Lawrence Livermore National Laboratory (LLNL)’s
JASPER gas gun has fired its 100th shot.
JASPER (the Joint Actinide Shock Physics
Experimental Research) is a key scientific tool for the National Nuclear
Security Administration’s Stockpile Stewardship Program (SSP). This program’s
combination of computer simulations, scientific theory and above-ground
experiments has allowed the United States to maintain its nuclear deterrent for
the past 20 years.
JASPER’s experiments at the Nevada National
Security Site (formerly the Nevada Test Site) have enabled LLNL scientists to
understand important properties and behaviors of plutonium and other special
nuclear materials without conducting underground nuclear tests.
JASPER is a two-stage light gas gun, about 20
m long, with a target chamber inside an 8-ft diameter containment chamber at
Projectiles are loaded into the primary
stage, which is fired with up to 8 lbs of gunpowder. The resulting detonation
pushes a heavy piston into the tube filled with a gas, such as hydrogen. The
piston’s action heats and compresses the gas to thousands of pounds per square
inch. Once the heat and pressure are high enough, a small steel rupture disk
bursts, accelerating the projectile into the second stage at up to about 17,000
miles/hr—about 10 times faster than a hunting rifle.
“Think about this,” says Neil
Holmes, JASPER’s chief scientist. “When it hits, you’ve got a bullet that
is about the size and weight of an ice cube. It has as much kinetic energy as a
Toyota Corolla going down the highway at 50 mph.” The impact of the bullet
on the plutonium target drives the experiment.
entire shot lasts roughly one-millionth of a second and can generate pressures
on the target of millions of times atmospheric pressure (80 million pounds per
square inch) and temperatures of thousands of degrees.
need to understand the properties of plutonium and other actinides under
extremely high temperatures and pressures,” says Holmes. “What makes
JASPER unique is the unprecedented accuracy we achieve.”
first time dynamic shock experiments have been accurate enough to meet the
needs of the SSP,” Holmes adds. “Those data are then used to study
the behaviors of those materials and help create numerical tables that express
our understanding of those properties. For example, we might list the
temperatures at specific pressures and densities. Those tables are then used in
our supercomputer simulations of nuclear weapons. And those simulations are one
important element in how we can assure that the stockpile remains safe and
the front plate of the projectile—typically a metal like aluminum or tantalum,
embedded in a Lexan and polyethylene device known as a sabot (French for
“shoe”)—hits the plutonium target, JASPER’s diagnostic equipment can
accurately measure the resulting shock wave to a data uncertainty that is typically
better than 0.5%.
the conclusion of each test, the inner target chamber remains sealed, and the
entire chamber is removed and sent for appropriate hazardous waste disposal.
first JASPER shot was conducted on March 19, 2001. Of the 100 shots that have
been executed, 41 have investigated plutonium material properties, while the
other shots supported those experiments by rigorously testing target design,
innovative measurement methods, and gun performance.
key finding involved the aging of plutonium, a manmade element first produced
during the Manhattan Project. Many of its properties remained unknown for
decades, and even today, are not completely understood.
a radioactive element, plutonium undergoes self-irradiation that can lead to
corrosion and changes in composition and dimensions that alter the properties.
For years, physicists were worried that these issues could possibly affect a
weapon’s performance after decades in storage.
made essential experimental contributions to a large body of scientific work
that helped to alleviate those concerns, and in fact, indicated that plutonium
can be viable in excess of 100 years.
and the JASPER team have not only produced the largest data return on plutonium
of any experimental facility, they have done it for the lowest cost per data
point, by far,” says Bruce Goodwin, principal associate director for the
Weapons and Complex Integration Directorate at LLNL. “It is a remarkable
facility and achievement. I look forward to JASPER and this team completing the
map-out of the physical properties of plutonium for the sustainment of the US
100th shot, on Sept. 25, 2012, was the first of its kind at JASPER, and in the
nuclear weapons complex.
this experiment, JASPER researchers measured how the velocity of the sample
responds to the impact, and also how the light emitted from the surface of the
plutonium varies with that velocity. Measuring the light is a real challenge,
and results from a collaboration on measurement technique, instrumentation and
target design between Lawrence Livermore and Los Alamos National Laboratories,
and National Security Technologies (NSTec), the management and operating
contractor for the Nevada National Security Site.
Laboratory operates JASPER in conjunction with Joint Laboratory
Operations-Nevada (JLON), a collaboration of Lawrence Livermore, Los Alamos,