PLASMA SEMINARS AND GROUP MEETINGS

Past seminar database:
Autumn 2007; Winter-Spring 2008; Summer 2008; Autumn 2008; HT 2009;; Summer 2009; MT 2009; HT 2009;2010; Summer 2010; MT 2010; HT 2011;;; MT 2011; HT 2012; TT 2012; Summer 2012; MT 2012; HT 2013; TT & Summer 2013; MT 2013; HT 2014; TT & Summer 2014; MT 2014; HT 2015; TT & Summer 2015; MT 2015; HT 2016; TT & Summer 2016; Autumn/MT 2016; HT 2017; TT & Summer 2017; Autumn/MT 2017;

Hilary Term of 2018

The seminars/group meetings will be on Thursday at 11:30 in 501 DWB, except where indicated otherwise below.

 If you know exactly what you are going to do, what is the point of doing it? Pablo Picasso Every line in your calculations ends with "=0". You are not making much progress! Kate Hammett We don't do the calculation because we don't know the answer, we do it because we have a conscience. Bryan Taylor Let's change the resolution on the Unknown. Gabe Plunk Let me put it differently: suppose we had a reactor... Per Helander Working together takes more than one person. Bill Dorland We can't do ultraviolence to that square bracket. Ian Abel Field lines are forever. Bryan Taylor This is not really an ill-posed problem, this is not a problem at all. Paul Dellar I am just doing mathematics at the moment, but it is mathematics that has some point. Bryan Taylor The equivalent of God in MAST is MHD, which is global and all powerful. Anthony Field I've got a fishbone coming up. Tim Horbury We have crossed all the i's and dotted all the t's. Job's a good'un. Ian Abel Let us not jump in front of the bandwagon! Anonymous It's not the triviality, it's the emptiness of it that bothers me. Bryan Taylor This is a very inefficient way of achieving nothing. François Rincon We Hankel all the way in and then Hankel all the way out. Joseph Parker For the sake of fairness, let me mention that some people have objections to this, none of which are particularly valid. Chris Chen It is better to be roughly right than precisely wrong. Maynard Keynes  Yes, Steve, you have always known what we have only just figured out. Alfred Mallet This is more or less right. Perhaps less. Alfred Mallet You go ahead with your argument. I'll think. Steve Cowley Too simple? At the end of my talk, you will beg for simplicity! Andrey Beresnyak The point is not the point! Anonymous This is why I am presenting this here and nowhere else: nothing is solved! Ian Abel This calculation is not intellectual masturbation: there's no orgasm. Anonymous There are many big Buts here... I like big Buts. Anonymous Previous studies of this problem have been either unsatisfactory or limited in scope.---What  is the difference between these?---This means either wrong or irrelevant. Anatoly Spitkovsky, Michael Medvedev and Steve Cowley (in conversation) I don't give a damn about astrophysics, explain to me what is going on. Anatoly Spitkovsky Have you subtracted the baby with the bathwater? Steve Balbus   This is not rigour, unless you mean rigor mortis. Ian Abel I wouldn't say these are theoretical arguments... Let's just call them arguments. François Rincon You can never be too happy with the state of your closure. Amitava Bhattacharjee For this plot, 1 is 6.--- Weeell, not even. Steve Cowley and Steve Balbus Это качественное объяснение недостаточно качественное. Eugene Churazov If you mean it seriously, this is actually a very good question. Minhyong Kim
[these quotes are mostly from Oxford plasma seminars and Vienna meetings]

 Wk Date Time & place Speaker & Topic Background reading Comings and goings (incl. visitors in town) Thu Jan 4 No seminar 0 Thu Jan 11 11:30501 DWB Plasma Seminar (organised by ALEX) Adnane Osmane (Aalto, Finland) --- Electron phase-space holes in planetary radiation belts ApJ 846, 83 (2017) PRL 111, 235002 (2013) Fri Jan 12 9:30 Culham Pease Rm CCFE Science Meeting (organised by SARAH NEWTON) Alex Schekochihin (Oxford) --- Two etudes on unexpected behaviour of drift-wave turbulence near stability threshold I will discuss some recent results — numerical and experimental — on the nature of drift-wave turbulence in MAST, obtained in the doctoral theses of Ferdinand van Wyk [1,4], Michael J. Fox [2] and Greg Colyer [3]. At ion scales, in the presence of flow shear, we find numerically [1,4] a type of transition to turbulence that is new (as far as we know) in the tokamaks, but reminiscent of some fluid dynamical phenomena (e.g., pipe flows or accretion discs in astrophysics): close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Such a transition has its roots in the subcritical nature of the turbulence in the presence of flow shear. It can be diagnosed in terms of the breaking of the statistical up-down symmetry of turbulence: this manifests itself in the form of tilted two-point correlation functions and skewed distributions of the fluctuating density field, found both in simulations and in BES-measured density fields in MAST [2]. The governing (order) parameter in the system is the distance from the threshold, rather than individual values of equilibrium gradients; the symmetries — and drift-wave/zonal-flow turbulence of conventional type — are restored away from the threshold. The experiment appears to lie just at the edge of this latter transition rather than at the exact stability threshold. At electron scales in MAST, the conventional streamer-dominated state of ETG turbulence turns out to be a long-time transient, during which an initially unimportant zonal component continues to grow slowly, eventually leading to a new saturated state dominated by zonal modes, rather similar to ITG turbulence [3]. In this regime, the heat flux turns out to be proportional to the collision rate, in approximate agreement with the experimentally observed collisionality scaling of the energy confinement in MAST. Our explanation of this effect is based on a model of ETG turbulence dominated by zonal–nonzonal interactions and on an analytically derived scaling of the zonal-mode damping rate with the electron–ion collisionality. These developments open some intriguing possibilities both for enterprising theoreticians tired of the V&V routine and for ingenious experimentalists interested in making use of tokamaks to probe transitions to turbulence in nonlinear plasma systems. [1] JPP 82, 905820609 (2016) [2] PPCF 59, 034002 (2017) [3] PPCF 59, 055002 (2017) [4] PPCF 59, 114003 (2017) I Thu Jan 18. 11:30 TBA Plasma Group Meeting (organised by MICHAEL) Free discussion of current affairs: contributions welcome Javier Maurino-Alperovich joins the group to work with Felix Parra as visiting student II Thu Jan 25. 11:30 501 DWB Plasma Group Meeting (organised by MICHAEL) Filomena Nave --- Experimental intrinsic rotation update III Thu Feb 1. 11:30 501 DWB Plasma Group Meeting (organised by FELIX) Javier Maurino-Alperovich (Imperial) --- Dependence of confinement scaling laws on aspect ratio in tokamak plasmas IV Thu Feb 8. 11:30 501 DWB Plasma Group Meeting (organised by MICHAEL) Michele Romanelli (UKAEA) --- Novel aspects of plasma dynamics in JT-60SA V Thu Feb 15. 11:30 501 DWB Plasma Group Meeting (organised by FELIX) Free discussion Peter Catto (MIT) VI Thu Feb 22. 11:30 501 DWB Plasma Group Meeting Cancelled due to UCU strike Peter Catto (MIT) VII Thu Mar 1 11:30 501 DWB Plasma Seminar (organised by ALEX) Peter Catto (MIT) --- Quasilinear theory: gyrokinetics isn't just for low frequencies JPP 83, 905830611 (2017) Peter Catto (MIT) VIII Thu Mar 8 11:30 501 DWB Plasma Group Meeting Cancelled due to UCU strike 9 Thu Mar 15 11:30 501 DWB Plasma SeminarCancelled due to UCU strike Ian Abel (Chalmers) Fri Mar 16 14:00 Culham CCFE Student Seminar Alex Schekochihin (Oxford) --- Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence JPP 82, 905820212 (2016) PoP 23, 070703 (2016) Tue Mar 20 11:30 501 DWB Plasma Seminar (organised by FELIX) Grisha Kagan (LLNL) --- Thermal and suprathermal particles in ICF implosions Experiments are indicative of substantial kinetic effects during the course of ICF implosion. The effects appear as the plasma mean-free-path grows relative to the background scale making standard rad-hydro single-fluid description invalid. To understand the consequences it is convenient to consider the thermal and suprathermal particles separately. For the former, sharp gradients can drive the inter-ion-species diffusion, so the fuel composition no longer remains constant unlike what the single-fluid codes assume. Atomic mix at interfaces is, fundamentally, due to the same diffusion process. For the latter, the mean-free-path is much larger than that of their thermal counterparts, so their distribution function may be far from Maxwellian, even if thermal ions are nearly equilibrated. It is these suprathermal, or tail, ions that fuse in subignited implosions. Their distribution is thus the key to proper interpretation of nuclear diagnostics employed in ICF experiments in general and to correct fusion yield prediction in particular. Furthermore, suprathermal electron distribution shows similar behavior, affecting the X-ray diagnostics. Basic mechanisms behind and practical consequences of these groups of effects will be discussed. Grisha Kagan (LLNL) Angelo Limone (Siemens) Thu Mar 22 11:30 501 DWB Plasma Seminar (organised by ALEX) Angelo Limone (Siemens Industry Software Computational Dynamics Ltd Digital Factory, London) --- Simulating the plasma state for industrial applications Plasma physicists traditionally focus their attention on astrophysics and nuclear fusion. However, a composite zoo of plasma applications does exist and---surprisingly---has even a certain economic impact. Thin semiconductor layers, for instance, used in our ubiquitous smartphones and displays are produced also via techniques that use the plasma state as catalyst. In circuit breakers of whichever voltage size the plasma state is something that has to be quenched, and quickly. Some other few applications of industrial plasmas will be described, in particular I will be discussing the tough challenges that the average engineer might have to tackle when trying to model plasma flows via numerical simulations and the problems that a Computational Fluid Dynamics software provider has to face in order to deliver a solver that can help the design engineer with realism and on an "industrially reasonable" timescale. Computers & Fluids 88, 872 (2013) J Phys D: Appl Phys 46, 065203 (2013) Mon Mar 26 11:30 Dobson Room Plasma Seminar (organised by ALEX) Archie Bott (Oxford ALP) --- When is collisional plasma a fluid? (1001 plasma instabilities at high beta) preprint from author on request Troy Carter (UCLA) Wed Mar 28 11:30 Dobson Room Plasma Seminar (organised by ALEX) Troy Carter (UCLA) --- Updates from LAPD: turbulence and energetic-ion-driven modes in high-beta plasmas RSI 87, 025105 (2016) PPCF 59, 024006 (2017) PRE 91, 013109 (2015) Thu Mar 29 9:30 Culham HOW Room Special JET Seminar (organised by JON HILLESHEIM) Troy Carter (UCLA) ---  Studies of ICRF physics using the Large Plasma Device The Basic Plasma Science Facility (BaPSF) at UCLA is a US national user facility for studies of fundamental processes in magnetized plasmas. The centerpiece of the facility is the Large Plasma Device (LAPD), a 20m long, magnetized linear plasma device. This LAPD has been utilized to study a number of fundamental processes, including: dispersion and damping of kinetic and inertial Alfven waves, flux ropes and magnetic reconnection, three-wave interactions and parametric instabilities of Alfven waves, turbulence and transport and interactions of energetic ions and electrons with plasma waves. A brief overview of research using the facility will be given, followed by a more detailed discussion of research relevant to ICRF heating and current drive in fusion devices. Recent experiments in LAPD have studied high power (~200kW) fast wave excitation (f ∼ 2 − 10fci). Highlights of this work include documenting: the structure and scaling of RF sheaths, the formation of convective cells and associated density modification, and parasitic coupling to the slow mode in the low density plasma in front of the antenna [Martin, et al., PRL 119, 205002 (2017)]. Thu Apr 5 11:30 501 DWB Plasma Group Meeting (organised by ALEX) TBA Troy Carter (UCLA)

Trinity Term and Summer of 2018