Ion Temperature Ti Research Articles

Important role of pedestal ion temperature in the ELM mitigation by supersonic molecular beam injection

Edge localized mode (ELM) is successfully mitigated by helium and deuterium supersonic molecular beam injections (SMBIs) on HL-2A. During the ELM mitigation by SMBIs, gradients of ion temperature (Ti) and electron density are softened in the pedestal. It has been observed that the averaged gradient of the Ti decreases around 44% and the well depth of radial electric field (Er) is reduced by the SMBI during ELM mitigation. Furthermore, at least 20% decrements of Ti have to be attained to achieve a noticeable increase (decrease) of the ELM frequency (amplitude). In addition, the duration of ELM mitigation with helium SMBI is much longer than that with deuterium, likely due to the higher level of recycling neutral gas compared to that of deuterium; in the case of ELM mitigation by helium SMBI, the recovery duration of the density gradient is much shorter (10–20 ms) than that of Ti (up to 40 ms or longer), indicating the importance of the Ti in the ELM mitigation by SMBI. Finally, it has been observed that the Ti is reduced before the beginning of the ELM mitigation, suggesting that the mechanism of the ELM mitigation by SMBI is closely related to the cooling effect.

The magnetic recoil spectrometer (MRSt) for time-resolved measurements of the neutron spectrum at the National Ignition Facility (NIF).

The next-generation magnetic recoil spectrometer for time-resolved measurements of the neutron spectrum has been conceptually designed for the National Ignition Facility. This spectrometer, called MRSt, represents a paradigm shift in our thinking about neutron spectrometry for inertial confinement fusion applications, as it will provide simultaneously information about the burn history and time evolution of areal density (ρR), apparent ion temperature (Ti), yield (Yn), and macroscopic flows during burn. From this type of data, an assessment of the evolution of the fuel assembly, hotspot, and alpha heating can be made. According to simulations, the MRSt will provide accurate data with a time resolution of ∼20 ps and energy resolution of ∼100 keV for total neutron yields above ∼1016. At lower yields, the diagnostic will be operated at a higher-efficiency, lower-energy-resolution mode to provide a time resolution of ∼20 ps.

Plasma sheath properties in a magnetic field parallel to the wall

Particle in cell simulations were carried out with a plasma bounded by two absorbing walls and a magnetic field applied parallel to them. Both the sheath extent and the potential drop in it were derived from simulations for different plasma parameters, such as the electron and ion temperature Ti, particle density, and ion mass. Both of them exhibit a power law dependent on the Larmor to plasma ion pulsation ratio Ωi. For increasing values of the magnetic field, the potential drop within the sheath decreases from a few Ti/e down to zero, where e stands for the electron charge. The space charge extent increases with Ωi and saturates to 2.15 ion Larmor radius. A simple model of sheath formation in such a magnetic field configuration is presented. Assuming strongly magnetized electrons, and neglecting collisions and ionizations, a new typical length is evidenced, which depends on the ratio Ωi. The charge separation sheath width is theoretically found to increase from a combination of the electron gyroradius and the ion Debye length for low Ωi ratios up to several ion gyroradii for strongly magnetized ions. Both the calculated sheath extent and plasma potential show a fair agreement with the numerical simulations.

Characteristics of toroidal rotation and ion temperature pedestals between ELM bursts in KSTAR H-mode plasmas

Steep pedestal profiles of ion temperature (Ti) and toroidal rotation (Vϕ) are routinely observed in neutral beam injection (NBI)-heated KSTAR H-mode plasmas [W. H. Ko et al., Nucl. Fusion 55, 083013 (2015)]. In this work, we report a result of detailed analysis of pedestal characteristics. By analyzing a set of data with different experimental conditions, we show that Ti and Vϕ pedestals are coupled to each other and correlation between them becomes stronger when NBI-torque is lower. This suggests the existence of intrinsic toroidal torque in the pedestal. Based on a 1D transport analysis, we find that the prevalence of residual micro-turbulences is necessary to explain momentum transport in the pedestal. The estimated strength of intrinsic torque is shown to be comparable to that from a 2.7 MW NBI source. Finally, we show that non-diffusive momentum flux is indispensable to explain momentum transport in the pedestal, and a residual stress model fits the observed momentum flux reasonably.

Current Issues in Finite-T Density-Functional Theory and Warm-Correlated Matter †

Finite-temperature density functional theory (DFT) has become of topical interest, partly due to the increasing ability to create novel states of warm-correlated matter (WCM).Warm-dense matter (WDM), ultra-fast matter (UFM), and high-energy density matter (HEDM) may all be regarded as subclasses of WCM. Strong electron-electron, ion-ion and electron-ion correlation effects and partial degeneracies are found in these systems where the electron temperature Te is comparable to the electron Fermi energy EF. Thus, many electrons are in continuum states which are partially occupied. The ion subsystem may be solid, liquid or plasma, with many states of ionization with ionic charge Zj. Quasi-equilibria with the ion temperature Ti ≠ Te are common. The ion subsystem in WCM can no longer be treated as a passive “external potential”, as is customary in T = 0 DFT dominated by solid-state theory or quantum chemistry. Many basic questions arise in trying to implement DFT for WCM. Hohenberg-Kohn-Mermin theory can be adapted for treating these systems if suitable finite-T exchange-correlation (XC) functionals can be constructed. They are functionals of both the one-body electron density ne and the one-body ion densities ρj. Here, j counts many species of nuclei or charge states. A method of approximately but accurately mapping the quantum electrons to a classical Coulomb gas enables one to treat electron-ion systems entirely classically at any temperature and arbitrary spin polarization, using exchange-correlation effects calculated in situ, directly from the pair-distribution functions. This eliminates the need for any XC-functionals. This classical map has been used to calculate the equation of state of WDM systems, and construct a finite-T XC functional that is found to be in close agreement with recent quantum path-integral simulation data. In this review, current developments and concerns in finite-T DFT, especially in the context of non-relativistic warm-dense matter and ultra-fast matter will be presented.

Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser

Retarding field energy analysers (RFEAs) have been used to compare the ion temperature (Ti) of large plasma filaments with the background plasma (composed of small scale filaments) at the midplane and divertor target in L mode discharges in the Mega Amp spherical tokamak (MAST). At low densities, at the midplane and divertor, at distances from 2 to 4 cm from the separatrix the temperature of ions in large filaments was found to be 2 to 3 times larger than the background plasma. At the midplane, the electron temperature for both large filaments and background plasma was around 3 to 7 times smaller than the ion temperature and had a flat profile across the scrape off layer (SOL). At higher densities, at the midplane and divertor, both the filament and background ion temperatures were smaller than at low density. At the midplane, the filament and background ion and electron temperature profiles across the SOL were relatively flat and of comparable magnitude, ranging in temperature from 5 to 25 eV.

Alpha heating and isotopic mass effects in JET plasmas with sawteeth

The alpha heating experiment in the Joint European Torus (JET) 1997 DTE1 campaign is re-examined. Several effects correlated with tritium content and thermal hydrogenic isotopic mass < A > weaken the conclusion that alpha heating was clearly observed. These effects delayed the occurrence of significant sawtooth crashes allowing the electron and ion temperatures Te and Ti to achieve higher values. Under otherwise equal circumstances Te and Ti were typically higher for discharges with higher < A >, and significant scaling of Ti, Te, and total stored energy with < A > were observed. The higher Ti led to increased ion–electron heating rates with magnitudes comparable to those computed for alpha electron heating. Rates of other heating/loss processes also had comparable magnitudes. Simulations of Te assuming the observed scaling of Ti are qualitatively consistent with the measured profiles, without invoking alpha heating

Simulating electron and ion temperature in a global ionosphere thermosphere model: Validation and modeling an idealized substorm

Electron and ion temperatures control many chemical and physical processes in the ionosphere–thermosphere system. Recently, improved electron and ion energy equations were implemented in the Global Ionosphere Thermosphere Model (GITM). The source energy of the electron temperature (Te) includes thermal conduction, heating due to photoionization, elastic collisions with ions, elastic and inelastic collisions with neutrals, auroral precipitation, and heat flux from inner magnetosphere. The source terms in the ion temperature (Ti) equation include thermal conduction, and elastic collisions with electrons and neutrals. The new implementation of Te improved the ionospheric density at middle and high latitudes with respect to IRI. The improved GITM also reproduced the diurnal variation in Te and Ti observed by incoherent scatter radars at low and middle latitudes. The model was used to investigate an idealized substorm statistically described by Clausen et al. (2014). It was found that the responses of the E-region Ne and Te were highly correlated with the variation in auroral hemispheric power. The change of the F-region Te was correlated with the E-region Te and Ne, which was consistent with observations. The response of the F-region Ne to the particle precipitation was delayed by about 30min, and lasted significantly longer than the enhanced precipitation. The variations of Ti in both the E- and F-regions were dominated by IMF-driven ion drifts through frictional energy coupling with the neutrals. It was also found that the increase of the mid-latitude heat flux by one order of magnitude enhanced Te, electron density and TEC by up to 120%, 80% and 80% respectively between dusk and midnight.

Development of a Laser Induced Fluorescence (LIF) system on thePlasma Material Interaction System (PLAMIS-II) device

A laser induced fluorescence (LIF) system has been developed for the plasma material interaction system (PLAMIS-II) device, which is equipped with a unique plasma gun composed of a LaB6 cathode and two anodes with electromagnets to generate a focused dense plasma. PLAMIS-II simulates the interactions of plasma with different materials and is to be used for the test of plasma facing components of fusion devices. The LIF system is composed of a seed laser with Littmann/Metcalf cavity and a master oscillator power amplifier to pump 3d4F7/2 metastable argon ion to 4p4D5/2 level at the wavelength of 668.61 nm, which has the following input parameters: laser power = 20 mW, line width < 100 kHz, and a mode-hop free tuning range > 70 GHz. For in-situ measurement of laser wavelength, the wavelength spectrum of an iodine cell was measured by a photo-transistor during LIF measurement. To measure argon ion temperature (Ti) and drift velocity (vd) in PLAMIS-II, the fluorescence light with the wavelength of 442.72 nm, emitted from 4p4D5/2 level to 4s4P3/2 level and passing through 1 nm band-width filter, was collected by the photomultiplier tube combined with a lock-in amplifier and a chopper with frequency of 3 kHz. Initial data of Ti and vd were analysed in terms of gas flow rate and applied power.

Thermal conductivity of condensed gold in states with the strongly excited electron subsystem

Data on thermal conductivity in states with hot electrons are necessary for the calculation of ultrashort laser exposure and the behavior of matter near the tracks of fast particles penetrating the condensed phase. The paper presents new analytical expressions describing the state of gold with the extra-high heat conductivity within a broad range of two-temperature phase diagram including the melting curve. This is a region in the threedimensional space defined by the electron temperature Te, ion temperature Ti and the density ρ, at which the thermal conductivity κ is one order of magnitude larger than the value related to the room temperature. The growth of heat transfer is due to a sharp increase in the heat capacity of carriers (electrons) when they are heated and, accordingly, the gradual loss of the degeneracy. The developed model is based on an exact solution of the kinetic equation, involving experimental data and calculations of the electronic spectrum by the density functional method. The model works well also at low temperatures Te that allows describing the crystallization of the melt as it cools down.

Simulations of the L–H transition dynamics with different heat and particle sources**Project supported by the Funds of the Youth Innovation Team of Science and Technology in Sichuan Province, China (Grant No. 2014TD0023), the National Natural Science Foundation of China (Grant Nos. 11447228 and 11205053), and the China National Magnetic Confinement Fusion Science Program (Grant No. 2013GB107001).

It is crucial to increase the total stored energy by realizing the transition from a low confinement (L-mode) state to a high confinement (H-mode) state in magnetic confinement fusion. The L–H transition process is simulated by using the predictive transport code based on Weiland’s fluid model. Based on the equilibrium parameters obtained from equilibrium fitting (EFIT) in the experiment, the electron density ne, electron temperature Te, ion temperatures Ti, ion poloidal Vp, and toroidal momenta Vt are simulated self-consistently. The L–H transition dynamic behaviors with the formation of the transport barriers of ion and electron temperatures, the electron density, and the ion toroidal momenta are analyzed. During the L–H transition, the strong poloidal flow shear in the edge transport barrier region is observed. The crashes of the electron and ion temperature pedestals are also observed during the L–H transition. The effects of the heating and particle sources on the L–H transition process are studied systematically, and the critical power threshold of the L–H transition is also found.

Application of particle swarm optimization method to incoherent scatter radar measurement of ionosphere parameters

AbstractSimultaneous derivation of multiple ionospheric parameters from the incoherent scatter power spectra in the F1 region is difficult because the spectra have only subtle differences for different combinations of parameters. In this study, we apply a particle swarm optimizer (PSO) to incoherent scatter power spectrum fitting and compare it to the commonly used least squares fitting (LSF) technique. The PSO method is found to outperform the LSF method in practically all scenarios using simulated data. The PSO method offers the advantages of not being sensitive to initial assumptions and allowing physical constraints to be easily built into the model. When simultaneously fitting for molecular ion fraction (fm), ion temperature (Ti), and ratio of ion to electron temperature (γT), γT is largely stable. The uncertainty between fm and Ti can be described as a quadratic relationship. The significance of this result is that Ti can be retroactively corrected for data archived many years ago where the assumption of fm may not be accurate, and the original power spectra are unavailable. In our discussion, we emphasize the fitting for fm, which is a difficult parameter to obtain. PSO method is often successful in obtaining fm, whereas LSF fails. We apply both PSO and LSF to actual observations made by the Arecibo incoherent scatter radar. The results show that PSO method is a viable method to simultaneously determine ion and electron temperatures and molecular ion fraction when the last is greater than 0.3.

Overview of transport and MHD stability study: focusing on the impact of magnetic field topology in the Large Helical Device

The progress in the understanding of the physics and the concurrent parameter extension in the large helical device since the last IAEA-FEC, in 2012 (Kaneko O et al 2013 Nucl. Fusion 53 095024), is reviewed. Plasma with high ion and electron temperatures (Ti(0) ∼ Te(0) ∼ 6 keV) with simultaneous ion and electron internal transport barriers is obtained by controlling recycling and heating deposition. A sign flip of the nondiffusive term of impurity/momentum transport (residual stress and convection flow) is observed, which is associated with the formation of a transport barrier. The impact of the topology of three-dimensional magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum, particle/impurity transport and magnetohydrodynamic stability is also discussed. In the steady state operation, a 48 min discharge with a line-averaged electron density of 1 × 1019 m−3 and with high electron and ion temperatures (Ti(0) ∼ Te(0) ∼ 2 keV), resulting in 3.36 GJ of input energy, is achieved.

Introducing a two temperature plasma ignition in inertial confined targets under the effect of relativistic shock waves: The case of DT and pB11

AbstractA criterion for a two temperature plasma nuclear fusion ignition is derived by using a common model. In particular, deuterium-tritium (DT) and proton–boron11 (pB11) are considered for pre-compressed plasma. The ignition criterion is described by a surface in the three-dimensional space defined by the electron and ion temperatures Te, Ti, and the plasma density times the hot spot dimension, ρ·R. The appropriate fusion ion temperatures Ti are larger than 10 keV for DT and 150 keV for pB11. The required value of ρ·R for pB11 ignition is larger by a factor of 50 or more than for DT, depending on the electron temperature. Furthermore, our ignition criterion obtained here for pB11 fusion is practically impossible for equal electron and ion temperatures. In this paper it is suggested to use a two temperature laser induced shock wave in the intermediate domain between relativistic and non-relativistic shock waves. The laser parameters required for fast ignition are calculated. In particular, we find that for DT case one needs a 3 kJ/1 ps laser to ignite a pre-compressed target at about 600 g/cm3. For pB11 ignition it is necessary to use more than three orders of magnitude of laser energy for the same laser pulse duration.

The solar cycle variations of plasma parameters and their correlations at topside ionosphere from DEMETER during 2005–2010

Based on the IAP (Instrument d’Analyse du Plasma) observing data onboard DEMETER satellite, the solar cycle variations in ion density (Ni), ion composition [O+,H+,He+] and ion temperature (Ti) were analyzed respectively in local daytime 10:30 and nighttime 22:30 during 2005–2010 during the 23rd/24th solar cycles, which would greatly contribute to the research of the topside ionospheric physics during this extremely low solar minimum. Based on analyzing the solar cycle variations of these plasma parameters, it was found that longitude-averaged Ni, [O+] and daytime Ti presented positive correlation with solar flux, while [H+], nighttime Ti and [He+] varied negatively to reach their maxima at the solar minimum. Furthermore, [O+], as the main composition at the altitude of DEMETER of 660km, showed typical seasonal variation and close relationship with sub-solar dynamics. Daytime [He+] was the most complex component, showing negative variation with solar activity at low latitudes over Southern Hemisphere and positive correlation at middle latitudes over Northern Hemisphere. The correlation of Ni and Ti in local daytime was dependent on season over two hemispheres, and the results illustrated negative correlation at low latitudes, and positive correlation at middle latitudes especially over Southern Hemisphere in solstitial seasons. While [H+] presented anti-correlation, especially the peak values with Ti valleys at 0–20°N in each year, which all might be related to the thermal diffusion and relative drift among different ions. Furthermore, the asymmetrical features of Ni over two hemispheres in solar minimum were widely revealed at different longitude sectors, latitudes and local times, which might be explained by the concentration of neutral oxygen, neutral winds, and also the lower atmospheric dynamics.

A spatial analysis on seismo-ionospheric anomalies observed by DEMETER during the 2008 M8.0 Wenchuan earthquake

This paper examines seismo-ionospheric anomalies (SIAs) observed by the French satellite DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) during the 12 May 2008 M8.0 Wenchuan earthquake. Both daytime and nighttime electron density (Ne), electron temperature (Te), ion density (Ni) and ion temperature (Ti) are investigated. A statistical analysis of the box-and-whisker method is utilized to see if the four DEMETER datasets 1–6days before and after the earthquake are significantly different. The analysis is employed to investigate the epicenter and three reference areas along the same magnetic latitude discriminating the SIAs from global effects. Results show that the nighttime Ne and Ni (daytime Ti) over the epicenter significantly decrease (increase) 1–6days before the earthquake. The intersections of the global distribution of the significant differences (or anomalous changes) in the nighttime Ne, the nighttime Ni, and the daytime Ti 1–6days before and after the earthquake specifically appear over the epicenter, which strongly suggests that DEMETER observes SIAs of the 2008 M8.0 Wenchuan earthquake.

Supply equipment to the new NBH system for the TCV tokamak

The TCV tokamak is equipped with a high power real time-controllable Electron Cyclotron Heating (ECH) system, made of 9 gyrotrons capable of 500kW RF power. One of the major scientific challenge, the TCV upgrades aimed to, will be the access to a wider range of temperature ratios up to Te/Ti∼1. For this purpose, the TCV heating system will be upgraded by the integration of a Neutral Beam Heating (NBH) system impacting directly on the ion temperature (Ti), while gyrotrons are used to vary mainly the electron temperature (Te). This NB Injector (NBI) will provide 1MW of neutral power during 2s into the TCV plasma, at a nominal energy of 30keV, for an electrical power installed of 2.2MVA. This paper describes the infrastructure required to implement successfully this novel NBI at CRPP premises.

Influence of Working Pressure on Ion Sensitive Probe Measurement in Microwave ECR Plasmas**supported by National Natural Science Foundation of China (No. 10875093)

In order to precisely measure the ion parameters in a microwave electron cyclotron resonance plasma using an ion sensitive probe, the dependences of the current-voltage (I-V) characteristics on the shielding height (h) and the potential difference between inner and outer electrodes (VB) have been investigated at different working pressures of 0.03 Pa and 0.8 Pa. Results show that the I-V curves at higher pressure are more sensitive to the variation of h than those at lower pressure. The influence of VB on ion temperature (Ti) measurement becomes more prominent when the pressure is increased from 0.03 Pa to 0.8 Pa. Under both pressures, the optimized h is obtained at the condition where the current reaches zero in the positive voltage region with a suitable VB of −1.5 V because of effective shielding of the electron E×B drift.

Formation of radiatively cooled, supersonically rotating, plasma flows in Z-pinch experiments: Towards the development of an experimental platform to study accretion disk physics in the laboratory

We present data from the first Z-pinch experiments aiming to simulate aspects of accretion disk physics in the laboratory. Using off axis ablation flows from a wire array z-pinch we demonstrate the formation of a supersonically (M ∼ 2) rotating hollow plasma cylinder of height ∼4mm and radius 2 mm. Using a combination of diagnostics we measure the rotation speed (∼60kms−1), electron density (1019cm−3), ion temperature (Ti ∼ 60eV) and the product of electron temperature and average ionisation (ZTe ∼ 150 to 200 eV). Using these parameters we calculate the Reynolds number for the plasma on the order 105 and magnetic Reynolds number as 10 – 100. The plasma flow is maintained for 150ns, corresponding to one rotation period, which should allow for studying fast instabilities which develop on this time-scale.

Two‐Temperature Pair Potentials and Phonon Spectra for Simple Metals in the Warm Dense Matter Regime

AbstractWe develop ion‐ion pair potentials for Al, Na and K for densities and temperatures relevant to the warm‐densematter (WDM) regime. Furthermore, we emphasize non‐equilibrium states where the ion temperature Ti differs from the electron temperature Te. This work focuses mainly on ultra‐fast laser‐metal interactions where the energy of the laser is almost exclusively transferred to the electron sub‐system over femtosecond time scales. This results in a two‐temperature system with Te &gt; Ti and with the ions still at the initial room temperature Ti = Tr. First‐principles calculations, such as density functional theory (DFT) or quantum Monte Carlo, are as yet not fully feasible for WDM conditions due to lack of finite‐T features, e.g. pseudopotentials, and extensive CPU time requirements. Simpler methods are needed to study these highly complex systems. We propose to use two‐temperature pair potentials Uii(r, Ti, Te) constructed from linear‐response theory using the non‐linear electron density n (r) obtained from finite‐T DFT with a single ion immersed in the appropriate electron fluid. We compute equilibrium phonon spectra at Tr which are found to be in very good agreement with experiments. This gives credibility to our non‐equilibrium phonon dispersion relations which are important in determining thermophysical properties, stability, energy‐relaxation mechanisms and transport coefficients. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)