Paul Fontana

• Seattle University

Maxwell’s demon is an entity in a 150-year-old thought experiment that paradoxically appears to violate the second law of thermodynamics by reducing entropy without doing work. It has increasingly practical implications as advances in nanomachinery produce devices that push the thermodynamic limits imposed by the second law. A well-known explanatio...

The control of matter motion at liquid–gas interfaces opens an opportunity to create two-dimensional materials with remotely tunable properties. In analogy with optical lattices used in ultra-cold atom physics, such materials can be created by a wave field capable of dynamically guiding matter into periodic spatial structures. Here we show experime...

http://www.nature.com/articles/ncomms14325 The control of matter motion at liquid–gas interfaces opens an opportunity to create two-dimensional materials with remotely tunable properties. In analogy with optical lattices used in ultra-cold atom physics, such materials can be created by a wave field capable of dynamically guiding matter into period...

Rotating wave visualized using diffusive light imaging technique. The axis of the rotation is the nodal point, where z = 0.

Theoretically simulated surface and contour plots of surface elevation on a 2x2 unit cell box. Time scale is one wave period.

Theoretically simulated contours of constant surface elevation and vectors of the potential velocity on a 2×2 unit cell box. Time scale is one wave period.

Supplementary Figures

Two-dimensional flows have different stability behavior than their three-dimensional counterparts due to enstrophy conservation, but they have not been studied as thoroughly in experiments. We present data from quasi-two-dimensional flow experiments suggesting that basic shear flows show instability not predicted by theory, while square-votex-latti...

Seattle University -- The effects of kinematic viscosity and surface drag are both significant factors in many experimental and natural quasi-two-dimensional (Q-2D) flows. These effects, however, are difficult to distinguish from one another. In a Q-2D experiment involving soap films in a circular Couette cell, we demonstrate precise independent me...

Many fluid flows in nature and the laboratory exhibit quasi-two-dimensional (Q2D) dynamics. Accurate measurements of viscosity and surface friction in Q2D flows are critical for comparing experiments with theoretical and numerical models, but have proven elusive. We demonstrate precise, independent measurements of both quantities in a Q2D experimen...

In many experimental and natural quasi-two-dimensional (Q-2D) flows the effects of internal viscosity and surface friction are significant but difficult to distinguish. We have made precise, independent measurements of both kinematic viscosity and coefficient of external drag as functions of film thickness in a Q-2D experiment using soap films in a...

In many experimental and natural quasi-two-dimensional (Q-2D) flows the effects of internal viscosity and surface friction are significant but difficult to distinguish. We demonstrate precise, independent measurements of both kinematic viscosity and coefficient of external drag in a Q-2D experiment using soap films in a circular Couette cell config...

A novel experiment to investigate fluid dynamics in quasi-two-dimensional flows has been built. A soap film is suspended horizontally in an annular channel with a rotating outer boundary, providing mean flow shear, and a vortex array is forced electromagnetically. The experiment will investigate sheared flow stability and the effect of mean flow sh...

Measurements of forced turbulence in the presence of mean flow shear in quasi-two-dimensional flows in a circular Couette cell are underway. Initial observations indicate suppression of the turbulence by the shear, as suggested by observations of transport barriers in geostrophic flows and laboratory fusion plasmas. The apparatus generates flows in...

An experiment to study turbulence in quasi-two-dimensional flows with a controlled mean flow shear has been built. Experiments are underway to investigate the suppression of turbulent transport by sheared flow as seen in geostrophic flows and laboratory fusion plasmas. The apparatus, a circular Couette cell, uses a liquid film of dilute soap soluti...

An experiment to study turbulence in quasi-two-dimensional flows with a controlled mean flow shear has been built. Experiments are underway to investigate the suppression of turbulent transport by sheared flow as seen in geostrophic flows and laboratory fusion plasmas. The apparatus, a two-dimensional Couette cell, uses a liquid film of dilute soap...

An experiment is under construction to study turbulence in two-dimensional flows with a controlled mean flow shear. The results will shed light on the suppression of turbulent transport by sheared flow seen in geostrophic flows and laboratory fusion plasmas. The apparatus uses a liquid film of dilute soap solution suspended freely in an annular cha...

An experiment is under construction to study turbulence in two-dimensional flows in the presence of a well-controlled mean flow shear. In quasi-two-dimensional contexts including geostrophic flows in the atmosphere and laboratory fusion plasmas, transport barriers have been observed in regions of high shear. This is apparently due to enhanced decor...

A new experiment seeks to examine equilibrium, stability, and confinement properties of toroidal electron plasmas. Electron plasmas with density about 3 x 10 (exp 6)/cu cm are trapped for ^100 micro seconds in a "partially" toroidal (or 'C'-shaped) trap (B^^200 G). Large amplitude oscillations are observed in the 100 kHz frequency range. The oscill...

Electron plasmas are trapped in a novel “partially” toroidal (or “C”-shaped) trap designed to study issues of equilibrium, stability, and confinement of toroidal nonneutral plasmas. Plasmas with densities as high as 3.3×106 cm−3 are trapped and decay on a 100 μs timescale in a 196 G magnetic field. Successful trapping of dense electron plasmas requ...

Improved confinement has been achieved in the MST through control of the poloidal electric field, but it is now known that the improvement has been limited by bursts of an edge-resonant instability. Through refined poloidal electric field control, plus control of the toroidal electric field, we have suppressed these bursts. This has led to a total...

With auxiliary inductive parallel current drive, fluctuation reduction and improved confinement are now routinely achieved in the MST. Most recently, this has resulted in an MST-record electron temperature of 840 eV, a total beta of 14 per cent, and an estimated RFP-record energy confinement time of 9 ms, which substantially exceeds the confinement...

Electron beams with n≈ 5× 10^5 cm-3 are generated in a toroidal magnetic field (B=120 G, R_o=43 cm, a=4.5 cm). Installation of a set of auxiliary electrodes permits application of a horizontal (major radial) electric field. The horizontal electric field produces a controlled vertical E× B drift which compensates for the curvature and nabla B dri...

Auxiliary edge current drive is routinely applied in the Madison Symmetric Torus [R. N. Dexter, D. W. Kerst, T. W. Lovell &etal;, Fusion Technol. 19, 131 (1991)] with the goal of modifying the parallel current profile to reduce current-driven magnetic fluctuations and the associated particle and energy transport. Provided by an inductive electric f...

The fluctuation-induced dynamo $〈\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathbf{v}}\ifmmode\times\else\texttimes\fi{}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathbf{b}}〉$ has been investigated by direct measurement of $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathbf{v}}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathbf{b}}$ in...

MHD dynamo activity is large in the MST Reversed-Field Pinch during sawtooth crashes, and small otherwise. During a sawtooth crash, ion temperature increases rapidly to a level several times as high as the temperature between sawteeth, which itself can be larger than the electron temperature. Several theories have been developed to explain this ion...

Reduction of core-resonant magnetic fluctuations and improved confinement in the MST is reliably achieved through control of the poloidal electric field. However, the achieved confinement has been limited by a burst-like instability originating in the plasma edge. Now, improved control of the poloidal and toroidal electric fields allows multi-ms su...

Insertable optical, magnetics, and Langmuir probe diagnostics have provided new measurements of ion flow related dynamics in the edge of MST including ion particle transport and the dynamo effect. Total fluctuation-induced transport is found to be bounded by a few x10^20particles/m^2s away from a sawtooth event and about 10^21particles/ m^2s during...

Parallel current density and heat flux have been measured in the outer 10% of MST reversed-field pinch plasmas during improved confinement brought about by Pulsed Poloidal Current Drive (PPCD), a technique which attempts to inductively increase the edge parallel current. Measured with insertable Rogowskii and pyrobolometer probes, respectively, the...

Plasma flow velocity fluctuations have been directly measured in the high-temperature magnetically confined plasma in the Madison Symmetric Torus (MST) Reversed-Field Pinch (RFP) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. These measurements show that the flow velocity fluctuations are correlated with magnetic field fluctuations such tha...

<?Pub Inc> The magnetohydrodynamic (MHD) dynamo, < v~ × b~ >, and edge plasma flow profiles have been measured spectroscopically in the edge of the Madison Symmetric Torus (MST) Reversed-Field Pinch (RFP). The dynamo has been anticipated by theory and experiment to drive current not accounted for by applied or induced electric fields in the RFP. Pr...

A novel insertable probe for local measurements of equilibrium and fluctuating plasma ion flow velocity and temperature via Doppler spectroscopy is described. Optical radiation is collected by two fused silica fiber optic bundles with perpendicular viewlines. Spatial resolution of about 5 cm is achieved by terminating each view with an optical dump...

Huge ( ~100-1000eV) jumps in ion temperature on a very fast ( ~60-80 ms) timescale have long been observed during sawteeth on MST, followed by slower cooling of the ions to pre-sawtooth energies. New measurements of the MST ion temperature profile during sawteeth have been made, combining data from charge-exchange measurements of bulk ions and from...

An upgrade of MST's Charge Exchange Analyzer (CXA) has provided measurements of the distribution function of the majority ion species with higher energy resolution. These measurements indicate nonthermal features in the tail of the distribution function that are localized in energy (width

One important step toward public education about fusion energy is to first elevate the public's appreciation of science in general. Toward this end, the Wonders of Physics program was started at the University of Wisconsin-Madison in 1984 as a public lecture and demonstration series in an attempt to stem a growing tide of science illiteracy and to...

Azimuthal localization of sound is determined by interaural time differences(ITD) and interaural intensity differences (IID). The relative importance of these cues in a localization decision is the subject of time?intensity trading. The plausibility hypothesis [B. Rakerd and W. M. Hartmann, J. Acoust. Soc. Am. 78, 524?533 (1985)] says that ITD cues...

The magnetic field configuration of the Reversed-Field Pinch (RFP) typically exhibits resistive tearing modes of poloidal mode number m = 1 resonant in the plasma core and m = 0 resonant in the plasma edge. In the Madison Symmetric Torus (MST) RFP, these fluctuations cause electromagnetic torques which alter the flow profile, and magnetic reconnect...

Improved confinement and beta have been obtained in the Madison Symmetric Torus1 (MST) reversed field pinch (RFP) by (1) programmed modification of the inductive electric field and (2) current injection from localized electrostatic sources distributed around the surface of the plasma. Both are attempts to modify the parallel current profile to redu...

A novel diagnostic for making local measurements of plasma ion velocity, both equilibrium and fluctuating, has been developed and implemented in the edge of MST. The diagnostic, the Ion Dynamics Spectrometry Probe (IDSP), measures two components of ion velocity simultaneously using the Doppler shift of impurity (HeII) line radiation viewed in two l...

Small dynamo events (SDE's) are burst-like instabilities accompanying (only) two types of enhanced confinement discharge in the MST RFP. One such discharge is brought about by edge auxiliary poloidal current drive, while the other occurs spontaneously (requiring, e.g., careful wall conditioning). SDE's normally occur every 1-2 ms, causing a momenta...

Measurement of electrostatic fluctuations, electrostatic fluctuation induced transport, and MHD dynamo will be reported for improved confinement plasmas in the MST RFP using Langmuir and magnetic probes in the edge of the plasma. In plasmas with inductive poloidal current drive(PPCD), the electrostatic current injection the fluctuation level depend...

A number of issues associated with the interaction of plasma flows and currents with plasma fluctuations in RFP plasmas are addressed. Self-consistency arguments on the structure of turbulent mean field forces imply a relaxation behavior for both the current and plasma momentum. Nonlinear tearing mode interaction affect flow profile evolution throu...