The impact of low-mode symmetry on inertial fusion energy output in the burning plasma state.

Indirect Drive Inertial Confinement Fusion Experiments on the National Ignition Facility (NIF) have achieved a burning plasma state with neutron yields exceeding 170 kJ, roughly 3 times the prior record and a necessary stage for igniting plasmas. The results are achieved despite multiple sources of degradations that lead to high variability in performance. Results shown here, for the first time, include an empirical correction factor for mode-2 asymmetry in the burning plasma regime in addition to previously determined corrections for radiative mix and mode-1. Analysis shows that including these three corrections alone accounts for the measured fusion performance variability in the two highest performing experimental campaigns on the NIF to within error. Here we quantify the performance sensitivity to mode-2 symmetry in the burning plasma regime and apply the results, in the form of an empirical correction to a 1D performance model. Furthermore, we find the sensitivity to mode-2 determined through a series of integrated 2D radiation hydrodynamic simulations to be consistent with the experimentally determined sensitivity only when including alpha-heating.

Rapid switching from levetiracetam to brivaracetam in pharmaco-resistant epilepsy in people with and without intellectual disabilities: a naturalistic case control study.

BACKGROUND: Approximately one quarter of people with an intellectual disability (PwID) have epilepsy of whom nearly three-quarters are pharmaco-resistant. There are higher reported neuropsychiatric side-effects to anti-seizure medication (ASM) in this group. Levetiracetam (LEV) is a first-line ASM with a stronger association with neuropsychiatric symptoms for PwID than other ASMs. Brivaracetam (BRV) is a newer ASM. Recent studies suggest a beneficial effect of swapping people who experience neuropsychiatric events with LEV to BRV. However, there is limited evidence of this for PwID. This evaluation analyses real world outcomes of LEV to BRV swap for PwID compared to those without ID. METHODS: We performed a multicentre, retrospective review of clinical records. Demographic, clinical characteristics and reported adverse events of patients switched from LEV to BRV (2016-2020) were recorded at 3 months pre and 6- and 12-month post-BRV initiation. Outcomes were compared between PwID and those without and summarised using cross-tabulations and logistic regression models. A Bonferroni correction was applied. RESULTS: Of 77 participants, 46 had ID and 52% had a past psychiatric illness. 71% participants switched overnight from LEV to BRV. Seizure reduction of > 50% was seen in 40% patients. Psychiatric illness history was predictive of having neuropsychiatric side-effects with LEV but not BRV (p = 0.001). There was no significant difference for any primary outcomes between PwID versus without ID. CONCLUSIONS: Switching from LEV to BRV appears as well tolerated and efficacious in PwID as those without ID with over 90% still on BRV after 12 months.

Exclusive Breastfeeding Measured by Deuterium-Oxide Turnover Method is Associated with Motor Development in Rural Senegalese Infants.

BACKGROUND: The findings on the relationship between breastfeeding and children's motor development are very poor, particularly in low and middle income countries, because of the use of inadequate measures of breastfeeding practices. OBJECTIVES: To assess the relationship between exclusive breastfeeding, measured by the deuterium-oxide turnover method (DTM), and the acquisition of motor development in a cohort of Senegalese children. METHODS: One hundred forty mother-infant (4-5 mo) pairs were recruited and monitored up to 18 mo. Breast milk intake and breastfeeding practices were measured by DTM. Six stages of motor development were assessed: "sitting without support," "hands-and-knees crawling," "standing with assistance," "walking with assistance," "standing alone," and "walking alone." Acquisition age of motor milestones between exclusively breastfed (EBF) and not exclusively breastfed (non-EBF) infants was compared using Student's and Wilcoxon's tests. Mixed linear regression, adjusted with confounding factors, was used to determine the association between EBF and motor development. RESULTS: Overall, 32.9% of infants were EBF at the enrollment at 4-5 mo of age. Breast milk intake of EBF infants was significantly higher than that of non-EBF infants (1039 ± 193 g/d compared with 915 ± 211 g/d; P < 0.01). At 4-5 mo of age, only "sitting without support" (67.4% compared with 47.9%, P = 0.02) and "hands-and-knees crawling" (17.4% compared with 4.3%, P = 0.01) were completed significantly in the EBF group. At 18 mo, all children had completed all 6 motor developmental milestones. However, their acquisition age was significantly earlier in the EBF group after adjustment. Non-EBF infants had a delay of 0.4 to 0.5 mo on the acquisition of the first 5 stages compared to EBF infants. For "walking alone," no difference was found after adjustment. CONCLUSIONS: Motor skill acquisition is earlier in EBF infants compared to non-EBF infants. This finding highlights the need to strengthen the advocacy for EBF up to 6 mo.

Experimental achievement and signatures of ignition at the National Ignition Facility.

An inertial fusion implosion on the National Ignition Facility, conducted on August 8, 2021 (N210808), recently produced more than a megajoule of fusion yield and passed Lawson's criterion for ignition [Phys. Rev. Lett. 129, 075001 (2022)10.1103/PhysRevLett.129.075001]. We describe the experimental improvements that enabled N210808 and present the first experimental measurements from an igniting plasma in the laboratory. Ignition metrics like the product of hot-spot energy and pressure squared, in the absence of self-heating, increased by ∼35%, leading to record values and an enhancement from previous experiments in the hot-spot energy (∼3×), pressure (∼2×), and mass (∼2×). These results are consistent with self-heating dominating other power balance terms. The burn rate increases by an order of magnitude after peak compression, and the hot-spot conditions show clear evidence for burn propagation into the dense fuel surrounding the hot spot. These novel dynamics and thermodynamic properties have never been observed on prior inertial fusion experiments.

Design of an inertial fusion experiment exceeding the Lawson criterion for ignition.

We present the design of the first igniting fusion plasma in the laboratory by Lawson's criterion that produced 1.37 MJ of fusion energy, Hybrid-E experiment N210808 (August 8, 2021) [Phys. Rev. Lett. 129, 075001 (2022)10.1103/PhysRevLett.129.075001]. This design uses the indirect drive inertial confinement fusion approach to heat and compress a central "hot spot" of deuterium-tritium (DT) fuel using a surrounding dense DT fuel piston. Ignition occurs when the heating from absorption of α particles created in the fusion process overcomes the loss mechanisms in the system for a duration of time. This letter describes key design changes which enabled a ∼3-6× increase in an ignition figure of merit (generalized Lawson criterion) [Phys. Plasmas 28, 022704 (2021)1070-664X10.1063/5.0035583, Phys. Plasmas 25, 122704 (2018)1070-664X10.1063/1.5049595]) and an eightfold increase in fusion energy output compared to predecessor experiments. We present simulations of the hot-spot conditions for experiment N210808 that show fundamentally different behavior compared to predecessor experiments and simulated metrics that are consistent with N210808 reaching for the first time in the laboratory "ignition."

Burning plasma achieved in inertial fusion.

Obtaining a burning plasma is a critical step towards self-sustaining fusion energy1. A burning plasma is one in which the fusion reactions themselves are the primary source of heating in the plasma, which is necessary to sustain and propagate the burn, enabling high energy gain. After decades of fusion research, here we achieve a burning-plasma state in the laboratory. These experiments were conducted at the US National Ignition Facility, a laser facility delivering up to 1.9 megajoules of energy in pulses with peak powers up to 500 terawatts. We use the lasers to generate X-rays in a radiation cavity to indirectly drive a fuel-containing capsule via the X-ray ablation pressure, which results in the implosion process compressing and heating the fuel via mechanical work. The burning-plasma state was created using a strategy to increase the spatial scale of the capsule2,3 through two different implosion concepts4-7. These experiments show fusion self-heating in excess of the mechanical work injected into the implosions, satisfying several burning-plasma metrics3,8. Additionally, we describe a subset of experiments that appear to have crossed the static self-heating boundary, where fusion heating surpasses the energy losses from radiation and conduction. These results provide an opportunity to study α-particle-dominated plasmas and burning-plasma physics in the laboratory.

Evidence of Three-Dimensional Asymmetries Seeded by High-Density Carbon-Ablator Nonuniformity in Experiments at the National Ignition Facility.

Inertial confinement fusion implosions must achieve high in-flight shell velocity, sufficient energy coupling between the hot spot and imploding shell, and high areal density (ρR=∫ρdr) at stagnation. Asymmetries in ρR degrade the coupling of shell kinetic energy to the hot spot and reduce the confinement of that energy. We present the first evidence that nonuniformity in the ablator shell thickness (∼0.5% of the total thickness) in high-density carbon experiments is a significant cause for observed 3D ρR asymmetries at the National Ignition Facility. These shell-thickness nonuniformities have significantly impacted some recent experiments leading to ρR asymmetries on the order of ∼25% of the average ρR and hot spot velocities of ∼100 km/s. This work reveals the origin of a significant implosion performance degradation in ignition experiments and places stringent new requirements on capsule thickness metrology and symmetry.

Saturn-ring proton backlighters for the National Ignition Facility.

Proton radiography is a well-established technique for measuring electromagnetic fields in high-energy-density plasmas. Fusion reactions producing monoenergetic particles, such as D3He, are commonly used as a source, produced by a capsule implosion. Using smaller capsules for radiography applications is advantageous as the source size decreases, but on the National Ignition Facility (NIF), this can introduce complications from increasing blow-by light, since the phase plate focal spot size is much larger than the capsules. We report a demonstration of backlighter targets where a "Saturn" ring is placed around the capsule to block this light. The nuclear performance of the backlighters is unperturbed by the addition of a ring. We also test a ring with an equatorial cutout, which severely affects the proton emission and is not viable for radiography applications. These results demonstrate the general viability of Saturn ring backlighter targets for use on the NIF.

Impact of Localized Radiative Loss on Inertial Confinement Fusion Implosions.

The impact to fusion energy production due to the radiative loss from a localized mix in inertial confinement implosions using high density carbon capsule targets has been quantified. The radiative loss from the localized mix and local cooling of the reacting plasma conditions was quantified using neutron and x-ray images to reconstruct the hot spot conditions during thermonuclear burn. Such localized features arise from ablator material that is injected into the hot spot from the Rayleigh-Taylor growth of capsule surface perturbations, particularly the tube used to fill the capsule with deuterium and tritium fuel. Observations, consistent with analytic estimates, show the degradation to fusion energy production to be linearly proportional to the fraction of the total emission that is associated with injected ablator material and that this radiative loss has been the primary source of variations, of up to 1.6 times, in observed fusion energy production. Reducing the fill tube diameter has increased the ignition metric χ_{no α} from 0.49 to 0.72, 92% of that required to achieve a burning hot spot.

Plasma Collision in a Gas Atmosphere.

We present a study on the impact of a gas atmosphere on the collision of two counterpropagating plasmas (gold and carbon). Imaging optical Thomson scattering data of the plasma collision with and without helium in between have been obtained at the Omega laser facility. Without gas, we observed large scale mixing of colliding gold and carbon ions. Once ambient helium is added, the two plasmas remain separated. The difference in ionic temperature is consistent with a reduction of the maximum Mach number of the flow from M=7 to M=4. It results in a reduction of a factor ∼10 of the counterstreaming ion-ion mean free path. By adding a low-density ambient gas, it is possible to control the collision of two high-velocity counterstreaming plasma, transitioning from an interpenetrating regime to a regime in agreement with a hydrodynamic description.

Neutron Time-of-Flight Measurements of Charged-Particle Energy Loss in Inertial Confinement Fusion Plasmas.

Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4 keV and particle densities of n≈(12-2)×10^{24} cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data.

Fusion Energy Output Greater than the Kinetic Energy of an Imploding Shell at the National Ignition Facility.

A series of cryogenic, layered deuterium-tritium (DT) implosions have produced, for the first time, fusion energy output twice the peak kinetic energy of the imploding shell. These experiments at the National Ignition Facility utilized high density carbon ablators with a three-shock laser pulse (1.5 MJ in 7.5 ns) to irradiate low gas-filled (0.3 mg/cc of helium) bare depleted uranium hohlraums, resulting in a peak hohlraum radiative temperature ∼290 eV. The imploding shell, composed of the nonablated high density carbon and the DT cryogenic layer, is, thus, driven to velocity on the order of 380 km/s resulting in a peak kinetic energy of ∼21 kJ, which once stagnated produced a total DT neutron yield of 1.9×10^{16} (shot N170827) corresponding to an output fusion energy of 54 kJ. Time dependent low mode asymmetries that limited further progress of implosions have now been controlled, leading to an increased compression of the hot spot. It resulted in hot spot areal density (ρr∼0.3 g/cm^{2}) and stagnation pressure (∼360 Gbar) never before achieved in a laboratory experiment.

Decreased tacrolimus plasma concentrations during HCV therapy: a drug-drug interaction or is there an alternative explanation?

Chronic hepatitis C virus (HCV) infection can cause severe liver cirrhosis, for which liver transplantation is the only therapy. To prevent organ rejection, transplanted patients are treated with immunosuppressive agents. We describe two transplanted patients treated with tacrolimus who were simultaneously treated with direct-acting antivirals (DAAs) for their chronic HCV infection. No pharmacokinetic drug-drug interactions (DDIs) were expected between tacrolimus and the selected DAAs. However, in both patients, tacrolimus plasma concentrations decreased during HCV treatment. We hypothesise that decreased plasma concentrations were not caused by a DDI but were an indirect result of the clearance of the HCV infection. During chronic HCV infection, pro-inflammatory cytokines may inhibit cytochrome P450 (CYP) enzymes, which are primarily responsible for tacrolimus metabolism. If this is true, then with clearance of the virus the activity of these enzymes will normalise and tacrolimus metabolism will increase. These changes were clinically relevant because the tacrolimus dosage needed to be adjusted. Therefore, physicians should be aware that CYP substrates with narrow therapeutic ranges might require dose adaption during HCV therapy with DAAs.

X-ray scattering measurements on imploding CH spheres at the National Ignition Facility.

We have performed spectrally resolved x-ray scattering measurements on highly compressed polystyrene at pressures of several tens of TPa (100 Mbar) created by spherically convergent shocks at the National Ignition Facility. Scattering data of line radiation at 9.0 keV were recorded from the dense plasma shortly after shock coalescence. Accounting for spatial gradients, opacity effects, and source broadening, we demonstrate the sensitivity of the elastic scattering component to carbon K-shell ionization while at the same time constraining the temperature of the dense plasma. For six times compressed polystyrene, we find an average temperature of 86 eV and carbon ionization state of 4.9, indicating that widely used ionization models need revision in order to be suitable for the extreme states of matter tested in our experiment.

Cervical myelopathy involving os odontoideum and retro-odontoid cyst treated with Harms C1-C2 arthrodesis.

An episode of acute decompensation of cervical myelopathy occurred after an injury without fracture of an os odontoideum associated with a compressive retro-odontoid cyst. The 51-year-old female patient presented Fränkel C, Nurick grade 4 neurological status and pyramid syndrome. The initial MRI demonstrated an intramedullary T2 hyperintense signal in the context of spinal cord narrowing. The retro-odontoid cyst demonstrates atlantoaxial instability related to the os odontoideum. Harms C1-C2 arthrodesis without laminectomy was performed and the cyst disappeared completely. Spinal cord decompression was thus obtained on the MRI taken 3 months later. Neurological recovery was complete and continued at 1 year.

Anatomic feasibility of a new endopelvic approach for iliac crest bone harvesting.

PURPOSE: For the past few years, anterior exposure for surgery of the lumbar spine has gained popularity for the treatment of disk disease or spondylosis. Cancellous bone remains the gold standard for fusion. Iliac crest bone harvesting is safe but there are donor site complications. Bone substitutes exist, like recombinant human bone morphogenic protein-2 rhBMP-2. This alternative offers a high rate of fusion but with local and general complications. The aim of our study is to show the feasibility of an endopelvic approach for iliac bone crest harvesting to avoid donor site complication. METHOD: Twenty anterior retroperitoneal lumbar spine approaches have been realized in the anatomy department of the University of Bordeaux. The volumes of cancellous bone have been measured and procedure complications have been reported. RESULTS: The mean volume of cancellous bone was 5.9 cc, the maximum volume was 8.2 cc and the minimum volume was 4.5 cc. No complications have been reported during the approach or the bone harvesting. CONCLUSIONS: Anterior retroperitoneal approach for iliac bone crest harvesting is a safe way to obtain sufficient volume of cancellous bone for a single lumbar spinal fusion. This exposure avoids the risks of an iliac crest donor site complications or rhBMP-2 complications.

[Are C2 pedicles always screwable? Calibration and planning with a pedicle-lamina angle]. / Les pédicules de C2 sont-ils toujours vissables ? Calibration et planification selon l'angle pédiculo-lamaire.

INTRODUCTION: Posterior cervical arthrodesis is associated with osteosynthesis. C2 pedicular screwing affords a good bone anchoring but involves neurological and vascular risks. PURPOSE: To determine C2 pedicular screwing feasibility from a large cohort of cervical CT scans. To describe the visible anatomical parameters during a surgical procedure in order to plan and secure it. MATERIALS AND METHODS: Retrospective consecutive series of 100 cervical CT scans was analyzed. Cases with upper cervical fracture were excluded. C2 surgical anatomy was assessed according to maximum length, minimum width and minimum height. Angular parameters were pedicle-transverse angle and sagittal angle. Original pedicle-lamina angle was used as a visible mark during the procedure independent of the patient's position. Pedicular screwing feasibility was evaluated. It was arbitrarily defined by a lower minimum height less than 4mm. RESULTS: Two hundred C2 pedicles were analyzed with 7.5% that were not screwable. Their mean length was 26.2mm, with a mean width of 5.2mm and a mean height of 9.2mm. Mean pedicle-transverse angle was 36.2°, mean sagittal angle was 25.8° and mean pedicle-lamina angle was 81.3°. CONCLUSION: C2 pedicle screwing feasibility is inconstant due to anatomical variability. In fact, 13% of patients have at least one non-screwable pedicle. Preoperative planning is essential to achieve this procedure. A pedicle-lamina angle can be used which remains independent from the patient's position.

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility.

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a "high-foot" laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10^{16} neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.