Physics in Intense Fields (PIF2013)

9 Jul 2013, 08:00 → 11 Jul 2013, 18:00 Europe/Berlin

Seminar Room 4a/b (Bulding 1C, DESY Hamburg)

Anthony Hartin (DESY)

Several new and existing physics experiments/facilities - future linear colliders, high intensity LASERs and FELs, interactions in crystalline lattices, heavy ion collisions and plasma acceleration - involve physics processes in ultra-intense electromagnetic fields. The field strengths seen by charged particles are a significant fraction of the Schwinger critical field (1.3x10¹⁸ V/m) at which real pairs are produced from the vacuum. It is of critical importance to consider interactions with such strong fields as precisely as possible in order to provide additional tests of our theoretical models and to stimulate the development of new experimental technologies.

The purpose of this workshop is to review the state of the art in strong field physics. Theoretical calculations, experimental tests and simulation of physics in high intensity fields will all be examined. There will be 3 days of talks including a keynote speaker, a Reception and a workshop dinner. The "early bird" registration fee is 160 Euros (200 Euros after 9th June). We welcome participation from all interested parties.

Physics in Intense Fields (PIF2013) is a followup workshop to the successful PIF2010 held at KEK in November 2010, and has strong links to previous workshops such as the Advanced QED methods for linear colliders held at the Cockcroft Insititute in March 2009 and the Workshop on Ultra High Intensity laser Nuclear and Particle Physics held in Trento in June 2008.

PIF2013 Workshop photo PIF2013_workshop_photo.jpg

Workshop documents

• Bulletin_1.pdf
• Bulletin_2.pdf
• pif2013_poster_v7.pdf

Tuesday 9 July

08:00 → 09:00 Registration

Registration for the workshop

09:00 → 10:30 Overview

09:00 Workshop Introduction

Speaker: Dr Anthony Hartin (DESY)

Slides Welcome.pdf

09:05 tribute to V. Baier

Speaker: Dr Ulrik Uggerhøj (Department of Physics and Astronomy, Aarhus University, Denmark)

Paper A ’translation’ into ’experimentalist terms’, see app. A V.N. Baier - Aarhus lectures

Slides Tribute_Baier.pdf

09:15 Probing of QED vacuum with superstrong laser field

The development of laser technologies promises very rapid growth of laser intensities in close future already. Two exawatt class facilities (ELI and XCELS, Russia) in Europe are already in the planning stage. Realization of these projects will make available a laser of intensity ~10^26 W/cm^2 or even higher. Therefore discussion of nonlinear optical effects in vacuum are becoming urgent for experimentalists and are currently gaining much attention. We show that, in spite of the fact that the respective field strength is still essentially less than E_S=m^2c^3/eħ=1.32•10^16V/cm, the nonlinear vacuum effects will be accessible for observation at ELI and XCELS facilities. The most promissory for observation is the effect of pair creation by laser pulse in vacuum. It is shown that at intensities \gtrsim 5•10^25 W/cm^2 creation even of a single pair is accompanied by development of an avalanchelike QED cascade. There exists an important distinctive feature of the laser-induced cascades, as compared with the air showers arising due to primary cosmic ray entering the atmosphere. In our case the laser field plays not only the role of a target (similar to a nucleus in the case of air showers). It is responsible also for acceleration of slow particles. It is shown that the effect of pair creation imposes a natural limit for attainable laser intensity. Apparently, the field strength ~ E_S is not accessible for pair creating electromagnetic field at all.

Speaker: Prof. Nikolay Narozhny (National Research Nuclear University MEPhI)

Slides Narozhny_DESY.pptx

10:00 Spin effects in laser-induced electron-positron pair production

Electron-positron pair production by an incident high-energy photon or a relativistic proton colliding with an intense laser field is considered. Our focus lies on the role played by the electron spin degree of freedom. A comparative study between production of Dirac versus Klein-Gordon pairs is performed [1,2] and a helicity analysis is carried out [3]. [1] S. Villalba-Chavez and C. Mueller, Phys. Lett. B 718, 992 (2013) [2] T.-O. Mueller and C. Mueller, Phys. Lett. B 696, 201 (2011) [3] T.-O. Mueller and C. Mueller, Phys. Rev. A 86, 022109 (2012)

Speaker: Prof. Carsten Mueller (Institute of Theoretical Physics, Heinrich Heine University Duesseldorf)

Slides DESY_PIF_2013_CMueller.pdf

10:30 → 11:00 Tea and Coffee

11:00 → 12:40 Ultra-Intense LASERs

11:00 Gamma-ray generation in strong laser field: QED cascading and laser-solid interaction in QED regime

We discuss generation of energetic photons in strong laser field at intensities above 10^23 W/cm^2. First we discuss production of electron-positron-gamma-quanta plasma at QED cascading. QED or electromagnetic cascades are one of the basic phenomena of high-field physics. QED cascades can efficiently convert laser radiation into gamma-quanta. The various methods and schemes to control of the efficiency, brightness and directivity of the gamma-ray source based on QED cascade are proposed. The proposed schemes are verified by numerical simulations with 3D QED PIC-MC code. We also discuss laser-solid interaction in QED regime when QED effects become significant. The conversion efficiency of the laser energy to the gamma-ray energy is calculated by 3D PIC-MC simulation for a wide range of laser-solid parameters. It is shown that in the low intensity regime the main part of the laser energy is converted into the ion motion while in the high intensity regime the gamma-ray generation becomes the key channel of the laser energy conversion.

Speaker: Dr Igor Kostyukov (Institute of Applied Physics RAS)

Slides desy2013-kostyukov.ppt

11:25 Birefringence, dichroism and Raman spectroscopy of the vacuum: searching minicharged particles in a high-intensity laser field

The quantum vacuum, polarized by a classical electromagnetic field, behaves as an active medium. Its absorptive and dispersive properties are studied in the presence of a high-intensity circularly polarized laser wave. The outcomes of this investigation reveal that, in the region relatively close to the threshold of the two-photon reaction, the birefringence and dichroism of the vacuum can be manifest with lasers of moderate intensities. We take advantage of such properties to impose upper bounds on the parameters associated with hypothetical minicharged particles. In addition, Raman-like electromagnetic waves resulting from a plausible inelastic interaction are suggested as an alternative form for finding exclusion limits on these charge carriers.

Speaker: Dr Selym Villalba-Chavez (Institut für Theoretische Physik I, Heinrich Heine Universität Dusseldorf)

Slides Hamburg-2013.pdf

11:50 Asymmetries of Azimuthal Photon Distributions in Non-Linear Compton Scattering in Ultra-Short Intense Laser Pulses

Non-linear Compton scattering in ultra-short intense laser pulses is discussed. The focus is on angular and azimuthal distributions of the emitted photon in intense single-cycle and few-cycle laser pulses. Asymmetries of the azimuthal distributions are predicted for both linear and circular polarization. For linear polarization, the dominant direction of the emission changes from a perpendicular pattern with respect to the laser polarization at low-intensity to a dominantly parallel emission for high-intensity laser pulses.

Speaker: Dr Daniel Seipt (Helmholtz-Institut Jena)

Slides seipt_PIF2013.pdf

12:15 Electron-seeded pair-creation in external fields

Motivated by the ever-increasing interest in simulating the intense irradiation of plasmas by combining the scales of classical plasma physics and strong-field QED processes, we present the results of two studies into common approximations. First, we derived polarised non-linear Compton scattering and pair-creation rates in a constant crossed field and studied their inclusion in simulations, finding good agreement in the spectra and number of photons generated when photons are treated as scalars but also a large asymmetry in the polarisation distribution [1]. Second, we derived electron-seeded pair creation (the trident process) in a constant crossed field to investigate the approximation of using chains of integrated tree-level processes to approximate higher-order ones [2]. The only disparity we recorded here was inclusion of photon polarisation which corresponded to less than 10% difference in the total rate. Furthermore, the results hint that short-pulse lasers and electron beams could be used to measure the one-step process mediated by a virtual photon. [1] B. King, N. Elkina and H. Ruhl, Photon polarisation in electron-seeded pair-creation cascades, Phys. Rev. A (accepted) http://arxiv.org/abs/1301.7001, (2013) [2] B. King and H. Ruhl, Trident pair creation in a constant crossed field, http://arxiv.org/abs/1303.1356, (2013)

Speaker: Dr Ben King (Ludwig-Maximilians-Universität München)

Slides king_pair_creation_curtailed_final.pdf

12:40 → 14:00 Lunch

14:00 → 15:30 Processes and Solutions

14:00 Nonlinear double Compton scattering in the ultrarelativistic quantum regime

A detailed analysis of the process of two-photon emission by an electron scattered from a high-intensity laser pulse is presented. The calculations are performed in the framework of strong-field QED and include exactly the presence of the laser field described as a plane wave [1]. We investigate the full nonlinear quantum regime of interaction with a few-cycle pulse, where nonlinear effects in the laser field amplitude, photon recoil, and the short pulse duration substantially alter the emitted photon spectra as compared to those in previously studied regimes. We provide a semiclassical explanation for such differences, based on the possibility of assigning a trajectory to the electron in the laser field before and after each quantum photon emission [2]. Our numerical results indicate the feasibility of investigating experimentally the full ultrarelativistic quantum regime of nonlinear double Compton scattering with available electron accelerator and laser technology. References [1] A. Di Piazza et al., Rev. Mod. Phys. 84, 1177 (2012). [2] F. Mackenroth and A. Di Piazza, Phys. Rev. Lett. 110, 070402 (2013).

Speaker: Dr Antonino Di Piazza (Max Planck Institute for Nuclear Physics)

Slides Di_Piazza_PIF2013.pptx

14:25 Resonances in the 2-vertex Furry picture processes and their potential experimental verification

Furry picture particle processes exactly include the contribution from the external field. For a circularly polarised external field the contribution is discrete being a multiple of the external field momentum. The 2-vertex Furry picture processes display interesting behaviour due to their propagators reaching the mass shell for particular kinematic combinations. I discuss this behaviour in the 2-vertex Compton scattering. The nature of the apparent divergences is analysed and their correction by inclusion of the electron self energy and the Furry picture vertex correction is discussed. Cross-sections obtained show large variation from the Klein-Nishina process and provide a new arena within which to test Furry Picture predictions. The Furry picture Compton scattering is amenable to experimentation since initial photons can be tuned to scan resonances, and event rates are easily sufficient for detection using the present laser intensities available. References: [1] Hartin A, Atti della Fondazione Giorgio Ronchi Vol XLIII, No 3, p 295-305 (1988) [2] Hartin A, PhD Thesis, University of London (2006)

Speaker: Dr Anthony Hartin (DESY)

Slides PIF2013_Hartin_2vertex_resonances_DESY_Jul2013_web.pdf

14:50 Analytical Solutions of the Dirac and the Klein-Gordon Equations in Plasma Induced by High Intensity Laser

We obtain analytical solutions of the Dirac and the Klein-Gordon equations coupled to a strong electromagnetic wave in the presence of plasma environment. These are a generalization of the familiar Volkov solutions. The contribution of the non-zero photon effective mass to the scalar and fermion wavefunctions, conserved quantities and effective mass is demonstrated for the first time. The new wavefunctions exhibit differences from Volkov solutions for nowadays available laser intensity

Speaker: Erez Raicher (Hebrew University of Jerusalem, Israel)

Slides PIF_Lecture_f.PPTX

15:10 Fermion production in inhomogeneous electric fields

We investigate fermion production in space- and time-dependent electric fields in 1+1 dimensional QED using real-time lattice techniques. We compute the non-equilibrium time evolution of gauge invariant observables and investigate the decay of the field due to the backreaction mechanism. The latter allows us to discuss the striking phenomenon of a linear rising potential building up between produced fermion bunches after the initial electric pulse has ceased.

Speaker: Dr Florian Hebenstreit (Heidelberg University)

Slides Hebenstreit_PIF_2013.pdf

15:30 → 16:00 Tea and Coffee

16:00 → 16:45 Quantum Dynamics

16:00 Ionic and nuclear quantum dynamics in intense low and high-frequency light fields

The interaction of highly charged ions and nuclei with intense light sources is introduced [1]. We begin discussing the quantum relativistic bound electron dynamics in highly charged ions and super intense laser fields [2,3]. Then, special attention is devoted to laser-induced tunneling in the relativistic regime. Here, we show that an intuitive picture can be developed for relativistic tunneling employing spatially dependent energy levels. Also the issue of time under the barrier is discussed at length and how the various times may leave detectable signatures [3]. In what follows, we investigate how populations may be transferred among nuclear states employing accelerators and XFEL light [4]. Then, various applications employing high frequency light are introduced such as high-precision determinations of nuclear lines and phase-sensitive storage schemes of x-ray photons [5]. Finally, resonance fluorescence of highly charged ions is discussed and how this may be favorably employed in laboratory astrophysics [6]. REFERENCES: [1] A. Di Piazza, C. Müller, K. Z. Hatsagortsyan, C. H. Keitel, Rev. Mod. Phys. 84, 1177-1228 (2012). [2] H. G. Hetzheim and C. H. Keitel, Phys. Rev. Lett. 102, 083003 (2009); B. Galow, Y. I. Salamin, T. Liseykina, Z. Harman and C. H. Keitel, Phys. Rev. Lett. 107 (185002) (2011). [3] M. Klaiber, E. Yakaboylu, H. Bauke, K. Z. Hatsagortsyan, and C. H. Keitel, Phys. Rev. Lett. 110, 153004 (2013). [4] W. Liao, A. Pálffy, C. H. Keitel, Physics Letters B 705, 134-138 (2011) and Phys. Rev. C 87, 054609 (2013). [5] O. Postavaru, Z. Harman, C. H. Keitel, Phys. Rev. Lett. 106, 033001 (2011); W. Liao, S. Das, C. H. Keitel, A. Pálffy, Phys. Rev. Lett. 109, 262502 (2012); W. Liao, A. Pálffy, C. H. Keitel, Phys. Rev. Lett. 109, 197403 (2012); B. W. Adams, C. Buth, S. M. Cavaletto, J. Evers, Z. Harman, C. H. Keitel, A. Pálffy, A. Picon, R. Rohlsberger, Y. Rostovtsev, K. J. Tamasaku, J. Mod. Opt. 60, 2 (2013). [6] S. Bernitt, G. V. Brown, J. K. Rudolph, R. Steinbrügge, A. Graf, M. Leutenegger, S. W. Epp, S. Eberle, K. Kubiček, V. Mäckel, M. C. Simon, E. Träbert, E. W. Magee, C. Beilmann, N. Hell, S. Schippers, A. Müller, S. M. Kahn, A. Surzhykov, Z. Harman, C. H. Keitel, J. Clementson, F. S. Porter, W. Schlotter, J. J. Turner, J. Ullrich, P. Beiersdorfer, J. R. Crespo López-Urrutia, Nature 492, 225 (2012).

Speaker: Prof. Christoph H. Keitel (Max Planck Institute for Nuclear Physics (MPIK))

Slides ham6.pptx

16:50 → 16:55 Workshop Photo

17:00 → 18:00 Special Lecture/DESY Seminar

Gerald Dunne presentation

17:00 The Search for the Schwinger Effect: Non-perturbative Pair Production from Vacuum

The prospect of next-generation ultra-high-intensity laser sources has prompted recent renewed study of the Schwinger effect, in which the instability of the QED vacuum is probed by external fields. Experimental observation of this long-sought effect would provide controlled access to non-perturbative processes in quantum field theory under extreme conditions, which is of direct interest in particle physics and astrophysical applications. I review why this is also such an interesting and challenging theoretical problem.

Speaker: Prof. Gerald Dunne (University of Connecticut)

Slides dunne-pif-2013-web.pdf

18:30 → 22:00 Workshop Reception

Workshop Reception

Wednesday 10 July

09:00 → 09:10 Workshop Greeting

09:00 Workshop Greeting

09:10 → 10:40 Heavy ion collisions

09:10 QCD with external magnetic fields

I review the recent progress concerning QCD with external fields, especially the catalysis resp. inverse catalysis of the quark condensate, the critical temperature, the magnetic susceptibility etc. from lattice simulations in comparison to other approaches.

Speaker: Dr Falk Bruckmann (Regensburg University)

Slides pif_bruckmann.pdf

09:35 Properties of photons and hadrons in strong magnetic fields

Extremely strong magnetic fields appear in high-energy heavy-ion collisions and compact stars like magnetars. Under such strong magnetic fields, photons and even hadrons show unusual behaviors. In this talk, I will explain photon's vacuum birefringence and decay into an e+e- pair [1,2] and the conversion of neutral pions into (virtual) photons [3] both of which are possible in strong magnetic fields. I will also discuss how these phenomena can manifest in heavy-ion collisions. [1] K. Hattori and K. Itakura,``Vacuum birefringence in strong magnetic fields: (I) Photon polarization tensor with all the Landau levels,'' Annals Phys.330 (2013) 23 [arXiv:1209.2663 [hep-ph]]. [2] K. Hattori and K. Itakura,``Vacuum birefringence in strong magnetic fields: (II) Complex refractive index from the lowest Landau level,'' Annals Phys.334 (2013) 58 [arXiv:1212.1897 [hep-ph]]. [3] K. Hattori, K. Itakura, S. Ozaki, ``Neutral-pion reactions induced by chiral anomaly in strong magnetic fields,'' arXiv:1305.7224 [hep-ph]

Speaker: Dr Kazunori Itakura (KEK Theory Center, IPNS, KEK)

Slides PIF2013-itakura.pptx

10:00 Particle production from expanding flux tubes

A high-energy nucleus can be viewed as a condensed state of high-density and weak-coupling gluons, which is called color glass condensate. After a collision of heavy nuclei, these gluons are emitted between the two nuclei and they can be interpreted as coherent classical chromo-electromagnetic fields polarized in the longitudinal beam direction. The strength of these fields is given by the scale Q_s, which characterize the gluon saturation phenomena in high-energy nuclei, and typically is the order of 1 GeV^2. As two nuclei recede from each other after the collision, these fields extend to the longitudinal direction with nearly the speed of light. In the transverse direction, these fields have a random distribution with a coherence length characterized by the scale Q_s. To investigate quark production from such inhomogeneous classical fields, we employ a Monte Carlo technique, which enable us to simulate the real-time dynamics of quantum fields interacting with a background classical field with a cheaper numerical cost compared with another method. We will show the results of numerical calculations in which realistic configurations of the color gauge fields in heavy-ion collisions are taken into account.

Speaker: Naoto Tanji (IPhT Saclay/ KEK)

Slides Tanji.pdf

10:20 QCD in Strong Magnetic Fields

We study electromagnetic and topological properties of the QCD vacuum and quark-gluon plasma in the background of strong (hadronic scale) magnetic fields comparable to the ones taking place in heavy-ion collisions. Among the properties are the following ones: electric conductivity, magnetization and magnetic susceptibility, local CP-violation and induced anomalous currents, distribution of the topological charge density, chiral symmetry breaking and the chiral condensate. I will mainly present the results obtained within the lattice QCD simulations and, if there is time left, with the use of original analytic methods.

Speaker: Dr Tigran Kalaydzhyan (DESY)

Poster poster.pdf

Slides PIF2013.pdf

10:40 → 11:00 Tea and Coffee

11:00 → 12:40 Strong field effects

11:00 Dynamically assisted Sauter-Schwinger effect

Recently it has been found that the superposition of a strong and slow electric field with a weaker and faster electromagnetic pulse can significantly enhance the probability for non-perturbative electron-positron pair creation out of the vacuum — the dynamically assisted Sauter-Schwinger effect. After a brief introduction into the basics of this effect, this talk will be devoted to the dependence of this enhancement mechanism on momentum and the pulse shape as well as further developments. References: Momentum dependence in the dynamically assisted Sauter-Schwinger effect Christian Fey and Ralf Schützhold Phys. Rev. D 85, 025004 (2012) Catalysis of Schwinger vacuum pair production Gerald V. Dunne, Holger Gies, and Ralf Schützhold Phys. Rev. D 80, 111301 (2009) Dynamically Assisted Schwinger Mechanism Ralf Schützhold, Holger Gies, and Gerald Dunne Phys. Rev. Lett. 101, 130404 (2008)

Speaker: Prof. Ralf Schuetzhold (Faculty of Physics, University of Duisburg-Essen)

Slides pif-schuetzhold.pdf

11:25 The Kapitza-Dirac effect in the relativistic regime

The Kapitza-Dirac effect is the diffraction of electrons at a standing wave of light [1]. We solve the relativistic quantum dynamics of this electron diffraction by integrating the Dirac equation numerically and perturbatively in momentum space and demonstrate that spin-flips can be observed in the Kapitza-Dirac effect with three interacting photons [2]. Our recent work shows that significant spin effects may also appear in the well known Kapitza-Dirac effect with two interacting photons [3,4] and we describe the spin dynamics as a rotation of the spin of the diffracted electron [5]. Furthermore, our numerical solution allows us to analyze the in-field quantum dynamics of the diffraction process and to verify a generalized Rabi theory for the description of the Bragg condition of the Kapitza-Dirac effect. [1] P. L. Kapitza, P. A. M. Dirac, Proc. Cambridge Philos. Soc. 29, 297-300 (1933) [2] S. Ahrens, H. Bauke, C. H. Keitel, C. Müller, Phys. Rev. Lett. 109, 043601 (2012) [3] D. L. Freimund, K. Aflatooni, H. Batelaan, Nature 413, 142-143 (2001) [4] D. L. Freimund and H. Batelaan, Phys. Rev. Lett. 89, 283602 (2002) [5] S. Ahrens, H. Bauke, C. H. Keitel, C. Müller, arXiv:1305.5507 [quant-ph] (2013)

Speaker: Dr Sven Ahrens (Max-Planck-Institut für Kernphysik)

Slides Slides of the presentation

11:50 Photon emission process from a charged particle under the strong laser field

We propose a uniform formulation to calculate photon emission processes from a charged scalar field or spinor field under the strong laser field. One photon emission from a charged particle, which is forbidden in the vacuum, can be observed in the strong EM field, for example, SLAC E-144 experiment (1997). The process is expressed as non-linear Compton scattering, which means the number of incident photons is 2, 3 or more. But in the short pulse strong laser field, the expression must be changed because the laser field includes various frequency photons. In this presentation, we show that not integer but real number photons interact with a charged particle under short pulse laser field, how to calculate these processes with non-linear QED and some numerical results.

Speaker: Takuya Shibata (Research Center for Nuclear Physics, Osaka University)

Slides 20130710.pdf

12:10 Electron-Positron Pair Production from Multi-Photon Absorption

The process of electron-positron pair production in rapidly time-dependent and linearly polarized electric fields is investigated within the quantum kinetic formalism. Similarities between atomic ionization and pair production are pointed out for field parameters where the Schwinger effect (tunneling) is contributing but subdominant against multi-photon absorption (above-threshold ionization). The non-monotonic dependence of the particle yield on the carrier frequency will be discussed as well.

Speaker: Mr Christian Kohlfürst (University of Graz)

Slides hamburg_kohlfuerst.pdf

12:40 → 14:00 Lunch

14:00 → 15:40 LASERs and Simulations

14:00 Straggling in laser-electron beam collisions

Current high intensity laser facilities can be used to reach the regime in which electron trajectories are strongly modified by the quantum equivalent of the radiation reaction force. We describe a Monte-Carlo simulation of a set-up in this regime and present results in which GeV electrons counter-propagate into a 10^{22} W/sq cm laser pulse. These show that the stochastic nature of quantum synchrotron emission results in many more high energy photons than expected from a purely classical calculation, and that electron-positron pair production by an analog of the nonlinear Breit-Wheeler process should be observable.

Speaker: Prof. John Kirk (MPI Kernphysik)

Slides slides.pdf

14:40 Numerical challenges in laser driven electron-positron plasma

The next generation of laser facilities will make possible to study electron-positron laser plasma arising due to electromagnetic cascades. The cascade consists of quantum electrodynamic effects of hard photon emission and electron-positron pair creation. A central problem in description of plasma with quantum electrodynamic effects is the need for a proper model for radiation, which would simultaneously account for both classical radiation responsible for collective emission and quantum recoil due to non-coherent hard photons. The mathematical description of the cascades boils down to a system of transport equations for particles distribution function and the Maxwell equations for electromagnetic fields. Numerical simulation of these equation in ultra-high intensity regime involves difficulties arising from broad spectrum of time and space scales simultaneously present in the problem. The major part of applied computations concerning the kinetic equation is based on the probabilistic Monte Carlo methods. However, the stochastic method heavily relies on the use of random sampling of transport integrals and may lead to noisy and possibly unstable solution of the transport equation. Alternative highly accurate deterministic methods for the kinetic equations are computationally demanding. In this context the adaptive grid refinement is advantageous because of electromagnetic cascades are localized at laser focus. In this talk, I will review recent advances in the computational algorithms for QED plasma and discuss open problems.

Speaker: Dr Nina Elkina (Ludwig-Maximilians University of Munich)

Slides numQED.pdf

15:00 Understanding the Dynamics of Particles in Intense Laser Fields

During the next few years a number of new laser facilities are expected to come online (such as ELI and XCELS). These will provide fields of unprecedented powers and intensities, allowing us to explore a range of physics under extreme conditions. In this talk I intend to discuss both classical and quantum aspects of laser-particle interactions and the boundary between the two regimes. I will begin by considering electron motion in an intense field, explaining what happens as we make the transition from continuous (classical) emissions of radiation to discrete (quantum) emissions. I will next describe how a laser pulse can be optimally focussed in order to lower the intensity threshold for pair production. Finally, I will discuss the dynamics of the created pairs and the impact of radiation damping on their dynamics.

Speaker: Dr Christopher Harvey (Queen's University Belfast, UK)

Slides c_harveyPIF.pdf

15:20 Development of the quasi-static Particle-In-Cell code HiPACE

High intensity laser- or particle beams excite large amplitude plasma waves when propagating in appropriate gas targets. The fields, carried by these plasma waves, can exceed 100 GV/m and are capable of accelerating particles to high energies within short distances. To design, advance and understand experiments, numerical investigations of the dynamics in such plasma accelerators are vital. Full Particle-In-Cell (PIC) simulations, however, are often computationally too expensive for parameter scans or detailed analyses. This talk will present a Highly efficient Plasma ACcelerator Emulation (HiPACE), which can allow for order of magnitude speedup compared to full PIC codes for a class of problems. The physical basis, numerical implementation, computational framework and parallel performance of this code will be discussed.

Speaker: Mr Timon Mehrling (DESY)

Slides 20130710_PIF_DESY.pdf

15:40 → 16:10 Tea and Coffee

16:10 → 18:30 Strong Field QFT

16:10 Strongly interacting matter: equation of state and transport properties from a gravity dual

Employing the AdS/QCD correspondence the graviton potential is adjusted in a bottom-up approach. Lattice QCD data for the equation of state at non-zero temperature serve as input. Transport coefficients follow then without further assumptions or fine tuning.

Speaker: Prof. Burkhard Kampfer (HZDR)

Slides Kampfer_PIF_2013.ppt

16:40 On the properties of the boost modes and existence of the Unruh effect

Recently, a significant amount of attention is payed in the literature to the proposals for experimental observation of the so-called "Unruh effect" and "Unruh radiation", in particular via application of the state-of-the-art laser facilities. In the papers [1-4] we have reconsidered the original derivation [5] of the Unruh effect. This "effect" originates essentially due to splitting of the field degrees of freedom into the "left" and "right" Unruh modes, the former considered invisible by a uniformly accelerating observer. However, we have demonstrated that existence of the "zero" mode, which is entirely responsible for singular contribution at the horizons, was ignored in [5] and by the successors. As a result, this zero mode is irretrievably lost in the course of such a naive separation, so that application of the Unruh quantization (giving rise to the Unruh effect in the sense of a universal QFT phenomenon) to the problem of the field in Minkowski spacetime is mathematically incorrect (though may be attributed to some different physical contexts). Neither transition to the smeared fields formalism, nor appeal to the Bisognano-Wichman theorem is capable for consistent correction of the derivation. In the talk, the arguments in favour of non-existence of the Unruh effect will be reviewed. [1] A.M. Fedotov, V.D. Mur, N.B. Narozhny, V.A. Belinskii, B.M. Karnakov, Phys. Lett. A254, 126 (1999). [2] N.B. Narozhny, A.M. Fedotov, B.M. Karnakov, V.D. Mur, V.A. Belinskii, Phys. Rev. D65, 025004 (2002). [3] N.B. Narozhny, A.M. Fedotov, B.M. Karnakov, V.D. Mur, V.A. Belinskii, Phys. Rev. D70, 048702 (2004). [4] E.G. Gelfer, A.M. Fedotov, V.D. Mur, N.B. Narozhny, arXiv:1107.0881v1. [5] W.G. Unruh, Phys.Rev. D14, 870 (1976).

Speaker: Dr Alexander Fedotov (National Research Nuclear University MEPhI)

Slides talk_Fedotov.pdf

17:10 Aspects of QED in an Intense Magnetic Field

In this talk we will discuss interesting aspects of QED in an intense magnetic field in the context of nonperturbative QED. We show that thanks to the magnetic catalysis of chiral symmetry breaking (i) there is a few percent increase in the electron mass around $10^{15}$ Gauss, the typical magnetic fields on the surface of young neutron stars, and (ii) the magnetized QED vacuum is stable for all values of the magnetic field.

Speaker: Shang-Yung Wang (Tamkang University)

Slides Wang_PIF13.pdf

17:40 Optical probes of the quantum vacuum

The photon polarization tensor is the central object in an effective theory describing photon propagation in the quantum vacuum. It accounts for the vacuum fluctuations of the underlying theory, and in the presence of external electromagnetic fields, gives rise to such striking phenomena as vacuum birefringence and dichroism. For homogeneous magnetic fields it is explicitly known at one-loop accuracy in momentum space. Most of the studies currently available are manifestly carried out in momentum space, and are often limited to both constant fields and on-the-light-cone dynamics. We aim at insights into the photon polarization tensor beyond this restrictions: We emphasize that the full momentum dependence is essential in the treatment of problems explicitly posed in position space. Moreover, we argue that considerations of this type can provide access to new phenomena, such as quantum reflection of probe photons off the polarized quantum vacuum.

Speaker: Dr Felix Karbstein

Slides talk_PIF_FelixKarbstein.pdf

19:00 → 22:30 Workshop Dinner

Thursday 11 July

09:00 → 10:40 Experiments and facilities

09:00 Present status of the conceptual design for the GEKKO-EXA laser system

The GEKKO-EXA project[1] was revised depending on the domestic user’s demand. Here presented is a revised proposal for the GEKKO-EXA project. The project is aiming at the investigation of the physics under the intense laser field up to 10^24 W/cm^2. As for the future application of the intensity laser, the intensity of 10^23W/cm^2 is one of the mile stone to be overcome since, in the region of radiation-dominated plasma, effective high energy gamma ray flush and its abundant applications are expected. From the physical interest, the process itself is to be demonstrated. The remedy for the radiation reaction in the analysis is still controversial and to be examined by experiment. Technologically, the repetitive high intensity laser system with the output power of several PW is desired to be developed. In the new design of the GEKKO-EXA, the split disk laser system[2] was picked up to deliver the k-J sub-nanosecond pulse with 0.01 Hz which will potentially provide a several PW pulse at the same repetition. At the intensity of 10^24 W/cm^2, QED avalanche is expected[3] and electron-positron plasma might be created effectively. As a final amp, the existing amplifier chain of the LFEX are to be utilized and the final output of 500 J in 20 fs, which makes 25 PW in the revised design of the GEKKO-EXA. The preliminary computational simulation for the experiments such as the QED avalanche will be also reported with the revised design of the laser system. [1] J. Kawanaka, LFEX- and EXA-team, International Committee on Ultra Intense Laser Conference (ICUIL 2010), Watkins Glen, New York, September 26-October 1, (2010). [2] H. Okada, H. Yoshida, H. Fujita and M. Nakatsuka Opt. Commun.261, p342-348 (2006), ibid 266, pp274-279 (2006). [3] A. R. Bell, Phys. Rev. Lett. 101, 200403(2008).

Speaker: Prof. Mitsuo Nakai (Institute of Laser Engineering, Osaka University)

Slides PIF2013(Nakai).pdf

09:20 Any Light Particle Search (ALPS) - II

The ALPS-II experiment at DESY combines expertise from cw-laser precision setups with low-flux photon detectors and high-field superconducting magnets to search for low-mass, weakly-interacting particles (WISPs) such as axion-like particles. After a brief introduction to the scientific goals of the three ALPS-II stages, I will review the crucial components of the setup, and comment on alternative search mechanisms for WISPs.

Speaker: Babette Döbrich (DESY)

Slides PIF_BD.pdf

09:40 J/Ψ photo-production in Pb-Pb and p-Pb ultra-peripheral collisions with ALICE at LHC

The photoproduction of vector mesons in Ultra-Peripheral Collisions (UPC) is a powerfull tool to probe the nuclear gluon-distribution, for which there is considerable uncertainty in the low-x region. We present the first measurements in Pb-Pb collisions at √s_NN = 2.76 TeV, performed with the ALICE detector. The J/ψ is identified via its dimuon decay in the forward rapidity region and via dimuon and dielectron decay at mid-rapidity. The results are compared to theoretical models for coherent J/ψ production and found to be in good agreement with models which include nuclear gluon shadowing. The cross section measurement for incoherent J/ψ and γγ->e+e- at mid-rapidity will be shown. Finally we present the first results on p-Pb UPC at √s_NN = 5.02 TeV.

Speaker: Mr Daniele De Gruttola (Centro Fermi Roma and Salerno INFN)

Slides PIF2013.pdf

10:00 Future linear colliders: an opportunity to study strong field QED

Future linear colliders will collide dense charge bunches generating very intense electromagnetic fields at the IP, often approaching or even exceeding the Schwinger critical field in the rest frame of the ultrarelativistic colliding particles. These strong fields affect all the processes happening at the IP, in particular, at 1st order, beamstrahlung and coherent pair production. The dense beams at the LC offer another opportunity to test strong field/nonlinear QED and a whole range of further predicted phenomena. We propose an experiment that will focus an intense laser on the LC electron beam post-IP. High energy electrons then undergo vacuum polarization effects when the field strength approaches the Schwinger critical field. Previously similar experiments at SLAC E144 have investigated nonlinear Compton scattering, Breit-Wheeler pair production and electron mass shift using an electron beam of 46.6 GeV; the higher and intense beam energies at the next LC would allow more precise studies of these phenomena. We also plan to test for the first time the radiative transitions between Zel'dovich electron quasi-levels in a laser.

Speaker: Stefano Porto (Hamburg University)

Slides Stefano_Porto_PIF2013.pdf

10:20 Quantum Synchrotron Radiation Measurements using Crystals

The classical description of synchrotron radiation fails at large Lorentz factors for relativistic electrons crossing strong transverse magnetic fields. When the Lorentz factor times the magnetic field is comparable to the so-called critical field of 4.4 GT, quantum corrections are essential for the description of synchrotron radiation. The radiation emission drastically changes character; not only in magnitude, but also in spectral shape and can only be described by quantum synchrotron radiation formulas. This has been experimentally tested with electrons of energies 10-150 GeV penetrating a germanium single crystal along the <110> axis. Apart from being a test of strong-field quantum electrodynamics, the results are also relevant for the design of future linear colliders where beamstrahlung - a closely related process - may limit the achievable luminosity.

Speaker: Kristoffer Andersen (Aarhus University)

Slides presentation_online.pptx

10:40 → 11:00 Tea and Coffee

11:00 → 12:40 Radiation reaction

11:00 Radiation reaction in QED: perturbative and non-perturbative approaches.

I will discuss recent theoretical results in radiation reaction (RR). In the first part of the talk I will describe how and where RR appears in QED, and the possibilities for measuring RR in different regimes and in different experiments (with say lasers, or Coulomb fields). RR effects are expected to become significant in the regimes reached by next generation laser facilities. Aside from a few exact solutions, there are though few nonperturbative treatments of RR available. In the second part of the talk I will describe a new non-perturbative approach to QED in strong background fields, called `basis lightfront quantisation'.

Speaker: Anton Ilderton (Chalmers Univesity)

Slides Ilderton-PIF2013-6.pdf

11:20 Effect of radiation reaction on the motion of a high energy particle

Radiation reaction effects, in particular the effects of stochasticity, in dynamics of a high energy particle are studied by using semiclassical approach to radiation reaction.

Speaker: Rashid Shaisultanov

Slides Shaisultanov_desy_talk_short.pdf

11:40 Radiation reaction effects on the interaction of an electron with an intense laser pulse

Rapid advances in laser technology have hastened the need for a consistent and physically reasonable model of how losses to radiation affect the motion of electrons. We report on a recent investigation of the Ford-O'Connell equation, exploring its relation to other commonly used descriptions of radiation reaction, in particular that of Landau and Lifshitz. By analysing the motion of an electron passing through a laser pulse, we find that radiation reaction effects prevent the particle from reaching a regime in which the Landau-Lifshitz approximation would break down.

Speaker: Dr Adam Noble (University of Strathclyde)

Slides PIF2013_noble.pdf

12:00 Radiation reaction directly from QED

There remains great interest in radiation reaction, both theoretically and experimentally, especially in the context of strong laser fields. In this talk I will derive classical radiation reaction directly from QED. The treatment is fully quantum and and we make no approximation except the usual coupling expansion of QED. We calculate the expectation value of the momentum and the position of an electron in QED. Taking the classical limit, hbar goes to zero, of these expectation values allows us to identify which of the many different classical equations proposed to describe radiation reaction are consistent with QED.

Speaker: Mr Greger Torgrimsson (Chalmers)

Slides Torgrimsson-PIF2013.pdf

12:20 Pre-acceleration from Landau-Lifshitz Series

The Landau-Lifshitz equation is considered as an approximation of the Abraham-Lorentz-Dirac equation. The former is derived from the latter by treating radiation reaction terms as a perturbation. However, while the Abraham-Lorentz-Dirac equation has pathological solutions of pre-acceleration and runaway, the Landau-Lifshitz equation and its finite higher order extensions are free of these problems. So it seems mysterious that the property of solutions of these two equations is so different. We show that the problems of pre-acceleration and runaway appear when one consider a series of all-order perturbation which we call it the Landau-Lifshitz series. The Landau-Lifshitz series diverges in general. Hence a resummation is necessary to obtain a well-defined solution from the Landau-Lifshitz series. This resummation leads the pre-accelerating and the runaway solutions.

Speaker: Dr Sen Zhang (Okayama Institute for Quantum Physics)

Slides slides

12:40 → 14:00 Lunch

14:00 → 15:20 Plasmas and Radiation Reaction

14:00 Relativistic plasmas and beams, and the radiative self-force

Contemporary advances in ultra-intense laser facilities have driven the recent surge of interest in the collective behaviour of charged matter in extreme conditions, and a particularly vexing topic in that context concerns the coupling of an electron to its own radiation field. In most practical cases, the Lorentz force on an electron, due to an applied electromagnetic field, is considerably larger than the force due to the electron’s emission and the effect of the recoil due to the emitted radiation is negligible or can be adequately represented using simple physical reasoning. Although such arguments avoid the difficulties that plague more comprehensive analyses, the parameter regimes promised by forthcoming ultra-intense laser facilities, such as ELI, ensure that more fundamental considerations are now of practical necessity. We will discuss recent developments in relativistic kinetic and fluid theory in the above context. Refs: J. Math. Phys. 54, 043101 (2013); arXiv:1303.7385

Speaker: Dr David Burton (Lancaster University &amp; Cockcroft Institute)

Slides Burton_PIF2013.pdf

14:20 Simulations of beam-driven plasma acceleration at FLASHForward

Plasma acceleration exploits extreme electric fields created in a plasma by high-current beams or high-intensity laser pulses, to accelerate charged particles. In current studies we explore prospects for beam-driven plasma acceleration within FLASHForward project at DESY, by means of 3D particle-in-cell simulations with the code OSIRIS. In particular, various techniques of injecting particles into a beam-driven wake are being considered. It is demonstrated that injecting particles by using transitions in plasma density allows for trapping and acceleration of electron beams, with final low emittance and low slice energy spread. The parameters of the driver beam and the plasma correspond to the current design for future experiments. Various parameter scans were performed, investigating sensitivity of the injected beam qualities, such its as length, charge, energy spread, and correlations in phase-spaces, to initial parameters of the driver and the plasma ramp.

Speaker: Dr Julia Grebenyuk (DESY)

14:40 Quantum radiation reaction in laser-electron beam collisions

The intensity of short pulse lasers is now sufficiently high that the dynamics of energetic electrons in these fields is dominated by quantum radiation reaction. We present simulations of an experiment that uses a laser wakefield to drive GeV electrons into a counterpropagating laser pulse of intensity 10^{22} Wcm^{-2}. The stochastic nature of photon emission leads to broadening of the electron beam's energy spectrum and to a yield of high energy gamma rays much greater than that predicted by classical radiation theory. These signatures of strong-field QED processes should be detectable with current high intensity laser facilities.

Speaker: Mr Tom Blackburn (Clarendon Laboratory, University of Oxford)

Slides tgb_qrr_talk.pdf

15:00 Radiation reaction force induced nonlinear mixing of Raman sidebands of an ultra-intense laser pulse in a plasma

Stimulated Raman scattering of an ultra-intense laser pulse in plasmas is studied by pertur- batively including the leading order term of the Landau-Lifshitz radiation reaction force in the equation of motion for plasma electrons. In this approximation, radiation reaction force causes phase lag in nonlinear current densities that drive the two Raman sidebands (anti-Stokes and Stokes waves), manifesting itself into the nonlinear mixing of two sidebands. This mixing results in a strong enhancement in the growth of the forward Raman scattering instability.

Speaker: Dr Naveen Kumar (Max-Planck-Institute für Kernphysik)

Slides PIF_July_2013_Hamburg.pdf

15:20 → 15:40 Tea and Coffee

15:40 → 16:30 Outlook

15:40 Testing non-linear QED with Lasers - Experiments feasible now.

The development of ultra-intense lasers has brought Physics in intense fields into sharp focus from a perspective of testing theoretical predictions - some quite longstanding - for the first time. Reaching a significant fraction of the critical QED field strength is still some way off for a real facility, however many possibilities exist with current technology or near-term achievable parameters and these will be the focus of the Presentation.

Speaker: Prof. Matthew Zepf (Queens University)

Slides QED_PIF13_DESY.ppt

16:25 Wrapup

Speaker: Dr Anthony Hartin (DESY)

Slides Wrapup.pdf