The influence of the state of a compressed thermonuclear substance on the combustion of inertial fusion targets under direct ignition by a short radiation pulse

One-dimensional numerical calculations were performed to study the dependence of conditions for initiating thermonuclear combustion and of the target gain of direct-ignition inertial fusion targets ignited by a short radiation pulse on the initial temperature of a preliminarily compressed fuel and the initial heat energy distribution between plasma electrons and ions in the ignition region (igniter). The igniter parameters at which an effective thermonuclear target explosion with a G ～ 10³ target gain occurred were shown to substantially depend on the initial temperature of the major fuel fraction and the initial heat energy distribution between igniter electrons and ions. The heat energy of the igniter passed a minimum as the size of the igniter decreased. The dependences of these minimum energies on the temperature of the major fuel fraction at various initial energy distributions between igniter electrons and ions were determined. An increase in the temperature of the major fuel fraction was shown to decrease the target gain.     

Microspectral analysis of dentine with femtosecond laser induced plasma

Microspectral analysis of dentine plasma produced by femtosecond laser radiation with intensities of I ～ 10¹³?10¹⁵ W/cm² in ambient atmosphere has been measured. C, O, Ca, Zn, Na, and Cu spectral lines were identified. The X-ray radiation with energies E > 30 keV has been observed upon laser beam intensities of I ～ 5 × 10¹⁵ W/cm².     

Fission fragment production from uranium carbide disc targets

A possible solution for a target system aimed at the production of exotic nuclei as a result of high-energy fissions in ²³⁸U compounds has been analyzed. The configuration proposed is constituted by a primary proton beam (40 MeV, 0.4 mA) directly impinging on a UC₂ multiple-disc target inserted within a cylindrical tungsten box. In order to extract the fission fragments, the tungsten box has to be kept at 2000 ^°C. This system has been conceived to obtain both a high number of fission fragments (about 2 ^. 10¹³ atoms/s) and a quite low power deposition in the target. The power release and the fragment distribution have been calculated by means of the Monte Carlo code MCNPX. The thermal analysis of the proposed configuration shows the capability of the thermal radiation to cool the discs with a reasonable margin below the material melting point. Moreover, the possibility of increasing such margin with simple modifications of the target design is shown by means of parametric analyses. The thermal analysis of the tungsten box, also cooled by radiation, points out the necessity to heat it and/or shield it thermally, in order to take it at the requested temperature. Preliminary calculations of the target-induced activity have also been performed.     

Internal photoemission and plasmon gain in solid and thin films of Al

Weak features in the electron spectrum of Al excited by bremsstrahlung radiation from a Cu anode have been studied using a recently developed multidetector. A feature at ～1410 eV which has been identified as the Al 2p internal photoelectron line was found to have an intensity 4.2 × 10^?3 times that of the Al KL_2,3L_2,3:¹D₂ Auger line, in agreement with a simple theoretical treatment. The identification of this feature is confirmed by the observation of an ～67% decrease in its intensity in spectra obtained from clean Al films in the thickness range 3.1–34.0 nm. The intensity of a plasmon gain peak at ～1404 eV is found to be independent of thickness for films of thickness greater than 7.5 nm.     

Black body radiation imploded inside a small cavity as an inertial confinement fusion driver

It is proposed to use black body radiation generated and imploded within a small cavity as a driver for inertial confinement fusion, with the thermonuclear target centered inside the cavity. By imploding the cavity the black body radiation confined in it is greatly amplified. The thermonuclear target placed inside the cavity in absorbing the energy from the incoming black body radiation is then ablatively imploded by this radiation. Since this radiation can have a rather short wave length, high density compression of the target seems to be attainable with relative ease. If the temperatureT in the cavity rises the energy absorbed by the target rises asT ^7.5 and most of the black body radiation is therefore absorbed by the target towards the end of the implosion process greatly increasing the power. To implode and thereby amplify the black body radiation inside the cavity requires a velocity not larger than ～50 km/s. This comparatively low velocity permits to implode the cavity by laser- or charged-particle beams of modest power. The required rather low cavity implosion velocity should be also attainable using magnetic travelling wave projectile accelerators not longer than a few 100 meters, making the concept also attractive for impact fusion.     

Effect of the spectral distribution of a chirped pulse on the interaction of the high-power laser radiation with matter

The interaction of high-power picosecond laser radiation with solid targets is experimentally studied for the first time at various spectral distributions of a chirped laser pulse. The interaction of the high-power laser radiation with the target is studied at four regimes of the experimental setup: (i) at a relatively high contrast (10³) in the picosecond (Δt ～ 25 ps) range, (ii) at a relatively low contrast (3 × 10¹) in the picosecond (Δt ～ 25 ps) range, (iii) with spectral distortions of the chirped pulse, and (iv) with a strongly modulated spectrum of the chirped pulse. The results obtained reveal a strong dependence of the atomic and nuclear processes in the laser picosecond plasma on the spectral distribution of the chirped laser pulse. The prospects for the application of the spectral interferometry of chirped pulses for the online control of the parameters of the high-power laser radiation are demonstrated.     

The orientational mechanism of nonlinearity and the self-focusing of He-Ne laser radiation in nematic liquid crystal mesophase (theory and experiment)

A giant optical nonlinearity of self-focusing type in the oriented mesophase of nematic liquid crystals (NLC) due to the director reorientation under the action of a light wave field is predicted. Self-focusing of He-Ne laser radiation with power ～10^?2 W and power density ～50 W/cm² in a planar oriented 60 μm thick NLC layer has been carried out experimentally. The measured value of the nonlinearity effective constant ?₂ = 0.07 cm³/erg corresponds to theoretical predictions, and turns out to be larger than the CS₂ nonlinearity by ? 10⁹ times.     

Interband phototransitions involving free electrons: III. Transmission of light through crystals

It has been shown that the two-electron mechanism of nonlinear optical absorption considered in the first two parts of our study, even at laser radiation intensities j ～ 10³-10⁴ W/cm² in the case of nanosecond pulses, can lead to almost complete absorption of light by crystals that are transparent to weak radiation of the same wavelength. A number of materials that can exhibit the considered effects have been described.     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

How to mine energy from a black hole

We describe a process by which energy literally can be mined from a black hole. We argue that the only limit placed by fundamental considerations on the rate at which energy can be extracted from a black hole by this process isdE/dt ～ 1 in Planck unitsG = c = ? = 1. This is far greater than the ratedE/dt ～ 1/M² at which the black hole spontaneously loses energy by Hawking radiation.     

On the expansion of radiation intensity into (a/γ) power series in electrodynamics

An expression for the radiation intensity of a nonrelativistic system of charges integrated over all angles is obtained as a series of powers of small parameter (a/γ) up to the terms ～(a/γ)² inclusive. It differs by a new term ～(a/γ)². Besides other reasons, the inclusion of that new term restores the invariance relative to the small (～a) displacement of the coordinate system origin which was violated by an earlier expression.     

Stochastic evolution of Schwarzschild black hole in a radiation heat bath

The mass of a Schwarzschild black hole in equilibrium with black-body radiation is shown to undergo a random drift with a diffusion coefficient D ～ M^-3. This follows from the master equation for the radiation in a stochastically bistable system of a black hole in an isolating cavity.     

Das Emissionsspektrum gebundener Excitonen in Zinkoxydkristallen in Abhängigkeit von Temperatur und uniaxialer Verspannung

The recombination radiation of bound excitons in ZnO-crystals (spectral range 3,38–3,35 eV at 4.2 °K) and the adjacent phonon-assisted spectrum have been studied at temperatures between 4.2 °K and 90 °K. The phonon-assisted spectrum changes its structure at about 30 °K. With increasing temperature the exciton lines shift toward smaller quantum energies (ΔE～T ²) and their half widthH increases (H～T ²). The line shift is explained by a band gap variation due to deformation potential coupling of the holes toTA phonons. The line width is explained by broadening of an infinitely sharp line under the influence of the mean square fluctuation of thermally generated crystal deformations. The influence of uniaxial stress on the spectral positions of the lines has been studied.     

Studies of neonL-shell excitation by impact of highly ionized heavy ions

Passage of foil-excited 1.4 MeV/A S and 1.1 MeV/A Cl ions of neon charge state ～ 12⁺ through neon gas targets at pressure ～100 mTorr has been found to be accompanied by copious production of Ne II–VIII excited states. Comparable excitation cross-sections ～10^?18 cm² are found for a large number of levels belonging to all of these charge states and corresponding to principal quantum numbersn=2, 3, 4. Vacancy distributions very similar to those found in beam-foil excitation of ～1MeV neon beams are found. Because the Ne recoil velocities are small compared to the fast beam velocities characteristic of the beam-foil source, it is possible to reduce both Doppler shifts and spreads by 3–4 order of magnitude for equivalent collimation. It has also been found that there is an excitation cross-section change of a factor ～5 for a corresponding projectile charge state change from 6⁺ to 12⁺, that efforts to classifyK x-ray satellite spectra byLshell vacancy labels (KL ⁰,KL ¹,...) are probably inaccurate due to extensive population ofn≧3 spectator levels, that both the recoil ion and beam-foil spectra exhibit few lines withn≧4, and that for the allowed transitions studied here, collisional excited states quenching effects due to the ～100mTorr target gas pressures used are negligible.     

Low-energy cross sections for11B(p, 3α)

The¹¹B(p, 3α) reaction has been investigated in the energy range fromE _c.m.=22 to 1100 keV with the use of either a proton beam and a¹¹B solid target or with the use of a¹¹B heavy ion beam incident on a hydrogen jet gas target. The reaction mechanisms have been studied via kinematically complete coincidence measurements showing that the reaction proceeds predominantly by a sequential decay via⁸Be. The measurement of absolute cross sections,α-angular distributions and excitation functions is reported. The astrophysicalS(E) factor has been described by means of an empirical fit to the data, leading to a zero-energy intercept ofS(0)=197±12 MeVb. Conclusions drawn on the use of this reaction as an advanced fuel in fusion reactors remain essentially unchanged by the present data.     

Luminescence of LaBr3: Ce,Hf crystals under photon excitation in the ultraviolet,vacuum ultraviolet,and X-ray ranges

This study has been carried out using synchrotron radiation, time-resolved luminescence ultraviolet and vacuum ultraviolet spectroscopy, optical absorption spectroscopy, and thermal activation spectroscopy. It has been found that, in scintillation spectrometric crystals LaBr₃: Ce,Hf characterized by a low hygroscopicity, along with Ce³⁺ centers in regular lattice sites, there are Ce³⁺ centers located in the vicinity of the defects of the crystal structure. It has also been found that the studied crystals exhibit photoluminescence (PL) of new point defects responsible for a broad band at wavelengths of 500–600 nm in the PL spectra. The minimum energy of interband transitions in LaBr₃ is estimated as E _g ～ 6.2 eV. The effect of multiplication of electronic excitations has been observed in the range of PL excitation energies higher than 13 eV (more than 2E _g ). Thermal activation studies have revealed channels of electronic excitation energy transfer to Ce³⁺ impurity centers.     

Thermonuclear gain of a two-cascade laser-fusion target

One-dimensional numerical calculations are used to explore the possibility of thermonuclear fuel “ignition” (achieving an energy gainG ～ 1) in two-cascade laser-fusion targets with a relatively small aspect ratio for the inner shell. It is demonstrated that the parameters of the laser-produced thermonuclear plasma for a laser pulse energy of 200 kJ, various wavelengths of the laser radiation, and a simple pulse shape closely correspond to the “ignition” state for a target with an inner shell having an aspect ratio of ～ 3–10. This is indicative of the high energy efficiency of two-cascade targets that appear to be characterized by high reliability with respect to evolution of hydrodynamic instabilities.     

Doppler-limited spectra of the ν3 vibration of 12CH4 and 13CH4

The tetrahedral splittings in the P and R branches of the ν₃ band of natural methane have been examined with Doppler-limited resolution using a difference-frequency spectrometer. The spectra obtained by this difference-frequency mixer are compared to recent high-resolution grating spectrometer studies of ¹²CH₄ and enriched ¹³CH₄. The resolution, selectivity and precision are improved over the conventional methods. The mixing spectrometer utilizes tunable, narrow linewidth infrared radiation generated in the nonlinear optical crystal, LiNbO₃ as the beat frequency between a CW argon ion and a tunable dye laser. This spectrometer covers the 2.2 to 4.2 μm infrared spectrum with an instrumental resolution of 5 × 10^?4 cm^?1 and continuous scans up to ～1 cm^?1 and with ir power ～1 μW.     

Electron temperature and concentration in the laser erosion plasma of lead and gallium

Time-averaged values of the electron temperature and concentration at distances of 1 and 7 mm from a target have been determined from the emission characteristics of the laser erosion plasma of lead and gallium. The plasma was produced in a vacuum (3–12 Pa) as the corresponding target was exposed to radiation of a neodymium laser (τ = 20 ns, λ = 1.06 μm, f = 12 Hz, W = 10⁸–10⁹ W/cm²). The energy distribution of excited atomic states has been analyzed. The time dependence of the electron temperature at a distance of 7 mm from the target is presented.     

Influence of Fuel Ratio in D–<Superscript>3</Superscript>He/ST Fusion Power Reactor

The effect of different fuel ratio f³ (the ratio between the ³He and D densities) on D–³He fusion reaction in spherical tokamak has been considered. By solving the zero dimensional particle and power equations numerically the temporal evolution plasma parameters such as the fusion power, synchrotron power and radiation power for different fuel ratios are calculated and compared to each others.