Around the Lab
Small 3-D Printing Supports the Large Omega User Community
Until recently, most of the research into nuclear fusion, which holds the promise of creating unlimited, clean power production, focused on either magnetic confinement (low plasma density) or inertial confinement (high plasma density). However, hybrid techniques such as magneto-inertial fusion, which combines aspects of magnetic confinement fusion with inertial confinement fusion, are gaining increased attention since their relatively smaller size, energy, and power-density requirements could potentially lower the cost of fusion devices.
The Magneto-Inertial Fusion Electrical Discharge System (MIFEDS) at LLE allows scientists to apply strong magnetic fields to high-energy-density plasmas to study these phenomena. Combining strong fields with dense plasmas allows processes that evolve over vast distances in outer space or astrophysics to be scaled down to experimental volumes smaller than a centimeter. MIFEDS has also been used to perform magnetized direct-drive inertial fusion implosions and scaled-down magnetized liner inertial fusion (MagLIF) implosions using very strong magnetic fields. MagLIF is able to exploit advances in pulsed-power technology.
MIFEDS requires disposable, non-conductive parts that can hold high-voltage, high-current wires in various shapes to avoid the beams of OMEGA and OMEGA EP. The extremely large currents necessary to create such strong magnetic fields vaporize the fine electrical coil carrying the current an instant after the experiment takes place. As such, the MIFEDS coils are inherently single-use. In addition, the design of each coil is unique for each experiment to produce the correct strength, size, and shape of the magnetic field required. Coil designs have tight tolerances of the order of fractions of a millimeter since any material or structural defects could interfere with the experiment, diagnostics, or laser beams. Manufacturing coil armatures using 3-D printing allows LLE to produce these custom-designed, single-use coils with the high accuracy required to enable cutting-edge experiments on the properties of magnetized plasmas. Experiments using this technology are carried out by a wide range of universities and institutions such as Lawrence Livermore, Sandia, and Los Alamos National Laboratories, MIT, the University of Chicago, and UCSD, to name a few.
3-D printed MIFEDS coil
Left: CAD design of a fill-tube target mounted inside a printed dodecahedral structure; Right: As-printed structure supporting a contiguous 50-nm-thick plastic film overcoated with 30 nm of gold
The qualities of the 3-D–printed material (vacuum compatibility and electrical insulation) have encouraged its use for insulation in many pieces of custom hardware at LLE. In the next generation of MIFEDS currently under development, 3-D–printed parts have been designed and printed to serve as high-voltage insulation throughout the unit, proving to be much less expensive and more versatile than the previous insulation method.
Use of 3-D printers has also accelerated the development of unique concepts at LLE by providing quick turnaround and production of test articles. For example, a unique inertial confinement fusion target concept using a dodecahedral shell surrounding a capsule was able to be brought forth, iterated, printed, and assessed for feasibility within a single month. This accelerated development allows for the quick assessment of any potential impediments for the concept in question, providing tangible pieces of equipment that can be used to judge feasibility.
Since the inception of MIFEDS 2.0 in 2013, scientists at LLE have:
- designed and shot over 120 different coil designs specific to each MIFEDS campaign, and
- determined that 3-D printing is the best method to quickly prototype and finalize unique components in minimal turnaround time.
Laser-fusion experiments sometimes employ cryogenically cooled targets, each of which contains a shell of solid hydrogenic fuel. The interior surface of the fuel (referred to as a “layer”) must be very smooth to prevent perturbations from magnifying and spoiling target performance. LLE’s 100-gigabar, fill-tube target project employs a vibration absorber in which 3-D springs are printed into the corners of each part. The springs reduce vibration in three dimensions. Normally such an assembly would be both difficult to machine and prohibitively expensive to deploy. However, using a 3-D printer allows for it to be made rapidly and inexpensively. This isolator is used to protect the cryogenic targets in the 100-Gbar fill-tube target project program from vibrations caused when the protective shroud is quickly retracted to expose the target to the laser beams.
3-D printed vibration absorber attached to the printer support structure
3-D printer forming a resistor tray