Seminars Trinity Term and Summer of 2023

PLASMA SEMINARS AND GROUP MEETINGS

The style of the seminars will be informal/chaotic/interactive, following the established tradition. The format of the presentations can be a tutorial on a topic of interest, a report on just completed/ongoing/just starting/potentially interesting research projects, a literature review, a lecture by a passing visitor or anything else worthwhile that anyone cares to suggest. The speakers will be interrupted freely and asked to defend themselves. For background reading, only the most relevant or the most recent references are posted; please follow the paper trail from there. The schedule is subject to change on short notice, but what you see posted here is always up to date; the seminars are also announced via the department's seminar server (group meetings are not). Please email Alex Schekochihin if you would like to receive email updates on these seminars. "Plasma group meetings (or journal clubs)" will discuss current affairs (ongoing projects, new litearture etc.) as well as feature some presentations that are even more informal than seminars. They are open to all members of the Oxford Plasma Theory Group. While some expected contributions are pre-announced, everything is TBC and people wishing their work to be discussed can volunteer contributions without prior notice. Unlike for the seminars, there will not be full-spam-list email reminders of the group meetings. The seminars and group meetings are organised by Michael Barnes and Alex Schekochihin, please contact them with any queries or if you wish to present something.

Past seminar database: Autumn 2007; Winter-Spring 2008; Summer 2008; Autumn 2008; HT 2009; TT 2009; Summer 2009; MT 2009; HT 2009; TT 2010; Summer 2010; MT 2010; HT 2011; TT 2011; Summer 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; HT 2018; TT & Summer 2018; MT 2018; HT 2019; TT & Summer 2019; MT 2019; HT 2020; TT & Summer 2020; MT 2020; HT 2021; TT & Summer 2021; Autumn/MT 2021; HT 2021; TT & Summer 2022; Autumn/MT 2022; HT 2023;

Trinity Term and Summer of 2023

The seminars/group meetings will be on Tuesday at 14:00 in the Simpkins Lee Room, Beecroft Building, except where indicated otherwise below, in red.
It will be possible to join these meetings (when they are held in SL Room) on ZOOM --- details available from Alex on request.
Those who join these meetings on ZOOM are asked keep their video cameras on.
The ZOOM system in Simpkins Lee Room does not display a list of participants whose cameras are off. It is not germane to these informal meetings to have invisible listeners of whom those present in the room are unaware, so if you are unable or unwilling to turn on your camera, you cannot join the meeting.
Here is a list of all Physics seminars.

If you know exactly what you are going to do, what is the point of doing it? Pablo Picasso
He goeth furthest who knows not whither he is going. Oliver Cromwell

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
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
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! Alex Schekochihin
It's not the triviality, it's the emptiness of it that bothers me. Bryan Taylor
Never take 0 for an answer. Alex Schekochihin
This is a very inefficient way of achieving nothing. Francois Rincon
For the sake of fairness, let me mention that some people have objections to this, none of which are particularly valid. Chris Chen
This is more or less right. Perhaps less. Alfred Mallet
Too simple? At the end of my talk, you will beg for simplicity! Andrey Beresnyak
What is the point? The point is not the point! Anonymous
This is why I am presenting this here and nowhere else: nothing is solved! Ian Abel
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 & 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

It is better to be vaguely right than exactly wrong. Carveth Read (usually attributed to Maynard Keynes)

I wouldn't say these are theoretical arguments... Let's just call them arguments. Francois Rincon
This qualitative explanation is not of sufficient quality. Eugene Churazov
If you mean it seriously, this is actually a very good question. Minhyong Kim
This paper is a tour de farce. Ian Abel
What is modelling? You run a simulation, you compare. If it coincides, great! If it doesn't coincide, fuck! Felix Parra
I have seen papers where the student wasn't the problem. Michael Hardman
There has been a lot of fascinating work on this subject, most of it kind of boring. Philipp Kempski
So now you want us to drop everything we are doing and start worrying about what the big questions are?! Ian Abel
Oh dear, I thought I had some conclusions. Nuno Loureiro
I've got my little fingers inside this plasma. Steve Cowley
Words will play a big role in this talk. Dmitri Uzdensky
Everything that can be done should be done---and that's the astrophysical attitude. Michael Medvedev
What I will talk about is not low-hanging fruit. A lot of people have looked at this. There is no fruit here at all.---What about sour grapes? Michael Medvedev & Nuno Loureiro
In order to have a disappointment, you first have to have an appointment. Alex Schekochihin
In our experiment, we observed strong absence of magnetic energy. Archie Bott
Much as I somewhat hate this approach... Peter Davidson
Your infinity is my zero. Mantas Abazorius
If I had known the outcome of this calculation, I would never have done it. Michael Hardman

Now that everyone knows this is the new Pandora's box, they are all going to jump into it. Francois Rincon
We must think outside the axisymmetric box. Georgia Acton

This is not real, it's a Platonic absolute.---The real thing is more Platonic and more absolute. Alex Schekochihin & Anthony Field
All I've done here is sacrificed equality in favour of inequality. Per Helander

[these quotes are mostly from these seminars and the Vienna meetings]

Wk	Date	Time & place	Speaker & Topic	Background reading	Visitors in town
0	Tue 18 Apr	14:00 Freeman Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by MICHAEL) Mads Senstius (DTU) --- Nonlinear wave-wave interactions in non-monotonic plasma density structures	PoP 23, 082503 (2016) NF 60, 106008 (2020) PPCF 63, 065018 (2021)
I	Tue 25 Apr	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting/Journal Club (organised by ALEX) Patrick Reichherzer will give an update on his investigations of CR scattering by micro-mirrors and also discuss the paper by Lemoine "Pitch-angle diffusion through localized interactions with sharp magnetic field bebds in MHD turbulence"	arXiv:2304.03023 MNRAS 460, 467 (2016) +preprint from author
II	Tue 2 May	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by JUAN) Open mic
III	Tue 9 May	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by ALEX) Open mic
IV	Tue 16 May	No seminar: TDoTP meeting in York
V	Tue 23 May	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by JUAN) Maurizio Giacomin (York) ---- Numerical investigation of microtearing modes in the core of experimentally relevant spherical tokamak scenarios Robin Greif (IPP Garching) --- AI-assisted plasma computations	arXiv:2303.02379	Maurizio Giacomin (York) Robin Greif (IPP Graching) Swadesh Mahajan (UT Austin)
V	Thu 25 May	14:00 J. Paton Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by MICHAEL) Swadesh Mahajan (UT Austin) --- Nonlinear light: high amplitude EM waves in a highly relativistic plasma This work seeks an answer to the fundamental question: what does relativistic intensity light look like when it propagates in a medium of very high energy constituents? We find that, instead of the somewhat drab sinusoidal waveform for ordinary low intensity light, the propagating wave form of high intensity light is spectacular. Rich in harmonics of an appropriately reduced frequency, it evokes a complex musical note rather than the monotonous pitch of a tuning fork. The eye-catching structure of light revealed in this study is a profound expression of two strongly interacting nonlinear systems: a plasma that is strongly affected by the propagating light, and a light wave that, in turn, is radically transformed by the plasma. Despite the complexity of the model system, one can analyze and predict the essential structure of ``Nonlinear Light" that is so visibly striking in numerical simulations. Since we have extracted, analytically, crucial signatures of its rich spectrum, this work may equip us to revisit and reinterpret (even suggest) laboratory experiments.
VI	Tue 30 May	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by MICHAEL) Richard Nies (PPPL) --- Perpendicular anisotropy and critical balance in electrostatic ITG turbulence	PRL 107, 115003 (2011) PRL 110, 145002 (2013)
VII	Tue 6 June	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting/Journal Club (organised by ALEX) Leo Turica will give an update on his investigations of JET pedestal profiles (including by an ML method) and also discuss the paper by Leppin et al. "Complex structure of turbulence across the ASDEX Upgrade pedestal"	PTRSA 381, 20210228 (2023) arXiv:2303.10596
VIII	Tue 13 June	10:30 Freeman Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by ALEX) Nick Lopez ---- New solution to Airy's equation for describing electromagnetic beams near turning points	arXiv:2301.12788	Dmitri Uzdensky (CU Boulder)
VIII	Prakriti Pal Choudhury joins the group as PDRA, to work with Archie Bott				Dmitri Uzdensky (CU Boulder)
9	Tue 20 June	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by MICHAEL) Ralf Mackenbach (Eindhoven) --- Available energy: a nonlinear measure for turbulent transport	AAS Lecture Notes sec 9.5 JPP 83, 715830401 (2017) JPP 86, 905860210 (2020) PRL 128, 175001 (2022)	Ralf Mackenbach (Eindhoven) Luis Silva (IST Lisbon)
9	Param Luhadiya (Oxford Physics, 2nd year) joins the group as a summer intern, to work with Plamen Ivanov & Toby Adkins; Om Gupta (also Oxford Physics, 2nd year) joins as summer intern to work with Michael Barnes				Ralf Mackenbach (Eindhoven) Luis Silva (IST Lisbon)
10	Tue 27 June	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by ALEX) Open mic		Ralf Mackenbach (Eindhoven) Luis Silva (IST Lisbon)
	Tue 4 July	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by ALEX) Luis Silva (IST Lisbon) --- Learning (1D) plasma dynamics with graph neural networks I will report on recent efforts in using Graph Neural Networks [1,2] to learn 1D electrostatic plasma dynamics [3]. Several fundamental plasma processes are recovered, including drag on a fast particle, Landau damping, the spectrum of electrostatic fluctuations, and thermalization. The results are compared and validated by both theoretical predictions and high-fidelity simulations performed with the original 1D plasma model [3]. I will also discuss surrogate models to speed up additional physics modules (e.g. Compton scattering) in particle-in-cell simulations [4].	[1] arXiv:1806.01261 [2] PMLR 119, 8459 (2020) [3] Phys. Fluids 5, 445 (1962); J. Dawson, Methods in Computational Physics 9 (1970) [4] JPP 88, 895880602 (2022)	Cary Forest (UW Madison) Luis Silva (IST Lisbon)
	Tue 11 July	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by ALEX & GIANLUCA) Charles Arrowsmith --- Extreme astrophysics with laboratory electron-positron pair jets Relativistic electron-positron pair plasma beams are expected to be found in energetic astrophysical environments, such as the winds of pulsars and magnetars, as well as Gamma-Ray Bursts (GRBs) and Fast Radio Bursts (FRBs) [1-4]. Plasma instabilities associated with such pair-dominated outflows play an important role in explaining their energy dissipation and the radiative signatures we observe from these objects on Earth [5-7]. Current-neutrality and mass equality of component species is expected to lead to significantly different instability growth for pair plasma jets compared with pure-electron beams and electron-ion plasmas. However, the difficulty of experimentally producing sufficient yields of electron-positron pairs has limited our understanding of pair plasma instabilities. Experiments are required to benchmark these simulations and probe regimes where instabilities have evolved to stages of non-linearity that are difficult to reach in PIC simulations [8]. In this talk, we show preliminary results from an experiment performed at the HiRadMat facility [9-11], within CERN's accelerator complex. We describe a newly developed experimental platform to study interactions of pair beams with ambient plasma [12] which mimics the interaction of pair jets with intergalactic plasma. The pair density and plasma extent are orders of magnitude larger than currently achievable at laser facilities, making our experiments superior to previous platforms as a means to address fundamental questions in pair plasma physics and laboratory astrophysics. The recently-performed experiment investigates the stability of the pair beam to collisionless kinetic beam plasma instabilities. An upper bound of the growth rate is experimentally obtained and we compare the results with detailed particle-in-cell simulations. The preliminary results support behaviour predicted by theory and exhibited in simulations that the instability growth rate is significantly suppressed when certain non-ideal conditions are assumed. Using the experimentally-obtained upper bound on the instability growth rate, we use astrophysical scaling arguments to infer a maximum growth rate of plasma instabilities for blazar pair jets propagating through cosmic voids. Finally, we will discuss the implications of this for processes of magnetization of the voids and the decay of primordial magnetic fields. [1] P. Goldreich and W. H. Julian, Astrophys. J. 157, 869 (1969). [2] J. Arons, Astrophys. J. 266, 215 (1983). [3] R. D. Blandford and R. L. Znajek, Mon. Not. R. Astron. Soc. 179, 433 (1977). [4] J. Wardle et al., Nature 395, 457 (1998). [5] A. Bret, Astrophys. J. 699, 990 (2009). [6] P. Chang, A. Spitkovsky, and J. Arons, Astrophys. J. 674, 378 (2008). [7] F. Miniati and A. Elyiv, Astrophys. J. 770.1 (2013). [8] L. O. Silva et al., Astrophys. J. Lett. 8 596, L121 (2003). [9] I. Efthymiopoulos et al., Proc. 2nd Int. Particle Accelerator Conf. (IPAC’11), TUPS058 (2011). [10] F. Harden et al., J. Phys. Conf. Series 1350 012162 (2019). [11] C. D. Arrowsmith et al, Phys. Rev. Res. 3, 023103 (2021). [12] C. D. Arrowsmith et al, JINST 18 P04008 (2023).	see refs in abstract	David Hatch (IFS Texas) Luis Silva (IST Lisbon)
	Tue 18 July	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by PATRICK) Jeremiah Luebke (Bochum) --- Towards a realistic model for synthetic magnetic turbulence	J. Phys. Complex. 4, 015005 (2023)	Jeremiah Luebke (Bochum)
	Tue 25 July	No seminar
	Tue 1 Aug	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by PLAMEN) Open mic		Yohei Kawazura (Tohoku U)
	Tue 8 Aug	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by TOBY) Pablo Bilbao (IST Lisbon) --- Nonlinear cooling and kinetic instabilities in strong field plasma physics Upcoming laser/beam-plasma experiments and astrophysical plasmas in extreme environments prompt the integration of strong field effects, such as radiation reaction, into classical plasma physics. We show that radiation reaction cooling leads to kinetically unstable plasmas. The radiation reaction force cools the momentum distribution nonlinearly causing kinetic plasma anisotropies and energy population inversion. We study the formation and evolution of ring momentum distributions in collisionless plasmas undergoing synchrotron cooling. We explore the resulting electron cyclotron maser instability leading to coherent radiation emission. This mechanism and maser emission are relevant to understanding radiation emission in astrophysical plasmas. Additionally, we investigate other electromagnetic field configurations, such as emittance damping of beams due to betatron oscillations in plasma accelerators. Particle-in-cell simulations with OSIRIS confirm our theoretical findings.	PRL 130, 165101 (2023)	Pablo Bilbao (IST Lisbon) Yohei Kawazura (Tohoku U)
	Tue 15 Aug	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by ALEX) Dan Kennedy (UKAEA) --- Update/discussion on KBMs, MTMS, TAIs and all that	arXiv:2307.01670 arXiv:2307.01669	Yohei Kawazura (Tohoku U) Jun Lau (UCL)
	Aneesh Agrawal (Cambridge NatSci, 3rd year) joins the group as a summer intern, to work with Archie Bott and Alex Schekochihin				Yohei Kawazura (Tohoku U) Jun Lau (UCL)
	Tue 22 Aug	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Seminar (organised by ALEX) Thales Silva (IST Lisbon) --- Electron-scale plasma instabilities: a perspective for laboratory astrophysics experiments	PRR 2, 023080 (2020) PRE 104, 035201 (2021) PoP 22, 023102 (2015) arXiv:2303.18114	Luis Silva, Thales Silva (IST Lisbon)
	Tue 29 Aug	14:00 SL Room & ZOOM (ask Alex for link)	Plasma Group Meeting (organised by ARCHIE) Open mic
	Om Gupta's and Param Luhadiya's summer internships end

Autumn/Michaelmas Term of 2023