Beryllium Plasma Research Articles

Influence of the ion core on relaxation processes in dense plasmas

AbstractThe effect of an ionic core on the temperature relaxation in dense hot plasma of beryllium is studied using the pseudpotential model by Gericke et al [Phys. Rev. E 2010, 81, 065401(R)]. Employing the screened version of the ion pseudpotential [by Ramazanov et al, Phys. Plasmas 2021, 28 (9), 092702], we computed the quantum transport cross section for the electron‐ion collisions in dense beryllium plasma, where screening is taking into account using the density response function in the long‐wavelength regime. The results for the transport cross section are used to compute a generalised Coulomb logarithm and electron‐ion collision frequency. Utilizing the latter, we show the effect of the ionic core on the temperature relaxation. To understand the role of the ionic core, we compare the results with the data computed considering ions as point‐like charges.

Soft X-ray and EUV emission spectra of beryllium plasma produced by neodymium-glass laser radiation with broad frequency and angular spectra

We present the results of an experimental study of soft X-ray (SXR) and extreme ultraviolet emission spectra of the plasma produced by exposing a plane solid beryllium target to laser radiation with broad frequency and angular spectra. SXR lines up to 1s – 9p of Be IV as well as the plasma continuum are recorded for a laser focal-spot intensity of 5.3 × 1013 W cm−2. To model the SXR beryllium plasma spectra, simulations are carried out using the INDHAUS programme and the FLYCHK code in the framework of local thermodynamic equilibrium model, which agree nicely with experimentally obtained results.

Thermal desorption spectrometry of beryllium plasma facing tiles exposed in the JET tokamak

The phenomena of retention and de-trapping of deuterium (D) and tritium (T) in plasma facing components (PFC) and supporting structures must be understood in order to limit or control total T inventory in larger future fusion devices such as ITER, DEMO and commercial machines. The goal of this paper is to present details of the thermal desorption spectrometry (TDS) system applied in total fuel retention assessment of PFC at the Joint European Torus (JET). Examples of TDS results from beryllium (Be) wall tile samples exposed to JET plasma in PFC configuration mirroring the planned ITER PFC is shown for the first time. The method for quantifying D by comparison of results from a sample of known D content was confirmed acceptable. The D inventory calculations obtained from Ion Beam Analysis (IBA) and TDS agree well within an error associated with the extrapolation from very few data points to a large surface area.

Tritium Plasma Experiment Upgrade and Improvement of Surface Diagnostic Capabilities at STAR Facility for Enhancing Tritium and Nuclear PMI Sciences

Recently, Tritium Plasma Experiment (TPE), a unique high-flux linear plasma device that can handle beryllium, tritium and neutron-irradiated plasma facing materials, has undergone major upgrades in its electrical and control systems. The upgrade has improved worker occupational safety, and enhanced TPE plasma performance to better simulate extreme plasma-material-interaction (PMI) conditions expected in ITER, Fusion Nuclear Science Facility (FNSF) and demonstration fusion power plant (DEMO). The PMI determines a boundary condition for diffusing tritium into bulk plasma-facing components (PFCs) and plays critical role in in-vessel and ex-vessel safety assessments. Enhancing surface capabilities for tritium-contaminated and radioactive samples is crucial for the PMI sciences in burning plasma long pulse operation. The TPE Upgrade and improvement of surface diagnostic capabilities for tritium-contaminated and radioactive samples at STAR facility help enhance tritium and nuclear PMI sciences for the development of reliable PFCs and tritium fuel cycle in ITER, FNSF and DEMO.

Nuclear-plus-interference-scattering effect on the energy deposition of multi-MeV protons in a dense Be plasma.

The nuclear plus interference scattering (NIS) effect on the stopping power of hot dense beryllium (Be) plasma for multi-MeV protons is theoretically investigated by using the generalized Brown-Preston-Singleton (BPS) model, in which a NIS term is taken into account. The analytical formula of the NIS term is detailedly derived. By using this formula, the density and temperature dependence of the NIS effect is numerically studied, and the results show that the NIS effect becomes more and more important with increasing the plasma temperature or density. Different from the cases of protons traveling through the deuterium-tritium plasmas, for a Be plasma, a prominent oscillation valley structure is observed in the NIS term when the proton's energy is close to E_{p}=7MeV. Furthermore, the penetration distance is remarkably reduced when the NIS term is considered.

TPE upgrade for enhancing operational safety and improving in-vessel tritium inventory assessment in fusion nuclear environment

The Tritium Plasma Experiment (TPE) is a unique high-flux linear plasma device that can handle beryllium, tritium, and neutron-irradiated plasma facing materials, and is the only existing device dedicated to evaluate in-vessel tritium inventory in the nuclear environment for fusion safety. The electrical upgrade were recently carried out to enhance operational safety and to improve plasma performance. New DC power supplies and a new control center enable remote plasma operations from outside of the contamination area for tritium, minimizing the possible exposure risk with tritium and beryllium and eliminating heat stress issue. In November 2015, the TPE successfully achieved first deuterium plasma via remote operation after a significant three-year upgrade. Simple linear scaling estimate showed that the TPE is expected to achieve Γimax of >1.0×1023m−2s−1 and qheat of >1MWm−2 with new power supplies. This upgrade not only improves operational safety of the worker, but also enhances plasma performance to better simulate extreme plasma-material conditions expected in ITER, FNSF, and DEMO for improving in-vessel tritium inventory assessment in fusion nuclear environment.

Generalized Lenard-Balescu calculations of electron-ion temperature relaxation in beryllium plasma.

The problem of electron-ion temperature relaxation in beryllium plasma at various densities (0.185-18.5g/cm^{3}) and temperatures [(1.0-8)×10^{3} eV] is investigated by using the generalized Lenard-Balescu theory. We consider the correlation effects between electrons and ions via classical and quantum static local field corrections. The numerical results show that the electron-ion pair distribution function at the origin approaches the maximum when the electron-electron coupling parameter equals unity. The classical result of the Coulomb logarithm is in agreement with the quantum result in both the weak (Γ_{ee}<10^{-2}) and strong (Γ_{ee}>1) electron-electron coupling ranges, whereas it deviates from the quantum result at intermediate values of the coupling parameter (10^{-2}<Γ_{ee}<1). We find that with increasing density of Be, the Coulomb logarithm will decrease and the corresponding relaxation rate ν_{ie} will increase. In addition, a simple fitting law ν_{ie}/ν_{ie}^{(0)}=a(ρ_{Be}/ρ_{0})^{b} is determined, where ν_{ie}^{(0)} is the relaxation rate corresponding to the normal metal density of Be and ρ_{0}, a, and b are the fitting parameters related to the temperature and the degree of ionization 〈Z〉 of the system. Our results are expected to be useful for future inertial confinement fusion experiments involving Be plasma.

Measurements of gross erosion of Al in the DIII-D divertor

Aluminum (Al) is a convenient proxy for beryllium (Be) plasma material interaction studies since they have a number of physical and chemical similarities. Al samples were exposed at the lower outer strike point of an L-mode divertor plasma in DIII-D (conditions 7–11×1018 D-ions cm−2s−1, Te=12–47eV). The gross erosion rate was directly measured using post-mortem ion beam analysis of small 1mm-sized samples where local re-deposition was determined to be negligible. The gross erosion rate was also calculated using spectroscopic methods, but these rates greatly underestimate the direct (i.e. non-spectroscopic) measurement. The direct measured erosion yields were within the range of published D+→Al ion beam sputtering yields. The ionizations per photon (S/XB) coefficients used in the spectroscopic analysis were determined in separate experiments using He plasmas at the PISCES-B linear plasma facility at UCSD. The measured S/XB coefficients were on average ∼6× higher than the theoretically calculated values.

Self-similar expansion of a warm dense plasma

The properties of an expanding plasma composed of degenerate electron fluid and non-degenerate ions are studied. For our purposes, we use fluid equations for ions together with the electron momentum equation that include quantum forces (e.g., the quantum statistical pressure, forces due to the electron-exchange and electron correlations effects) and the quasi-neutrality condition. The governing equation is written in a tractable form by using a self-similar transformation. Numerical results for typical beryllium plasma parameters revealed that, during the expansion, the ion acoustic speed decreases for both isothermal and adiabatic ion pressure. When compared with classical hydrodynamic plasma expansion model, the electrons and ions are found to initially escape faster in vacuum creating thus an intense electric field that accelerates most of the particles into the vacuum ahead of the plasma expansion. The relevancy of the present model to beryllium plasma produced by a femto-second laser is highlighted

Composition of Dense Beryllium, Boron and Carbon Plasmas

AbstractIn the present paper we determine the composition of dense beryllium, boron and carbon plasma by solving the Saha equations with corrections due to non‐ideality. The lowering of the ionization potentials is calculated on the basis of effective potentials by taking into account screening and quantum diffraction effects. The considered range of density and temperature covers plasmas with a very low degree of ionization up to full ionization with ions having the maximum ionization state. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The role of JET for the preparation of the ITER exploitation

The JET programme is devoted to the consolidation of ITER design choices and the qualification of ITER integrated regimes of operation. During the experimental campaigns carried out in 2008 and 2009 attention focussed on the test of the ITER-like ICRH antenna, the ITER scenario preparation, the verification of the adequacy of the ITER poloidal field coil design and the test of disruption mitigation methods such as massive gas injection. From 2011 the new ITER-like wall with all beryllium and tungsten plasma facing components, the neutral beam power upgrade and the enhanced control and diagnostic capability will allow key questions on plasma-wall interactions, fuel retention and plasma impurity control with the foreseen ITER wall materials to be addressed. Finally, feasibility studies have confirmed the option of installing an ITER-technology based 170 GHz/10 MW electron cyclotron resonance heating system for the control of MHD activity and the development of advanced tokamak scenarios, and 32 in-vessel coils for ELM control capable of producing magnetic perturbation spectra with a Chirikov parameter above unity for plasma currents up to 5 MA. During the ITER construction phase, JET will be the only device of its class in operation and will therefore play a key role in the preparation of ITER operations – saving time and reducing risk from the ITER programme.

Generation of lower and higher harmonics in different plasma media with small Z

The generation of lower (third) and higher harmonics of femtosecond laser radiation in plasmas produced by laser ablation of different targets with a small atomic number Z (B, Be, Li) has been investigated. The high (10−3) efficiency of third-harmonic generation was observed in plasma produced on the boron surface. Efficient third-harmonic generation was also observed in beryllium plasma using femtosecond pulses of Ti:sapphire laser radiation (λ = 790 nm) and its second harmonic (395 nm). We could tune the higher harmonics generation spectrum by tuning the crystal converter when using 395-nm radiation to be converted. It is shown that, in plasmas formed on targets with small Z, the conversion efficiency and limiting generated harmonic order depend on the delay between the ablation pulse and the pulse to be converted.

X-ray Thomson scattering for measuring dense beryllium plasma collisionality

We are developing a target platform that utilizes short-pulse (10 ps) generated hot electrons (∼200 keV) to isochorically heat solid density beryllium up to temperatures of several 10 eV. We use x-ray Thomson scattering to characterize the plasma conditions. X-rays from a Cl Ly-α line source at 2.96 keV are scattered off the plasma in forward direction where the inelastically scattered signal is sensitive to plasma oscillations. Besides Landau-damping the strong energy down-shifted plasmon signal is also broadened by electron-ion collisions which, in turn, allows to infer the collision rate and thus the conductivity in these plasmas. A precise knowledge of the collisionality in the parameter regime we are aiming at with these experiments is important to correctly model the conditions encountered during capsule implosions at the National Ignition Facility.

On temperature bifurcation of beryllium and lithium plasma facing components

The mechanism of temperature bifurcation of plasma contacting surfaces due to recycling of the ionized surface material vapor is considered. It is shown that this mechanism can lead to overheating of beryllium and lithium plasma facing components (in particular, in fusion devices) prior to the thermionic electron emission mechanism. The surface temperatures and the plasma parameters, at which the considered mechanism triggers the local overheating of beryllium and lithium components, are evaluated. The increase in the surface heat load due to secondary electron emission is also considered. It is shown that the combined effects of energy and impact angle distributions of the plasma electrons can increase the averaged secondary electron emission yield to values higher than unity and can lower the average electron energy, at which such yields are achieved.

Application of beryllium plasma for the harmonic generation of Ti:sapphire laser radiation

We report the studies of the low- and high-order harmonic generation (HHG) in beryllium plasma using the Ti:sapphire laser radiation (790 nm) and its second harmonic (395 nm). We achieved the tuning of HHG spectra by tuning the nonlinear optical crystal used for the second harmonic generation of fundamental radiation. The role of restricting factors during the HHG in a beryllium plume is discussed.

Hypernetted Chain Calculations for Two‐Component Plasmas

AbstractWe have performed HNC calculations for dense beryllium plasma as studied experimentally using x‐ray Thomson scattering, recently. We treated non‐equilibrium situations with different electron and ion temperatures which are relevant in pump‐probe experiments on ultra‐short time scales. To consider quantum effects adequately, we used effective pair potentials to describe the interactions. Results are compared with classical as well as quantum corrected Debye model calculations. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Influence of beryllium plasma seeding on the erosion of carbon

This paper is concerned with the influence of beryllium (Be) impurities in a deuterium (D) plasma on the erosion of graphite (C). C targets biased at −50V were exposed to a Be seeded D plasma in the temperature range from 500K to 1280K and Be plasma concentrations in the range from 0.01% to 0.3% in the PISCES-B divertor simulator. It was found that even at these low Be concentrations, the C samples are covered with a shielding Be layer which almost eliminates chemical and physical erosion of the C sample in the observed target temperature range. A combinatorial approach was used to model these experimental results by using the well established Monte Carlo code TRIDYN together with an analytical model. The paper gives an overview of the experimental data, how the modelling results compare with the experiments and how these results can be extrapolated to ITER.

On neutron generation in beryllium plasma under the effect of a fast-electron beam

1. The overwhelming majority of present-day neutron sources belong to the type of solid-state generators where neutrons are produced in solid-state targets via nuclear reactions induced by fast ions or energetic bremsstrahlung photons. Plasma neutron sources, whose operation is based on initiating reactions in a relatively cold plasma upon irradiation with a particle beam, have not yet received adequate study. At the same time, reactions in plasmas possess important special features, themain of these being the suppression of the channel of ionization losses—that is, of the useless loss of the charged-particle energy by medium ionization. This leads to an increase in the projectile-particle range and to the enhancement of the yield of nuclear reactions in plasma targets. For example, it was shown in [1, 2] that plasma sources of neutrons can ensure sizable fluxes; therefore, they can be applied in solving a number of scientific and technological problems. Employing electron beams in creating neutron sources may prove to be efficient, at least from the economic point of view. At present, relatively cheap and reliable facilities for producing intense beams of fast electrons have been developed, the efficiency of the input-energy transformation into the beam energy being there as high as 85 to 90%. In neutron sources, an electron beam can perform two functions. First, it is able to transform the target into a plasma state; second, it can initiate nuclear processes in the target that are accompanied by neutron generation. These are the electrodisintegration of target nuclei via (e, e′n) reactions and secondary photonuclear reactions (γ, n) induced by bremsstrahlung photons. Photonuclear reactions have already been employed in experimental neutron sources. As to electrodisintegration processes, the question of whether their application will be promising has so far received very little study. However, the traditional opinion is that, in all probability, their role cannot be significant because of the smallness of the cross sections for (e, e′n) reactions.

Electrodisintegration reaction in beryllium plasma as a source of neutrons

We analyze the generation of neutrons in a dense beryllium plasma induced by a powerful electron beam. It is shown that under appropriate conditions the flux of neutrons produced in the plasma can reach the level of 2 × 10 13 n/s. An essential point is that such a high yield is provided by only one of the possible generation mechanisms in the system—via the reaction of electrodisintegration 9Be(e,e′n) 8Be. This rather unexpected result is a serious argument in favor of detailed experimental studies of the interaction of modern high-intensity electron beams with beryllium targets.

Influence of beryllium plasma impurities on the erosion of graphite

This paper is concerned with the importance of mixed-material effects that could mitigate the problems associated with chemical erosion of carbon in the next step fusion device ITER. It presents experiments on the influence of beryllium (Be) impurities in deuterium (D) plasmas on the erosion properties of graphite. Graphite (C) targets were exposed to a Be seeded steady state D plasma in the PISCES-B divertor simulator. The Be plasma concentrations and the changes in chemical and physical erosion were measured using a visible light spectroscopy system. During all experiments a bias voltage of −50 V was applied to the C target, the target temperatures were in the range from 500 to 1280 K and the Be plasma concentration was in the range from 0.02% to 0.2%. It was found that even at these low Be concentrations, the C targets are covered with a shielding Be layer that eliminates both chemical and physical erosion of the underlying C target. The formation of this shielding Be layer also results in diminishing C and large Be concentrations in the material co-deposited on a collector probe that was shielded from direct plasma impact.