Springer : Laboratory realization of relativistic pair-plasma beams

Arrowsmith, C.D.; Bott, A.F. A.; Burger, S.; Cruz, F.D.; Froula, D.H.; Stergiou, V.; Gudmundsson, J.T.; Miniati, F.; Trines, R.M. G.M.; Iaquinta, S.; Bilbao, P.J.; Sarkar, S.; Simpson, R.; Vieu, T.; Schekochihin, A.A.; Huffman, B.T.; Efthymiopoulos, I.; Hodge, T.; Silva, L.O.; Goillot, A.M.; Chen, H.; Bingham, R.; Halliday, J.W. D.; Haberberger, D.; Gregori, G.; Reville, B.; Charitonidis, N.; Davenne, T.; Simon, P.

doi:10.1038/s41467-024-49346-2

Article
Report number	arXiv:2312.05244
Title	Laboratory realization of relativistic pair-plasma beams
Author(s)	Arrowsmith, C.D. (Oxford U.) ; Simon, P. (CERN ; Darmstadt, GSI) ; Bilbao, P.J. (Lisbon, IST) ; Bott, A.F. A. (Oxford U.) ; Burger, S. (CERN) ; Chen, H. (LLNL, Livermore) ; Cruz, F.D. (Lisbon, IST) ; Davenne, T. (Rutherford) ; Efthymiopoulos, I. (CERN) ; Froula, D.H. (Rochester U.) ; Goillot, A.M. (CERN) ; Gudmundsson, J.T. (Iceland U. ; Royal Inst. Tech., Stockholm) ; Haberberger, D. (Rochester U.) ; Halliday, J.W. D. (Oxford U.) ; Hodge, T. (Oxford U. ; Reading U.) ; Huffman, B.T. (Oxford U.) ; Iaquinta, S. (Oxford U.) ; Miniati, F. (Oxford U.) ; Reville, B. (Heidelberg, Max Planck Inst.) ; Sarkar, S. (Oxford U.) ; Schekochihin, A.A. (Oxford U.) ; Silva, L.O. (Lisbon, IST) ; Simpson, R. (LLNL, Livermore) ; Stergiou, V. (Oxford U. ; CERN ; Natl. Tech. U., Athens) ; Trines, R.M. G.M. (Rutherford) ; Vieu, T. (Heidelberg, Max Planck Inst.) ; Charitonidis, N. (CERN) ; Bingham, R. (Rutherford ; Strathclyde U.) ; Gregori, G. (Oxford U.)
Publication	2024-06-12
Imprint	2023-12-08
Number of pages	14
Note	14 pages, 8 figures
In:	Nature Commun. 15 (2024) 5029
DOI	10.1038/s41467-024-49346-2 (publication)
Subject category	hep-ex ; Particle Physics - Experiment ; astro-ph.HE ; Astrophysics and Astronomy ; physics.plasm-ph ; Other Fields of Physics
Abstract	Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black holes and neutron star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with such pair plasmas. Their behaviour is quite different from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components and their role in the dynamics of such compact objects is believed to be fundamental. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies which are rather limited. We present first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN's Super Proton Synchrotron (SPS) accelerator. The produced pair beams have a volume that fills multiple Debye spheres and are thus able to sustain collective plasma oscillations. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations.
Copyright/License	publication: © 2024 The Author(s) (License: CC-BY-4.0) preprint: (License: CC BY 4.0)

${\bf Experimental setup.} Protons with 440 GeV/c momentum are extracted from the SPS ring with maximum fluence exceeding $3\times10^{11}$ protons in a single bunch of duration \SI{250}{\pico\second} (1-$\sigma$), and transverse size $\sigma_r = \SI{1}{\milli\metre}$. The transverse beam profile of the secondary beam is imaged using a $70$~mm~$\times\, 50$~mm~$\times \, 0.25$~mm chromium-doped (Chromox) luminescence screen positioned 10~cm downstream of the target, and a blocker foil (\SI{50}{\micro\metre} aluminium) is used to minimize stray optical light. The Chromox plate is oriented at 45$^{\circ}$ to the beam path and viewed by a digital camera which has an exposure time of 24~ms to capture the entire scintillation of the screen. The \SI{3.8}{\metre} standoff distance of the digital camera leads to image resolution of \SI{50}{\micro\metre}, however the actual resolution is \SI{100}{\micro\metre} due to the translucence of the Chromox. At a distance \SI{2}{\metre} downstream of the target, electrons and positrons are separated from the secondary beam and spectrally resolved using a magnetic spectrometer comprised of an electromagnet and a pair of luminescence screens ($200$~mm~$\times\, 50$~mm~$\times \, 1$~mm) centred at a distance \SI{240}{\milli\metre} off-axis. 20-cm thick bricks of concrete (not shown in the diagram) are placed at the entrance of the electromagnet, leaving a \SI{40}{\milli\metre} wide aperture. Concrete is also placed to block the target from the direct view of the cameras to minimize speckle background arising on the camera images from the impact of high energy hadrons scattered around the experimental area.$ ${\bf Transverse beam profile imaged using a luminescence screen.} (a) Direct comparison of FLUKA Monte-Carlo simulations with raw image data obtained when the target is irradiated and the secondary beam is produced (`Target in'), versus when the target is removed and only the primary proton beam irradiates the screen (`No target'). An absolute fluence calibration is obtained using the known density profile of the primary proton beam. (b) Integrated image intensity (total intensity) from 70 shots is converted to an absolute particle number, showing the case where the target is irradiated (red circles, 47 shots), and when it is removed (black diamonds, 23 shots). The error bars reflect the standard errors of the fitted parameters for each shot. FLUKA Monte-Carlo simulations of the predicted light yield are shown for both cases (black-dashed and red-dashed lines), showing strong agreement with the experimental data. The blue dot-dashed line shows the contribution from e$^{\pm}$ in the FLUKA simulation, highlighting that this is the dominant contribution to the enhanced signal.$ ${\bf Magnetic particle spectrometer.} The energy spectra of e$^-$ (blue) and e$^+$ (red) are obtained from images of luminescence screens (dimensions $200$~mm~$\times\,50$~mm~$\times\,1$~mm) centred \SI{240}{\milli\metre} from the beam axis on either side (see Figure~1). Electrons and positrons are deflected onto the screens by the vertically-oriented dipole magnetic field of the electromagnet, whilst hadrons with a higher momentum and uncharged $\gamma$-rays are mostly absorbed by the beam dump behind the electromagnet. The spectrum in the energy range $30\leq E~\mbox{[MeV]}\leq220$ is constructed by piecing together images from multiple shots using different magnetic field strengths ($B=0.1-$\SI{0.34}{\tesla}). The shaded regions correspond to the error associated with the absolute calibration. FLUKA simulations (histograms) are able to accurately predict the experimentally obtained spectra.$ Show more plots

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