The Potential of Fast Ignition and Related Experiments with a Petawatt Laser Facility

A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuterium-tritium fuel, is used to show the potential for 300× gain with a driver energy of 1 MJ, if the National Ignition Facility (NIF) were to be adapted for fast ignition. The physics of fast ignition has been studied using a petawatt laser facility at the Lawrence Livermore National Laboratory. Laser plasma interaction in a preformed plasma on a solid target leads to relativistic self-focusing evidenced by x-ray images. Absorption of the laser radiation transfers energy to an intense source of relativistic electrons. Good conversion efficiency into a wide angular distribution is reported. Heating by the electrons in solid density CD₂ produces 0.5 to 1 keV temperature, inferred from the D-D thermo-nuclear neutron yield.     

The Ignition Requirements of the Degeneracy Microspheres of Deuterium Helium-3 Mixture with Low-Radioactive

This paper examines the burn characteristics for inertial confinement D/³ He fuel pellets with different concentrations of Helium-3. It is shown that the Helium-3 relative density of the fuel mixture plays a significant role in determining the burn characteristics and fuel gain. In spite of the safety of the plasma degeneracy of D/³ He fuel with fraction of y?=?0.2 (y: Helium-3 content parameter), ignition of fuel is impossible. In design fuel extra to safety should be considered fractional burn-up and fuel gain. The main contribution of this research is to show that the plasma degeneracy of equimolar mixture of D/³ He fuel lowers the ignition temperature and increases fuel gain. The results indicate that a $n_{D} /n_{{^{3} He}}$ ?≤?0.3 is difficult to ignite reasonable driver energy. A fuel gain of 378 can be obtained with a D/³ He fuel with fraction of y?=?0.33, and areal density (ρR) of 12 g/cm². It is found that the fuel gain of an equimolar D/³ He fuel at temperature of 70?keV and ρR value of 8.5 g/cm² is 480. This value gain is higher by about 22% than the case of the pellets (y?=?0.33).     

Effect of Internal Breeding of Tritium and Helium-3 on the Ignition of an ICF Fuel Pellet

Self-heating condition and following ignition in an Inertial Confinement Fusion (ICF) fuel pellet is evaluated by calculating the power equations, dynamically. In fact, the self-heating condition is a criterion that determines the minimum parameters of a fuel (such as temperature, density and areal density) that can be ignited. Deuterium is the main component of ICF fuels as large amounts of it are naturally available. In addition, the use of deuterium as a fuel in ICF causes the production of tritium and helium-3. However, pure deuterium has a high ignition temperature (\(\hbox {T}\ge 40\,\hbox {keV}\)) which makes it inefficient. In this paper, the power equations are solved, dynamically, and it has been indicated that internal tritium and helium-3 production at early evolution of compressed deuterium fuel causes ignition at lower predicted temperatures.     

Recent results on Nova

On the Nova Laser at LLNL, we have recently demonstrated many of the key elements required for assuring that the next proposed laser, the National Ignition Facility (NIF) will reach ignition. In particular, we have achieved a drive of 300 eV in laser heated hohlraums; have shown good understanding and control of symmetry in hohlruams; created large NIF-Scale plasmas with plasma and irradiation conditions relevant to NIF targets that showed low levels of plasma instabilities; demonstrated a good understanding of hydrodynamic instability and subsequent pusher/fuel mix in implosions by means of spectroscopic tracers; and performed integrated implosion experiments that have performed well even under stringent convergences of order 25, which is well into the NIF ignition target regime.     

CdZnTe quasi-hemispherical detector for gamma–neutron detection

Quasi-hemispherical CdZnTe detector was manufactured successfully to fully understand the performance in the mixed gamma–neutron detection field. Together with the software of COMSOL, Geant4, and Matlab, the detector structure has been optimized. The CdZnTe detector performs good energy resolutions for ²⁴¹Am, ⁵⁷Co, and ¹³⁷Cs radiation sources, especially for ¹³⁷Cs (10.91 keV full width at half maximum [FWHM] at 662 keV). A linear relationship between the energy positions and spectrum channels indicates that the detector is effective for the precise energy detection from 59.5 to 662 keV. Finally, neutron and gamma events were detected simultaneously at room temperature using ²⁴¹AmBe neutron source. The spectrum shows good energy resolution for neutron capture gamma ray (14.28 keV FWHM at 558 keV). Our work demonstrates that the quasi-hemispherical CdZnTe detector is promising for simultaneous detection of neutrons and gamma radiation.     

Numerical Study of Radiation Emission from the Argon Plasma Focus

Ion populations and emitted spectrum of argon plasma have been calculated using the POPULATE and SPECTRA codes of the RATION suite at different conditions (electron temperatures, electron densities, ion densities, plasma size) for LTE and NLTE models. Expected argon plasma spectra at certain electron temperature range have been plotted. The suitable electron temperatures ranges for argon plasma soft X-ray (3–4 keV) emission and EUV (60–200 eV) emission have been investigated. POPULATE and SPECTRA codes have been presented as a good assisted tools for plasma focus diagnostics.     

Radiation effect on partial pressure of fission product iodine

The knowledge of the partial pressure of fission product iodine is important for evaluating the FCCI (fuel cladding chemical interaction) in FBR. Thermodynamical analysis shows that iodine is believed to react with cesium so strongly that the partial pressure of iodine is kept too low to cause FCCI. A molecule of cesium iodide is, however, excited by radiation in the reactor and dissociates into radical and ion. In this work, the radiation effect on the partial pressure of iodine is theoretically studied for the gaseous cesium-iodine system. Fission fragment flux is considered as the radiation and the iodine partial pressure is evaluated based on the theory of gaseous reaction. The results of the calculation show that the partial pressure of iodine can be increased enough to cause FCCI in the radiation field. In the case of the FBR fuel pin, the partial pressure of iodine under radiation conditions can be calculated to be ~ 10^?2 Pa (~10^?7 atm), which is higher than that of the non-radiation condition ~10^?9 Pa (~10^?14 atm). These calculations were carried out under the assumption that the cladding inner surface temperature was 873 K (600°C) and the oxygen potential was ?418 kJ/mol (?100 kcal/mol).     

Measurement of Radiative Collapse in 2.2 kJ PF: Achieving High Energy Density (HED) Conditions in a Small Plasma Focus

Radiative collapse in the plasma focus (PF) pinch creates extreme high energy density (HED) in the laboratory. The Pease–Braginskii current is that current flowing in a hydrogen pinch which is just large enough for bremsstrahlung to balance Joule heating; this threshold value being 1.4 MA. For high-Z gases undergoing strong line-radiation the radiation-cooled threshold current is considerably lowered. Recent work applied to a MJ PF has revealed that even if a threshold current is exceeded there is a condition that the characteristic depletion time of the pinch energy by radiation should be of the order of the pinch time in order for strong radiative collapse to be observed, thus explaining why no radiative collapse may be expected in deuterium; and also in helium; even in multi-MA PF devices. This paper extends the computation of depletion times to a kJ PF, the INTI PF showing that in the INTI PF only a small reduction in radius ratio may be anticipated in Ne whilst in Ar, Kr and Xe strong radiative collapse is expected. Two useful Tables are obtained applicable to kJ PF devices, one of reduced Pease–Braginskii currents in various high-Z gases and the other of corresponding characteristic depletion times. Two earlier papers using the Lee code had already demonstrated that radiative collapse occurs in plasma focus operated in high-Z gases. However in those papers computation could only be carried out up to a cut-off radius set at 0.01 of anode radius. Thus as shown in this paper most of the radiative compression was not computed or measured. This paper reports the measurement of the pinch trajectory in Kr by the fitting of a measured current waveform using the code with the cut-off radius successfully removed, so that the fitting fully follows the compression to its minimum radius and beyond to the rebound of the trajectory. The measured current waveform shows radiative collapse to a minimum radius ratio of 0.0014 or 0.0013 cm. Ion density reached 3.7 × 10²⁶ m^?3; and an immense burst of radiation is emitted with peak power of 10¹² W, radiating 30 J in 50 ps, during the time of peak radiative compression. The energy density at peak compression is 4 × 10¹³ J m^?3 or 40 kJ mm^?3. This is the first time such a measurement has been made; and indicates that even in a kJ plasma focus, such a HED state is achieved.     

Fluxes of charged and neutral particles from tokamaks

The performance of present tokamak devices is significantly influenced by neutral atom and impurity ion populations originating at the wall or aperture limiter. Plasma instability and diffusion mechanisms cannot be identified until these surface-related processes are accurately described. Central neutral densities in the Oak Ridge tokamak vary from 2 × 10⁸ cm^?3 to 2 × 10⁹ cm^?3 and agree well with values predicted by our theoretical model. We extrapolate this model to the larger, denser and hotter plasmas foreseen in the next generation of experiments and beyond. We calculate the rate of impurity generation by charge exchange bombardment. Impurities will influence scientific feasibility experiments which burn D-T by raising ignition temperatures. In a version of our code which incorporates alpha heating, bremsstrahlung, synchrotron and line radiation we calculate the effects of small admixtures of high $\text{Z}$ ions on the injection power required to reach ignition and on the required pulse duration. We give the wall energy fluxes to the expected and the relative fractions of energy conduction and radiation.     

Preliminary Results of IS Plasma Focus as a Breeder of Short-Lived Radioisotopes 12C(d,n)13N

Modified IS (Iranian Sun) plasma focus (10 kJ,15 kV, 94 ??F, 0.1 Hz) has been used to produce the short-lived radioisotope ¹³N (half-life of 9.97 min) through ¹²C(d,n)¹³N nuclear reaction. The filling gas was 1.5?C3 torr of hydrogen (60%) deuterium (40%) mixture. The target was solid nuclear grade graphite with 5 mm thick, 9 cm width and 13 in length. The activations of the exogenous target on average of 20 shots (only one-third acceptable) through 10?C13 kV produced the 511 keV gamma rays. Another peak found at the 570 keV gamma of which both was measured by a NaI portable gamma spectrometer calibrated by a ¹³⁷Cs 0.25 ??Ci sealed reference source with its single line at 661.65 keV and ²²Na 0.1 ??Ci at 511 keV. To measure the gamma rays, the graphite target converts to three different phases; solid graphite, powder graphite, and powder graphite in water solution. The later phase approximately has a doubled activity with respect to the solid graphite target up to 0.5 ??Ci of 511 keV and 1.1 ??Ci of 570 keV gamma lines were produced. This increment in activity was perhaps due to structural transformation of graphite powder to nano-particles characteristic in liquid water.     

Investigation of Fuel Energy Gain for Tritium-Poor Fuels in Fast Ignition Fusion Approach

One of the most fascinating ignition schemes for the inertial fusion energy that might be feasible is fast ignition.Its targets are ignited on the outside surface so there is no need to low density and high temperature center is required by central hot spot ignition.Fast ignition concept is noteworthy for a simple but fundamental reason:In principle it requires less total energy input to achieve ignition.In this paper,fuel energy and fuel energy gain of nearly pure deuterium capsule are calculated.This capsule is ignited by a deuterium-tritium seed,which would reduce the tritium inventory to a few percentages.The variations of fuel energy gain versus fuel density have been studied and submitted.On the basis of different physical parameters the following results of the investigation are presented and discussed.The energy gain curves for different tritium concentrations are found and limiting gain curves are derived.Finally,tritium-poor fast ignitor is compared to equimolar deuterium-tritium fast ignitor.     

What Can Be Expected from High-Z Semiconductor Detectors?

It has been hoped that high-Z semiconductors would offer efficient ?-ray detection at or near ambient temperatures with energy resolution significantly better than NaI (T1) scintillators. For use at X-ray energies, this goal has been achieved with both HgI2, CdTe, and GaAs detectors. However, at higher energies (~660 keV) all current detectors have one or more significant deficiencies in terms of attainable volume, charge collection efficiency, and polarization effects. Starting with first principles, all potential compounds which can be formed by the binary combination of elements from the periodic chart were considered as possible detector materials. A rank-ordered listing of the most promising materials for further development is given as well as an assessment of the prospects for future success.     

Simulation of Low–High Transition by Neutral Beam Injection in Edge Plasma of Small Size Divertor Tokamak

This paper reports simulation of L–H transition by fluid transport code B2SOLPS0.5.2D at low ion plasma density on neutral beam injection (NBI) in the edge plasma of small size divertor tokamak. The simulation provides the following results: (1) the transition is possible at plasma density 2 × 10¹⁹ m^?3 with NBI at temperature heating T^heating 3.62 keV. (2) The simulation predicts the generation of large negative radial electric field E _r, which is thought to help L–H transition during NBI, is suggested in the edge plasma of small size divertor tokamak. (3) The toroidal current density in the edge plasma of small size divertor tokamak is plasma density and direction of NBI dependence. (4) Parallel flux transport by anomalous viscosity (turbulent) through separatrix leads to the variation of toroidal current density.     

Direct-Drive Implosion Experiments on the SG-II Laser Facility

SG-II, a 8-beam Nd:glass laser with an output energy capability of 6kJ at 1.053m, was built and direct-drive implosions were successfully performed early in 2000. Both exploding pusher and ablative targets were imploded using glass capsules with diameters of 200 and 500m, and a wall thickness of about 1m. The deuterium and tritium (DT) gas pressure filled in these capsules were 2.0 and 0.5MPa, respectively. Sophisticated diagnostics were deployed to measure laser absorption, hot electron temperature and fraction, thermal electron temperature, neutron yields, ion temperature, temporally resolved x-ray images, fuel areal density, alpha particle image, and so on. Significant results, such as neutron yields up to 4 × 10⁹ for exploding pushers with 100-ps laser pulse irradiation and 6 × 10⁸ for ablative targets with 1-ns pulses and clear x-ray images to see the compression process, were obtained. Numerical simulations were conducted to optimize target and laser parameter design and to duplicate the results afterwards with the specific shot parameters used in the experiment.     

Candidates for Laser Fusion Energy with Minimized Radioactivity

The new candidates for laser fusion energy with minimized radioactivity were presented. The possibility of side-on laser ignition of H–¹¹B with negligible radioactivity encouraged to study the fusion of solid state H–⁷Li fuel which again turns out to be only about ten times more difficult than the side-on ignition of solid deuterium–tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included. In other words, the specific approach discussed here involves inducing a fusion burn wave without radioactivity by laser-driven impact of a relatively large block of plasma on the outside of a solid density H–¹¹B and H–⁷Li targets.     

The Effect of Plasma Profiles on the Critical Value of $$n\uptau_{E}$$ for Ignition

The effect of plasma profiles for ignition condition in a stationary D–T plasma is investigated using the energy conservation equations for ions and electrons, assuming that steady state fusion power is produced with no external power. The alpha power heating is sufficiently large to sustain the plasma and to balance the combined Bremsstarhlung and thermal conduction losses. The space dependent Lawson criteria is derived and critical condition is identified. As a result of this analysis we have shown that the optimum temperature might be \(\bar{T} \approx 26\,{\text{keV}}\) and that the peaked profiles with \(n\sim\left( {1 - \frac{{r^{2} }}{{a^{2} }}} \right)^{{v_{n} }}\), ν _n  = 1, and \(T\sim\left( {1 - \frac{{r^{2} }}{{a^{2} }}} \right)^{{v_{T} }} ,\,v_{T} = 2\) are good to minimizing \(\bar{n}\uptau_{E}\) for ignition. The results for these profiles show the critical value of \((\bar{n}\uptau_{E} )_{min} = 0.08 \times 10^{20 } \,{\text{m}}^{ - 3} \,{\text{s}}\) showing the reduction by 1/3 from the reference value limit ν _n  = ν _T  = 0. For a 26 keV plasma with an energy confinement time of 1 s, a pressure of about 6.24 atm is required for the plasma to be ignited; that is, it is sustained purely by the self-heating of the fusion alpha particles.     

Tungsten Blister Formation Kinetic as a Function of Fluence,Ion Energy and Grain Orientation Dependence Under Hydrogen Plasma Environment

This work deals with the formation kinetic of tungsten (W) blisters under smooth plasma conditions, i.e. low hydrogen flux and energy in order to analyze the first stages of their formation. In addition, we focus on determining the W grain orientation where blisters grow preferentially. For this purpose, mirror-polished polycrystalline tungsten samples were exposed to hydrogen plasma under fixed hydrogen flux of 2.2 × 10²⁰ m^?2 s^?1, with a fluence in the range of?~?10²⁴ m^?2, ion energy of?~?20, 120 and 220 eV, and sample surface temperature of?~?500 K. The formation of blisters at the surface was investigated using SEM, AFM and EBSD to determine the size, the distribution and the orientation of grain where blisters are formed, respectively. The critical fluence for initiating blisters was established around 2.3 × 10²⁴ m^?2. The evolution of blister size distribution and density is discussed as function of fluence and ion energy. At lower ion energy, i.e. 20 eV, only nanoblisters (less than 150 nm) are observed whatever the fluence value (1.5 and 2.3 × 10²⁴ m^?2). At higher ion energy i.e. 120 and 220 eV, micrometric (~ few to tens of µm) blisters are observed and their density highly depends on fluence. We show that blisters can also be formed on (001) oriented grains contrarily to previous results from the literature where the (111) orientation seemed more favorable. Such information is of importance for tungsten based fusion tokamak operation and design.     

Isentrope Parameter Effect in the Compression Process of the Fusion Advanced Fuel

In inertial confinement fusion, Fermi degeneracy plays an important role in reducing the cost of driver energy. In this research, based on recent progresses in the laser electron accelerators research, we have physically designed a D/³ He target and examine the isentropic parameter of a D/³ He fuel to achieve the goal of gains of order 500. The design target significantly depends on the isentrope parameter and the pressure of the D/³ He fuel. In during the compression, If the D/³ He fuel stays in the degeneracy state, the compression energy is smaller than the ignition energy for the same amount of fuel. The energy requirement to compress a D/³ He fuel with density 2.9 × 10⁴ g/cm³ is 4.2 × 10⁷ J/g. Also, the driver energy needed to achieve these gains is estimated to be 1000 MJ when the coupling efficiency is 10 % and isentropic parameter is 1.5.     

Shut-down margin study for the next generation VVER-1000 reactor including 13 × 13 hexagonal annular assemblies

Shut-Down Margin (SDM) for the next generation annular fuel core of typical VVER-1000, 13 × 13 assemblies are calculated as the main aim of the present research. We have applied the MCNP-5 code for many cases with different values of core burn up at various core temperatures, and therefore their corresponding coolant densities and boric acid concentrations. There is a substantial drop in SDM in the case of annular fuel for the same power level. Specifically, SDM for our proposed VVER-1000 annular pins is calculated when the average fuel burn up values at the BOC, MOC, and EOC are 0.531, 11.5, and 43 MW-days/kg-U, respectively.     

Ti-T靶中~3He测量

一、引言轻元素在材料中的含量及分布情况,是应用物理、应用技术等领域感兴趣的问题。目前,国外正在用各种核技术对此进行测量和研究。通常使用的Ti-T靶,因T的β衰变(T_(1/2)为12.33a),靶内~3He的含量将随制成靶的时间不同而变化。本文试图通过对不同时间制备的Ti-T靶中~3He的测量,探索测量和分析~3He的某种途径。