Recent progress on the Tokamak Fusion Test Reactor

The deuterium-tritium (D-T) experiments on the Tokamak Fusion Test Reactor (TFTR) have yielded unique information on the confinement, heating and alpha particle physics of reactor scale D-T plasmas as well as the first experience with tritium handling and D-T neutron activation in an experimental environment. The D-T plasmas produced and studied in TFTR have peak fusion power of 10.7 MW with central fusion power densities of 2.8 MWm^–3 which is similar to the 1.7 MWm^–3 fusion power densities projected for 1,500 MW operation of the International Thermonuclear Experimental Reactor (ITER). Detailed alpha particle measurements have confirmed alpha confinement and heating of the D-T plasma by alpha particles as expected. Reversed shear, highl _i and internal barrier advanced tokamak operating modes have been produced in TFTR which have the potential to double the fusion power to 20 MW which would also allow the study of alpha particle effects under conditions very similar to those projected for ITER. TFTR is also investigating two new innovations, alpha channeling and controlled transport barriers, which have the potential to significantly improve the standard advanced tokamak.     

The reversed-field-pinch (RFP) fusion neutron source: A conceptual design

The conceptual design of an ohmically heated, reversed-field pinch (RFP) operating at 5-MW/m² steady-state DT fusion neutron wall loading and 124-MW total fusion power is presented. These results are useful in projecting the development of a cost effective, low-input-power (206 MW) source of DT neutrons for large-volume (10 m³), high-fluence (3.4 MW yr/m²) fusion nuclear materials and technology testing.Work supported by U.S. DOE.     

Progress of Ambipolar Mirror Trap

Essential experimental results at ambipolar (tandem) mirror traps are briefly reviewed. Progress on longitudinal plasma confinement by ambipolar barriers (plugs) and on suppression of transverse anomalous plasma losses in a solenoid are noted. Experimental exploration of MHD-stabilization of high pressure plasma ( 1) by vacuum chamber walls and of ion pumping from stationary thermal barriers is emphasized. Geometry of an axisymmetric trap, in which self-sustaining D-T reaction is possible, is briefly described.     

Inertial Confinement Fusion with a Heavy-Ion Driver-Accelerator and a Cylindrical Target

An economically efficient power plant burning deuterium-tritium fuel can be built using a powerful heavy-ion accelerator of a new type. A multilinear cryogenic cylindrical target, 1 cm long, 0.44 cm in radius, and containing 7.8 mg equimolar DT fuel, is studied as an example. The driver-accelerator gives two different target irradiation regimes. In both regimes, the beams consist of platinum ions, accelerated up to 100 GeV, with different isotopic composition, charged in the first regime only positively and in the second regime positively and negatively. In the first regime, the beam energy is 4.8 MJ and the beam heats in 60 nsec only the target shell. High heating symmetry is achieved by rapidly rotating the beam around the target axis with frequency 1 GHz. The fuel is compressed into a dense filament, where the condition for propagation of a fusion burn wave is satisfied – R 0.4 g/cm². In the second regime, a beam with 0.4 MJ ions heats in 0.2 nsec compressed fuel with power density 2.5·10⁷ TW/cm² up to ignition temperature. The computed energy amplification factor in the target is 200.     

Report of panel 2: Post-TFTR initiatives

Conclusion The Panel finds that the steady-state/advanced-to-kamak mission is a critical element in the U.S. fusion strategy as established by FPAC. An attractive SS/AT device can be constructed for about the $400M FY'92 guideline proposed by the SEAB-TF. The design and construction of such a facility should proceed on a schedule to enter operation in 1990–00. Adequate funding for peak construction years should become available following the D-T operation of TFTR. In all its phases, the new device should be managed as a national facility.This report was prepared by a panel established by, and reporting to, the Fusion Energy Advisory Committee (FEAC). The report of this panel should not be construed as representing the views, official advice or recommendations of FEAC.This document uses SS/AT to identify the mission and TPX to identify a generic facility addressing the mission.     

Initial high beta operation of the HBT-EP Tokamak

HBT-EP is a new research tokamak designed and built to investigate passive and active feedback techniques to control MHD instabilities. In particular, HBT-EP will be able to test techniques to control fast MHD instabilities occurring at high Troyon-normalized beta, _N Ba/I_p [Tm/MA], since it is equipped with a thick, close-fitting, and adjustable conducting shell. The major goals of the initial operation of HBT-EP have been the achievement of high beta operation (_N 3) using only ohmic heating and the observation of MHD instabilities. By using a unique fast startup technique, we have successfully achieved these goals. A variety of MHD phenomena were observed during the high beta operation of HBT-EP. At modest beta (_N 2), discharges have been maintained for more than 10 msec, and these discharges exhibit saturated resistive instabilities. When _N approaches 3, major disruptions occur preceded by oscillating, growing precursors. During start-up, one or more minor disruptions are usually observed. A 1-D transport code has been used to simulate the evolution of the current profile, and these early minor instabilities are predicted to be double tearing modes. The simulation also reproduces the observed high beta operation when saturated neo-Alcator energy confinement scaling is assumed.     

Calculation of neutron and gamma-ray energy spectra for fusion reactor shield design: Comparison with experiment-II

Measured and calculated neutron and gamma-ray energy spectra resulting from the transport of 14 MeV neutrons through a 0.30-m-thick lithium hydride slab and through a 0.05-m-thick lead slab followed by 0.30 m of lithium hydride are compared. Also reported are comparisons of the measured and calculated neutron energy spectra behind an 0.80-m-thick assembly comprised of stainless steel type 304 and borated polyethylene. The spatial dependence of the gamma-ray energy deposition rate measured using thermoluminescent detectors is compared with calculated data. The calculated data obtained using two-dimensional radiation transport methods and ENDF/B-IV cross-section data are in good agreement for all of the experimental configurations. Calculated integral neutron energy spectra agree with the measured data within 5 to 20% depending on neutron energy for the LiH and Pb plus LiH assemblies. The gamma-ray spectra agree within 20% for these slabs. The measured and calculated neutron energy spectra behind the SS-304-borated polyethylene assembly agree within 5% except at neutron energies below 5 MeV where background radiation influences the measured spectra. The gamma-ray energy deposition rates as a function of depth agree within a factor of two at all detector locations.     

Fusion Safety Studies in Russia in 1996

The paper seeks to provide a summary report of observations and results of some Russian fusion safety studies performed in 1996. Release of tritium and helium from neutron irradiated beryllium at relatively high neutron fluences has a burst nature. With the growth of the beryllium temperature-increase rate to 90 K/s, the temperature of tritium burst release decreases from 800 to 450–500°C and for helium decreases from 1200 to 500°C. Characterization of carbon and tungsten dust produced in experiments simulating plasma disruptions revealed that dust particle distribution of sizes for graphites and carbon fiber composites has a bimodal nature with maxima in the range of 0.01–0.03 and 2–4 m for composite UAM and in the range of 0.14–0.18 and 2–4 m for graphite MPG-8. Chemical reactivity of beryllium with air was studied as well. A mathematical model for beryllium weight gain under its chemical interaction with air at temperatures of 700–800°C as a function of beryllium porosity, temperature, and interaction duration was developed.     

The action of α-radiation on aqueous acid solutions

We investigated the action of polonium -radiation on a 0.8 N aqueous solution of sulfuric acid.It was established that over a wide range of dissolved polonium concentrations (0.1–12 mC/ml), the initial radiation-chemical hydrogen peroxide yield remains the same and equals 1.20 molecules per 100 ev of absorbed energy and that the hydrogen peroxide concentration tends toward a limit. The equilibrium limit of hydrogen peroxide concentration in 0.8 N sulfuric acid is 5–8·10¹⁸ molecules/ml.     

Some characteristics ofγ-ray scattering at the boundary of two media

The characteristics of -ray scattering (0.33 E 1,25 MeV) at the boundary between two media were experimentally investigated. It was established that the scattered radiation was produced mainly by a narrow beam of primary radiation. The effective scattering area was contained within a region with a radius r 10h (for h z). The contribution to the total energy from radiation scattered by the medium increased for angles of incidence of the primary narrow beam up to 85–88 °, and then decreased monotonically.An estimate was made of the effective dimensions of the area from which scattered quanta were emitted into the backward half-space when an isotropie source was located at the surface of the scatterer.The energy flux of the scattered radiation was measured with a gas counter which had a practically constant sensitivity for -rays of different energies.The authors are deeply grateful to Prof. O. I. Leipunskii and to A. S. Strelkov for assistance and for discussions of the results.     

Experimental results of the erosion of molybdenum due to blistering by He+ bombardment

We report some preliminary measurement of the erosion rate of plasma dumps when bombarded with 100 keV He⁺ ions at high power density ( 1 MW/m²). The expected erosion rates, based on measurements of He blistering that were made at lower power density ( 0.3 MW/m²), indicate a potentially serious problem for fusion reactors. Our tests use a reactorlike power density and produce He blisters at a rate that is slower than predicted by 2 to 4 orders of magnitude, depending on the temperature of the molybdenum target.     

Plane-turns superconducting magnets: Option for fusion

A new concept for large size, complex geometry high field superconducting (SC) magnets has been proposed. According to the approach, a coil is comprised of plane helical turns with insulating layers between them. In this paper, the term superconducting plane-turns helical magnet or helicoid is often substituted by plane-turns magnet or plane-turns coil in order to avoid possible interpretation as the well-known fusion magnetic confinement scheme helical devices. The following advantages of these magnets over traditional ones are outlined for fusion applications: high bending stiffness, optimal current distribution, favorable high current design, and the possible utilization of brittle materials such as ceramics (HTc superconductors, insulators of high radiation tolerance). Some limitations resulting from hysteresis losses restrict the range of application by stationary mode magnetic systems. It is shown that these limitations aren't so severe for toroidal coils and that poloidal fields slightly affect operating characteristics, thus the design seems to be attractable for tokamaks. Brief theoretical and experimental foundation as well as some consideration on conceptual plane-turns SC coil for fusion are presented.     

Universal apparatus with a Co60 γ-ray source with an activity of 60,000 g-eq of Ra for simulating radiation-chemical apparatus,and investigations (the “K-60,000”)

The article describes a universal apparatus for radiation-chemical investigations with a Co⁶⁰ -ray source possessing an activity of about 60,000 g-eq of Ra. The design of the apparatus makes it possible to simulate radiation-chemical apparatus with powerful isotopic -ray sources of various configurations and dimensions: a cylindrical radiating element, a radiating element in the form of two plates, a radiating element in the form of a heat exchanger, and a radiating element in the form of one or more rods. The dosage rate (without taking into account the attenuation in the protective vessels) varies from250 r/sec in a volume of 36 liters to 3000 r/sec in a volume of 0.1 liter. The apparatus is designed for carrying out radiation-chemical investigations under practically any physicochemical parameters; it ensures the possibility of remote control and observations both of the experimental conditions and the processes taking place in the investigated systems during irradiation.The authors wish to express their thanks to V. I. vainshtein, M. A. Dembrovskii, and N. P. Syrkus, who took part in the discussionof individual problems of the design of the apparatus, and also to A. I. Dombrovskii, V. M. Kasatkin, A. V. Tatov, D. V. Yasinskii, I. A. Gromov, V. G. Ivanov, M. N. Demichev, V. V. Serebryakobaya, N. V. Troinov, and others, who took part in the construction and assembly of the apparatus.     

Methods for suppressing the longitudinal instability of a bunched beam with the help of landau damping

Conclusions The insertion of an additional accelerating system with multiplicity nq is desirable only in a synchrotron with a well-bunched beam, where the natural nonlinearity A ₀ ² is small.When the amplitude of the additional voltage is limited by the quantity nV_n/V_o1, there are two approximately equivalent schemes for switching on the harmonics nq (see Secs. 3 and 4), which permit obtaining an instability suppression factor of _max10/A _o ² with n_opt5/A_o.The efficiency of both schemes has been confirmed experimentally in ISR storage rings [1, 5], but there are no data for making quantitative comparisons of the experimental results with our calculations. At the same time switching on the harmonic n=2 in the PSB synchrotron without satisfying the condition (39) only increased the longitudinal instability of the beam [6].By raising significantly the amplitude of the additional voltage in the state of Sec. 3, which is equivalent to transferring to an acceleration multiplicity nq while keeping constant the number of bunches, it is possible to raise the instability suppression factor to _max 5/A _o ² with n_opt2.3/A_o[nV_n/V_o]^1/4.Translated from Atomnaya Énergiya, Vol. 62, No. 2, pp. 98–104, February, 1987.     

Connections between physics and economics for Tokamak fusion power plants

A simplified physics, engineering, and costing model of a tokamak fusion reactor is used to examine quantitatively the connection between physics performance and power-plant economics. The material contained herein was generated as part of a broader study of the economic, safety, and environmental impact of fusion based on a range of confinement schemes, fusion fuels, blanket/shield configurations, power-conversion schemes, and commercial end products. Only a DT-fuelled tokamak reactor that produces electricity through an intermediate heat exchange and a conventional thermal-electric conversion cycle is considered; a self-cooled lithium-metal blanket with vanadium-alloy structure, steel shield, and superconducting magnets is used for all cases studied. An optimistic extension of Troyon scaling is applied to a high-elongation ( = 2.5) and low-safety-factor (q =2.3) plasma with =0.1 and efficient (I P _CD =0.2 A/W) current drive. This 1200-MWe (net) power plant provides an economically competitive base case with which to compare other approaches to tokamak fusion power. The base case chosen for comparisons represents an optimistic extrapolation of present tokamak physics and technology. Troyon scaling with a coefficient B a/I equal to 0.04 is applied; the impact of an ad hoc but pessimistic scaling that diminished the Troyon coefficient with plasma elongation was also examined. Additionally, a constant current-drive efficiency, =nI R _T /P _CD =0.2 A/W, atT=10 keV plasma temperature is assumed; although representing an aggressive R&D target relative to present experience, the realization of bootstrap currents for the basecase, and especially for the second-stability-region tokamak, can significantly reduce this problem. The impact and reoptimization for a constant normalized current-drive efficiency, =nI R _T/P _CD, was also examined. Although the focus of this study has been the optimistic basecase tokamak, comparisons are made with tokamaks based on (a) operation in the second-stability region (=0.2, increased aspect ratio, reduced elongation), (b) super high-field but low-beta operation, (c) very low aspect ratio and highly elongated spherical torus, and (d) a direct application of the present database using a long-pulsed, low-beta tokamak. The economic impact of a range of base-case parameters and operating variables is examined, including current-drive efficiency, beta, stability limits, advanced magnets, economy of scale, blanket/shield lifetime, blanket thickness, and plant lead time. It is found that a range of tokamak options, relative to the optimistic base case selected for this study, may provide economically competitive power plants. Areas where physics and technology advances are needed to achieve this attractive end product are quantitively elucidated for all tokamak options considered.     

Ion beam propagation and focusing

Inertial confinement fusion with ion beams requires the efficient delivery of high energy (1 MJ), high power (100 TW) ion beams to a small fusion target. The propagation and focusing of such beams is the subject of this paper. Fundamental constraints on ion beam propagation and focusing are discussed, and ion beam propagation modes are categorized. For light ion fusion (LIF), large currents (2–33 MA) of moderate energy (3–50 MeV) ions of low atomic number (1A12) must be directed to a target of radius 1 cm. The development of pulsed power ion diodes for LIF is discussed, and the necessity for virtually complete charge neutralization during transport and focusing is emphasized. Fornear-term LIF experiments, the goal is to produce pellet ignition without the standoff needed for the ultimate reactor application. Ion diodes for use on Sandia National Laboratories Particle Beam Fusion Accelerators PBFA-I (2–4 MV, 1 MJ, 30 TW, operational) and PBFA-II (2–16 MV, 3.5 MJ, 100 TW, scheduled for operation in 1985) are discussed. Ion beam transport from these diodes to the pellet is examined in reference to the power brightness . While values of =2–5 TW/cm²/sr have been achieved to date, a value of 100 TW/cm²/sr is needed for breakeven. Research is now directed toward increasing , and means already exist (e.g., scaling to higher voltages, enhanced ion diode current densities, and bunching), which indicate that the required goal should be attainable. Forfar-term LIF applications, the goal is to produce net energy gain with standoff suitable for a reactor. This may be achieved by ion beam transport in preformed, current-carrying plasma channels. Channel transport research is discussed, including experiments with wire-initiated, wall-initiated, and laser-initiated discharge channels, all of which have demonstrated transport with high efficiency (50–100%). Alternate approaches to LIF are also discussed, including comoving electron beam schemes and a neutralized beam scheme. For heavy ion fusion (HIF), moderate currents (10 kA) of high energy (10 GeV) ions of high atomic number (A200) must be directed to a target of radius 0.3 cm. Conventional accelerator drivers for HIF are noted. For a baseline HIF reactor system, the optimum transport mode for low charge state beams is ballistic transport in near vacuum (10^–4–10^–3 Torr lithium), although a host of other possibilities exists. Development of transport modes suitable for higher charge state HIF beams may ultimately result in more economical HIF accelerator schemes. Alternate approaches to HIF are also discussed which involve collective effects accelerators. The status of the various ion beam transport and focusing modes for LIF and HIF are summarized, and the directions of future research are indicated.     

Fuel provision for nonbreeding deuterium-tritium fusion reactors

Nontritium-breeding D-T reactors have decisive advantages in minimum size, unit cost, variety of applications, and ease of heat removal over reactors using any other fusion cycle, and significant advantages in environmental and safety characteristics over breeding D-T reactors. Considerations of relative energy production demonstrate that the most favorable source of tritium for a widely deployed system of nontritium-breeding D-T reactors is the very large (10 GW thermal) semicatalyzed-deuterium (SCD), or sub-SCD reactor, where none of the escaping³He (> 95%) or tritium (< 25%) is reinjected for burn-up. Feasibility of the ignited SCD tokamak reactor requires spatially averaged betas of 15 to 20% with a magnetic field at the TF coils of 12–13 T.On leave from Dept. of Electronic Engineering, University of Tokyo, Tokyo, Japan.     

Measurement of neutron emission from Ti and Pd in pressurized D2 gas and D2O electrolysis cells

Experiments using high-efficiency neutron detectors have detected neutron emission from various forms of Pd and Ti metal in pressurized D₂ gas cells and D₂O electrolysis cells. Four independent neutron detectors based on³He gas tubes were used. Both random neutrons (0.05–0.2 n/s) and time-correlated neutron bursts (10–280 n) of 100-s duration were measured using time-correlation counting techniques. The majority of the neutron burst events occurred at –30°C as the samples were warming up from the liquid nitrogen temperature.     

Slowing down of fission neutrons by uranium-Water media

The spatial distribution of resonance neutrons (E = 1.46 ev) which results from the slowing down of U²³⁵ fission neutrons emitted by a point source is measured for three variations of a uranium-water lattice made of thick slugs (35 mm) of natural uranium enclosed in cadmium tubes. The absence of anisotropies in the distribution of slowed-down neutrons is demonstrated, and the values of determined.In conclusion the authors express their gratitude to Professor I. I. Gurevich for discussions of the results of this work, and to V. K. Makayin A. I. Maleev, V. I. Baranov, and B. V. Sokolov, who helped in performing the measurements.     

Nuclear fusion from crack-generated particle acceleration

Summary In summary, the high-voltages necessary to accelerate deuterons to energies sufficient to produce modest numbers (10⁴–10⁵/sec) of d-d neutrons appears to be possible as a result of cracking or fracture of the metal lattice in the cold fusion experiments.This mechanism requires neither massive electrons nor exotic nuclear reactions to explain the apparent cold fusion d-d neutron production results. Instead, it is possible that high voltage electrostatic fields, known to be associated with cracking, can reside across a crack gap long enough for the deuterons to be accelerated to sufficiently high energy to produce the d-d reactions. Interestingly, the electrostatic acceleration is quite similar to that of laboratory accelerators except for its submicron scale. Clearly, much work is still required to determine whether such a crack-generated acceleration mechanism, a quasi-particle mechanism, some combination of these, or some other, as yet unidentified mechanism is responsible for the nuclear effects seen in cold fusion experiments.Presented at the Workshop on Cold Fusion Phenomena, Sante Fe, New Mexico, May 23–25, 1989.