- PlasmaTalks: Ron Davidson and Cédric Villani
- Author Interview: Rudolf Neu and Guy Matthews
- Author Interview: David Schaffner
- Author Interview: Ellen Zweibel
- Author Interview: Liu Chen

## PlasmaTalks - Conversations Between Experts

To accompany the recent publication of the Special Tutorial: Particle systems and nonlinear Landau damping by 2010 Fields Medalist Professor Cédric Villani, *Physics of Plasmas* is glad to announce PlasmaTalks: conversations between experts. In this PlasmaTalks episode: Ron Davidson, *Physics of Plasmas’* Editor-in-Chief, interviews Cédric Villani.

### PlasmaTalks: Ron Davidson interviews Cédric Villani

PhotothèqueCNRS - Sebastien Godefroy.

In this fascinating exchange, Cédric Villani and Ron Davidson discuss a wide range of topics, going from Professor Villani’s path into the study of Mathematics and Physics, to possible generalizations of the Landau damping theoretical model, plasma physics challenging problems and open questions, to name a few. Join the conversation by clicking to play the full podcast (38:10) or its segments.

**Links to the Interview Sections**

0:00 - Ron Davidson introduces Cédric Villani

3:34 - What inspired Cédric Villani to enter a career in Mathematics and Physics

6:40 - Aspects of plasmas that attracted Cédric Villani to study their fundamental properties

### About Cédric Villani

Cédric Villani is Professeur at Université de Lyon. He received the Fields Medal in 2010 for his proofs of nonlinear Landau damping and convergence to equilibrium for the Boltzmann equation. His awards include the Jacques Herbrand Prize of the French Academy of Science (2007), the Prize of the European Mathematical Society (2008), the Henri Poincaré Prize of the International Association for Mathematical Physics, and the Fermat Prize (2009). In 2009, he was appointed as the director of the Institut Henri Poincaré (IHP) in Paris, and part-time visitor at the Institut des Hautes Etudes Scientifiques (IHES).

### Read More from Cédric Villani in AIP Publishing Journals

**Particle systems and nonlinear Landau damping**

Cédric Villani

Phys. Plasmas **21**, 030901 (2014)

** Landau damping**

C. Mouhot and C. Villani

J. Math. Phys. **15**, 015204 (2010)

## PoP Podcasts

In PoP Podcasts selected authors are invited to present their recent contributions to the journal. Experimental and theoretical advances in plasma physics are discussed, reflecting the richness of the original work published in *Physics of Plasmas.*

### Author Interview: Rudolf Neu and Guy Matthews

**
First operation with the JET International Thermonuclear Experimental Reactor-like wall **

R. Neu, G. Arnoux, M. Beurskens, V. Bobkov, S. Brezinsek, J. Bucalossi, G. Calabro, C. Challis, J. W. Coenen, E. de la Luna, P. C. de Vries, R. Dux, L. Frassinetti, C. Giroud, M. Groth, J. Hobirk, E. Joffrin, P. Lang, M. Lehnen, E. Lerche, T. Loarer, P. Lomas, G. Maddison,C. Maggi, G. Matthews, S. Marsen, M.-L. Mayoral, A. Meigs, Ph. Mertens, I. Nunes, V. Philipps, T. Pütterich, F. Rimini, M. Sertoli, B. Sieglin, A. C. C. Sips, D. van Eester, G. van Rooij and JET-EFDA Contributors

Phys. Plasmas **20**, 056111 (2013)

Click to Play or Download (9:55)

To consolidate International Thermonuclear Experimental Reactor (ITER) design choices and prepare for its operation, Joint European Torus (JET) has implemented ITER's plasma facing materials, namely, Be for the main wall and W in the divertor. In addition, protection systems, diagnostics, and the vertical stability control were upgraded and the heating capability of the neutral beams was increased to over 30 MW. First results confirm the expected benefits and the limitations of all metal plasma facing components (PFCs) but also yield understanding of operational issues directly relating to ITER. H-retention is lower by at least a factor of 10 in all operational scenarios compared to that with C PFCs. The lower C content (≈ factor 10) has led to much lower radiation during the plasma burn-through phase eliminating breakdown failures. Similarly, the intrinsic radiation observed during disruptions is very low, leading to high power loads and to a slow current quench. Massive gas injection using a D2/Ar mixture restores levels of radiation and vessel forces similar to those of mitigated disruptions with the C wall. Dedicated L-H transition experiments indicate a 30% power threshold reduction, a distinct minimum density, and a pronounced shape dependence. The L-mode density limit was found to be up to 30% higher than for C allowing stable detached divertor operation over a larger density range. Stable H-modes as well as the hybrid scenario could be re-established only when using gas puff levels of a few 10^{21} es^{−1}. On average, the confinement is lower with the new PFCs, but nevertheless, H factors up to 1 (H-Mode) and 1.3 (at

In the figure: JET ITER-like Wall in the final phase of installation. The remote handling manipulator which was used to replace the ~4000 tiles can be seen. The main wall tiles are mostly beryllium, beryllium coated Inconel and the divertor tungsten coated carbon fibre tiles and a bulk tungsten central tile.

### About the Authors

Rudolf Neu entered fusion research as a postdoc in 1992 at the Max Planck Institut für Plasmaphysik (IPP). From 1995 on he coordinated the activities related to the use of tungsten plasma facing components at the Tokamak ASDEX Upgrade leading to the first tokamak with all W PFCs in 2007, which provided the basis for the use of W PFCs in JET and ITER. In 2006 he became Leader of the Plasma Wall Interaction Group at ASDEX Upgrade and in 2011 Deputy Head of the department “Plasma Edge and Wall” at IPP. In 2009 he became co-leader with Guy Matthews of the JET Task Force responsible for first scientific exploitation of the new JET wall. Since 2012 he is Head of the ITER Physics Department of the European Fusion Development agreement.

Guy Matthews has worked in magnetic fusion research at the Culham Centre for Fusion Energy since 1984 when he completed his doctoral studies in plasma physics at Oxford University. In 1993 he was appointed Leader of the Plasma Boundary Group at the Joint European Torus (JET) which is still the world’s largest magnetic fusion facility. He became Project Leader for the JET ITER-like Wall Project in 2005 which changed the JET wall material from carbon to beryllium and tungsten. This change has enabled JET to address critical issues for the international ITER machine which is under construction. In 2009 he became co-leader with Rudi Neu of the JET Task Force responsible for first scientific exploitation of the new JET wall.

### Background to JET and ITER

The Joint European Torus was built as part of European fusion programme and is operated as a shared facility currently within the framework of the European Fusion Development Agreement. It is the world’s largest tokamak and has achieved the record for fusion power production (16MW) using deuterium /tritium plasmas. The international ITER machine which is currently under construction aims to increase this record to 500MW. Since completion of the ITER-like Wall project in 2011, JET is the only machine operating with beryllium and tungsten wall surfaces. Current research is focused on building the necessary experience for efficient exploitation of the ITER tokamak with particular emphasis on issues related to wall materials.

### Read More from the Authors in AIP Publishing Journals

**Benefits and Challenges of the Use of High‐Z Plasma Facing Materials in Fusion Devices**

R. Neu

AIP Conf. Proc. **1237**, 62 (2010)

**Particle and impurity transport in the Axial Symmetric Divertor Experiment Upgrade and the Joint European Torus, experimental observations and theoretical understanding **

C. Angioni, L. Carraro, T. Dannert, N. Dubuit, R. Dux, C. Fuchs, X. Garbet, L. Garzotti, C. Giroud, R. Guirlet, F. Jenko, O. J. W. F. Kardaun, L. Lauro-Taroni, P. Mantica, M. Maslov, V. Naulin, R. Neu, A. G. Peeters, G. Pereverzev, M. E. Puiatti, T. Pütterich, J. Stober, M. Valovič,M. Valisa, H. Weisen, A. Zabolotsky, ASDEX Upgrade Team and JET EFDA Contributors

Phys. Plasmas **20**, 055905 (2007)

**Tungsten Spectroscopy for Fusion Plasmas**

R. Neu, T. Pütterich, R. Dux, A. Pospieszczyk, G. Sergienko, ASDEX Upgrade Team andTEXTOR Team

AIP Conf. Proc. **901**, 85 (2007)

**Development of an ITER relevant advanced scenario at ASDEX Upgrade **

O. Gruber, A. C. C. Sips, A. Staebler, R. Dux, J. Hobirk, L. D. Horton, C. F. Maggi, A. Manini, M. Maraschek, R. Neu, ASDEX Upgrade Team and Y. S. Na

Phys. Plasmas **12**, 056127 (2005)

## PoP Podcasts

In PoP Podcasts selected authors are invited to present their recent contributions to the journal. Experimental and theoretical advances in plasma physics are discussed, reflecting the richness of the original work published in *Physics of Plasmas.*

### Author Interview: David Schaffner

**Turbulence and transport suppression scaling with flow shear on the Large Plasma Device**

D. A. Schaffner, T. A. Carter, G. D. Rossi, D. S. Guice, J. E. Maggs, S. Vincena and B. Friedman

Phys. Plasmas **20**, 055907 (2013)

Click to Play or Download (9:43)

Continuous control over azimuthal flow and shear in the edge of the Large Plasma Device (LAPD) [W. Gekelman et al., Rev. Sci. Instr. 62, 2875 (1991)] has been achieved using a biasable limiter. This flow control has allowed a careful study of the effect of flow shear on pressure-gradient-driven turbulence and particle transport in LAPD. The combination of externally controllable shear in a turbulent plasma along with the detailed spatial diagnostic capabilities on LAPD makes the experiment a useful testbed for validation of shear suppression models. Motivated by these models, power-law fits are made to the density and radial velocity fluctuation amplitudes, particle flux, density-potential crossphase, and radial correlation length. The data show a break in the trend of these quantities when the shearing rate ( *γ**s*=∂*V**θ*/∂*r* ) is comparable to the turbulent decorrelation rate ( 1/*τ*ac ). No one model captures the trends in the all turbulent quantities for all values of the shearing rate, but some models successfully match the trend in either the weak ( *γ**s**τ*ac<1 ) or strong ( *γ**s**τ*ac>1 ) shear limits.

### About the Authors

David Schaffner is a postdoctoral researcher at Swarthmore College working on the Swarthmore Spheromak Experiment (SSX). He completed his Ph.D. in Plasma Physics at the University of California, Los Angeles in 2013 with an experiment on the Large Plasma Device (LAPD) at the Basic Plasma Research Facility. He also received his B.S. in Physics from UCLA in 2006.

Troy Carter is Professor of Physics at UCLA where he has been since 2001. He received a B.S. in Physics and a B.S. in Nuclear Engineering from North Carolina State University in 1995. His graduate work was completed at Princeton University, where he earned a Ph.D. in Astrophysical Sciences (Plasma Physics) in 2001. He uses laboratory experiments and computation to study fundamental processes in plasmas, including nonlinear waves, instabilities, turbulence, and transport. Motivation for his work comes from magnetic fusion energy and from space and astrophysical plasmas.

### Read More from the Authors in AIP Publishing Journals

**Nonlinear instability in simulations of Large Plasma Device turbulence**

B. Friedman, T. A. Carter, M. V. Umansky, D. Schaffner, and I. Joseph

Phys. Plasmas **20**,055704 (2013)

**Alfvén wave collisions, the fundamental building block of plasma turbulence. III. Theory for experimental design **

G. G. Howes, K. D. Nielson, D. J. Drake, J. W. R. Schroeder, F. Skiff, C. A. Kletzing, and T. A. Carter

Phys. Plasmas **20**, 072304 (2013)

**Alfvén wave collisions, the fundamental building block of plasma turbulence. IV. Laboratory experiment **

D. J. Drake, J. W. R. Schroeder, G. G. Howes, C. A. Kletzing, F. Skiff, T. A. Carter, and D. W. Auerbach

Phys. Plasmas **20**,072901 (2013)

**Investigation of an ion-ion hybrid Alfvén wave resonator**

S. T. Vincena, W. A. Farmer, J. E. Maggs, and G. J. Morales

Phys. Plasmas **20**,012111 (2013)

**Energy dynamics in a simulation of LAPD turbulence **

B. Friedman, T. A. Carter, M. V. Umansky, D. Schaffner, and B. Dudson

Phys. Plasmas **19**,102307 (2012)

**Sheared-flow induced confinement transition in a linear magnetized plasma **

S. Zhou, W. W. Heidbrink, H. Boehmer, R. McWilliams, T. A. Carter, S. Vincena, B. Friedman, and D. Schaffner

Phys. Plasmas **19**, 012116 (2012)

**Experimental investigation of geodesic acoustic mode spatial structure, intermittency, and interaction with turbulence in the DIII-D tokamak **

J. C. Hillesheim, W. A. Peebles, T. A. Carter, L. Schmitz and T. L. Rhodes

Phys. Plasmas **19**, 022301 (2012)

**The many faces of shear Alfvén waves **

W. Gekelman, S. Vincena, B. Van Compernolle, G. J. Morales, J. E. Maggs, P. Pribyl, and T. A. Carter

Phys. Plasmas **12**,055501 (2011)

**Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves **

D. W. Auerbach, T. A. Carter, S. Vincena and P. Popovich

Phys. Plasmas **18**, 055708 (2011)

**Modifications of turbulence and turbulent transport associated with a bias-induced confinement transition in the Large Plasma Device **

T. A. Carter and J. E. Maggs

Phys. Plasmas **16**, 012304 (2009)

## PoP Podcasts

In PoP Podcasts selected authors are invited to present their recent contributions to the journal. Experimental and theoretical advances in plasma physics are discussed, reflecting the richness of the original work published in *Physics of Plasmas.*

### Author Interview: Ellen Zweibel

**The microphysics and macrophysics of cosmic rays **

Ellen G. Zweibel

Phys. Plasmas **20**, 055501 (2013)

Click to Play or Download (12:25)

This review paper commemorates a century of cosmic ray research, with emphasis on the plasma physics aspects. Cosmic rays comprise only ∼ 10−9 of interstellar particles by number, but collectively their energy density is about equal to that of the thermal particles. They are confined by the Galactic magnetic field and well scattered by small scale magnetic fluctuations, which couple them to the local rest frame of the thermal fluid. Scattering isotropizes the cosmic rays and allows them to exchange momentum and energy with the background medium. I will review a theory for how the fluctuations which scatter the cosmic rays can be generated by the cosmic rays themselves through a microinstability excited by their streaming. A quasilinear treatment of the cosmic ray–wave interaction then leads to a fluid model of cosmic rays with both advection and diffusion by the background medium and momentum and energy deposition by the cosmic rays. This fluid model admits cosmic ray modified shocks, large scale cosmic ray driven instabilities, cosmic ray heating of the thermal gas, and cosmic ray driven galactic winds. If the fluctuations were extrinsic turbulence driven by some other mechanism, the cosmic ray background coupling would be entirely different. Which picture holds depends largely on the nature of turbulence in the background medium.

### About Ellen G. Zweibel

Ellen G. Zweibel is William L. Kraushaar Professor of Astronomy and Physics and Director of the Center for Magnetic Self Organization at the University of Wisconsin-Madison. She received her AB degree in Mathematics from the University of Chicago in 1973 and her PhD in Astrophysical Sciences from Princeton University in 1977. After a postdoctoral appointment at the Institute for Advanced Study from 1977-1978 and a staff appointment at the High Altitude Observatory, she held a faculty position at the University of Colorado from 1981 to 2003, where she was also a Fellow of JILA. She moved to Wisconsin in 2003.

### Read More from the Author in AIP Publishing Journals

**Magnetic reconnection in partially ionized plasmas **

Ellen G. Zweibel, Eric Lawrence, Jongsoo Yoo, Hantao Ji, Masaaki Yamada, and Leonid M. Malyshkin

Phys. Plasmas **18**, 111211 (2011)

**Effects of line-tying on magnetohydrodynamic instabilities and current sheet formation **

Yi-Min Huang, A. Bhattacharjee, and Ellen G. Zweibel

Phys. Plasmas **17**, 055707 (2010)

**Effects of line tying on resistive tearing instability in slab geometry **

Yi-Min Huang and Ellen G. Zweibel

Phys. Plasmas **16**, 042102 (2009)

**m=1 ideal internal kink modes in a line-tied screw pinch **

Yi-Min Huang, Ellen G. Zweibel, and Carl R. Sovinec

Phys. Plasmas **13**, 092102 (2006)

**Magnetohydrodynamics problems in the interstellar medium **

Ellen G. Zweibel

Phys. Plasmas **6**, 1725 (1999)

**Fast reconnection of weak magnetic fields **

Ellen G. Zweibel

Phys. Plasmas **5**, 247 (1998)

**Tilt stability of rotating current rings with resistive conductors **

Ellen G. Zweibel and Neil Pomphrey

Phys. Fluids **28**, 2517 (1985)

**Nonlinear periodic solutions for the isothermal magnetostatic atmosphere **

B. C. Low, A. J. Hundhausen, and Ellen G. Zweibel

Phys. Fluids **26**, 2731 (1983)

**A high magnetic Reynolds number dynamo **

F. W. Perkins and E. G. Zweibel

Phys. Fluids **30**, 1079 (1987)

## PoP Podcasts

*Physics of Plasmas.*

### Author Interview: Liu Chen, 2012 James Clerk Maxwell Prize for Plasma Physics

**On nonlinear physics of shear Alfvén waves **

Liu Chen and Fulvio Zonca

Phys. Plasmas **20** 055402 (2013)

Shear Alfvén waves (SAW) are electromagnetic oscillations prevalent in laboratory and nature magnetized plasmas. Due to their anisotropic nature, it is well known that the linear wave propagation and dispersiveness of SAW are fundamentally affected by plasma nonuniformities and magnetic field geometries, such as the existence of continuous spectrum, spectral gaps, and discrete eigenmodes in toroidal plasmas. This work discusses the pure Alfvénic state and demonstrates the crucial roles that finite ion compressibility, non-ideal kinetic effects, and geometry play in breaking it and, thereby, the nonlinear physics of SAW wave-wave interactions.

On this podcast session: Professor Chen discusses the nonlinear physics of shear Alfvén waves and introduces a theoretical framework based on the properties of the pure Alfvénic state (Part 1). He then addresses his commitment in training the next generation of Plasma Physicists (Part 2).

### About Liu Chen

Professor Liu Chen received the Bachelor's degree from National Taiwan University in 1966, and the Ph.D. degree from the University of California at Berkeley in 1972. From 1972 to 1974, he was a postdoctoral staff member at Bell Laboratories, Murray Hill, New Jersey. In 1974, he joined the Princeton Plasma Physics Laboratory as a research scientist, and later also became a faculty member in the Department of Astrophysical Sciences at Princeton University. In 1993, he was appointed as Professor in the Department of Physics and Astronomy at the University of California, Irvine, California, and in March 2012 he became an Above-scale Professor Emeritus. Currently, he is a Professor of Physics and the Director of the Institute for Fusion Theory and Simulation of Zhejiang University, Hangzhou, China. Professor Liu Chen is a preeminent theoretical plasma physicist with broad research interests. His current research is focused on waves, instabilities, and turbulence in magnetized laboratory and space plasmas, as well as the nonlinear dynamics of coherent high-power radiation devices. (Read more)

### Read More from the Authors in AIP Publishing Journals

**Geodesic acoustic mode excitation by a spatially broad energetic particle beam **

Z. Qiu, F. Zonca, and L. Chen

Phys. Plasmas **19**,082507 (2012)

**Linear and nonlinear behaviors of gyrotron backward wave oscillators **

Shih-Hung Chen and Liu Chen

Phys. Plasmas **19**, 023116 (2012)

**Investigation of tearing instability using GeFi particle simulation model **

X. Y. Wang, Y. Lin, L. Chen, X. Lu, and W. Kong

Phys. Plasmas **18**,122102 (2011)

**An extended hybrid magnetohydrodynamics gyrokinetic model for numerical simulation of shear Alfvén waves in burning plasmas **

X. Wang, S. Briguglio, L. Chen, C. Di Troia, G. Fogaccia, G. Vlad, and F. Zonca

Phys. Plasmas **18**,052504 (2011)

**Shear Alfvén wave continuous spectrum within magnetic islands **

Alessandro Biancalani, Liu Chen, Francesco Pegoraro, and Fulvio Zonca

Phys. Plasmas **17**,122106 (2010)

**A particle simulation of current sheet instabilities under finite guide field **

X. Y. Wang, Y. Lin, L. Chen, and Z. Lin

Phys. Plasmas **15**, 072103 (2008)

**Theory of charged particle heating by low-frequency Alfvén waves**

Zehua Guo, Chris Crabtree, and Liu Chen

Phys. Plasmas **15**, 032311 (2008)

**Role of nonlinear toroidal coupling in electron temperature gradient turbulence **

Z. Lin, L. Chen, and F. Zonca

Phys. Plasmas **12**,056125 (2005)

**Excitation of zonal flow by drift waves in toroidal plasmas **

Liu Chen, Zhihong Lin, and Roscoe White

Phys. Plasmas **7**, 3129 (2000)

**Existence of ion temperature gradient driven shear Alfvén instabilities in tokamaks **

Fulvio Zonca, Liu Chen, J. Q. Dong, and Robert A. Santoro

Phys. Plasmas **6**, 1917 (1999)

**Theory of toroidal Alfvén modes excited by energetic particles in tokamaks **

Fulvio Zonca and Liu Chen

Phys. Plasmas **3**, 323 (1996)

**Theory of magnetohydrodynamic instabilities excited by energetic particles in tokamaks **

Liu Chen

Phys. Plasmas **1**, 1519 (1994)

**Theory of kinetic ballooning modes excited by energetic particles in tokamaks **

Shih-Tung Tsai and Liu Chen

Phys. Plasmas **B 5**, 3284 (1993)

**Ballooning instabilities in tokamaks with sheared toroidal flows **

F. L. Waelbroeck and L. Chen

Phys. Plasmas **B 3**, 601 (1991)

**Microinstabilities in weak density gradient tokamak systems **

W. M. Tang, G. Rewoldt, and Liu Chen

Phys. Plasmas **29**, 3715 (1986)

**Resistive ballooning modes in an axisymmetric toroidal plasma with long mean free path **

J. W. Connor and Liu Chen

Phys. Plasmas **28**, 2201 (1985)

**Ion-temperature-gradient instability in toroidal plasmas**

P. N. Guzdar, Liu Chen, W. M. Tang, and P. H. Rutherford

Phys. Plasmas **26**, 673 (1983)

**Drift-wave eige nmodes in toroidal plasmas**

Liu Chen and C. Z. Cheng

Phys. Plasmas **23**, 2242 (1980)