A search for neutrons from fusion in a highly deuterated cooled palladium thin film

We have carried out an experiment to search for neutrons released from a thin film of Pd-10% Ir. A film of thickness 2000 Å was prepared by sputtering. The film was then cooled to 77 K and was charged with deuterons by low-energy ion implantation. Deuterium was incident on the film as neutral D and D₂ with a kinetic energy of 1000 eV. Paraffin was used as a neutron moderator and absorber, with a Nal detector to observe the 2.22-MeV -ray expected from neutron capture by hydrogen neuclei. The high local concentration of deuterons in the film could, in some fusion scenarios, have produced a high rate of deuterium fashion. If this happened, this implantation technique could form the basis of a viable fusion power generator. However, we observed no excess neutron production over background. We were also sensitive to 23.8-MeV -rays (from fusion producing⁴He) but observed no peak at this energy.     

Containment of plasma in a trap with combined magnetic field

The containing properties of an adiabatic trap with a magnetic field increasing in the longitudinal and radial directions are investigated. This field is obtained from a combination of the ordinary mirror field configuration (main field H0) and the field of a system of current-carrying conductors laid parallel to the axis of the trap (stabilizing field H). The conductors are placed uniformly in azimuth around the side walls. The trap is filled with plasma of density n10⁹–10¹⁰ cm^–3 and proton energy T_i5eV (T_e20 eV). The plasma lifetime is measured as a function of H. and the neutral gas pressure. From the results obtained, it is concluded that such combined fields ensure stable containment of the plasma, unbroken by magnetohydrodynamic instabilities [at any rate for = nI/(H²/8) 10^–4]. The stabilization of the instability is confirmed by analysis of the plasma oscillations for various values of H. The disintegration of the plasma is determined by the charge exchange of fast ions in the residual gas; the maximum containment time which can be achieved is 0.06 sec for p = 7.10^–9mmHg. A qualitative picture of the plasma density over the radius of the trap is obtained.Translated from Atomnaya Énergiya, Vol. 17, No. 5, pp. 366–375, November, 1964     

Experiments and nuclear measurements in search of cold fusion processes

This paper reports a collaborative effort of a team which formed at Los Alamos to investigate the announcement that cold fusion may be occurring in electrochemical cells using palladium cathodes and platinum anodes in a LiOD electrolyte. Four electrochemical cells were construced and operated for 3–5 weeks under various geometrical and electrical conditions. Nuclear diagnostic measurements included high and low resolution gamma-ray spectroscopy, integral neutron counting with well detectors and banks of³He tubes, and neutron spectroscopy withNE-213 scintillators. For one of the cells, the deuterium loading of the cathode was determined from resistance measurements to beD/Pd 0.8. No conclusive evidence was found for the production of neutrons or 2.223-MeV gammas above levels consistent with background. The results of the measurements of tritium levels in the cell electrolytes are also reported. Experiments to reproduce the observation of neutrons from high pressureTi-D ₂ gas experiments were also performed with negative results.Work supported by the U.S. Department of Energy under contract with the University of California.     

Impurity Transport in a Simulated Gas Target Divertor

Future generation fusion reactors and tokamaks will require dissipative divertors to handle the high particle and heat loads leaving the core plasma (100–400 MW/m² in ITER). A radiative divertor is proposed as a possible scenario, utilizing a hydrogen target gas to disperse the plasma momentum and trace impurity radiation to dissipate the plasma heat flux. Introducing an impurity into the target hydrogen gas enhances the radiative power loss but may lead to a significant impurity backflow to the main plasma. Thus, impurity flow control represents a crucial design concern. Such impurity flows are studied experimentally in this thesis. The PISCES-A linear plasma device (n 3 × 10¹⁹ m^–3, kT _e 20 eV) has been used to simulate a gas target divertor. To study the transport of impurities, a trace amount of impurity gas (i.e., neon and argon) is puffed near the target plate along with the hydrogen gas. Varying the hydrogen gas puffing rate permits us to study the effects of various background plasma conditions on the transport of impurities. A 1-1/2-D fluid code has been developed to solve the continuity and momentum equations for a neutral and singly ionized impurity in a hydrogen background plasma. The results indicate an axial reduction in the impurity concentration upstream from the impurity puffing source. Impurity entrainment is more effective for higher hydrogen target pressures (and for higher hydrogen plasma densities). However, if there is a reversal of the background plasma flow, impurity particles can propagate past the plasma flow reversal point and are then no longer entrained.     

Tritium Depth Profiling Study on Titanium Tritide Target for Generating 14-MeV Neutrons

In-situ measurements of the depth profiles of tritium in a titanium tritide target for generating 14-MeV neutrons have been made with the method of the ion beam analysis using the T(d, α)n nuclear reaction. The initial distribution of tritium in the unirradiated target has been observed to be nearly uniform over the depths. After the irradiation of 390-keV D₃ ⁺ ions at a temperature of about 10°C a dip has been found in the depth profile around the depth of the projected range of the ions. By the successive isochronal anneal-ings at temperatures below 130°C the tritium has been uniformly redistributed. The behavior of tritium in the target and the effectiveness of the depth profiling for evaluating the energy spectrum and the yield of source neutrons are discussed.     

D-T experiments on TFTR

Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, alpha confinement, alpha heating and possible alpha driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of 20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T/D density ratio of 1 and yielded a maximum fusion power of 9.2 MW. The fusion power density in the core of the plasma was 1.8 MW m^–3 approximating that expected in a D-T fusion reactor. In other experiments TFTR has produced 6.4 MJ of fusion energy in one pulse satisfying the original 1976 goal of producing 1 to 10 MJ of fusion energy per pulse. A TFTR plasma with T/D density ratio of 1 was found to have 20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass, A, of _E. The core ion temperature increased from 30 keV to 37 keV due to a 35% improvement of ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 keV to 10.6 keV can be attributed to electron heating by the alpha particles. At fusion power levels of 7.5 MW, fluctuations at the Toroidal Alfvén Eigenmode frequency were observed by the fluctuation diagnostics. However, no additional alpha loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.Work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.     

The high-density Z-pinch as a pulsed fusion neutron source for fusion nuclear technology and materials testing

The dense Z-pinch (DZP) is one of the earliest and simplest plasma heating and confinement schemes. Recent experimental advances based on plasma initiation from hair-like (10s m in radius) solid hydrogen filaments have so far not encountered the usually devastating MHD instabilities that plagued early DZP experimenters. These encouraging results along with the debut of a number of proof-of principle, high-current (1–2 MA in 10–100 ns) experiments have prompted consideration of the DZP as a pulsed source of DT fusion neutrons of sufficient strength (S _N 10¹⁹ n/s) to provide uncollided neutron fluxes in excess ofI _w = 5–10 MW/m² over test volumes of 10–30 liters or greater. While this neutron source would be pulsed (100s ns pulse widths, 10–100 Hz pulse rate), giving flux time compressions in the range 10⁵–10⁶, its simplicity, near-term feasibility, low cost, high-Q operation, and relevance to fusion systems thatmay provide a pulsed commercial end-product, e.g., inertial confinement or the DZP itself, together create the impetus for preliminary consideration as a neutron source for fusion nuclear technology and materials testings. The results of a preliminary parametric systems study (focusing primarily on physics issues), conceptual design, and cost vs. performance analyses are presented. The DZP promises an inexpensive and efficient means to provide pulsed DT neutrons at an average rate in excess of 10¹⁹ n/s, with neutron currents I_w10 MW/m² over volumes V_exp 30 liter using single-pulse technologies that differ little from those being used in present-day experiments.Work supported by U.S. DOE.     

Techniques for measuring the alpha-particle distribution in magnetically confined plasmas

Methods are proposed for measuring the alpha-particle distribution in magnetically confined fusion plasmas using neutral-atom doping beams, ultraviolet spectroscopy, and neutral particle detectors. In the first method, single charge exchange reactions, A⁰+He²⁺A⁺ +(He⁺)^*, are used to populate then=2 andn=3 levels of He⁺. The ultraviolet photons from the decaying excited states are Doppler shifted by 5–10 Å from those produced by the thermalized alpha-particle ash. In the second method, double charge exchange reactions, A⁰+He²⁺A²⁺+He⁰, enable fast neutralized alpha particles to escape from the plasma and be detected by neutral particle analyzers. These methods are distinguished from similar techniques of observing plasma impurities in that, in principle, they allow a determination of the dependence of the distribution function on energy and pitch angle, as well as on spatial position. Detector configurations are analyzed, count rates are estimated, and the detector feasibility is discussed. A preliminary analysis of the feasibility of the required neutral beams is presented, and exploratory experiments on existing devices are suggested.     

Neutral beam deposition in large,finite-beta noncircular tokamak plasmas

A parametric pencil beam model is introduced for describing the attenuation of an energetic neutral beam moving through a tokamak plasma. The nonnegligible effects of a finite beam cross-section and noncircular shifted plasma cross-sections are accounted for in a simple way by using a smoothing algorithm dependent linearly on beam radius and by including information on the plasma flux surface geometry explicitly. The model is bench-marked against more complete and more time-consuming two-dimensional Monte Carlo calculations for the case of a large D-shaped tokamak plasma with minor radiusa=120 cm and elongationb/a=1.6. Deposition profiles are compared for deuterium beam energies of 120–150 keV, central plasma densities of 8×10¹³ to 2×10¹⁴ cm^–3, and beam orientation ranging from perpendicular to tangential to the inside wall.     

Plasma jet deflection in magnetic fields

We investigated the motion of plasma jets in a quadripole magnetic field produced by four current conductors whose axial lines were bent through 90° (the curvature radius was 30 cm). The maximum strength of the magnetic field in the slit between the current conductors was 6 kOe. The plasma jet, which was produced by means of a coaxial gun, was injected along the axis of the magnetic system. The magnetic system was adequate for defecting the plasma jet, which had an initial velocity of 8×10⁶ cm/sec and a maximum concentration before deflection of 2×10¹⁵ cm^–3. The jet velocity was equal to 7×10⁶ cm/sec. In spite of the considerable loss of particles (due to the presence of slits in the magnetic system), the ion concentration in the jet beyond the turn attained 2×10¹⁴ cm^–3, while the over-all number of particles was as large as 10¹⁷.As a result of deflection, it was possible to eliminate completely the neutral gas accompanying the jet and to obtain virtually totally ionized plasma. The optimum value of the magnetic field's strength was 8 kOe.Translated from Atomnaya Énergiya, Vol. 19, No. 4, pp. 329–335, October, 1965     

Total cross sections of Re185 and Re187

A method is described, and results given, for measurements, made at the VVR-M reactor of the Institute of Physics of the Ukrainian Academy of Science, of the total neutron cross sections of the isotopes Re¹⁸⁵ and Re¹⁸⁷ in the resonance, thermal, and cold regions of the neutron spectrum. The cross section of these isotopes follow the 1/v law with good accuracy below 0.08 eV; however,the positive levels of Re¹⁸⁵ are responsible for only 56% of the total cross section in the thermal region, and those of Re¹⁸⁷ for only 3%. An analysis of the cross sections shows that the energy of the negative level in Re¹⁸⁷ closest to zero is 5 eV|e₀|10 eV; in Re¹⁸⁵, |E₀|10 eV.Translated from Atomnaya Énergiya, Vol. 19, No. 3, pp. 250–252, September, 1965     

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.     

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.     

Paramagnetic effect under the influence of high-frequency pressure and electron paramagnetic resonance in plasma

The interaction of uhf fields ( = 2· 10¹⁰ sec^–1) in a space resonator containing dense plasma (n 10¹³ – 10¹⁴ cm^–3) in a steady magnetic field was studied experimentally. Under the influence ofhf pressure a paramagnetic current arises in the plasma; the associated effect of an increase in the static magnetic field inside the plasma agrees closely with the calculated relation.For _H/ = 0.5 paramagnetic resonance of the electrons takes place; this leads to a sharp rise in plasma pressure p₀, up to =8p₀/H₀ ²0.2.Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 401–407, May, 1966.     

Ignition in a tokamak reactor with INTOR-like parameters

The requirements for ignition in a tokamak reactor with INTOR-like parameters were studied using a one-dimensional transport code. With empirical electron energy diffusivity _e , ignition was obtained with 60–75 MW of neutral beam injection at a volume average pressure ratio =4–5% under a variety of conditions. Changing _e gave ignition at the same if the plasma minor radius varied asa _e ^1/2 . The maximum impurity concentration which allows ignition was found to be comparable to that for the much simpler case of a homogeneous plasma with radiative losses only. In long pulse simulations with efficient helium pumping, the maximum toroidal field ripple which allowed ignition was 2.0% (peak-to-peak) at the plasma edge. Ignition was maintained with over 99% recycling of helium ash using 5% less than maximum ripple.     

Compact ignition test reactor (CITR)

Design considerations have been developed for a compact ignition test reactor (CITR). The objectives of this tokamak device are to achieve ignition, to study the characteristics of plasmas that are self-heated by alpha particles, and to investigate burn control. To achieve a compact design, the toroidal field magnet consists of copper-stainless steel plates to accommodate relatively high stresses; it is inertially cooled by liquid nitrogen. No neutron shielding is provided between the plasma and the toroidal field magnet. The flat-top of the toroidal field magnet is 10 s. Strong auxiliary heating is employed. In one design option, adiabatic compression in major radius is employed to reduce the neutral beam energy required for adequate penetration; thiscompression boosted design option has a horizontally elongated vacuum chamber; illustrative parameters are a compressed plasma witha=0.50 m, R=1.35 m,B _T =9.1 T, and a neutral beam power of 15 MW of 160 keVD ⁰ beams. A design option has also been developed for alarge bore device, which utilizes a circular vacuum chamber. Thelarge bore design provides increased margin and flexibility; both direct heating with RF or neutral beam injection and compression boosted startup are possible. The large bore design also facilitates the investigation of high-Q driven operation. Illustrative plasma parameters for full use of the large bore area=0.85 m,R=1.90 m, andB _T =7.5 T.     

A molecular dynamics study of diamond exposed to tritium bombardment for fusion applications

Diamond, with its low atomic number and high thermal conductivity, is being assessed as a possible plasma facing material within a fusion reactor. Molecular dynamics simulations using the AIREBO potential were performed simulating the exposure of diamond to a plasma in conditions similar to those of the divertor region of a tokamak. Diamond surfaces at temperatures of 300 and 600 K were bombarded with 15 eV tritium at a high flux (10²⁹ ions m⁻² s⁻¹). A layer-by-layer etching process was observed which, with the lack of any tritium diffusion though the remaining diamond structure, was responsible for limiting damage, and thus tritium retention, to the top 4-5 diamond layers. Analysis of this damaged region also showed a large amount of residual structure suggesting that bombardment below the physical sputtering threshold (∼30 eV) may not lead to amorphisation of the surface.     

Measurement of the Efficiency of a 6LiD Thermal-to-14 MeV Neutron Converter in the Experimental Channel of an IVV-2M Reactor

The results of measurements of the efficiency of a ⁶LiD thermal-to-fast neutron converter for neutrons from DT and ⁶LiT fusion reactions with energy 14 MeV in the experimental channel of an IVV-2M reactor are presented. The first experimental estimates of the conversion coefficients for the corresponding fusion reactions are obtained: K ^D 2.11·10^–4 and K ^Li 1.36·10^–4. The value found in this work for the total conversion coefficient 3.47·10^–4 is approximately 1.7 times greater than the previously measured value and about 20% greater than the maximum computed estimate for a ⁶LiD converter.An experimental apparatus with a ⁶LiD converter in an IVV-2M channel is an accessible, comparatively inexpensive, and unique (for now) source of 14 MeV neutrons that can provide continuous and approximately uniform irradiation of Ø4 × 20 cm samples by neutrons from DT and ⁶LiT fusion 2.7·10¹⁰ sec^–1·cm^–2 for a comparatively long time (500 h).     

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.