| 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 |
It is
better to be roughly right than precisely wrong. Maynard
Keynes 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 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 EDQNM is not rigour, unless you mean rigor mortis. Ian Abel |
| Wk | Date |
Time & place |
Speaker & Topic |
Background reading |
Comings and goings (incl. visitors in town) |
| 0 |
Thu Apr 20 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by ALEX) Spring resolutions |
Everything is out now: Ball: arXiv:1703.03375 PPCF 59, 024007 (2017) Bott: arXiv:1702.03016 Colyer: PPCF 59, 055002 (2017) Geraldini: PPCF 59, 025015 (2017) Fox: PPCF 59, 034002 (2017) PPCF 59, 044008 (2017) Mallet: arXiv:1612.07604 MNRAS 466, 3918 (2017) van Wyk: arXiv:1704.02830 JPP 82, 905820609 (2016) ... |
|
| I |
Thu Apr 27 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by FELIX) Valerian Chen --- Beam tracing |
Hye-Sook Park (LLNL) |
|
| Fri Apr 28 |
14:00 A. Wood Room |
ALP Seminar (organised
by GIANLUCA) Hye-Sook Park (LLNL) --- Frontiers in high-energy density physics at the National Ignition Facility and other high-power laser facilities |
PRL 114, 065502 (2015) Nature Phys 11, 173 (2015) |
||
| II |
Thu May 4. |
11:30 501 DWB |
Plasma
Group Meeting (organised
by MICHAEL) Free discussion |
Swadesh
Mahajan (UT Austin) |
|
| 1-12 May |
Les Houches-2017
School om Plasma Physics |
||||
| III |
Thu May 11 |
11:30 501 DWB |
Plasma Seminar (organised
by MICHAEL) Swadesh Mahajan (UT Austin) --- Relativistic-amplitude electromagnetic waves: beating the “magnetic” barrier The
"dispersion'' characteristics of an arbitrary-amplitude circularly
polarized electromagnetic wave, propagating in a highly (thermally and
kinematically) relativistic plasma, are shown to approach those of a
linear wave in an unmagnetized, non-relativistic plasma. Further aided
by high relativistic temperatures, the cut-off frequency tends to
become anomalously small; waves with frequencies well below the nominal
plasma and the cyclotron frequencies find the plasma to be essentially
transparent. This spectacular relativistic phenomenon will greatly
advance our ability to understand and model the dynamics of a large
class of astrophysical and laser-produced high electromagnetic-energy
density systems. It is speculated that the enormous reduction in the
effective cyclotron frequency may be a fundamental mechanism for
facilitating waves - at the lower end of the electromagnetic spectrum -
to escape from highly magnetized plasma like that of a pulsar
magnetosphere.
|
JPP 83, 905830101 (2017) |
Swadesh
Mahajan (UT Austin) |
| IV |
Thu May 18 |
11:30 501 DWB |
Plasma
Seminar (organised
by ALEX) Jono Squire (Caltech) --- Compressible turbulence: overview + recent ideas on density statistics |
arXiv:1702.07731 |
Swadesh
Mahajan (UT Austin) Jono Squire (Caltech) |
| V |
Thu May 25 |
No seminar |
Swadesh
Mahajan (UT Austin) Jono Squire (Caltech) |
||
| 24-26 May |
1st
JPP Frontiers in Plasma Physics Conference in Spineto |
||||
| VI |
Thu June 1 |
11:30 501 DWB |
Plasma
Seminar (organised
by FELIX) Jesus Ramos (MIT) --- Stability criteria for Kinetic MHD |
JPP
82, 905820607 (2016) JPP 81, 905810325 (2015) JPP 81, 905810111 (2015) |
Jesus
Ramos (MIT) Adwiteey Mauriya rejoins the group |
| VII |
Thu June 8 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by MICHAEL) Filomena Nave --- JET intrinsic rotation update |
||
| VIII |
Thu June 15 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by ALEX) Michael Hardman --- ETG turbulence update |
||
| 9 |
Thu June 22 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by FELIX) Valerian Chen --- Modelling the effect of the misalignment of the probe beam and the magnetic field in Doppler backscattering measurements of fusion plasmas Magnetic
confinement fusion is a promising candidate for carbon-free energy.
Unlike renewables, fusion energy will be able to provide the base load
power. However, it is still a work in progress. I will give a brief
overview of some of the current challenges, and introduce the research
being done at the Oxford Plasma Theory Group and the Culham Centre for
Fusion Energy, which is home to two of the world's leading fusion
experiments (JET and MAST). I will then present the recent results of
our research on improving the Doppler Backscattering (DBS) microwave
diagnostic. DBS enables the non-perturbative characterisation of
density fluctuations and flows, both at the edge and the core of the
plasma. However, the use of DBS in spherical tokamaks (like MAST) is
complicated since the magnetic pitch angle is large (up to 35◦,
compared to 15◦ in standard tokamaks like JET). Moreover the pitch
angle varies both spatially and temporally. Consequently, the DBS probe
beam and the magnetic field may not be normal to each other. This
misalignment, which affects the backscattered signal, can be
empirically optimised with 2D beam steering. Unfortunately, this
significantly increases the amount of experiment time required, which
is already in short supply. To get around this problem, we used the
beam tracing code Torbeam to determine the beam width, curvature, and
location of scattering. Using this information, we have developed a
model to determine the backscattered power and its dependence on the
mismatch angle, thereby accounting for the misalignment of DBS
measurements. The results are compared to scans of the toroidal launch
angle from MAST data. With insight from our model, we also assessed the
measurement capabilities for the planned MAST-U DBS system.
|
||
| 10 |
Thu June 29 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by MICHAEL) Nicolas Christen --- Momentum transport and rotation for JET/ITER plasmas |
||
| 3-5 July |
D. Sciama LT DWB |
Workshop on Plasma Astrophysics: From the Laboratory to the Non-Thermal Universe (in homour of Tony Bell and John Kirk) (organised by Katherine Blundell) Right here in Oxford: an opportunity to learn everything you ever wanted to know about plasma astrophysics but were afraid to ask Tony! |
Roger Blandford (Stanford) Lorenzo Sironi (Columbia) Anatoly Spitkovsky (Princeton) Alessandro Zocco (IPP Greifswald) Joe Abbate (Princeton), Ching Chong (Oxford) & David Hosking (Oxford) join as summer interns with F. Parra and A. Schekochihin, resp. |
||
| Thu July 6 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by ALEX) 1) Valerian Chen and Adwiteey Mauriya to report on the EPS Plasma Meeting in Belfast 2) Alessandro Zocco (IPP Greifswald) --- Update on resonant destabilisation of ITGs in stellarators and tokamaks |
2) preprint on request |
||
| Thu July 13 |
11:30 501 DWB |
Plasma Seminar (organised
by ALEX) David Hatch (UT Austin) --- Flow shear suppression of pedestal turbulence A combined
analytic and computational gyrokinetic approach is developed to address
the question of the scaling of pedestal turbulent transport with
arbitrary levels of ExB shear. Due to strong gradients and shaping in
the pedestal, the instabilities of interest are not curvature-driven
like the core instabilities. By extensive numerical (gyrokinetic)
simulations, it is demonstrated that pedestal modes respond to shear
suppression very much like the predictions of a basic analytic
decorrelation theory. The quantitative agreement between the two
provides us with a new dependable, first principles (physics based)
theoretical framework to predict the efficacy of shear suppression in
burning plasmas that lie in a low-shear regime not accessed by present
experiments.
|
Phys. Fluids B 4, 1385 (1992) arXiv:1706.08406 |
Roger Blandford (Stanford) Daniel Dunai (Wigner, Budapest) David Hatch (UT Austin) Alessandro Zocco (IPP Greifswald) |
|
| Fri July 14 |
16:00 New Seminar Rm, StJ |
Workshop on hot QFT (organised
by Andrei Starinets) (16:00) Pavel Kovtun (Victoria) --- Relativistic magneto-hydrodynamics I will discuss
relativistic magneto-hydrodynamics, which is hydrodynamics coupled to
dynamical electromagnetic fields. Until recently, there seemed to be no
consensus in the literature on a) what does the relevant thermodynamics
look like, and b) what is the number of transport coefficients. I will
describe my take on the subject, through Maxwell's equations in matter
in a covariant form. Simple examples include Alfven, magnetosonic, and
other waves. For a parity-preserving fluid in 3+1 dimensions, there are
seven dissipative and four non-dissipative transport coefficients at
first order in derivatives.
(17:30) Saso Grozdanov (Leiden) --- Generalised global symmetries and
dissipative magnetohydrodynamics: field theory and holographyI will discuss a new
symmetry-based approach to dissipative relativistic
magnetohydrodynamics (MHD), which allows for a formulation of MHD in
plasmas with any equation of state and transport coefficients, in
weakly- and strongly-interacting theories. After constructing MHD at
ideal and dissipative levels, I will present new predictions for the
behaviour of MHD waves (Alfven and magnetosonic waves) in dense plasmas
with strong magnetic fields. Furthermore, I will claim that MHD may
persist to be a good low-energy effective theory in the limit of zero
temperature where it becomes non-dissipative with corrections
controlled by second-order hydrodynamics. Finally, I will discuss a new
construction of a holographic dual to MHD, from which relevant
microscopic details (equations of state and seven transport
coefficients) can be extracted to study MHD waves in a model of a
strongly interacting plasma.
|
JHEP05(2017)001 PRD 95, 096003 (2017) |
||
| Thu July 20 |
No seminar |
Daniel Dunai (Wigner, Budapest) |
|||
| 17-28 July |
10th Plasma Kinetics Working Meeting in Vienna |
Daniel Dunai (Wigner, Budapest) |
|||
| Thu July 27. |
11:30 501 DWB |
Plasma
Group Meeting (organised
by FELIX) Free discussion |
|||
| Thu Aug 3 |
11:30 501 DWB |
Plasma Seminar (organised
by MICHAEL) Chris Bambic (Maryland) --- Observational and theoretical insights on AGN feedback: constraints on turbulent heating |
ApJ 815, 41 (2015) |
Bill Dorland, Chris Bambic (Maryland) |
|
| Thu Aug 10 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by ALEX) Discussion of summer interns' projects (Ching Chong and David Hosking) |
|||
| Thu Aug 17 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by FELIX) Free discussion |
Hermite spectrum paper: arXiv:1707.08180 |
||
| Thu Aug 24 |
11:30 501 DWB |
Plasma
Group Meeting (organised
by MICHAEL) TBA |
|||
| Thu Aug 31 |
11:30 501 DWB |
Plasma Seminar (organised
by ALEX) Thomas Antonsen (Maryland) --- Reciprocity and adjoint methods applied to charged particle dynamics |
Thomas Antonsen (Maryland) Adwiteey Mauriya leaves the group |
||