košice nuclear demagnetization refrigerator

Abstract A nuclear demagnetization refrigerator with diffusion-welded copper nuclear stage has been constructed and successfully operated. The stage consists of 80 mol of copper and is capable, starting from an initial magnetic field of 6.4 T, of cooling the superfluid 3 He-B down to temperatures of ~280 μK in a single-walled experimental cell. The apparatus is currently used to study the magnetic relaxation processes in superfluid 3 He.

Microcomputer‐controlled, programmable current source for NMR measurements at very low temperatures

The construction and electrical characteristics of a programmable, microprocessor‐controlled current source are described. The source is suitable for supplying superconducting nuclear magnetic resonance magnets as well as for general applications. The source has a bipolar output with maximum output current ±5 A/±10 V with stability better than 5×10−5 and the current step 160 μA. The rate of excitation of the output current may be varied from 2 ms to 9.999 s per step, with 1 ms resolution. The source is fully programmable via HP‐IB bus.

Simple continuous level meter for cryogenic liquids

Abstract Very simple continuous level meter with capacitive transducer for cryogenic liquids (LO 2 , LN 2 and LHe) is presented. The principle of the level meter operation is based on the phase-locked loop (PLL) technique of capacity measurements which results in a high linearity and good stability of the level measurement.

Observation of a new relaxation mechanism in3He-B

Abstract Homogeneously precessing domain (HPD) has been studied by CW NMR at low pressures and temperatures down to 0.28 T c . We observed, inconsistently to existing theory, a large absorption term linear with HPD length and inversely proportional to the temperature.

A spin laser? The persistent precessing domain in superfluid 3He-B at ultralow temperatures

We discuss various properties of the persistent precessing domain (PPD, formerly PIS) in superfluid He-3-B. These exotic NMR domains can only be excited at ultralow temperatures. At the lowest temperatures they freely precess for periods up to 2000 s. We identify various behaviors depending on the texture and magnetic field profile. We can create the domains with small generating pulses or excite them continuously but only with an excitation frequency higher than that of the domain precession. Remarkably, we can excite and sustain the precession by the application of white noise. Thus,. unusually, the coherent domain can extract energy from an incoherent energy source.

Forced oscillation of the A–B phase boundary in superfluid 3He

We present measurements conducted on the oscillating interface between superfluid He-3 A and B. The measurements, made at 150 mu K, are taken at frequencies between 100 mHz, where the boundary moves almost in thermal equilibrium with the fluid, and several kHz, where the boundary motion is highly non-linear and out of equilibrium. Driving the oscillations to higher amplitudes seems to produce different friction mechanisms dominant only after certain thresholds. As yet these phenomenon have defied any explanation, theoretical or otherwise.

Precision analog integrator with voltage hold.

In some applications, like a magnetization and demagnetization of ordinary and superconducting magnets driven by the voltage controlled current sources, it is desirable to change the voltage smoothly and linearly toward an adjusted value and then hold this value in time. A circuit is presented that allows: (i) the slow, smooth, and linear change of the integrator output voltage without steps and (ii) the ability to hold the output voltage at a value given by a reference source. In a hold regime, the output voltage is stabilized by a negative feedback. A stability of one part of 10(5) at the output voltage of 2 V was achieved over a 12 h period.

The Unique Superfluid 3He A-B Interface: Surface Tension and Contact Angle

We have measured the A-B boundary wall contact angle and the phase interface surface tension in superfluid 3He. The measurements have been made in the ballistic temperature regime at zero pressure in magnetic fields up to 400 mT. We infer the surface energies from the behaviour of the phase boundary moving in and out of a stack of glass capillary tubes. We measure the wall contact angle from the observed capillary height and obtain the interphase surface tension from the level of over- or under-magnetisation when the interface “pops” out of the capillaries. This is the first measurement of both the surface tension and contact angle in high magnetic fields.

The thermodynamics of the A–B transition in superfluid 3He as a probe of the A-phase gap node geometry

We have used a magnetic field gradient to stabilise the phase boundary between the A- and B-phases of superfluid He-3 inside a quasiparticle black body radiator down to 146 mu K; The radiator technique enables us to measure very accurately the density of quasiparticle excitations and therefore the temperature of the B-phase inside the radiator. As we ramp the held through the transition we can observe the cooling (warming) effect when the volume of A-phase is increased (decreased). From these measurements we deduce the temperature dependence of the latent heat, which provides the lowest temperature verification yet of the existence of nodes in the A-phase order parameter.