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.

Time-resolved X-ray diffraction diagnostic development for the National Ignition Facility

We present the development of an experimental platform that can collect four frames of x-ray diffraction data along a single line of sight during laser-driven, dynamic-compression experiments at the National Ignition Facility. The platform is comprised of a diagnostic imager built around ultrafast sensors with a 2-ns integration time, a custom target assembly that serves also to shield the imager, and a 10-ns duration, quasi-monochromatic x-ray source produced by laser-generated plasma. We demonstrate the performance with diffraction data for Pb ramp compressed to 150 GPa and illuminated by a Ge x-ray source that produces ∼7 × 1011, 10.25-keV photons/ns at the 400 μm diameter sample.

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.

Upgrade of the gated laser entrance hole imager G-LEH-2 on the National Ignition Facility

A major upgrade has been implemented for the ns-gated laser entrance hole imager on the National Ignition Facility (NIF) to obtain high-quality data for Hohlraum physics study. In this upgrade, the single "Furi" hCMOS sensor (1024 × 448 pixel arrays with two-frame capability) is replaced with dual "Icarus" sensors (1024 × 512 pixel arrays with four-frame capability). Both types of sensors were developed by Sandia National Laboratories for high energy density physics experiments. With the new Icarus sensors, the new diagnostic provides twice the detection area with improved uniformity, wider temporal coverage, flexible timing setup, and greater sensitivity to soft x rays (<2 keV). These features, together with the fact that the diagnostic is radiation hardened and can be operated on the NIF for high neutron yield deuterium-triterium experiments, enable significantly greater return of data per experiment.

The single-line-of-sight, time-resolved x-ray imager diagnostic on OMEGA

The single-line-of-sight, time-resolved x-ray imager (SLOS-TRXI) on OMEGA is one of a new generation of fast-gated x-ray cameras comprising an electron pulse-dilation imager and a nanosecond-gated, burst-mode, hybrid complementary metal-oxide semiconductor sensor. SLOS-TRXI images the core of imploded cryogenic deuterium-tritium shells in inertial confinement fusion experiments in the ∼4- to 9-keV photon energy range with a pinhole imager onto a photocathode. The diagnostic is mounted on a fixed port almost perpendicular to a 16-channel, framing-camera-based, time-resolved Kirkpatrick-Baez microscope, providing a second time-gated line of sight for hot-spot imaging on OMEGA. SLOS-TRXI achieves ∼40-ps temporal resolution and better than 10-μm spatial resolution. Shots with neutron yields of up to 1 × 10¹⁴ were taken without observed neutron-induced background signal. The implosion images from SLOS-TRXI show the evolution of the stagnating core.

Sub-nanosecond single line-of-sight (SLOS) x-ray imagers (invited)

A new generation of fast-gated x-ray framing cameras have been developed that are capable of capturing multiple frames along a single line-of-sight with 30 ps temporal resolution. The instruments are constructed by integrating pulse-dilation electron imaging with burst mode hybrid-complimentary metal-oxide-semiconductor sensors. Two such instruments have been developed, characterized, and fielded at the National Ignition Facility and the OMEGA laser. These instruments are particularly suited for advanced x-ray imaging applications in Inertial Confinement Fusion and High energy density experiments. Here, we discuss the system architecture and the techniques required for tuning the instruments to achieve optimal performance. Characterization results are also presented along with planned future improvements to the design.

A high-speed two-frame, 1-2 ns gated X-ray CMOS imager used as a hohlraum diagnostic on the National Ignition Facility (invited)

A novel x-ray imager, which takes time-resolved gated images along a single line-of-sight, has been successfully implemented at the National Ignition Facility (NIF). This Gated Laser Entrance Hole diagnostic, G-LEH, incorporates a high-speed multi-frame CMOS x-ray imager developed by Sandia National Laboratories to upgrade the existing Static X-ray Imager diagnostic at NIF. The new diagnostic is capable of capturing two laser-entrance-hole images per shot on its 1024 × 448 pixels photo-detector array, with integration times as short as 1.6 ns per frame. Since its implementation on NIF, the G-LEH diagnostic has successfully acquired images from various experimental campaigns, providing critical new information for understanding the hohlraum performance in inertial confinement fusion (ICF) experiments, such as the size of the laser entrance hole vs. time, the growth of the laser-heated gold plasma bubble, the change in brightness of inner beam spots due to time-varying cross beam energy transfer, and plasma instability growth near the hohlraum wall.

Measurement of Hydrodynamic Growth near Peak Velocity in an Inertial Confinement Fusion Capsule Implosion using a Self-Radiography Technique

First measurements of hydrodynamic growth near peak implosion velocity in an inertial confinement fusion (ICF) implosion at the National Ignition Facility were obtained using a self-radiographing technique and a preimposed Legendre mode 40, λ=140  μm, sinusoidal perturbation. These are the first measurements of the total growth at the most unstable mode from acceleration Rayleigh-Taylor achieved in any ICF experiment to date, showing growth of the areal density perturbation of ∼7000×. Measurements were made at convergences of ∼5 to ∼10× at both the waist and pole of the capsule, demonstrating simultaneous measurements of the growth factors from both lines of sight. The areal density growth factors are an order of magnitude larger than prior experimental measurements and differed by ∼2× between the waist and the pole, showing asymmetry in the measured growth factors. These new measurements significantly advance our ability to diagnose perturbations detrimental to ICF implosions, uniquely intersecting the change from an accelerating to decelerating shell, with multiple simultaneous angular views.

African American renal transplant recipients (RTR) require higher tacrolimus doses to achieve target levels compared to white RTR: does clotrimazole help?

The number of African Americans (AAs) on the kidney waiting list is increasing in the United States. Several studies showed that AAs are at higher risk for rejection and graft loss. Because of genetic polymorphisms, AAs may metabolize calcineurin inhibitors faster than Caucasian (C) individuals. The goal of this study is to evaluate the tacrolimus (TAC) dose required to reach therapeutic levels and to assess the impact of clotrimazole on TAC metabolism in AAs compared to C patients. One hundred forty-two AA renal transplant recipients (RTRs) were compared to 309 C RTRs. Demographics were similar in both groups. Induction therapy and maintenance immunosuppression were similar in both groups and included TAC, mycophenolate acid (MPA), and steroids. The goal in all RTRs was to maintain a 12-hour trough level of 10 to 15 ng/mL in the first 3 months, 8 to 10 ng/mL for the first year, and 5 to 8 ng/mL thereafter. To achieve these levels, AA RTRs require a significantly higher dosage of TAC compared to C patients (5.9 ± 2.9 vs 3.6 ± 2 mg/d, respectively, P < .0001). By multivariate analysis, TAC dose requirements were not affected by age, gender, MPA or prednisone dose, diabetes, and renal function. Adding clotrimazole (CTM) to the RTR regimen significantly reduced the TAC dose requirements in all RTRs. When CTM was used, the TAC dose requirement was not statistically significantly different between AA and C patients (2.6 ± 1.2 mg/d vs 1.8 ± 1.5 mg/d, P = .07). We conclude that AAs required a higher TAC dose to reach the desired trough level in RTRs compared to C RTRs. The use of CTM eliminates the need for higher doses of TAC in AA RTRs. Thus, CTM may aid AA RTRs in achieving therapeutic TAC levels while reducing drug costs.

The role of ureteral stents for all ureteroneocystostomies in kidney transplants

BACKGROUND

Despite significant advancements in renal transplantation, certain basic surgical practices such as the routine use of ureteral stents (US) remain controversial. A recent met-analysis of ureteral stenting concluded that the routine use of US resulted in improved outcomes. In contrast, the indiscriminate use of US can lead to adverse complications.

OBJECTIVE

To better define this question, we reviewed our single center experience in which US were placed selectively.

METHODS

301 patients were eligible to be enrolled. 55 living donor and 246 deceased-donor charts were analyzed for donor and recipient clinical characteristics, immunosuppressive therapy and outcomes.

RESULTS

28 US were placed for either small bladder capacity (n=7), unhealthy appearing bladder tissue (n=8) or for an uncertain vascular supply to the ureter (n=13). Patients with US did not develop urinary leaks, 8 (28%) developed complications including obstruction, encrustation, and urinary tract infections. 12 (4.3%) non-stented patients developed a clinically significant urinary leak. Risk factors for urinary leaks included dual and en-bloc pediatric donor kidney transplants, extended criteria donors and the use of single U stitch technique for ureteral anastomoses.

CONCLUSION

Our results demonstrate that the majority of patients can be successfully transplanted without the routine use of US. Selective use of US should be reserved for high-risk situations.

Results after colectomy for colonic inertia: a sixteen-year experience

BACKGROUND

Colonic inertia (CI) is a disturbance of colonic motility characterized by severe constipation and abdominal pain. This study was conducted to assess the results of total abdominal colectomy (TAC) in the management of CI.

METHODS

A retrospective chart review of 55 patients who underwent TAC for CI was conducted.

RESULTS

Forty-eight patients (87%) were female with an average age of 40; severe constipation existed 2 years prior to surgery. Symptoms included severe constipation (100%) and abdominal pain (84%); diagnostic workup included sitz marker study, anal manometry, and Gastrografin enema. In all cases, sitz marker studies were abnormal and anal manometry was normal. Histologically, no patient had absence of neuroenteric plexuses. Complications included prolonged ileus (24%) and small bowel obstruction (8%). Some 49 patients (89%) had "good" or "excellent" results and 6 patients (11%) had "poor" results. Postoperative stool frequency was 5, 4, and 3 per day at 1, 2, and 12 months, respectively.

CONCLUSIONS

TAC results in resolution of constipation in most patients. We conclude that TAC is effective treatment in patients with CI.

Does volume of patients seen in an outpatient setting impact test scores?

BACKGROUND

Methods of teaching surgery in the outpatient setting and means to measure the effectiveness of these methods have not been defined. This study was designed to evaluate the impact of number of outpatient encounters on test scores for third-year medical students.

METHODS

Students rotating on the required third-year surgery clerkship between July 1994 and June 1996 kept a log of their activities including number of patients seen in clinic, number of cases scrubbed, and pages read. At the end of the rotation the students were given an essay examination and a multiple-choice examination. The data were analyzed looking for correlation between examination scores and volume of patients seen. United States Medical Licensing Examination (USMLE) Step 1 scores were used as a baseline measure to compare the rotation groups.

RESULTS

USMLE scores did not differ between groups. Mean essay examination scores varied significantly between some rotation groups, but did not follow a pattern. There was no correlation between the number of patients seen in clinic and essay examination scores. There was a significant correlation between essay score and USMLE Step 1 score (Pearson's r = 0.398) and between essay and multiple-choice examination scores (Pearson's r = 0.313). There was a significant negative correlation between number of patients seen in clinic and number of cases scrubbed (Pearson's r = -0.347).

CONCLUSIONS

Participation in outpatient surgery clinics did not result in improved performance on written examinations in this surgery clerkship. To achieve the most benefit from the outpatient clinic, objectives of the experience need to be determined and appropriate tools used to measure their successful achievement.