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.

Indications of flow near maximum compression in layered deuterium-tritium implosions at the National Ignition Facility

An accurate understanding of burn dynamics in implosions of cryogenically layered deuterium (D) and tritium (T) filled capsules, obtained partly through precision diagnosis of these experiments, is essential for assessing the impediments to achieving ignition at the National Ignition Facility. We present measurements of neutrons from such implosions. The apparent ion temperatures T_{ion} are inferred from the variance of the primary neutron spectrum. Consistently higher DT than DD T_{ion} are observed and the difference is seen to increase with increasing apparent DT T_{ion}. The line-of-sight rms variations of both DD and DT T_{ion} are small, ∼150eV, indicating an isotropic source. The DD neutron yields are consistently high relative to the DT neutron yields given the observed T_{ion}. Spatial and temporal variations of the DT temperature and density, DD-DT differential attenuation in the surrounding DT fuel, and fluid motion variations contribute to a DT T_{ion} greater than the DD T_{ion}, but are in a one-dimensional model insufficient to explain the data. We hypothesize that in a three-dimensional interpretation, these effects combined could explain the results.

Generation and Beaming of Early Hot Electrons onto the Capsule in Laser-Driven Ignition Hohlraums

In hohlraums for inertial confinement fusion (ICF) implosions on the National Ignition Facility, suprathermal hot electrons, generated by laser plasma instabilities early in the laser pulse ("picket") while blowing down the laser entrance hole (LEH) windows, can preheat the capsule fuel. Hard x-ray imaging of a Bi capsule surrogate and of the hohlraum emissions, in conjunction with the measurement of time-resolved bremsstrahlung spectra, allows us to uncover for the first time the directionality of these hot electrons and infer the capsule preheat. Data and Monte Carlo calculations indicate that for most experiments the hot electrons are emitted nearly isotropically from the LEH. However, we have found cases where a significant fraction of the generated electrons are emitted in a collimated beam directly towards the capsule poles, where their local energy deposition is up to 10× higher than the average preheat value and acceptable levels for ICF implosions. The observed "beaming" is consistent with a recently unveiled multibeam stimulated Raman scattering model [P. Michel et al., Phys. Rev. Lett. 115, 055003 (2015)], where laser beams in a cone drive a common plasma wave on axis. Finally, we demonstrate that we can control the amount of generated hot electrons by changing the laser pulse shape and hohlraum plasma.

First high-convergence cryogenic implosion in a near-vacuum hohlraum

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α∼3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8×10(15) neutrons, with 20% calculated alpha heating at convergence ∼27×.

Charged-particle spectroscopy for diagnosing shock ρR and strength in NIF implosions

The compact Wedge Range Filter (WRF) proton spectrometer was developed for OMEGA and transferred to the National Ignition Facility (NIF) as a National Ignition Campaign diagnostic. The WRF measures the spectrum of protons from D-(3)He reactions in tuning-campaign implosions containing D and (3)He gas; in this work we report on the first proton spectroscopy measurement on the NIF using WRFs. The energy downshift of the 14.7-MeV proton is directly related to the total ρR through the plasma stopping power. Additionally, the shock proton yield is measured, which is a metric of the final merged shock strength.

Measurement of electron temperature of imploded capsules at the National Ignition Facility

The electron and ion temperatures of the imploded core plasma are two of the most important metrics of inertial confinement fusion experiments. We have developed a technique for inferring electron temperatures from the contrast of x-ray images observed through a group of x-ray filters. Generally, the plasma electron temperature exhibits spatial and temporal variations, so time-averaged and time-resolved measurements are expected to yield somewhat different results. By analyzing the intensity of images observed with both a time-integrated detector (imaging plates) and a time-resolved detector (gated micro-channel plate), we found the electron temperature observed from x-ray images to be systematically higher than the ion temperature inferred from fusion neutron spectroscopy.

Amplification of light in a plasma by stimulated ion acoustic waves driven by multiple crossing pump beams

Experiments demonstrate the amplification of 351 nm laser light in a hot dense plasma similar to those in inertial confinement fusion ignition experiments. A seed beam interacts with one or two counter-propagating pump beams, each with an intensity of 1.2×10(15) W/cm2 at 351 nm, crossing the seed at 24.8° at the position where the flow is Mach 1, allowing resonant stimulation of ion acoustic waves. Results show that the energy and power transferred to the seed are increased with two pumps beyond the level that occurs with a single pump, demonstrating that, under conditions similar to ignition experiments where each beam has a low gain exponent, the total scatter produced by the multiple beams can be significantly larger than that of the individual beams. It is further demonstrated that the amplification is greatly reduced when the pump polarization is orthogonal to the seed, as expected from models of stimulated scatter.

Measuring symmetry of implosions in cryogenic Hohlraums at the NIF using gated x-ray detectors (invited)

Ignition of imploding inertial confinement capsules requires, among other things, controlling the symmetry with high accuracy and fidelity. We have used gated x-ray imaging, with 10 μm and 70 ps resolution, to detect the x-ray emission from the imploded core of symmetry capsules at the National Ignition Facility. The measurements are used to characterize the time dependent symmetry and the x-ray bang time of the implosion from two orthogonal directions. These measurements were one of the primary diagnostics used to tune the parameters of the laser and Hohlraum to vary the symmetry and x-ray bang time of the implosion of cryogenically cooled ignition scale deuterium/helium filled plastic capsules. Here, we will report on the successful measurements performed with up to 1.2 MJ of laser energy in a fully integrated cryogenics gas-filled ignition-scale Hohlraum and capsule illuminated with 192 smoothed laser beams. We will describe the technique, the accuracy of the technique, and the results of the variation in symmetry with tuning parameters, and explain how that set was used to predictably tune the implosion symmetry as the laser energy, the laser cone wavelength separation, and the Hohlraum size were increased to ignition scales. We will also describe how to apply that technique to cryogenically layered tritium-hydrogen-deuterium capsules.

The first measurements of soft x-ray flux from ignition scale Hohlraums at the National Ignition Facility using DANTE (invited)

The first 96 and 192 beam vacuum Hohlraum target experiments have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr as viewed by DANTE representing an ∼20 times flux increase over NOVA/Omega scale Hohlraums. The vacuum Hohlraums were irradiated with 2 ns square laser pulses with energies between 150 and 635 kJ. They produced nearly Planckian spectra with about 30±10% more flux than predicted by the preshot radiation hydrodynamic simulations. To validate these results, careful verification of all component calibrations, cable deconvolution, and software analysis routines has been conducted. In addition, a half Hohlraum experiment was conducted using a single 2 ns long axial quad with an irradiance of ∼2×10(15) W/cm(2) for comparison with NIF Early Light experiments completed in 2004. We have also completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1×10(14) W/cm(2) over 5 ns) to avoid sensitivity to modeling uncertainties for nonlocal heat conduction and nonlinear absorption mechanisms, to compare with similar intensity, 3 ns OMEGA sphere results. The 2004 and 2009 NIF half-Hohlraums agreed to 10% in flux, but more importantly, the 2006 OMEGA Au Sphere, the 2009 NIF Au sphere, and the calculated Au conversion efficiency agree to ±5% in flux, which is estimated to be the absolute calibration accuracy of the DANTEs. Hence we conclude that the 30±10% higher than expected radiation fluxes from the 96 and 192 beam vacuum Hohlraums are attributable to differences in physics of the larger Hohlraums.

Shaping biomedical research priorities: the case of the National Institutes of Health

Despite the international interest in priority setting as an important tool for health policy, there has been comparatively little interest in the setting of research priorities. One of the few places where there has been such an interest is at the National Institutes of Health (NIH) in the United States. Under pressure from Congress to explain its priority setting process, the NIH has tried to explain the criteria and process it uses. The NIH procedure is described, and the problems created by the criteria it uses are analyzed. Although it uses the language of priority setting, it is uncertain whether it does have a real method of setting priorities. Nonetheless, despite the lack of a method, the results of its work are lauded. In the long run, however, NIH will need a more rigorous method of setting priorities.

First results from the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg d of Ge net exposure after cuts for recoil energies between 10 and 100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross section for all WIMP masses above 15 GeV/c2, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10(-43) cm2 at a WIMP mass of 60 GeV/c2.

Principlism and communitarianism

The decline in the interest in ethical theory is first outlined, as a background to the author's discussion of principlism. The author's own stance, that of a communitarian philosopher, is then described, before the subject of principlism itself is addressed. Two problems stand in the way of the author's embracing principlism: its individualistic bias and its capacity to block substantive ethical inquiry. The more serious problem the author finds to be its blocking function. Discussing the four scenarios the author finds that the utility of principlism is shown in the two scenarios about Jehovah's Witnesses but that when it comes to selling kidneys for transplantation and germline enhancement, principlism is of little help.

The future of the medical profession between bioethics and the market: a final comment

For a variety of historical and professional reasons the field of bioethics has paid little attention to the market. It has tended to treat the market with suspicion or hostility. Now, however, the market must be taken seriously. It has become a world-wide force in health care, and there is every reason to believe it will remain strong in the future. For that reason, it is wise to see what can be taken from the market, rather than simply dismiss it altogether. The market has various aspects: a theory of human nature, a view of human behavior, and an ideological aspect, with proponents stressing the necessary connection between political and market freedom. This article argues that only its view of human behavior should be accepted, particularly the possibility of using incentives, positive and negative, to change behavior. That can be helpful in health care, whereas the market's view of human nature should be rejected.

Job-based health insurance. Who has the duty to lead?

A noted medical ethicist argues that only the business community has the collective power and resources to create a "sustainable medicine" for the nation's health care. But will employers have sufficient incentive and motivation to do so?

Health care for children: a community perspective

There are two puzzles about health care for children that need explanation. Why is it the sentimentality Americans express about children has not been backed by solid health care programs? If children are to have good health care, how can a case for their high priority be made, particularly in light of the fact that their health is the best of all age groups in the country? The first question is explored, but the second question is the focus of this paper. A priority system for health care is proposed, and at the same time an argument is presented for why children should have a high priority despite their generally good health.

Judging the future: Whose fault will it be?

This paper looks at the future from the perspective of the way in which present thinking can influence what the future might be. It assumes that history shapes the future and that the present generation is in a position to shape it. It looks at the future of medicine as a science and a professional discipline, of health care as policy and politics, of culture and ideology as forces shaping medicine and health care, and of biomedical ethics as an influential source of wisdom and perspective. The paper argues that a strong future for bioethics requires a broad rather than a reductionistic vision of its proper work.

Oregon's first year: the medicalization of control

The results of Oregon's first year with physician-assisted suicide raise two questions. First, how will it be possible to evaluate what is actually going on in Oregon if there is no public access to the records and if physicians are shielded by patient confidentiality rules? The second question is whether the public understood that many, if not most, of those who want physician-assisted suicide want it not to relieve suffering as ordinarily understood but to maintain control over their dying, something that may not correlate at all with suffering from illness and disease. This commentary reviews the existing evidence from the Netherlands and suggests that abuse of the vulnerable will likely occur in Oregon over time. It also reviews the insufficiency of the data emerging from Oregon. Finally, it addresses the various issues raised by other commentators to the main article.

Medicine and the market: a research agenda

One of the most important developments in international medicine over the past two decades has been a turn to the market as a way of coping with rising costs and responding to calls for more freedom from government control. A full moral evaluation of the relationship of medicine and the market requires asking a wide range of questions bearing on the meaning and impact of market strategies on the economics of health care and on the clinical and public health outcomes of those strategies. A number of the leading questions are presented and some provisional answers offered.

Balancing efficiency and need in allocating resources to the care of persons with serious mental illness

The care of patients with serious mental illness, for whom a cure is unlikely and costs are high, is difficult to justify using ordinary standards of efficient resource allocation. The author examines the difficulties of using conventional utilitarian, cost-benefit, moral, and political arguments to justify allocation of resources to the care of persons with serious mental illness and offers an alternative approach to this problem based on the goals of medicine. Although care for persons with serious mental illness may not meet the usual standards of efficient health care spending, their treatment is justified by central and long-standing goals of medicine such as relief of pain and suffering and care of those who cannot be cured. This approach suggests that the idea of efficiency in health care spending should be adapted to the goals of medicine rather than making those goals adapt to the idea of efficiency.

Is aging a preventable or curable disease?

The question of whether aging is a disease is old and controverted. Three possible positions are outlined: (i) aging is a natural event, not a disease; (ii) aging is a disease, to be combated by medical knowledge and skills; and (iii) aging, while natural, can be treated as if it is a disease and efforts made to lessen its undesirable impact. The last position seems, de facto, the one that is being pursued by contemporary medicine; however, in such a pursuit, important issues will be raised of intergenerational justice in paying for advances in medicine, and the need to balance the medical goals of care for aged people against other important social needs.