Experimental results from a beam direct converter at 100 kV

A direct-energy converter was developed for use on neutral-beam injectors. The purpose of the converter is to raise the efficiency of the injector by recovering the portion of the ion beam not converted to neutrals. In addition to increasing the power efficiency, direct conversion reduces the requirements on power supplies and eases the beam dump problem. The converter was tested at Lawrence Berkeley Laboratory on a reduced-area version of a neutral-beam injector developed for use on the Tokamak Fusion Test Reactor at Princeton. The conversion efficiency of the total ion power was 65 ±7% at the beginning of the pulse, decaying to just over 50% by the end of the 0.6-s pulse. Once the electrode surfaces were conditioned, the decay was due to the rise in pressure of only the beam gas and not to outgassing. The direct converter was tested with 1.7 A of hydrogen ions and with 1.5 A of helium ions through the aperture with similar efficiencies. At the midplane through the beam, the line power density was 0.7 MW/m, for comparison with our calculations of slab beams and the prediction of 2–4 MW/m in some reactor studies. Over 98 kV was developed at the ion collector when the beam energy was 100 keV. When electrons were suppressed magnetically, rather than electrostatically, the efficiency dropped to 40%. However, a better designed electron catcher could improve this efficiency. New electrode material released gas (mostly H₂ and CO) in amounts that exceeded the input of primary gas from the beam. The electrodes were all made of 0.51-mm-thick molybdenum cooled only by radiation. This allowed the heating by the beam to outgas the electrodes and for them to stay hot enough to avoid the reabsorption of gas between shots. By minor redesign of the electrodes, adding cryopanels near the electrodes, and grounding the ion source, these results extrapolate with high confidence to an efficiency of 70–80% at a power density of 2–4 MW/m. Higher power may be possible with magnetic electron suppression.     

The Fusion Science Research Plan for the Major U.S. Tokamaks

This is the May 1996 report of a subpanel of the US Department of Energy Fusion Energy Sciences Advisory Committee (FESAC), charged with conducting a review of the progress, priorities and potential near-term contributions of TFTR, DIII-D and Alcator C-MOD (and other facilities as appropriate) as part of the transition to a Fusion Energy Sciences Program and produce an optimum plan for obtaining the most scientific benefit from them.     

Some studies on transient behaviours of sheath formation in dusty plasma with the effect of adiabatically heated electrons and ions

Based on quasipotential analysis, a plasma sheath is studied through the derivation of the Sagdeev potential equation in dusty plasma coexisting with adiabatically heated electrons and ions. Salient features as to the existence of sheaths are shown by solving the Sagdeev potential equation through the Runge–Kutta method, with appropriate consideration of adiabatically heated electrons and ions in the dynamical system. It has been shown that adiabatic heating of plasma sets a limit to the critical dust speed depending on the densities and Mach number, and it is believed that its role is very important to the sheath. One present problem is the contraction of the sheath region whereby dust grains levitated into the sheath lead to a crystallization similar to the formation of nebulons and are compressed to a larger chunk of the dust cloud by shrinking of the sheath. Our overall observations advance knowledge of sheath formation and are expected to be of interest in astroplasmas.     

Calibration of Power Systems and Measurements of Discharge Currents Generated for Different Coils in the EGYPTOR Tokamak

The EGYPTOR tokamak is a small device of rectangular cross section 25 × 20 cm. Its major (R) and minor (A) radius are 30 and 10 cm, respectively. The aspect ratio is 3. The present work is devoted to measure the absolute values of the discharge currents and to calibrate the different power systems used to supply different coils in the tokamak. Two different methods are applied to measure the discharge currents from different capacitor banks. The first is the direct method employing a calibrated resistance R=0.008 Ω; this resistance was prepared and calibrated in the IPP of the Czech Academy of Sciences, Czech Republic. The second is the indirect method using a calibrated Rogowski coil, fabricated and calibrated also in Prague (Czech Rogowski coil). Both methods are applied simultaneously. Details of each power system presently used are reported. Sensitivity calibration of two different Rogowski coils is also done, and comparison with the calculated sensitivity shows good agreement.     

Absolute Measurements of the Magnetic Field Generated by Different Coils in the Center of EGYPTOR Tokamak

The present work is devoted to measure the absolute magnetic field produced by different coils in the EGYPTOR tokamak using a calibrated pickup coil. Scaling these measurements in different equations connected with the discharge currents from each supply system are performed. The pickup coil used in the present study is well calibrated with Helmholz coils at the IPP in Prague, Czech Republic. A 0.2% deviation has been found between an evaluation done in the present study and the calibration using Helmholz coils. Experimental measurements of the toroidal magnetic field are in good agreement with calculations to within 2%. Very low values of stray magnetic field components arising from TF and OH coils are recorded which proves that the compensation coils for these components are sufficient.     

Dose rates from the induced activity in the ETF neutral beam injector

The dose equivalent rates outside the Engineering Test Facility neutral beam injector shield from the induced radioactivity have been calculated for the reactor operating at 1140 MW for 1, 30, and 365 days. The dose rates at one day after shutdown are large even after one day of operation. Depending on the location and operating time, cooling times from 30 days to 5 years are required before the dose rates are sufficiently low to allow routine maintenance work in the vicinity of the NBI shield.     

Effect of polarization force on the Jeans instability in collisional dusty plasmas

The Jeans instability in collisional dusty plasmas has been analytically investigated by considering the polarization force effect.Instabilities due to dust-neutral and ion-neutral drags can occur in electrostatic waves of collisional dusty plasmas with self-gravitating particles.In this study,the effect of gravitational force on heavy dust particles is considered in tandem with both the polarization and electrostatic forces.The theoretical framework has been developed and the dispersion relation and instability growth rate have been derived,assuming the plane wave approximation.The derived instability growth rate shows that,in collisional dusty plasmas,the Jeans instability strongly depends on the magnitude of the polarization force.     

Solvent Extraction Behavior of Macroamounts of Elements in 100 % TBP-Nitric or Hydrochloric Acid Systems

The acid dependence curves of 15 inorganic ions in macroamounts were surveyed for the system of 100% TBP-HC1 and HNO₃, and compared with results obtained in tracer work previously reported. In most cases, theKd values measured in a system containing 0.1m/l salt are little different from those determined by radioactive tracers. The acid dependence behavior of ferric and zinc chloride were especially studied with varying metal ion concentrations. Additional experiments were carried out for ferric and zinc chloride in the system of 1 % (w/v) TBPO and 5 % (w/v) TOPO toluene-HCl. In these cases theKd values lowered with increasing chloride concentration.     

Measurement of Cold Neutron Spectrum with Liquid Mirror Reflection

Making use of the wavelength dependency of the critical angle for the total reflection of neutrons, the possibility of determining the energy spectrum of cold neutrons by means of a liquid mirror is examined. A carbon tetrachloride mirror, combined with a pair of fine slits, are used for the measurement of the angular distribution of the reflection intensity of beryllium filtered neutrons. For determining the correction required to account for non-reflected neutrons detected by the counter, the direct beam component is measured by disturbing the liquid mirror surface with small ripples generated by an ultrasonic vibrator submerged in the liquid, and the value obtained with this clouded mirror is subtracted from that determined with the clear undisturbed liquid mirror. The experimental results qualitatively show good agreement with those obtained with a helical-slot neutron velocity selector, and further reveal even better resolution than possible with the latter method, in the cold neutron energy region.     

Propagation characteristics of microwaves in dusty plasmas with multi-collisions

In this study, we consider three main collisions in dusty plasmas and investigate the effects of dust grains on the propagation of electromagnetic(EM) waves through uniform, unmagnetized and weakly ionized dusty plasma. The Drude model is improved to describe the dielectric property of dusty plasmas, which accounts for collisions including electron–molecule, electron–ion, and electron–dust particles. Based on the improved Drude model, the propagation characteristics of microwaves in dusty plasmas have been numerically calculated and studied.The results show that the propagation characteristics of microwaves through dusty plasmas are different from those through normal plasmas. The effects of dust density and size are mainly studied. Numerical results indicate that the momentum transfer between electrons and dust grains makes more energy loss. The dust density and dust size have a similar influence on EM wave propagation, resulting in less transmission and more absorption.     

Propagation of Nonlinear Solitary Waves in Nonuniform Dusty Plasmas with Two-Ion Temperature

The nonlinear properties of dust acoustic solitary waves in inhomogeneous dusty plasmas with two-ion temperature are investigated. By using the reductive perturbation theory, a modified variable coefficients Korteweg-de Vries （MKdV） equation is derived. The typical integral form of the Sagdeev potential is examined numerically. The numerical results show that the inhomogeneity, the two-ion temperature have strong influence on the nonlinear properties of dust acoustic solitary waves.     

Calculation of the Anisotropic Diffusion Coefficient

The one-group anisotropic diffusion coefficient is calculated for slab and square lattice cells with use made of Benoist's formula. In utilizing the integral transport theory, only several collisions suffered by a neutron have hitherto been considered. In this paper, we adopt the integral theory and take into consideration the effect of an infinite number of collisions suffered by a neutron, this being made possible by solving simultaneous equations. Further, we consider the anisotropic scattering through the generalized first-flight collision probability. Then we estimate the fundamental and the additional terms in the Benoist formula for slab and square lattice cells.     

Interaction of hydrogen isotopes with metals: Deuterium trapped at lattice defects in palladium

From an interplay between theory based on the effective-medium scheme and experiments, an extremely simple picture has evolved which is capable of describing a vast number of experimental quantities related to interaction of hydrogen with metals, especially the trapping of hydrogen at defects. It is shown that the trap strengths are determined mainly by the interstitial electron density, and any open structures in the lattice leads to a trap, with the vacancies and voids being the strongest traps. It is also found theoretically and experimentally that up to six hydrogen atoms can be accomodated in a vacancy, and the change in trap strengths with occupancy has been determined. Recent results for the trapping of deuterium to defects in Pd are discussed.     

Calcuiational Method for Neutron Heating in Dense Plasma Systems, (II)

Abstract

The effect of neutron heating on the burn characteristics of inertial confinement fusion pellets is investigated by applying the calcuiational method developed in an earlier paper (Part I). The basic equations are time-dependent transport equations for fusion neutrons and recoil ions, being written in terms of the modified Eulerian coordinates originally proposed by Wienke (1974). After incorporating these equations into the one-dimensional hydrodynamics code MEDUSA, burn simulations are made for isobaric D-T pellets models compressed to 1,000 times the liquid density. It is found that in reactor-grade pellets, the inclusion of neutron heating decreases the fuel gain from the values obtained by neglecting the neutron heating. Calculations neglecting the energy transport by recoil ions overestimate the neutron energy deposition to plasma ions. The energy spectrum of neutrons emitted out of a typical D-T burning pellet is also shown. These neutrons contain fast components whose energies reach more than 20MeV.     

Ignition Approach by Neutral Beam Injection Heating in Impurity Contaminated Tokamak Reactors

Available heating power by neutral beam injection in a tokamak reactor is evaluated semi-empirically. Using this estimated value, device and plasma parameters to ignite the plasma in impurity contaminated tokamak reactors are investigated. By lowering the plasma density and concurrently by enlarging the plasma minor radius or aspect ratio, the difficulty of NBI heating can be avoided, and the ignition is almost always possible both for trapped ion mode and Alcator scaling laws.     

中子土壤水分探测仪在农田建设和土壤改良中的应用

当快中子与土壤中的氢发生弹性碰撞时,快中子慢化成热速度,中子仪是根据中子的特性制造的,以便测定土壤的水分含量。在农田建设和土壤改良中经常需了解土壤的含水量和它随深度和时间的变化。 根据上述数据,人们可以计算土壤剖面的水量平衡和储量以及水分的亏损。因此决定灌溉淋洗盐碱土的需水量和作物的需水量。 中子仪可以提供一种快速非破坏的监测土壤含水量的方法和土壤水分随空间和时间上的变化。     

A Method to Construct Plasma with Nonlinear Density Enhancement Effect in Multiple Internal Inductively Coupled Plasmas

A method is proposed to built up plasma based on a nonlinear enhancement phenomenon of plasma density with discharge by multiple internal antennas simultaneously. It turns out that the plasma density under multiple sources is higher than the linear summation of the density under each source. This effect is helpful to reduce the fast exponential decay of plasma density in single internal inductively coupled plasma source and generating a larger-area plasma with multiple internal inductively coupled plasma sources. After a careful study on the balance between the enhancement and the decay of plasma density in experiments, a plasma is built up by four sources, which proves the feasibility of this method. According to the method, more sources and more intensive enhancement effect can be employed to further build up a high-density, large-area plasma for different applications.     

On peak current in atmospheric pulse-modulated microwave discharges by the PIC-MCC model

Pulse modulation provides a new way to tailor the electron density,electron energy and gas temperature in atmospheric radio-frequency (rf) discharges.In this paper,by increasing the rf frequency to several hundreds of MHz,or even much higher to the range of GHz,a very strong peak current in the first period (PCFP) with much larger electron energy can be formed during cthe power-on phase,which is not observed in the common pulse modulation discharges at a rf frequency of 13.56 MHz.The PIC-MCC model is explored to unveil the generation mechanism of PCFP,and based on the simulation data a larger voltage increasing rate over a quarter of a period and the distribution of electron density just before the power-on phase are believed to play key roles;the PCFP is usually produced in the rnicroplasma regime driven by the pulsed power supply.The effects of duty cycle and pulse modulation frequency on the evolution of PCFP are also discussed from the computational data.Therefore,the duty cycle and pulse modulation frequency can be used to optimize the generation of PCFP and high-energy electrons.