The Laboratory in the News

Visualizing High-Energy Electrons in Fast Ignition

Recent fast-ignition (FI) research by an international team of scientists, including researchers from Lawrence Livermore, produced the first visualization of fast-electron spatial energy deposition in a laser-compressed, cone-in-shell FI target. The research was published in the January 11, 2016, issue of Nature Physics and opened the door for optimizing the FI target design. The paper’s lead author is Charlie Jarrott, who recently joined Livermore as a postdoctoral researcher.

FI is an alternative approach to conventional inertial-confinement fusion that involves separating the compression and heating phases of implosion. This separation allows fuel to be compressed isochorically, resulting in reduced fuel density requirements or increasing the mass of fuel that can be compressed, potentially leading to higher gain. The process requires efficient heating of precompressed, high-density fuel by an intense, relativistic electron beam produced from laser–matter interactions. To facilitate FI research, scientists doped the shell of the cone-in-shell FI target with copper and imaged the K-shell x-ray radiation.

The experiments showed the spatial distribution of fast electrons and revealed key parameters affecting energy coupling. The results also exhibited a significantly improved laser-to-core coupling energy efficiency of seven percent—a factor-of-four improvement over previous results using similar techniques and the highest coupling efficiency ever reported with the Omega Laser Facility at the University of Rochester, where the experiments were conducted. The experiments’ success has the far-reaching implications of applicability to megajoule-scale laser facilities such as Lawrence Livermore’s National Ignition Facility.
Contact: Charlie Jarrott (925) 422-4524 (jarrott1 [at] (jarrott1[at]llnl[dot]gov)).

Printing Three-Dimensional Supercapacitors

For the first time, scientists at Lawrence Livermore and the University of California at Santa Cruz have successfully used a three-dimensional (3D) printing technique to create supercapacitors made from ultralight graphene aerogel. Their results were published on January 28, 2016, in the online journal Nano Letters. The research opens the door to novel, unconstrained designs of highly efficient energy-storage systems for devices such as smartphones, implantable devices, electric cars, and wireless sensors. “This breaks through the limitations of what two-dimensional manufacturing can do,” states Livermore engineer Cheng Zhu, the paper’s lead author.

Using a 3D printing process called direct ink writing and a graphene-oxide composite ink designed at the Laboratory, the scientists printed microarchitected electrodes and built supercapacitors with an energy capacity similar to those made with electrodes 10 to 100 times thinner. This method of using graphene-based inks to produce 3D supercapacitors has multiple benefits. They provide an ultrahigh surface area, are lightweight, and exhibit elasticity and superior electrical capacity. Supercapacitors can also charge remarkably fast. In addition, the graphene-composite aerogel supercapacitors are extremely stable and can retain their energy capacity after 10,000 consecutive charge–discharge cycles.

“Additively manufactured 3D architectures for energy storage will improve energy and power characteristics for supercapacitors, enabling lightweight, miniaturized power sources,” says Livermore materials engineer Eric Duoss. The implications of the study are vast—Zhu and his fellow researchers believe newly designed 3D-printed supercapacitors will be used to create unique electronics in the future, such as fully customized smartphones and paper-based or foldable devices while concurrently achieving unprecedented levels of performance.
Contact: Cheng Zhu (925) 423-5503 (zhu6 [at] (zhu6[at]llnl[dot]gov)).

Shock Waves Induce Protein Damage in TBI Patients

New research by Lawrence Livermore scientists has revealed how shock waves can damage membrane proteins in traumatic brain injury (TBI) patients. The research appears in the January 5, 2016, edition of Biophysical Journal.

Blast-induced TBI is the most frequent wound produced from conflicts in Afghanistan and Iraq, but it has never been clear how energy from a blast is transmitted to the brain. To better understand this process, Livermore physicists Edmond Lau and Eric Schwegler, along with University of North Carolina colleague Max Berkowitz, used molecular dynamics simulations to examine the effects of shock waves on the brain. The researchers found that shock waves alone do not significantly damage ion channels, but with the presence of bubbles, the shock wave–induced damage is magnified.

Previous simulations of bubble–shock interactions have shown that the force generated by bubble collapse can cause pore formation in membranes. These pores likely lead to unregulated ion exchange, causing an imbalance within cells that can eventually lead to the initial symptoms of TBI, such as headaches and seizures.

Other molecular simulations have shown that membranes can self-heal from nanometer-sized pores in tens of nanoseconds. Ion channels, on the other hand, may not self-heal as rapidly. “Ionic imbalances likely play an important role in the cellular damage incurred from TBI,” says Schwegler.
Contact: Eric Schwegler (925) 424-3098 (schwegler1 [at] (schwegler1[at]llnl[dot]gov)).