Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

First measurements of remaining shell areal density on the OMEGA laser using the Diagnostic for Areal Density (DAD)

A glass Cherenkov detector, called the Diagnostic for Areal Density (DAD), has been built and implemented at the OMEGA laser facility for measuring fusion gammas above 430 keV, from which remaining shell ⟨ρR⟩ _abl can be determined. A proof-of-principle experiment is discussed, where signals from a surrogate gas Cherenkov detector are compared with reported values from the wedge range filter and charged particle spectrometer and found to correlate strongly. The design of the more compact port-based DAD diagnostic and results from the commissioning shots are then presented. Once absolutely calibrated, the DAD will be capable of reporting remaining shell ⟨ρR⟩ _abl for plastic and glass capsules within minutes of a shot and with potentially higher precision than existing techniques.

Monte Carlo validation experiments for the gas Cherenkov detectors at the National Ignition Facility and Omega

The gas Cherenkov detectors at NIF and Omega measure several ICF burn characteristics by detecting multi-MeV nuclear γ emissions from the implosion. Of primary interest are γ bang-time (GBT) and burn width defined as the time between initial laser-plasma interaction and peak in the fusion reaction history and the FWHM of the reaction history respectively. To accurately calculate such parameters the collaboration relies on Monte Carlo codes, such as GEANT4 and ACCEPT, for diagnostic properties that cannot be measured directly. This paper describes a series of experiments performed at the High Intensity γ Source (HIγS) facility at Duke University to validate the geometries and material data used in the Monte Carlo simulations. Results published here show that model-driven parameters such as intensity and temporal response can be used with less than 50% uncertainty for all diagnostics and facilities.

Gamma-to-electron magnetic spectrometer (GEMS): an energy-resolved γ-ray diagnostic for the National Ignition Facility

The gamma-to-electron magnetic spectrometer, having better than 5% energy resolution, is proposed to resolve γ-rays in the range of E(o) ± 20% in single shot, where E(o) is the central energy and is tunable from 2 to 25 MeV. Gamma-rays from inertial confinement fusion implosions interact with a thin Compton converter (e.g., beryllium) located at approximately 300 cm from the target chamber center (TCC). Scattered electrons out of the Compton converter enter an electromagnet placed outside the NIF chamber (approximately 600 cm from TCC) where energy selection takes place. The electromagnet provides tunable E(o) over a broad range in a compact manner. Energy resolved electrons are measured by an array of quartz Cherenkov converters coupled to photomultipliers. Given 100 detectable electrons in the energy bins of interest, 3 × 10(14) minimum deuterium/tritium (DT) neutrons will be required to measure the 4.44 MeV (12)C γ-rays assuming 200 mg/cm(2) plastic ablator areal density and 3 × 10(15) minimum DT neutrons to measure the 16.75 MeV DT γ-ray line.

Mach-Zehnder recording systems for pulsed power diagnostics

Fiber-optic transmission and recording systems, based on Mach-Zehnder modulators, have been developed and installed at the National Ignition Facility (NIF), and are being developed for other pulsed-power facilities such as the Z accelerator at Sandia, with different requirements. We present the design and performance characteristics for the mature analog links, based on the system developed for the Gamma Reaction History diagnostic at the OMEGA laser and at NIF. For a single detector channel, two Mach-Zehnders are used to provide high dynamic range at the full recording bandwidth with no gaps in the coverage. We present laboratory and shot data to estimate upper limits on the radiation effects as they impact recorded data quality. Finally, we will assess the technology readiness level for mature and developing implementations of Mach-Zehnder links for these environments.

Diagnosing inertial confinement fusion gamma ray physics (invited)

The gamma reaction history (GRH) diagnostic is a multichannel, time-resolved, energy-thresholded γ-ray spectrometer that provides a high-bandwidth, direct-measurement of fusion reaction history in inertial confinement fusion implosion experiments. 16.75 MeV deuterium+tritium (DT) fusion γ-rays, with a branching ratio of the order of 10(-5)γ/(14 MeV n), are detected to determine fundamental burn parameters, such as nuclear bang time and burn width, critical to achieving ignition at the National Ignition Facility. During the tritium/hydrogen/deuterium ignition tuning campaign, an additional γ-ray line at 19.8 MeV, produced by hydrogen+tritium fusion with a branching ratio of unity, will increase the available γ-ray signal and may allow measurement of reacting fuel composition or ion temperature. Ablator areal density measurements with the GRH are also made possible by detection of 4.43 MeV γ-rays produced by inelastic scatter of DT fusion neutrons on (12)C nuclei in the ablating plastic capsule material.

Gamma bang time analysis at OMEGA

Absolute bang time measurements with the gas Cherenkov detector (GCD) and gamma reaction history (GRH) diagnostic have been performed to high precision at the OMEGA laser facility at the University of Rochester with bang time values for the two diagnostics agreeing to within 5 ps on average. X-ray timing measurements of laser-target coupling were used to calibrate a facility-generated laser timing fiducial with rms spreads in the measured coupling times of 9 ps for both GCD and GRH. Increased fusion yields at the National Ignition Facility (NIF) will allow for improved measurement precision with the GRH easily exceeding NIF system design requirements.

GEANT4 simulations of Cherenkov reaction history diagnostics

This paper compares the results from a GEANT4 simulation of the gas Cherenkov detector 1 (GCD1) with previous simulations and experimental data from the Omega laser facility. The GCD1 collects gammas emitted during a deuterium-tritium capsule implosion and converts them, through several processes, to Cherenkov light. Photon signals are recorded using subnanosecond photomultiplier tubes, producing burn reaction histories. The GEANT4 GCD1 simulation is first benchmarked against ACCEPT, an integrated tiger series code, with good agreement. The simulation is subsequently compared with data from the Omega laser facility, where experiments have been performed to measure the effects of Hohlraum materials on reaction history signals, in preparation for experiments at the National Ignition Facility.

Development and characterization of sub-100 ps photomultiplier tubes

We describe the evaluation of a microchannel plate (MCP) photomultiplier tube (PMT), incorporating a 3 μm pore MCP and constant voltage anode and cathode gaps. The use of the small pore size results in PMTs with response functions of the order of 85 ps full-width-half-maximum, while the constant electric field across the anode and cathode gaps produces a uniform response function over the entire operating range of the device. The PMT was characterized on a number of facilities and employed on gas Cherenkov detectors fielded on various deuterium tritium fuel (DT) implosions on the Omega Laser Facility at the University of Rochester. The Cherenkov detectors are part of diagnostic development to measure Gamma ray reaction history for DT implosions on the National Ignition Facility.

Gamma bang time/reaction history diagnostics for the National Ignition Facility using 90 degrees off-axis parabolic mirrors

Gas Cherenkov detectors (GCDs) have been used to convert fusion gamma into photons to achieve gamma bang time and reaction history measurements. The GCDs designed for OMEGA used Cassegrain reflector optics in order to fit inside a 10 in. manipulator. A novel design for the National Ignition Facility using 90 degrees off-axis parabolic mirrors will increase light collection efficiency from fusion gammas and achieve minimum time dispersion. The broadband Cherenkov light (from 200 to 800 nm) is relayed into a high-speed detector using three parabolic mirrors. Because light is collected from many source planes throughout the CO(2) gas volume, the detector is positioned at the stop position rather than at an image position. The stop diameter and its position are independent of the light-generation location along the gas cell. The current design collects light from a 100 mm diameter by 500 mm long gas volume. Optical ray tracings demonstrate how light can be collected from different angled trajectories of the Compton electrons as they fly through the CO(2) gas volume. A cluster of four channels will allow for increased dynamic range as well as for different gamma energy threshold sensitivities.

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Open-ended and point-of-service plans are relatively new methods of financing and delivering health care, writes Joseph Mack, M.P.A. He describes both plans in detail, along with the operational aspects of a medical group's involvement in such arrangements.

Two false-negative results using morphine sulfate in hepatobiliary imaging

Morphine sulfate has been used in hepatobiliary imaging to cause contraction of the sphincter of Oddi, thereby increasing pressure in the biliary tree. If the cystic duct is patent, the increased pressure usually causes bile to flow into the cystic duct with filling of the gallbladder. Using this technique, the authors have encountered two false-negative cases. Both patients received 0.04 mg/kg of morphine sulfate intravenously, 40 minutes after the intravenous administration of 5 mCi of technetium 99m-DISIDA. Although both patients filled their gallbladders within 1 hour, they both underwent surgical exploration because of high clinical suspicion of acute cholecystitis. Both were found to have acute cholecystitis.

Nuclear medicine studies of aging--VII. Humeral deltoid tuberosity on bone scans and radiographs

Because of the occasional finding of increased deposition of bone imaging agent in the area of the humeral deltoid tuberosity, we analyzed both bone scans and radiographs to determine if there were age related correlations. Only 29% of patients of age 35 years or younger showed any radiographic evidence of deltoid tuberosity. This increased to 48% in the 36-64 y age group (and 46% in those of age 65 y and above). Bone scans (99mTc-MDP) of the humerus showed that 26% of individuals of ages 20-39 y had increased uptake in the deltoid tuberosity area. The figure was 21% of those in the 85-94 y age group. However, distribution between sexes in the 20-39 y age cohort was asymmetric (44% of males showed the bone scan finding, but only 15% of the females). We then reviewed cases that had shown the most prominent deltoid tuberosity on humeral radiographs. Thirteen of the 14 cases (93%) were males. Deposition of bone imaging agent in the deltoid tuberosity region was thus only slightly correlated with age (more common after age 35 y), but strongly correlated with sex (males more common) in all three major age groups (35 and under, 36-64, and 65 years and over). Possible interrelations with bone size and muscle mass were pointed out.

Delayed accumulation (flip flop) of Tc-99m DTPA in a leiomyosarcoma

An 85-year-old woman with leiomyosarcoma occupying the abdominopelvic area had a renal dynamic study with Tc-99m DTPA. The tumor area initially showed almost no content of the radiopharmaceutical. At 24 hours, there was retention of activity in the leiomyosarcoma as compared with surrounding tissues (flip flop). It was noted that, based on literature reports, tumors of mesodermal origin (leiomyoma, spindle cell sarcoma, neurofibroma) may have the ability to concentrate Tc-99m DTPA.

Circadian disruption and surgical recovery

Circadian rhythms were investigated in rats following surgery, as measured by body temperature and locomotor activity, and postoperative recovery was measured by activity level. Eight randomly selected Sprague-Dawley rats were implanted with radio temperature-transmitters under general anesthesia. Timer-controlled cassette recorders recorded body temperature at predetermined intervals. To monitor activity, the rats were placed in individual metabolic cages equipped with infrared-sensitive locomotor activity monitors. Temperature was sampled hourly. Activity was measured continuously and summed every 15 minutes for sampling. Measurement was begun before surgery and continued from 12 to 20 days following surgery, depending on when the animals regained their typical rhythmic patterns. Temperature and activity rhythms were altered and uncoupled from external cues in a manner similar to that previously found in humans. The animals demonstrated individual variation in their return to presurgical activity levels. Six days after surgery, the rats experienced a second period of disrhythmic and decreased activity. Rats with the greatest activity phase-shifts took longest to return to presurgical activity levels. This suggests that the degree of circadian alteration following surgery is positively related to the time required for recovery and reentrainment of rhythmicity.

Recovery of femoral head perfusion after drainage of septic joint

A 64-year-old woman was febrile and had pain near the right hip. Blood cultures grew beta hemolytic streptococci. A bone scan showed reduced activity in the right femoral head and neck compared with the left femoral head and neck. She was treated with intravenous antibiotics and surgical decompression of a tense and bulging right hip joint. Five days later, a repeat bone scan revealed much of the femoral head activity to have returned. By day 20 after the initial bone image, there was intense activity throughout the femoral head and neck. Prompt relief of a distended hip joint can result in reperfusion of the femoral head and neck.