Tritium Ions Research Articles

Low-energy tritium ion erosion of graphite

Chemical erosion of pyrolytic graphite was measured over the temperature range 300–950K, using a mass-analyzed tritium ion beam. The T2+ beam was produced by cycling 10 Ci (1mg) of T2 gas through the ion source from source getter to pumping getter and back. The T2+ beam current was up to 0.66μA (∼1018T+/m2s) at energies of 50–500eV/T+. Hydrocarbon formation rates were measured in the residual gas using quadrupole mass spectroscopy. CxTy hydrocarbon formation yields were similar to those obtained for H+ and D+ (0.002–0.1). As with H+ and D+, the T+-induced yields at 200–250eV/T+ tend to peak at about 700–800K, with a shift to lower temperature and flatter distributions at lower ion energies.

Shape of Electrodes for High Performance of Inertial Electrostatic Confinement Fusion

Inertial electrostatic confinement (IEC) fusion is a scheme of producing deuterium, tritium, and helium-3 ions between the anode and the hollow cathode in the concentric sphere by glow discharge, accelerating the ions into the spherical center and giving rise to the fusion reactions between the accelerated ions or between the accelerated ions and the background neutrals. The current feed-through is connected to the cathode through the anode in order to apply the negative high potential. Some of accelerated ions directly bombard the feed-through as well as the cathode, and the ions, the orbits of which are deformed by lack of symmetry, hit the cathode after several bounce motions through it. The existence of the feed-through breaks the spherical symmetry of the device and shortens the lifetime of the accelerated ions. The hollow cathode also distorts a spherical potential near it. First, the effects of the structure of the spherical hollow cathode on the life are studied at various birth positions of the ions by numerically tracking the trajectory of ions in three dimensional spaces. Second, the effects of the shapes of the cathode and the anode on the life are investigated. The shapes of the cathode and the anode that assure a longer life are examined, and the virtual transparency of the cathode is numerically derived from the time dependent reduction of ions. It is revealed that the lifetime of accelerated ions becomes three times longer by deforming a hemisphere of the anode pierced by the feed-through into a hemi-ellipsoid. The results are useful in designing an anode and cathode to achieve high performance of an IEC fusion neutron source.

Design and simulation of ion optics for ion sources for production of singly charged ions

During the last 2 years different types of the singly charged ion sources were developed for FLNR (JINR) new projects such as Dubna radioactive ion beams, (Phase I and Phase II), the production of the tritium ion beam and the MASHA mass separator. The ion optics simulations for 2.45 GHz electron cyclotron resonance source, rf source, and the plasma ion source were performed. In this article the design and simulation results of the optics of new ion sources are presented. The results of simulation are compared with measurements obtained during the experiments.

Gas dynamic trap as high power 14 MeV neutron source

It is now widely recognized that further progress toward a commercial fusion reactor critically depends on the availability of low activated materials to be operated for many years in the fusion neutron environment without degradation of their properties. Therefore, high power neutron source (NS) for extensive material tests is in great demand. The realistic NS can be built on the basis of the gas dynamic trap (GDT) which is one of the simplest system for magnetic plasma confinement. GDT is an axisymmetric mirror machine of the Budker–Post type, but with a high mirror ratio ( R>10), and operated with warm and relatively dense plasma. Thus, due to frequent collisions, the plasma confined in a trap is very close to isotropic Maxwellian, and hence many instabilities are not excited and plasma behavior is similar to a classical one. It is proposed to use the oblique injection of neutral tritium and deuterium beams with an energy of the order of 100 keV into the GDT “warm” target plasma (electron temperature T e≥750 eV) to produce high intensity neutron flux. In this case, due to the ionization and charge-exchange collisions with plasma particles the energetic atoms will turn into ions confined in the trap. The axial density profile of these anisotropic energetic ions will be strongly inhomogeneous. Namely, the maximum of the fast ion density will be located in the vicinities of mirrors and the minimum—at the middle plane of the device. Thus, a strongly inhomogeneous fusion neutron flux, mostly generated in the fast deuterium–tritium (D–T) ion collisions will appear. GDT NS looks to be rather flexible system. It enables to construct the source stepwise, starting from rather moderate parameters. Increasing the testing zone length and neutral beam power one can increase both neutron flux and the flux density. Calculations show that even in the modest version of the NS with T e∼250 eV quite appreciable neutron flux density in the range of 0.2–0.3 MW/m 2 can be produced. At present, the maximum temperature about 130 eV is obtained in the experiments at the model GDT device at Budker INP. Further increase of the electron temperature in the device requires higher neutral beam power and now is considered to be straightforward.

Neutral particle analyzer/isotope separator for measurement of hydrogen isotope composition of JET plasmas

This article describes a neutral particle analyzer/isotope separator (ISEP) developed for measurement of the relative hydrogen isotope composition of Joint European Torus (JET) plasmas. The ISEP deployed on the JET can be regarded as a prototype of an instrument proposed for measurement of the spatial profile of the ratio of the density of deuterium and tritium ions in the plasma, nD(r)/nT(r), in the International Thermonuclear Experimental Reactor (ITER). The ISEP makes simultaneous measurements of the energy distribution of efflux of hydrogen isotope atoms (H, D, and T) from the plasma. From such measurements it is possible to deduce the radial profile of the relative hydrogen isotope ion composition of the plasma and radial transport of ions of one isotope across the plasma of another isotope species. The main elements of the ISEP are (a) use of a thin carbon foil for reionization of the incident atoms, thereby eliminating gas stripping cells and gas sources of conventional neutral particle analyzers (NPAs), (b) acceleration of secondary ions in order to access the regime of higher detection efficiency of the NPA and to better separate ion pulses from neutron/γ-ray induced pulses in scintillator detectors, (c) E‖B dispersion of the secondary ions in specially designed nonuniform magnetic and electric fields to provide focusing in the detector plane, increased throughput and greater contrast between neighboring isotopes, and (d) counting of energy and mass analyzed secondary ions using detectors consisting of thin [1⩽t (μm)⩽7] CsI(Tl) scintillators deposited directly on miniature thin window photomultiplier tubes mounted in vacuum. The ISEP has high contrast between atoms of neighboring masses (⩾103 for E≈5 keV and much greater at higher energies), and high detection efficiency (0.06⩽ε⩽0.83 for atoms of 5⩽ (keV)⩽150. ISEP detectors have very low sensitivity to neutrons and γ rays (⩽10−7 of ion sensitivity), making it feasible to use the ISEP in JET DT experiments without any shielding. Only a modest amount of neutron/γ-ray shielding would be required in the ITER for similar applications of the ISEP. The initial experiments on JET plasmas using the ISEP demonstrate well the capabilities of the instrument for measurement of the hydrogen isotope composition of the plasma and the energy distribution function of isotope ions.

Tritium permeation study through tungsten and nickel using pure tritium ion beam

Permeation behavior of tritium (T) implanted into tungsten and nickel has studied by using pure tritium ion beam. Tritium permeation characteristics of steady and transient states were obtained and were compared with the result of deuterium (D) under the same experimental conditions. It was concluded from the steady state results of T and D that the permeation was controlled by diffusion in implantation side – diffusion in permeation side process for tungsten and recombination at the implantation surface – diffusion in the permeation side process for nickel. Effective diffusivities were evaluated from the permeation behavior of pure T and D. Isotope effect on the diffusivity between D and T did not agree with the classical diffusion theory, but could be explained by a quantum statistical diffusion model for nickel. The results indicated that diffusivity of T could be larger than that of D in W and Ni, respectively.

Exchange of tritium implanted into oxide ceramics for protium by exposure to air vapors at room temperature

The exchange of tritium, implanted into an oxide ceramic with a pure tritium ion beam, for protium by exposure to normal air at room temperature has been measured in a collaboration experiment with the Tritium Laboratory group, JAERI. It is shown that the release of THO produced by the exchange H 2O+T→THO+H at the surface of the crystallites decreases monotonically with exposure time, while the release of TH gas increases in the beginning, reaches a maximum and decreases monotonically as the time increases. The latter behavior of TH gas release gives an important evidence for bulk recombination of H uptaken from the surface with T implanted. These results are discussed based on the one-way diffusion model proposed previously for the explanation of the D–H exchange experiment.

Tritium accumulation in structures of clay minerals

AbstractTritium accumulation in clay minerals (kaolinite, montmorillonite, palygorskite) was studied experimentally over a one year contact with tritiated water (initial activity 1.676x109 Bq/m3) under room conditions, and was compared to theoretical calculations. The amounts of tritium ions in bound water and structural hydroxyls were measured by the activity of water fractions released at characteristic temperatures determined on the basis of the mineral DTA patterns. Experiments showed that after a 400 day contact with tritiated water, tritium exchange rates (θ) were highest in palygorskite (θa = 0.42 in bound water and θs = 0.51 in the structure) compared to montmorillonite (θa = 0.15 and θs = 0.11, respectively) and kaolinite (θa = 0.34 and θs = 0.02, respectively). This could be due to different tritium concentrations in the solution near the bound-water layers, and also to certain features of the mineral structures, most of the kaolinite structural hydroxyls not interacting directly with bound HTO molecules.Tritium accumulation in these minerals, under room conditions, can be described by a relatively simple two-stage isotope exchange model in which tritium ions first migrate from the solution to the bound layers and then substitute the protons of the structural hydroxyls. Rate constants for both stages of this isotope exchange were calculated on the basis of the experimental data.

High-Resolution Cross-Section Measurements for Production of the 0.478-MeV Gamma Ray from the 9Be(n,xγ)7Li Reaction for Neutron Energies Between 12 and 200 MeV with Insight into the 10Be Level Scheme

Because of the low-energy threshold and relatively large cross section of the 9Be(n,2n) reaction, beryllium is a very attractive neutron multiplier for some fast-neutron systems, such as those used in the production of fusion energy. But, tritium is also produced when beryllium is irradiated with 14-MeV neutrons emitted from the fusion of deuterium and tritium ions. Among the two exit channels of the 9Be(n,t)7Li reaction of ˜14-MeV incident-neutron energy, the 9Be(n,t1γ)7Li channel also emits a 0.478-MeV gamma ray. The purpose of the present study is to measure the cross section for the 9Be(n,t1γ)7Li reaction and also that of the more general 9Be(n,xγ)7Li reaction with the production of the same 0.478-MeV gamma ray for incident-neutron energies from the 12-MeV threshold to 200 MeV. Because the 7Li levels excited above 0.478 MeV are unstable against particle emission, the study of the 9Be(n,t1γ)7Li reaction gives direct access to the cross section for the formation of 7Li* in its 0.478-MeV excited state. The few previous experimental data for this reaction are restricted to incident-neutron energies of ˜14 MeV with large discrepancies between the results. The present data are obtained with a BeO sample, using the pulsed source of high-energy neutrons of the Weapons Neutron Research Facility (WNR) at the Los Alamos Neutron Science Center (LANSCE). The 478-keV gamma rays emitted in 9Be(n,xγ)7Li reactions are detected with two high-resolution Ge detectors. The data thus obtained are presented and compared with previous data on the 9Be(n,t1γ)7Li and the 9Be(n,t)7Li reactions. Examination of the present data also provides insight into the 10Be level scheme.

First observation of pT fusion in JET tritium plasmas with ICRF heating of protons

High power ICRF heating of a hydrogen minority ion species in JET tritium plasmas has generated a total neutron rate that is about 40% larger than the 14 MeV neutron rate originating from fusion reactions between bulk tritium ions and deuterium minority ions. The T(p,n)3He fusion reaction, caused by ICRF accelerated protons, is identified as a source for producing the excess neutron emission. This reaction is endothermic and has a proton energy threshold of about 1 MeV and a peak cross-section at about 3.0 MeV. The presence of protons with such high energies is detected in gamma ray and high energy neutral particle analyser measurements and is also confirmed by ICRF modelling with the PION code. The fast proton energy content and the pT fusion reactivity as simulated by the PION code are compared with the experimental measurements when classical slowing down and confinement of ICRF accelerated protons are assumed in the simulations.

Tritium permeation behavior implanted into pure tungsten and its isotope effect

A first tritium permeation experiment with pure tungsten specimen, which was 25 μm thick, and annealed at 1273 K for 3 h, was successfully carried out using pure tritium ion beam. The deuterium permeation experiment was also carried out using the same tungsten specimen. The permeation of deuterium and tritium at steady state was found to be controlled by diffusion at implantation side and permeation side (DD regime). No significant isotope effect was observed on the steady-state permeation behavior between deuterium and tritium. On the other hand, the isotope effect on the effective diffusion coefficient in tungsten, derived from the analysis of transient permeation behavior, was observed between deuterium and tritium. The result indicates tritium has larger activation energy of effective diffusion than deuterium. It was not inconsistent with the reported isotope effects of diffusion coefficient for bcc metal, to which tungsten belongs.

Nondestructive measurement of surface tritium by β-ray induced X-ray spectrometry (BIXS)

Abstract Applicability of a newly developed β-ray induced X-ray spectrometry (BIXS) has been examined to measure nondestructively tritium retained on/in the graphite samples. Examination was carried out by using the graphite plates irradiated with tritium ions and an ALT-II limiter tile exposed to D-plasmas in TEXTOR. For the former samples, a sharp intense peak and a broad weak peak appeared clearly in the spectra; the former peak was attributed to the characteristic X-rays from argon used as a working gas, and the latter peak was assigned to the bremsstrahlung X-rays from sub-surface layers of graphite. On the other hand, for the latter sample, a rather weak characteristic X-ray peak was observed along with a diminutive bremsstrahlung X-ray peak. Although the intensities of those X-rays differed from spot to spot, the tritium levels retained on the limiter tile were determined to be 58–132 Bq / cm 2 . It was concluded, therefore, that valuable information on the amount and the distribution of tritium retained on/in the wall materials can be nondestructively obtained by using the BIXS.

Behavior of tungsten exposed to high fluences of low energy hydrogen isotopes

Tungsten is a candidate plasma facing material under investigation in a Sandia National Laboratories project conducted at Los Alamos National Laboratory. Samples of 99.95% tungsten provided by Plansee Aktiengesellschaft were exposed to 100 eV deuterium and tritium ions at a range of fluxes from 2.3×10 17 to 1.3×10 18 ions/ cm 2 s for one hour at 623 K in the tritium plasma experiment. The samples were outgassed to determine the amount of retained hydrogen isotopes. The retention scaled at slightly greater than the square root of the fluence. The fractional retention was on the order of 10 −5. The data from these experiments were combined with previous results to construct a comprehensive model of the migration and retention behavior for hydrogen in tungsten. A second set of experiments involved exposing 99.95% tungsten foils provided by ÆSAR to 100 eV deuterons at a flux of 6×10 17 D/ cm 2 s for 30 min at 423 and 373 K. Scanning Electron Microscopy analysis was performed on the samples to determine the effects of the plasma exposure. Unannealed samples revealed extensive blistering with many blister caps removed. Samples annealed to 1473 K showed minor blistering, and samples annealed to 1273 K showed no blistering. The SEM analysis was used in conjunction with the retention results to understand the role of annealing and defects in trapping within the tungsten.

Tritium depth profiling by AMS in carbon samples from fusion experiments

Tritium depth profiling measurements by accelerator mass spectrometry have been performed at a facility installed at the Rossendorf 3 MV Tandetron. In order to achieve an uniform erosion at the target surface inside of a commercial Cs ion sputtering source and to avoid edge effects, the samples were mechanically scanned inside of a commercial Cs sputter ion source. The sputtered negative ions were mass analysed by the injection magnet of the Tandetron. The tritium ions are counted after the acceleration with semiconductor detectors. Depth profiles have been measured for carbon samples which had been exposed to the plasma at the first wall of the Garching fusion experiment ASDEX-Upgrade and from the European fusion experiment JET, Culham/UK. A dedicated AMS facility with an air-insulated 100 kV tandem accelerator for depth profiling measurements at samples with high tritium concentration is under construction. First results of test operation are presented.

From 3He@C60 to 3H@C60: Hot-Atom Incorporation of Tritium in C60

The introduction of tritium into the cavity of C60 using hot-atom chemistry was studied. Neutron irradiation of 3He in 3He@C60 produced tritium ions and atoms which enter the C60. 3H@C60 was detected with a scintillation counter. The Bingel reaction was carried out on this material under conditions so that the monoadduct formed predominantly, and the products were probed for tritium activity. Analysis with 3He NMR gave a peak with the characteristic 3He shift for the malonate product. The product fractions gave only 33% of the original activity; most was recovered in the unreacted C60 portion. No reaction was observed between C60 and the stable radical di-tert-butylnitroxide; all tritium activity was recovered in the C60 peak. These results suggest similarities in properties between 3H@C60 and pure C60, implying that the tritium exists as a free atom inside the molecule.

Tritium Conductivity and Isotope Effect in Proton‐Conducting Perovskites

The tritium ion conductivities of and have been measured by ac impedance analysis. The high tritium conductivity of these perovskites could potentially lead to their application as an electrochemical membrane for the recovery of tritium from tritiated gas streams. The conductivities of these perovskites, along with , were also measured in hydrogen‐ and deuterium‐containing atmospheres to illustrate the isotope effect. For the strontium zirconate and barium cerate samples, the impedance plot consists of two clearly resolved arcs, a bulk and a grain boundary arc, in the temperature range 50–350°C. However, for the strontium cerate sample, the clear resolution of the bulk conductivity was not possible and only the total conductivity was measurable. Thus, the isotope effect was clearly established only for the strontium zirconate and barium cerate samples. The decrease in bulk conductivity with increasing isotope mass was found to be a result of an increase in the activation energy for conduction accompanied by a decrease in the pre‐exponential factor. Since the concentration of the mobile species (H+, D+, or T+) should remain relatively constant at T < 350°C, this increase in activation energy is directly attributable to the increased activation energy for the isotope mobility. © 1999 The Electrochemical Society. All rights reserved.

Ballistic Bunching of Fast Ions in a Mirror Trap

The fast ions produced inside a mirror trap by neutral beam injection could form periodic short-lived density peaks near a turning point if the injection energy is properly modulated in time. Achievable parameters of thus formed fast ion bunches are analyzed in this paper. The theory is illustrated by estimates for the neutron source based on a gas-dynamic trap. The bunching of deuterium and tritium ions can produce periodic short bursts of neutron radiation with the intensity 1.5 times higher than the average level. The modulation of the neutron flux could extend the field of application for the neutron source. Also, the bunching could serve as a precise plasma diagnostics in mirror traps.

A Plasma Neutron Source with an Electromagnetic Trap as the Base

Consideration is given to the possibility of creating a plasma neutron source based on the electromagnetic trap with a multipole magnetic field configuration. The number of magnetic slits is reduced down to two axial holes, through which high-energy electrons are injected. The deuterium plasma target of 2·1014 cm−3 density is formed by electronic ionization of deuterium arriving at the trap. Tritium ions are produced on the edge of the potential well and are then accelerated by the electric space-charge field of electrons. With a tritium rate of 10−4 g/s the source is capable to produce up to 5·1018 n/s with a fluence of 2·1014 n/cm2·s on the surface of specimens under irradiation.

Broadening of the particle resonance drift trajectory and tritium injection into a fusion reactor with an I=3 helical winding

Two fusion reactor problems, removal of helium ash and fuel (tritium) injection, can be solved using the concept of “drift island motion.” The motion of a drift island is an indicator of the broadening of the resonant trajectory of a charged particle guiding center. This trajectory broadening occurs if two conditions are satisfied. First, the drift pitch angle of the particle is equal to the resonance values i*=n/m, where n and m are the “wave numbers” of the perturbing magnetic field. Second, the drift pitch angle i*=n/m “moves” over the plasma cross section as the particle moves. This displacement is caused by a slow change in the helical magnetic field with time as the particle moves. It is shown that this effect may occur in a fusion reactor with an l=3 helical winding and may be used for tritium ion injection.

Modelling of tritium permeation through beryllium as plasma facing material

Due to a number of technological properties and, first of all, to a low atomic number, beryllium will be used as plasma facing material in ITER. Tritium control, including both the permeation through and inventory in the beryllium, is of great importance for the safety of the device. Experimental data have shown that, under ITER-like plasma conditions, the plasma facing surfaces of the beryllium develop high porosity (bubbles) and become saturated with bubbles, leading to a strong uptake of tritium and deuterium ions almost independent of the incident flux. At fluxes typical of ITER, surface erosion of beryllium should be also taken into account. A computational model has been used with the computer code TMAP4 to reproduce the available experimental data concerning hydrogen ion implantation in beryllium. The results described in this paper refer to the first wall of the European Helium Cooled Pebble Bed Blanket (HCPB) Test Blanket Module (TBM-I).