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We show that an x-ray emission signature associated with acceleration phase mass injection [R. C. Shah et al., Phys. Rev. E 103, 023201 (2021)PRESCM2470-004510.1103/PhysRevE.103.023201] correlates with poor experimental hot-spot convergence and a reduced neutron production relative to expectations. It is shown that with increased target mass as well as with higher-design adiabats, this signature is reduced, whereas with increased debris on the target, the signature is increased. We estimate that the vapor region in typical best designs may have up to 2× the assumed hydrogen mass at the start of deceleration.

In direct-drive inertial confinement fusion, the laser bandwidth reduces the laser imprinting seed of hydrodynamic instabilities. The impact of varying bandwidth on the performance of direct-drive DT-layered implosions was studied in targets with different hydrodynamic stability properties. The stability was controlled by changing the shell adiabat from (α_{F}≃5) (more stable) to (α_{F}≃3.5) (less stable). These experiments show that the performance of lower adiabat implosions improves considerably as the bandwidth is raised indicating that further bandwidth increases, beyond the current capabilities of OMEGA, would be greatly beneficial. These results suggest that the future generation of ultra-broadband lasers could enable achieving high convergence and possibly high gains in direct drive ICF.

Statistical modeling of experimental and simulation databases has enabled the development of an accurate predictive capability for deuterium-tritium layered cryogenic implosions at the OMEGA laser [V. Gopalaswamy et al.,Nature 565, 581 (2019)10.1038/s41586-019-0877-0]. In this letter, a physics-based statistical mapping framework is described and used to uncover the dependencies of the fusion yield. This model is used to identify and quantify the degradation mechanisms of the fusion yield in direct-drive implosions on OMEGA. The yield is found to be reduced by the ratio of laser beam to target radius, the asymmetry in inferred ion temperatures from the ℓ=1 mode, the time span over which tritium fuel has decayed, and parameters related to the implosion hydrodynamic stability. When adjusted for tritium decay and ℓ=1 mode, the highest yield in OMEGA cryogenic implosions is predicted to exceed 2×10^{14} fusion reactions.

A new tri-particle mono-energetic backlighter based on laser-driven implosions of DT 3 He gas-filled capsules has been implemented at the OMEGA laser. This platform, an extension of the original D 3 He backlighter platform, generates 9.5 MeV deuterons from the T 3 He reaction in addition to 14.7 and 3.0 MeV protons from the deuterium and helium-3 reactants. The monoenergetic 14.7 and 3.0 MeV protons have been used with success at OMEGA and the NIF for both radiography and stopping-power studies. There are several advantages of having a third particle to diagnose plasma conditions: an extra time-of-flight-separated radiograph and an improved ability to discern between electric and magnetic fields. In cases where the 3.0 MeV protons cannot penetrate an experiment, the benefit of the additional 9.5 MeV deuterons is magnified. This capability is well-suited for NIF experiments, where large fields and plasma densities often preclude useful 3.0 MeV proton data. The advantages are demonstrated with radiographs of OMEGA plasmas with magnetic and electric fields. Tests using backlighter-scale 420 μm diameter thin glass capsules validate the platform's extended backlighting capability. The performance characteristics of this backlighter, such as source size and timing, are discussed.

A dual-channel electrical stimulation system with a stimulator and a programmer/stride analyzer was designed for clinical rehabilitation of gait and for subsequent daily use as an orthotic aid. The stimulator, with controls to adjust amplitude only (50 mA), adapts chosen stimulation sequences to the walking rate of a patient. Pulse duration (50-500 microseconds), frequency (5-120 Hz), shape (symmetrical biphasic, monophasic), stimulation sequences (16 stride segments) and their cycle (2-12 sec), and right/left foot-switch choices are selected for each patient and programmed into a separate unit. The programming unit also statistically processes the foot-switch data collected by the stimulator. The device was evaluated with regard to the programmable parameters, effectiveness during gait, and feasibility in clinical use. It was applied to 11 stroke patients and 10 brain injury patients during gait, stimulating 22 combinations of peroneal nerve and hamstring, quadriceps, triceps brachii, and gluteus maximus muscles. Forces on both feet, equinovarus, knee extension and hyperextension, elbow flexion, and hip extension were corrected. Selection of the stimulation sequences, their adaptation, range of pulse duration, and valid statistics were verified. Improved forces and joint angles were recorded together with significant changes in the stride time, length, and velocity by the stimulation.

Therapeutic effects in ten hemiplegic patients and one paraparetic patient treated by multisite electric stimulation of gait were compared with effects in ten hemiplegic patients treated by standard rehabilitation methods after 2.6 months of extensive therapy. Average step length and gait velocity, ground reaction forces and their distribution under both feet, and crutch loading were measured; goniograms of joint angles, kinesiologic gait analysis, and EMG recordings from the main muscles used in ambulation and in standing, were made while patients in both groups walked without stimulation. Quantitative measurements before, during, at the end, and 8.4 months posttherapy were taken based on at least 40 strides per patient. The results for the stimulated group in midtherapy indicated faster recovery rates (3.15 times in step length and 2.25 times in gait velocity) than in the control group, and at the end of therapy the stimulated group had higher improvement levels (2.14 times in step length, 1.42 times in gait velocity, and 1.63 times in kinesiologic gait analysis). The differences between the two groups faded after 8.4 months without treatment, and some kinesiologic deficits reappeared, mostly those in the more distal muscle groups. These findings indicate a need for a simpler orthotic electric stimulation after multisite therapy in several cases. Immediate effects of the six-site stimulation were also considered for orthotic possibilities after the therapy.

Implantation of subcutaneous peroneal stimulators requires careful positioning to obtain a good response. With the patient lying down during the surgical procedure, ankle dorsal flexion was not always satisfactory during gait. Instead of dorsal flexion the stimulus could give an excessive eversion or a coactivation of ankle antagonists. To select the correct electrode position, the responses to single stimulation pulses were monitored in the tibialis anterior, peroneus longus and triceps surae muscles by surface EMG electrodes. With the patient standing, a strong contraction of the anterior tibial muscle without excessive contraction of the peroneus longus muscle was first determined by surface stimulation. The EMG responses were then recorded with the patient lying in the position required for implantation. The records were used as a guideline during surgery, during which positioning of the electrodes was monitored by the EMG responses. The method, tested on 2 healthy adults and 13 patients, resulted in reliable positioning of the stimulating electrodes.

The effects of long-term electrical stimulation on reflex hyperactivity and voluntary muscle control were studied. Eight hemiplegic patients with implanted peroneal stimulator were included. After six months of functional electrical stimulation (FES) there was a decrease of tonic activity in both tibialis anterior and triceps surae muscles. The phasic stretch reflex activity in the stimulated tibialis anterior muscle increased. The resulting resistance during passive movements decreased due to diminution of tonic activity. The absence of tonic activity also resulted in improvement of voluntary control, particularly in the tibialis anterior muscle.