Process leading to supernova explosions and cosmic radio bursts
unearthed

Date:
October 5, 2021
Source:
DOE/Princeton Plasma Physics Laboratory
Summary:
A process important to black holes and supernovas has for the
first time been demonstrated in a laboratory.



FULL STORY ==========================================================================
A promising method for producing and observing on Earth a process
important to black holes, supernova explosions and other extreme
cosmic events has been proposed by scientists at Princeton University's Department of Astrophysical Sciences, SLAC National Acceleraor Laboratory,
and the U.S. Department of Energy's (DOE) Princeton Plasma Physics
Laboratory (PPPL). The process, called quantum electrodynamic (QED)
cascades, can lead to supernovas -- exploding stars -- and fast radio
bursts that equal in milliseconds the energy the sun puts out in three
days.


========================================================================== First demonstration The researchers produced the first theoretical demonstration that colliding a laboratory laser with a dense electron beam
can produce high-density QED cascades. "We show that what was thought
to be impossible is in fact possible," said Kenan Qu, lead author of a
paper in Physical Review Letters (PRL) that describes the breakthrough demonstration. "That in turn suggests how previously unobserved
collective effects can be probed with existing state-of-the-art laser and electron beam technologies." The process unfolds in a straightforward
manner. Colliding a strong laser pulse with a high energy electron
beam splits a vacuum into high-density electron- positron pairs that
begin to interact with one another. This interaction creates what are
called collective plasma effects that influence how the pairs respond collectively to electrical or magnetic fields.

Plasma, the hot, charged state of matter composed of free electrons and
atomic nuclei, makes up 99 percent of the visible universe. Plasma
fuels fusion reactions that power the sun and stars, a process
that PPPL and scientists around the world are seeking to develop on
Earth. Plasma processes throughout the universe are strongly influenced
by electromagnetic fields.

The PRL paper focuses on the electromagnetic strength of the laser
and the energy of the electron beam that the theory brings together to
create QED cascades. "We seek to simulate the conditions that create electron-positron pairs with sufficient density that they produce
measurable collective effects and see how to unambiguously verify these effects," Qu said.

The tasks called for uncovering the signature of successful plasma
creation through a QED process. Researchers found the signature in the
shift of a moderately intense laser to a higher frequency caused by
the proposal to send the laser against an electron beam. "That finding
solves the joint problem of producing the QED plasma regime most easily
and observing it most easily," Qu said. "The amount of the shift varies depending on the density of the plasma and the energy of the pairs."
Beyond current capabilities Theory previously showed that sufficiently
strong lasers or electric or magnetic fields could create QED pairs. But
the required magnitudes are so high as to be beyond current laboratory capabilities.

However, "It turns out that current technology in lasers and relativistic
beams [that travel near the speed of light], if co-located, is sufficient
to access and observe this regime," said physicist Nat Fisch, professor
of astrophysical sciences and associate director for academic affairs
at PPPL, and a co-author of the PRL paper and principal investigator of
the project. "A key point is to use the laser to slow down the pairs so
that their mass decreases, thereby boosting their contribution to the
plasma frequency and making the collective plasma effects greater,"
Fisch said. "Co-locating current technologies is vastly cheaper than
building super-intense lasers," he said.

This work was funded by grants from the National Nuclear
Security Administration and the Air Force Office of Scientific
Research. Researchers now are gearing up to test the theoretical findings
at SLAC at Stanford University, where a moderately strong laser is being developed and the source of electrons beams is already there. Physicist Sebastian Meuren, a co-author of the paper and a former post-doctoral
visitor at PPPL who now is at SLAC, is centrally involved in this effort.

"Like most fundamental physics this research is to satisfy
our curiosity about the universe," Qu said. "For the general
community, one big impact is that we can save billions
of dollars of tax revenue if the theory can be validated." ========================================================================== Story Source: Materials provided by
DOE/Princeton_Plasma_Physics_Laboratory. Original written by John
Greenwald. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Kenan Qu, Sebastian Meuren, Nathaniel J. Fisch. Signature of
Collective
Plasma Effects in Beam-Driven QED Cascades. Physical Review Letters,
2021; 127 (9) DOI: 10.1103/PhysRevLett.127.095001 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211005175432.htm

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