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Argon Fluoride Laser Marks Breakthrough
by U.S. Naval Research Laboratory
September 30, 2020
The U.S. Naval Research Laboratory research team set a new energy
record on March 5, 2020 using an argon fluoride laser. This energy
is twice the previous record.
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September 22, 2020 - (Left)
The Electra electron-beam pumped amplifier (before x-ray shielding was installed). (Right) The Electra diode’s vertical dimension was reduced from 30 cm to 10 cm to provide higher pump intensity for argon fluoride laser (ArF) operation. The specific pump rate for ArF has a lower small signal gain and higher saturation flux than krypton fluoride (KrF). The image shows a time resolved measurement of the emitted light produced by the reduced size electron beam interacting with the laser gas along the laser axis. (U.S. Naval Research Laboratory image by Daniel Parry)
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It delivered a laser beam capable of applying more force
to implode a laser fusion target than any other laser technology,
which is the oomph needed for a nuclear fusion reaction.
The research team tested this capability by
computer simulations with a small pellet about the size of a pea
made of deuterium and tritium.
Deuterium and tritium are
isotopes of hydrogen that have additional neutrons in the nucleus.
The chemical elements were frozen together and formed the inner skin
of the hollow pellet.
“If the density and temperature are
high enough, it ignites the nuclear fusion reaction and produces
much more energy, 100 times more than the laser took to do all of
this,” Andrew Schmitt, a physicist at NRL, said.
The NRL team
wants to develop the science and technologies to a much higher
energy scale between 500,000 to million joules to drive a higher
performance fusion implosion.
To produce a higher energy
laser it will require a facility specifically designed for argon
fluoride.
NRL researchers already leverage the laser fusion
technologies they developed for krypton fluoride on their argon
fluoride experiments. They hope a new laser facility specifically
designed for argon fluoride will further prove the viability of this
gas as a cost-effective alternative to current laser fusion
approaches.
Matthew Wolford, a research chemist, has
investigated excimer laser technology for more than 18 years. An
excimer laser usually contains a mixture of noble gas such as
krypton or argon and a halogen gas such as fluorine. The gas mixture
is irradiated by powerful electron beams and in response it emits a
beam of deep ultraviolet light.
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June 1, 2020 - Matthew Wolford, a U.S. Naval Research Laboratory research chemist, inspects an argon fluoride (ArF) laser to be tested with new thicker stainless foils at Washington, D.C. Wolford was part of a team of researchers who outfitted the ArF laser with new foils in hopes of increasing laser output. The ArF laser is the world’s largest studying the physics of developing a high efficiency electron-beam pumped ArF laser at 193 nanometers.
(U.S. Naval Research Laboratory image by Jonathan Steffen)
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“We haven’t built an argon
fluoride facility yet with the energy required to achieve laser
fusion,” Wolford said. “We got 200 joules out of the NRL Electra
facility. We need on the order of half a megajoule to compress
enough hydrogen for fusion to occur. We have to go up three orders
of magnitude. We would want to build a small facility and show that
we can do the target physics.”
The energy output of 200
joules is enough energy to power a 20-watt LED light for 10 seconds.
A half megajoule is enough energy to power the LED for 14 hours.
“Due to the higher argon fluoride laser efficiency we expect to
build laser fusion facilities with lower cost, smaller size and
lower electrical power requirements,” Wolford said. “It would
provide a source of energy that would be cleaner than present day
technologies such as fossil fuels. It’s the energy source of the
future.”
Steve Obenschain, a physicist and head of the NRL
Laser Plasma Branch, said argon fluoride laser is the shortest
wavelength laser with the theoretical capability to deliver the high
energies needed to drive laser fusion implosions to produce much
more energy than the incident laser beams.
Laser fusion
involves many laser beams to uniformly illuminate at high power
hollow spherical targets to cause an implosion with speeds more than
a 1000 times that of a jet airliner.
If done with sufficient
precision, the deuterium and tritium fuel within the target will
ignite and through a thermonuclear burn produce much more energy
than needed to implode the pellet,” Obenschain said.
If
successful, laser fusion has applications as a test bed for defense
tests and would be an attractive future power source. The short
wavelength and other attributes make the argon fluoride laser the
ideal laser to obtain high performance fusion implosions. However,
because of its extremely short wavelength and other technical
challenges, high-energy argon fluoride laser lasers were thought to
be much too difficult to build.
“NRL was already the world
leader in the similar but longer wavelength krypton fluoride laser
technology,” Obenschain said. “The team decided to explore the
feasibility of employing argon fluoride laser as a fusion driver.
In parallel, massive computer simulations investigated the
advantages of utilizing the argon fluoride laser for fusion
implosions. The results so far indicate argon fluoride laser could
be a game changing driver for high performance laser fusion.”
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About the U.S. Naval Research
Laboratory
NRL is a scientific and engineering command dedicated to
research that drives innovative advances for the U.S. Navy and
Marine Corps from the seafloor to space and in the information
domain. NRL is located in Washington, D.C. with major field sites in
Stennis Space Center, Mississippi; Key West, Florida; and Monterey,
California, and employs approximately 2,500.
U.S. Naval Research Laboratory
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