Fusion Reaction Products Research Articles

Analysis on the Effect of Nuclear Fusion Reaction Products in a Plasma Facing Material

Analysis on the Effect of Nuclear Fusion Reaction Products in a Plasma Facing Material

Fusion Nuclear Science Facility Candidates

To move to a fusion DEMO power plant after ITER, a Fusion Nuclear Science Facility (FNSF) is needed in addition to ITER and research in operating tokamaks and those under construction. The FNSF will enable research on how to utilize and deal with the products of fusion reactions, addressing such issues as how to extract the energy from neutrons and alpha particles into high-temperature process heat streams to be either used directly or converted to electricity, how to make tritium from the neutrons and lithium, how to deal with the effects of the neutrons on the blanket structures, and how to manage the first wall surface erosion caused by the alpha particle heat appearing as low-energy plasma fluxes to those surfaces. Two candidates for the FNSF are considered in this paper: normal and low aspect ratio copper magnet tokamaks. The methods of selecting optimum machine design points versus aspect ratio are fully presented. The two options are compared and contrasted; both options appear viable.

Paul Ion Trap as a Diagnostic for Plasma Focus

The plasma discharge contamination by high and low Z Impurities affect the rate of nuclear fusion reaction products, specially when light particles have to be confined. These impurities should be analyzed and can be fairly controlled. This paper reports on the development of a Paul ion trap with ion sources by impact electron ionization as a diagnostic for the 10 kJ Iranian sunshine plasma focus device. Preliminary results of the residual gas are analyzed and presented.

Application of SSNTDs for measurements of fusion reaction products in high-temperature plasma experiments

The paper describes the application of SSNTDs of the PM-355 type to diagnostics of reaction products emitted from high-temperature deuterium plasmas produced in Plasma Focus (PF) facilities. Acceleration processes occurring in plasma lead often to the generation of high-energy ion beams. Such beams induce nuclear reactions and contribute to the emission of fast neutrons, fusion protons and alpha particles from PF discharges with a deuterium gas. Ion measurements are of primary importance for understanding the mechanisms of the physical processes which drive the charged-particle acceleration. The main aim of the present studies was to perform measurements of spatial- and energy-distributions of fusion-reaction protons (about 3 MeV) within a PF facility. Results obtained from energy measurements were compared with the proton-energy spectra computed theoretically. The protons were measured by means of a set of ion pinhole cameras equipped with PM-355 detectors, which were placed at different angles relative to the electrode axis of the PF facility.

Ignition of a Deuterium Micro-Detonation with a Gigavolt Super Marx Generator

The Centurion–Halite experiment demonstrated the feasibility of igniting a deuterium–tritium micro-explosion with an energy of not more than a few megajoule, and the Mike test, the feasibility of a pure deuterium explosion with an energy of more than 106 MJ. In both cases the ignition energy was supplied by a fission bomb explosive. While an energy of a few megajoule, to be released in the time required of less than 10−9 s, can be supplied by lasers and intense particle beams, this is not enough to ignite a pure deuterium explosion. Because the deuterium–tritium reaction depends on the availability of lithium, the non-fission ignition of a pure deuterium fusion reaction would be highly desirable. It is shown that this goal can conceivably be reached with a “Super Marx Generator”, where a large number of “ordinary” Marx generators charge (magnetically insulated) fast high voltage capacitors of a second stage Marx generator, called a “Super Marx Generator”, ultimately reaching gigavolt potentials with an energy output in excess of 100 MJ. An intense 107 Ampere-GeV proton beam drawn from a “Super Marx Generator” can ignite a deuterium thermonuclear detonation wave in a compressed deuterium cylinder, where the strong magnetic field of the proton beam entraps the charged fusion reaction products inside the cylinder. In solving the stand-off problem, the stiffness of a GeV proton beam permits to place the deuterium target at a comparatively large distance from the wall of a cavity confining the deuterium micro-explosion.

Probing of incomplete fusion dynamics by spin-distribution measurement

Aiming to probe incomplete fusion dynamics in 16O + 169Tm system, spin-distributions of various reaction products populated via xn-, α/2αxn-channels have been measured at E≈5.6MeV/nucleon. Prompt γ-rays in coincidence with fast charged particles (Z=1,2) have been recorded to achieve the information about involved reaction processes on the basis of their experimentally observed spin-populations during de-excitation. The experimentally observed spin-distributions for direct-α-emitting channels (associated with incomplete fusion) have been found to be distinctly different than that observed for fusion–evaporation (complete fusion) channels. The mean value of driving input angular momenta associated with various direct-α/2αxn-channels have been found to be higher than that observed for fusion–evaporation xn/αxn-channels, and increases with direct-α-multiplicity in forward cone. Experimentally measured, normalized production yields of fusion–evaporation xn/αxn-channels have been found to be in good agreement with the predictions of theoretical model code PACE4. Further, in order to understand the feeding probability in both complete and incomplete fusion reaction products, an attempt has been made to generate feeding intensity profiles from spin-distribution data. It has been observed that the complete fusion products are strongly fed over a broad spin range, while incomplete fusion products are found to be less fed and/or the population of lower spin states are strongly hindered.

Towards optical spectroscopy of the element nobelium ( ${\sf Z }= \mathsf{102}$ ) in a buffer gas cell

For the investigation of the atomic level structure of heavy elements which can only be produced at on-line facilities such as GSI, a novel experimental procedure has been developed. It is based on Radiation Detected Resonance Ionization Spectroscopy (RADRIS) and can be applied to elements like nobelium produced at rates of a few ions per second. Fusion reaction products are separated from the primary beam by the velocity filter SHIP at GSI, stopped in a buffer gas cell, collected on a tantalum filament and then re-evaporated as atoms. The ions produced by resonance ionization with tunable laser beams are detected via their characteristic α decay. First on-line experiments on α-active 155 Yb, which is supposed to have an atomic level structure similar to nobelium, were performed. These test experiments focused on the optimization of the collection and re-evaporation process of the radioactive ions, the laser ionization efficiency and the detection via α decay. An overall efficiency for RADRIS of 0.8% with respect to the target production rate was measured. While further improvements of this efficiency are in progress it should already be sufficient for the search for atomic levels in nobelium.

Distribution function of fusion reaction products and entropy evolution

One of the outcomes of nuclear reactions is that reaction products have at birth distribution functions far from Maxwellian. What role do those distribution functions play in the evolution of the entropy of the system? The purpose of this work is to show the effect of the distribution functions of reactant and reaction products on the entropy of a system undergoing DD nuclear fusion reactions. This analysis is conducted with the help of the H-theorem, in the framework of kinetic theory. It will be found that at the onset of this reaction, generalized system entropy decreases markedly.

High spin studies of the Er and Tm isotopes around A= 166

Fusion and incomplete fusion evaporation channels were studied in the 7Li +164Dy reaction at the INFN Laboratory, Legnaro, Italy. The Tandem-XTU accelerator was used to accelerate a beam of 7Li ions to 55 MeV. The highly sensitive GASP γ-detector array coupled with the selectivity of the ISIS charged particle ΔE–E telescope array provided a powerful tool for studies of high spin states in the fusion and incomplete fusion reaction products. Rotational sequences in the Er and Tm isotopes around A = 166 have been observed and extended to higher spin states. Comparisons of the experimental data with the results of the cranked shell model give some insight into the configuration dependence of the crossing of the ground-state band with the aligned i13/2 two quasineutron configuration.

Power generation system using two models for an inertial confinement fusion reactor

In this study, the series cooling model and the parallel cooling model of inertial confinement fusion reactor were used as a heat source for driving the MHD/Gas Turbine combined power generation system. This reactor is designed with the first wall and the blanket, which are used to collect the products of fusion reactions (including X-ray, charged particles, and neutrons) and to convert the fusion energy into thermal energy. In the series cooling model, the coolant after being heated in the blanket is re-heated again in the first wall, therefore, > 2000 K working gas can be obtained. In the parallel cooling model, 1300-1700 K working gas was extracted from the blanket for driving the Gas Turbine cycle and high temperature 2000-2400 K working gas can be extracted from the first wall for driving the MHD cycle. The system using the series cooling model reached a highest plant efficiency of 58.34 per cent whereas the system using the parallel cooling model reached a highest plant efficiency of 57.49 per cent. It was found that the enthalpy extraction and the first wall output temperature both affected the fusion output power, therefore, the plant efficiency was greatly affected by these factors. With the increase of reactor output temperature, the plant efficiency increased, however, because of the temperature limitation of the Gas Turbine and blanket, an output temperature > 2400 K from reactor cannot be used.

Overview of University of Wisconsin Inertial-Electrostatic Confinement Fusion Research

In Inertial Electrostatic Confinement (IEC) devices, a voltage difference between concentric, nearly transparent spherical grids accelerates ions to fusion-relevant velocities. The University of Wisconsin (UW) operates two IEC devices: a cylindrical aluminum chamber and a spherical, water-cooled, stainless-steel chamber, with a power supply capable of 75 mA and 200 kV. The research program aims to generate fusion reaction products for various applications, including protons for creating radioisotopes for nuclear medicine and neutrons for detecting clandestine materials. Most IEC devices worldwide, including the UW devices, presently operate primarily in a pressure range (1-10 mtorr) that allows ions to make only a few passes through the core before they charge exchange and lose substantial energy or they collide with cathode grid wires. It is believed that fusion rates can be raised by operating at a pressure where neutral gas does not impede ion flow, and a helicon ion source has been developed to explore operation at pressures of ~0.05 mtorr. The UW IEC research group uses proton detectors, neutron detectors, residual gas analyzers, and spectroscopic diagnostics. New diagnostic techniques have also been developed, including eclipse disks to localize proton production and chordwires to estimate ion fluxes using power balance.

A gas cell for thermalizing, storing and transporting radioactive ions and atoms. Part II: On-line studies with a laser ion source

The application of a gas cell filled with noble gas (helium or argon) for thermalizing, storing and transporting trace radioactive ions and atoms has been studied in on-line conditions. Radioactive ions produced in nuclear reactions and stable energetic ions have been resonantly re-ionized by laser light via a two-step resonant process after thermalization and neutralization in high-pressure noble gas. The influence of the ion–electron density created by the projectile beam on the recombination of exotic ions has been investigated in different experimental conditions, including DC and RF electrical fields in the gas cell. Results for the laser ion source efficiency and selectivity for heavy-ion induced fusion reaction products are given. For the Rh isotopes the efficiency reaches up to 12%.

A gas cell for thermalizing, storing and transporting radioactive ions and atoms. Part II: On-line studies with a laser ion source

The application of a gas cell filled with noble gas (helium or argon) for thermalizing, storing and transporting trace radioactive ions and atoms has been studied in on-line conditions. Radioactive ions produced in nuclear reactions and stable energetic ions have been resonantly re-ionized by laser light via a two-step resonant process after thermalization and neutralization in high-pressure noble gas. The influence of the ion–electron density created by the projectile beam on the recombination of exotic ions has been investigated in different experimental conditions, including DC and RF electrical fields in the gas cell. Results for the laser ion source efficiency and selectivity for heavy-ion induced fusion reaction products are given. For the Rh isotopes the efficiency reaches up to 12%.

Conceptual design of beam-ion profile diagnostics for the DIII-D tokamak

Three diagnostic concepts that measure the radial profile of deuterium beam ions are assessed. One diagnostic exploits 3 MeV protons that are lost on their first orbit. Since beam-plasma reactions usually predominate in the discharges of interest, the beam-ion density profile can be inferred from the d-d fusion reaction profile. The relatively modest plasma current (∼1.6 MA) implies that a significant fraction of the charged d-d fusion reaction products are unconfined. The second diagnostic employs a neutron collimator. For this diagnostic, neutron scattering is a major concern. Both fusion product diagnostics are sensitive to uncertainties in the thermonuclear rate, so the anomalous beam-ion transport must exceed DB≳1.0 m2/s to be detectable. The third diagnostic employs an array of natural diamond detectors that is configured to measure the signal from beam ions that charge exchange with neutrals in a modulated heating beam. The sensitivity to uncertainties caused by pitch-angle scattering of the beam ions can be minimized by a prudent choice of detection angle. Because of attenuation of the escaping neutrals the effective resolution is DB∼0.5 m2/s.

Evaporation residue collection efficiencies and position spectra of the Dubna gas-filled recoil separator

The focal-plane position spectra and collection efficiencies of the Dubna gas-filled recoil separator at the U400 cyclotron used to separate evaporation residues of complete fusion reaction products are described. The separator consists of a 23°-dipole magnet and a quadrupole doublet and is filled with hydrogen at a pressure of about 1 Torr. After passing through the time-of-flight system, the separated evaporation residues are collected in a 120 mm×40 mm position-sensitive semiconductor detector at the focal plane. Depending on the asymmetry of the projectile, target combinations, the measured collection efficiencies were 3–45%, with suppression factors exceeding 10 15 and 10 4 for beam and target-like particles, respectively. The ANAMARI code that is used to determine the separator settings is described and its predictions for the evaporation residue position spectra and collection efficiencies are compared with experimental data.

Method of investigation of nuclear reactions in charge-nonsymmetrical muonic complexes

A method for experimental determination of the nuclear fusion rates in the dμ He molecules in the states with J=0 and J=1 ( J is the orbital moment of the system) and of the effective rate of transition between these states (rotational transition 1–0) is proposed. It is shown that information on the desired characteristics can be found from joint analysis of the time distribution and yield of products of nuclear fusion reactions in deuterium–helium muonic molecules and muonic X-ray obtained in experiments with the D 2 +He mixture at three (and more) appreciably different densities. The planned experiments with the D 2+ He mixture at the meson facility PSI (Switzerland) are optimized to gain more accurate information about the desired parameters on the assumption that different mechanisms for the 1–0 transition of the dμ He complex are realized.

Confined alpha particles near the plasma edge in tokamaks

The properties of classically confined high-energy alpha particles near the outer midplane of a tokamak torus are considered in order to provide the basic information required for theoretical studies of the superthermal ion cyclotron emission which has been observed in tokamak experiments. An analytical expression for the velocity distribution function of fusion reaction products has been derived, which generalizes previous results. The alpha-particle distribution function for test case data corresponding to typical parameters of the JET preliminary tritium experiment has been calculated using a three-dimensional Fokker-Planck code and it has been shown that this function can be well approximated by the derived analytical expression. The number of alpha particles produced in a pure deuterium plasma due to secondary fusion reactions has been evaluated. It is shown that, due to orbital effects, the local alpha-particle density in a deuterium plasma can be comparable to the density of protons which are produced directly by the DD reactions.

Excitation of Contained Modes by High Energy Nuclei and Correlated Cyclotron Emission

In experiments with fusing plasmas, enhanced radiation emission at the harmonics of the cyclotron frequency of fusion reaction products has been observed. A theory is presented that explains key features of these observations and indicates the possibility of extracting significant information about the fusion product population distribution, both in velocity space and over the plasma cross section. The considered model is consistent in particular with the fact that, in DT plasmas, the radiation peaks occur at frequencies corresponding to harmonics of the αparticles' cyclotron frequency Δ αevaluated at the outer edge of the plasma column, and that a transition to a “continuum” spectrum at high frequencies ( ω≳7 Δ α ) can be identified. In this model, the radiation is the result of the excitation of radially “contained” modes which are driven unstable by the fusion products. The modes considered to be responsible for the discrete part of the spectrum are spatially localized near the plasma edge. The radial containment, which is associated mainly with the inhomogeneity of the plasma density, is in fact a fundamental characteristic since only contained modes can grow out of a relatively weak mode–particle interaction and justify the detected emission power levels. The contained mode is a solution to a set of macroscopic equations, in which the electron motion is tied to that of the magnetic field (Hall effect). The growth rate has been evaluated considering the particle orbits in a toroidal confinement configuration and modelling the distribution function of the interacting particles with the energy at birth before slowing down occurs. The growth rate depends linearly on the α-particle density and can be larger than, or of the order of, the bounce frequency of the magnetically trapped α-particles, which can have a resonant interaction with the mode. According to the theoretical model presented, the discrete part of the observed spectrum of emission yields specific information about the trapped, energetic particles with large orbits that reach the edge of the plasma column, while the continuum spectrum can give information about the average density of high energy particles which have orbits well within the plasma column. The possibility to influence α-particle transport through coupling with externally applied modes having frequencies in the range considered is pointed out.

Focal plane detector of the Dubna gas-filled recoil separator

The focal plane detector of the Dubna gass-filled recoil separator has been developed to study fusion reaction products from heavy-ion-induced nuclear reactions in the region of heavy nuclei with Z > 104. It consists of a 12 strip position-sensitive silicon detector to measure the energy/position of implanted nuclides and decay products and two low-pressure proportional chambers to generate a TOF signal. Additional information on ΔE from the STOP chamber is stored to provide an opportunity to discriminate alpha decays to the ground state of daughter product from the ones accompanied by conversion electron emission. The detector was successfully applied for the nuclear reactions which led to the discovery of new nuclides with Z = 108, 110 ( A = 267, 273). An appropriate data acquisition system is described.

Antiproton Catalyzed Fusion Propulsion for Interplanetary Missions

Interplanetary trips using chemical propellants require years to complete. A recently completed study on an antiproton catalyzed fusion reaction propulsion system has shown that the specie c impulses that can be obtained are between 1500 s for a contained system to over 100,000 s for a system that directly uses the fusion reaction products. Thrust-to-weight ratios exceeding 1 can be sustained. This allows considerably shorter solar system travel times than conventional chemical propellants. Missions considered range from inner to outer solar system distances. A tradeoff can be made between reducing travel time and reducing initial mass in low Earth orbit. Missions to the inner planets can be shortened considerably for a given mass ratio, whereas missions to the outermost planets will be several weeks in duration.