The introduction of tritium is of high technical interest because a 50/50 mix of tritium and deuterium — the two isotopes of hydrogen — emits 80 times more neutrons, and 500 times more energy, than deuterium alone. Energy from deuterium — in a manner of speaking, a relatively low-octane fuel — has been the upper limit on output at Z.
They are currently adding 0.1% tritium.
But it’s still early days. A dry run in July, testing containment hardware and instrumentation, preceded Z’s first tritium experiment three weeks later, when a fraction of a percent was cautiously introduced into the experiment’s fuel.
“We’re going to crawl before we walk and run,” said Cuneo. “We will gradually increase that fraction in contained experiments as we go.”
Currently adding 0.1% tritium
Sandia’s Z machine has a project called MagLIF for magnetized liner inertial fusion. The Z-machine stared conducting MagLIF experiments in November 2013 with a view towards breakeven experiments using D-T fuel in 2018
Inertial confinement fusion creates nanosecond bursts of neutrons, ideal for creating data to plug into supercomputer codes that test the safety, security and effectiveness of the U.S. nuclear stockpile. The method could be useful as an energy source down the road if the individual fusion pulses can be sequenced like an automobile’s cylinders firing.
MagLIF uses a laser to preheat hydrogen fuel, a large magnetic field to squeeze the fuel and a separate magnetic field to keep charged atomic particles from leaving the scene.
It only took the two magnetic fields and the laser, focused on a small amount of fusible material called deuterium (hydrogen with a neutron added to its nucleus), to produce a trillion fusion neutrons (neutrons created by the fusing of atomic nuclei). Had tritium (which carries two neutrons) been included in the fuel, scientific rule-of-thumb says that 100 times more fusion neutrons would have been released. (That is, the actual release of 10 to the 12th neutrons would be upgraded, by the more reactive nature of the fuel, to 10 to the 14th neutrons.)
Still, even with this larger output, to achieve break-even fusion — as much power out of the fuel as placed into it — 100 times more neutrons (10 to the 16th) would have to be produced.
The actual MagLIF procedure follows this order: The Helmholtz coils are turned on for a few thousandths of a second. Within that relatively large amount of time, a 19-megaAmpere electrical pulse from Z, with its attendant huge magnetic field, fires for about 100 nanoseconds or less than a millionth of a second with a power curve that rises to a peak and then falls in intensity. Just after the 50-nanosecond mark, near the current pulse’s peak intensity, the laser, called Z-Beamlet, fires for several nanoseconds, warming the fuel.
10 tesla magnetic field
2 kJ laser
In 2014, the test yielded up to 2×10^12 D-D neutrons under the following conditions:
10 tesla magnetic field
2.5 kJ laser
Experiments aiming for energy breakeven with D-T fuel are expected to occur in 2018.
To achieve scientific breakeven, the facility is going through a 5-year upgrade to :
8 kJ laser
D-T fuel handling