Fast Deuterons Research Articles

Energy Transformations in Column of Plasma-Focus Discharges With Megaampere Currents

Energy transformations are estimated from experimental results obtained on the PF-1000 plasma focus facility operated with a deuterium gas filling and maximum current of 2 MA, which enabled the neutron yield of >; 1011 to be obtained. Use was made of the laser interferometry images and the recorded signals of hard X-rays (HXRs) and neutrons, as well as voltage, current, and current-derivative waveforms. The calculations of the inductance, derivative of inductance, and resistance of the current sheath enabled the evaluation of energy delivered to the plasma. It was estimated that, during the intensive pulses of the HXRs and neutrons, energy of 3-11 kJ is delivered to the plasma column probably through an anomalous resistance at the time closely before and during pulses of HXR and neutron production. A predominant portion of this energy is effectively used for the acceleration of fast deuterons capable of producing fusion neutrons.

Fusion Generated Fast Particles by Laser Impact on Ultra-Dense Deuterium: Rapid Variation with Laser Intensity

Nuclear fusion D+D processes are studied by nanosecond pulsed laser interaction with ultra-dense deuterium. This material has a density of 1029 cm−3 as shown in several previous publications. Laser power is <2 W (0.2 J pulses) and laser intensity is <1014 W cm−2 in the 5–10 μm wide beam waist. Particle detection by time-of-flight energy analysis with plastic scintillators is used. Metal foils in the particle flux to the detector remove slow ions, and make it possible to convert and count particles with energy well above 1 MeV. The variation of the signal of MeV particles from D+D fusion is measured as a function of laser power. At relatively weak laser-emitter interaction, the particle signal from the laser focus varies as the square of the laser power. This indicates collisions in the ultra-dense deuterium of two fast deuterons released by Coulomb explosions. During experiments with stronger laser-emitter interaction, the signal varies approximately as the sixth power of the laser power, indicating a plasma process. At least 2 × 106 particles are created by each laser pulse at the maximum intensity used. Our results indicate break-even in fusion at a laser pulse energy of 1 J with the same focusing, in approximate agreement with theoretical results for ignition conditions in ultra-dense deuterium. Radiation loss at high temperature will however require higher laser energy at break-even.

Experimental studies of radiation resistance of boron nitride, C2C ceramics Al2O3 and carbon–fiber composites using a PF-1000 plasma-focus device

This paper reports on experiments undertaken to compare the radiation resistance of two types of ceramics, boron nitride (BN) and pure alumina (Al2O3), which are used in a TAEA antenna coil installed in the MAST spherical tokamak. Samples of the investigated materials (bulk BN and a 20 μm film of Al2O3 on Al substrate) were exposed on the axis of the plasma-focus PF-1000 device, which can emit intense streams of hot plasma (v≈107 cm s−1 and Npl≈1018 cm−3) and fast deuteron beams (Ei≈100 keV). The most powerful plasma-ion pulse lasted 0.2–1.0 μs and its intensity decayed in about 100 μs. The irradiation process was diagnosed using fast optical cameras, laser interferometry and optical spectrometry. Experiments were performed at power flux densities equal to 109–1010 W cm−2 or 108–109 W cm−2 during the most powerful stage of the interaction process. The irradiated specimens were investigated by means of optical microscopy and x-ray structure analysis (XRSA). It was shown that at 1010 W cm−2 pulses the Al2O3 coating was completely evaporated, whereas a surface of the BN sample became smoother than in the virgin one. A direct comparison of both samples after the action of 108 W cm−2 pulses demonstrated a wave-like structure (more distinct on Al2O3). Weighing of these samples showed, however, that the evaporation of BN was about two times stronger than that of Al2O3 in spite of the lower irradiation flux; the XRSA showed no evidence of cracking of Al2O3 after these pulses. The insulation properties of Al2O3 did not decline, and the Al2O3 coating may be potentially more beneficial, provided that it is kept below its melting point. Characteristic features of damages of a material based on the carbon–fiber composite with additions of silicium carbide (SiC; 8–40% volumetric) were also investigated. It was found that at q=109 W cm−2, the surface erosion is associated with sputtering and evaporation. The degree of this erosion depends on the fibers’ orientation in relation to the direction of the plasma-ion streams, and on the percentage of the SiC admixture.

Results of Predictive Fokker–Planck Modelling of NBI Deuterons in ITER

First an analytical formalism is presented for calculating the source distribution of ions generated by neutral beam injection (NBI) in tokamak plasmas. A general NBI ion source term, applicable to studies in the phase space up to 6 dimensions, is provided for neutral beams with finite thickness and divergence. Further, using this source term for the envisaged NBI in ITER, we carry out 3D Fokker–Planck modelling of the steady-state deuteron distribution function of NBI produced fast deuterons relaxing on bulk plasma components. For two basic ITER scenarios we demonstrate the poloidal profiles of the beam deuteron density, of the NBI generated current as well as of the NBI power deposition to bulk electrons and ions. Further, we evaluate the capability of gamma and NPA diagnostics of NBI ions in ITER and demonstrate the sensitivity of the distributions of NBI generated ions to different ITER operation scenarios.

Spontaneous Transformation in the Pinched Column of the Plasma Focus

The laser interferometry and X-ray diagnostic studies were performed within the PF-1000 facility operated with the maximum current of 2 MA and the deuterium gas filling (ensuring neutron yield above ). At this current, the plasmoidal, helical and toroidal structures were formed inside the plasma column. Some of them penetrated the column surface and later on were dissolved inside the dense plasma column. The period of their life was from a few tens to hundreds of nanoseconds and a plasma density was higher than in neighbor regions. It could be explained as a result of the plasma pinching by a magnetic field originating from the internal currents. Hard X-rays and fusion neutrons were produced during four different phases of plasma column transformations, i.e., in the period of the formation of a dense plasmoid, in the period of an escape of the plasma from the region between the dense structure and anode, during the interruption of the constriction, and during the integration of a “plasma lobule” with the pinch column. Fast electrons and deuterons were probably accelerated at the same region, during the same period of explosions of the plasma structures with a density ranging above . The plasma evolution could be explained by a spontaneous transformation of azimutal and poloidal components of magnetic fields. The poloidal component could be self-generated during the implosion of the current sheath.

Efficient production of 100 keV deuterons in deuterium gas puff Z-pinches at 2 MA current

Deuterium gas puff experiments were carried out on the S-300 Z-pinch at the Kurchatov Institute in Moscow. Gas puffs imploded onto the axis before a current peak at about 100 ns. Fusion neutrons were generated after the gas puff implosion during global expansion of a plasma column. Neutron emission lasted on average 35 ± 5 ns (full width half maximum, FWHM). In the downstream direction (on the Z-pinch axis behind the cathode), a mean neutron energy was 2.6 ± 0.1 MeV. Side-on neutron energy spectra peaked at 2.40 ± 0.05 MeV with about 600 ± 150 keV FWHM. A broad width of side-on neutron spectra implied a high radial component of deuteron velocities. An average kinetic energy of fast deuterons, which produced fusion neutrons, was 150 keV. A peak neutron yield reached a value of 6 × 1010 on a current level of 1.5 MA. It was by one order higher in comparison with other deuterated loads used on the same current generator. On the basis of experimental observations, we concluded that a total energy of deuterons accelerated to fusion energies was above 1.5 kJ. It is more than 15% of the energy input into a plasma. Therefore gas puff Z-pinches seem to be not only powerful sources of x-ray radiation but also efficient sources of 100 keV deuterons. Such a result is consistent with high neutron yields observed on the Angara Z-pinch and plasma foci with similar currents.

Laser-induced variable pulse-power TOF-MS and neutral time-of-flight studies of ultradense deuterium

The ultradense atomic deuterium material named D(−1) is conveniently studied by laser-induced Coulomb explosion methods. A well-defined high kinetic energy release (KER) from this material was first reported in Badiei et al (2009 Int. J. Hydrog. Energy34 487) and a two-detector setup was used to prove the high KER and the complex fragmentation patterns in Badiei et al (2009 Int. J. Mass Spectrom. 282 70). The common KER is 630 ±30 eV, which corresponds to an interatomic distance D–D of 2.3 ±0.1 pm. In both ion and neutral time-of-flight (TOF) measurement, two similar detectors at widely different flight distances prove that atomic particles are observed. New results on neutral TOF spectra are now reported for the material D(−1). It is shown that density changes of D(−1) are coupled to similar changes in ordinary dense D(1), and it is proposed that these two forms of dense deuterium are rapidly transformed into each other. The TOF-MS signal dependence on the intensity of the laser is studied in detail. The fast deuteron intensity is independent of the laser power over a large range, which suggests that D(−1) is a superfluid with long-range efficient transport of excitation energy or particles.

Measurements of fast deuterons from plasma accelerator by means of PM-355 track detectors

This paper reports on studies of fast ions (mostly deuterons) emitted from an RPI (Rod-Plasma-Injector) plasma accelerator. The first aim was the verification of applicability of PM-355 track detectors for dosimetry of lower-energy (<200 KeV) deuterons. The second aim was information about energy spectra of deuterons from RPI-IBIS device in different operational modes. Mass- and energy spectra of ions were investigated with a Thomson-analyzer and PM-355 detectors. On the recorded deuteron-parabolas we chose points, and from numbers of tracks we determined the deuteron energy distribution. In the slow-mode the energy distribution peak was observed at about 40 keV, while the maximum energy amounted to about 150 keV. Those measurements confirmed an influence of the initial gas-conditions on energy distributions of the deuteron streams. The results are of importance for plasma-physics and applications. Another result was the confirmation that PM-355 detectors might be used for accurate measurements of low-energy (<200 keV) deuterons.

Neutron Production at the Small Plasma-Focus Device With Antianode

Neutrons from deuteron-deuteron fusion reactions were used for the study of pinch dynamics in a modified small plasma-focus device at a current peak of 200 kA. In front of the inner electrode (anode), an antielectrode was placed. Neutron yield reached 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> - 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> per shot. The time-resolved neutron signals were registered with two scintillation detectors positioned end-on and side-on at the same distance of 150 cm from the interelectrode gap. They enabled the comparison of difference in energies and estimation of directions of fast deuterons producing neutrons. The XUV frames imaged the pinch configuration at the moment of X-ray and neutron emission and differed in shots with high and low neutron yields. Interferograms enabled the evaluation of distribution of plasma density. The presence of the antianode decreased the neutron yield and influenced the distribution of the plasma density in front of the anode.

Neutron Energy Distribution Function Reconstructed From Time-of-Flight Signals in Deuterium Gas-Puff $Z$-Pinch

The implosion of a solid deuterium gas-puff Z-pinch was studied on the S-300 pulsed power generator [A. S. Chernenko, , Proceedings of 11th Int. Conf. on High Power Particle Beams, 154 (1996)]. The peak neutron yield above 1010 was achieved on the current level of 2 MA. The fusion neutrons were generated at about 150 ns after the current onset, i.e., during the stagnation and at the beginning of the expansion of a plasma column. The neutron emission lasted on average 25 ns. The neutron energy distribution function was reconstructed from 12 neutron time-of-flight signals by the Monte Carlo simulation. The side-on neutron energy spectra peaked at 2.42 plusmn 0.04 MeV with about 450-keV FWHM. In the downstream direction (i.e., the direction of the current flow from the anode toward the cathode), the peak neutron energy and the width of a neutron spectrum were 2.6 plusmn 0.1 MeV and 400 keV, respectively. The average kinetic energy of fast deuterons, which produced fusion neutrons, was about 100 keV. The generalized beam-target model probably fits best to the obtained experimental data.

Measurement of thepn→dK+K−total cross section close to threshold

Measurements of the pd{yields}p{sub sp}dK{sup +}K{sup -} reaction, where p{sub sp} is a spectator proton, have been undertaken at the Cooler Synchrotron COSY-Juelich by detecting a fast deuteron in coincidence with a K{sup +}K{sup -} pair in the ANKE facility. Although the proton beam energy was fixed, the moving target neutron allowed values of the nonresonant quasifree pn{yields}dK{sup +}K{sup -} total cross section to be deduced up to an excess energy {epsilon}{approx_equal}100 MeV. Evidence is found for the effects of K{sup -}d and KK final state interactions. The comparison of these data with those of pp{yields}ppK{sup +}K{sup -} and pp{yields}dK{sup +}K{sup 0} shows that all the total cross sections are very similar in magnitude.

Determination of Deuteron Energy Distribution From Neutron Diagnostics in a Plasma-Focus Device

Fast neutrons from deuteron-deuteron fusion reactions were used for a study of fast deuterons in the PF-1000 plasma-focus device. The energy spectrum of neutrons was determined by the time-of-flight method using ten scintillation detectors positioned downstream, upstream, and side-on the experimental facility. Neutron energy-distribution functions enabled the determination of axial and radial components of energy of deuterons producing the fusion neutrons, as well as a rough evaluation of the total energy distribution of all fast deuterons in the pinch. It was found that the total deuteron energy-distribution function decreases with the deuteron energy more slowly than the tail of the Maxwellian distribution for 1-2-keV deuterons.

Comparison of collective Thomson scattering signals due to fast ions in ITER scenarios with fusion and auxiliary heating

Auxiliary heating such as neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH) will accelerate ions in ITER up to energies in the MeV range, i.e. energies which are also typical for alpha particles. Fast ions of any of these populations will elevate the collective Thomson scattering (CTS) signal for the proposed CTS diagnostic in ITER. It is of interest to determine the contributions of these fast ion populations to the CTS signal for large Doppler shifts of the scattered radiation since conclusions can mostly be drawn for the dominant contributor. In this study, distribution functions of fast ions generated by NBI and ICRH are calculated for a steady-state ITER burning plasma equilibrium with the ASCOT and PION codes, respectively. The parameters for the auxiliary heating systems correspond to the design currently foreseen for ITER. The geometry of the CTS system for ITER is chosen such that near perpendicular and near parallel velocity components are resolved. In the investigated ICRH scenario, waves at 50 MHz resonate with tritium at the second harmonic off-axis on the low field side. Effects of a minority heating scheme with 3He are also considered. CTS scattering functions for fast deuterons, fast tritons, fast 3He and the fusion born alphas are presented, revealing that fusion alphas dominate the measurable signal by an order of magnitude or more in the Doppler shift frequency ranges typical for fast ions. Hence the observable CTS signal can mostly be attributed to the alpha population in these frequency ranges. The exceptions are limited regions in space with some non-negligible signal due to beam ions or fast 3He which give rise to about 30% and 10–20% of the CTS signal, respectively. In turn, the dominance of the alpha contribution implies that the effects of other fast ion contributions will be difficult to observe by CTS.

Neutron emission generated during wire array Z-pinch implosion onto deuterated fiber

The implosion of both cylindrical and conical wire arrays onto a deuterated polyethylene fiber was studied on the S-300 pulsed power generator [A. S. Chernenko et al., Proceedings of the 11th International Conference on High Power Particle Beams (Academy of Science of Czech Republic, Prague, 1996), p. 154]. Neutron measurements were used to obtain information about acceleration of fast deuterons. An average neutron yield approached 109 on the current level of 2MA. In the case of conical wire arrays, side-on neutron energy spectra peaked at 2.48±0.05MeV with 450±100keV full width at half-maximum. In the downstream direction, the peak neutron energy and the width of a neutron spectrum were 2.65±0.10MeV and 350±100keV, respectively. The total number of fast deuterons was 1015 and their average kinetic energy was about 150keV. Most of the deuterons were directed toward the cathode. The broad width of neutron spectra in the side-on direction implied a high radial component of deuteron velocity. With regard to the emission time, neutron pulses temporally correlated with hard x rays and also with measured voltage. The neutron emission lasted on average 30±5ns and it was observed during the stagnation and at the beginning of the expansion of a plasma column. At this moment, the plasma impedance reached 0.2–0.4Ω. In the post-stagnation phase, this value was formed significantly by enhanced plasma resistance. Similar experimental results were observed also with cylindrical wire arrays imploding onto a deuterated fiber.

Generation of neutrons at the relaxation of fast deuterons in deuterium matter

We analyze the fusion process involving two deuterium nuclei in the case of deceleration of a fast deuteron with an energy of approximately 100 keV located in a deuterium target. We calculate the probability ω fus(e) of generating a neutron by a fast deuteron with an initial kinetic energy e during its deceleration. The mean free path of fast deuterons with respect to their relaxation is found for various deuterium targets. The data are analyzed for neutron generation in deuterium cluster beams under laser irradiation. The method of neutron generation in the collision of two deuterium cluster beams is suggested.

Precision Measurement of the Quasifreepn→dϕReaction Close to Threshold

The quasifree $pn\ensuremath{\rightarrow}d\ensuremath{\phi}$ reaction has been studied at the Cooler Synchrotron COSY---J\"ulich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the ${K}^{+}{K}^{\ensuremath{-}}$ decay of the $\ensuremath{\phi}$ meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with $s$-wave production, the kaon angular distributions show the presence of $p$ waves at quite a low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the $\ensuremath{\eta}$ meson.

Time delay of the hard X-ray and neutron emission at PF 1000 facility

The PF 1000 plasma focus device with deuterium as filling gas is used for the study of hard X-rays and neutrons (originated from D-D fusion reactions). The time of generation and energy distribution of neutrons were determined using the time-of-flight method and MC simulations. The hard X-ray and neutron signals have usually two pulses: the first at the minimum of current derivative and the second 120 ÷ 170 ns later. An experimentally observed asymmetry of neutron pulses detected with scintillation detectors in axial z-direction downstream and upstream is explored by simple model in which each of both neutron pulses is decomposed into two components: the asymmetry one with energy above 2.45 MeV downstream and the symmetry one with the maximum of 2.45 MeV. In this article we describe in detail the shot No. 5566. The asymmetry component has energy downstream 2.55 ÷ 2.85 MeV (the first peak) or/and 2.70 ÷ 3.00 MeV (the second peak). The symmetric component in the energy range 2.2 ÷ 2.7 MeV is generated a few tens ns after the asymmetric one and it contains a lower part 25 ÷ 35 % of neutrons. In this presented shot the onset of neutrons was observed before the onset of hard X-rays. This fact declares the possibility of acceleration of a fraction of the fast energy deuterons before the fast electrons.

Formation and role of filaments in high-current discharges of the pinch type

The paper concerns distinct current filaments which appear inside plasma layers and columns produced by high-current pulse discharges of the Z-pinch and Plasma-Focus (PF) type. Results obtained previously, e. g. pictures taken with high-speed cameras, soft X-ray pinhole images, measurements of angular distributions of fast deuterons, images of so-called hot-spots inside the pinch column etc., have been reviewed and explained on the basis of the filamentary model. For the first time results of the measurements of fusion-produced protons, which were performed at different azimuthal angles (around the pinch column), have been presented. These results constitute a new experimental evidence of the appearance and role of the current filaments in pinch-type discharges.

‘Burning plasma’ diagnostics for the physics of JET and ITER

JET's recent experimental programme proved that ‘burning plasma diagnostics’, i.e. neutron, alpha particle, He ash, and fuel mixture measurements, can provide very useful information about crucial physical aspects of great reactor relevance. First of all, several of these diagnostics can improve the diagnostic capability of the ion fluid significantly. During TTE spatially resolved neutron measurements at JET were essential in obtaining the isotopic composition and the transport of the hydrogen isotopes, allowing a direct comparison between the measured transport coefficients and the neoclassical theory. The neutron emission profiles can also give crucial indications for assessing the merits of various heating schemes and their current drive capability. Neutron spectroscopy in its turn provides a clear and direct measurement of the temperature and the velocity distribution of the fuel ions. For example, the dependence of the toroidal velocity from the ion cyclotron radiofrequency heating phasing was clearly seen during TTE. The requirements of accurate neutron measurements are also promoting considerable research in detector technology, in particular in the fields of compact spectrometers and solid state detectors. ‘Burning plasma’ diagnostics can also strongly contribute to the physics of energetic particles and their interaction with the main plasma. γ-Ray spectroscopy is now an established method to determine the spatial localization, to visualize the trajectories of the alpha particles and the fast deuterons and to obtain estimates of their slowing down. A completely new method to detect the energetic particles, exploiting the line intensity ratio of extreme ultraviolet radiation emitted by suitable extrinsic impurities, is also being pursued. This technique allows investigating the energy range below 600 keV, extremely interesting for the study of wave–particle interactions.

Study of X-ray and Neutron Emission in Experiments with Al Wires in an MA Plasma Focus

Results are presented from experimental studies of the correlation between X-ray and neutron emissions generated in the implosion of a deuteron plasma shell onto an Al wire. The experiments were carried out on the PF-1000 facility at currents of 1.5–1.8 MA. An Al wire 80 μm in diameter and 7–9 cm in length was placed at the end of the inner electrode. During the implosion of the plasma shell, Al K-shell X-rays were first emitted at the dip of the current derivative. After the X-ray pulse, a relatively stable corona with a diameter of 2–3 mm and lifetime of a few hundred nanoseconds formed around the wire. The presence of the wire did not considerably reduce the total neutron yield (at most 1011 neutrons per shot) in comparison to discharges without a wire. As a rule, the intensity of neutron emission was maximal a few tens of nanoseconds after the peak of X-ray emission. A detailed comparison of two shots with low and high neutron yields have shown that the neutron yield depends on the configuration and dynamics of the discharge. The possible influence of the self-generated axial component of the magnetic field on the development of the plasma focus and the acceleration of fast deuterons is discussed.