Minority Ion Research Articles

Modeling of ion cyclotron resonance frequency heating of proton-boron plasmas in EHL-2 spherical tokamak

Ion cyclotron resonance heating (ICRH) stands out as a widely utilized and cost-effective auxiliary method for plasma heating, bearing significant importance in achieving high-performance discharges in p-11B plasmas. In light of the specific context of p-11B plasma in the EHL-2 device, we conducted a comprehensive scan of the fundamental physical parameters of the antenna using the full-wave simulation program TORIC. Our preliminary result indicated that for p-11B plasma, optimal ion heating parameters include a frequency of 40 MHz, with a high toroidal mode number like to heat the majority H ions. In addition, we discussed the impact of concentration of minority ion species on ion cyclotron resonance heating when 11B serves as the heavy minority species. The significant difference in charge-to-mass ratio between boron and hydrogen ions results in a considerable distance between the hybrid resonance layer and the tow inverted cyclotron resonance layer, necessitating a quite low boron ion concentration to achieve effective minority heating. We also considered another method of direct heating of hydrogen ions in the presence of boron ion minority. It is found that at appropriate boron ion concentrations ( ), the position of the hybrid resonance layer approaches that of the hydrogen ion cyclotron resonance layer, thereby altering the polarization at this position and significantly enhancing hydrogen ion fundamental absorption.

Recent progress in improvement in ion cyclotron range of frequencies coupling and power absorption with new antennas of Experimental Advanced Superconducting Tokamak (EAST)

Efficient ion cyclotron range of frequencies (ICRF) wave heating requires good wave coupling at the plasma edge and good radio frequency power absorption in the plasma core. This study reviews recent progress in improving these two aspects of ICRF heating with the new two-strap antennas through various experiments and simulations on the Experimental Advanced Superconducting Tokamak (EAST). Our study shows that the ICRF coupling can be significantly improved by decreasing the parallel wave number, increasing the local scrape-off layer (SOL) density by midplane gas puffing, and increasing the global SOL density by decreasing the separatrix–antenna distance. It can also be improved by increasing the core plasma density, changing the divertor strike point position, and optimizing the antenna phasing. The core ICRF power absorption can be increased by optimizing the cyclotron resonance position and minority ion concentration and by applying new heating schemes such as three-ion heating. Although some of the methods have been previously studied on other devices, improving ICRF coupling by shifting the divertor strike point was tested on EAST for the first time. Quantitative characterization of these methods and the conclusions drawn from this study can provide important insights for achieving more efficient ICRF heating in current and future fusion machines.

A full wave solver integrated with a Fokker–Planck code for optimizing ion heating with ICRF waves for the ITER deuterium–tritium plasma

Efficient ion heating is crucial for future fusion devices, and the only way to heat ions directly is ion cyclotron resonance heating. Reported here is a full wave solver integrated with a Fokker–Planck code for optimizing ion heating with ion cyclotron range of frequency waves for the International Thermonuclear Experimental Reactor deuterium–tritium plasma. Both the direct absorption of minority ions and the power transfer to bulk ions via collisions are considered, while also accounting for the edge effects on ion absorption near the core. The simulation results show that the appropriate scrape-off layer density profile and parallel wave number lead to enhanced edge coupling and broaden the absorption region with moderate absorption intensity of the minority ions, which is very important for ion heating. More power from the heated ions is transferred to bulk ions than to electrons through collisions in our simulation via optimization, and reducing the total RF power results in a significant increase of the absorbed fraction of bulk ions.

Numerical study of minority ion heating scenarios in a spherical tokamak plasma

In this study, D(H) minority ion cyclotron resonance heating (ICRH) scenarios in Nan Chang spherical tokamak (NCST) were simulated using the full-wave code TORIC. NCST is a low-aspect-ratio (R/a = 1.67) spherical tokamak, with its core plasma parameters characterized by a magnetic field intensity of 0.36 T and a density of 1018 m−3. Our simulation results demonstrate that the ion cyclotron wave can penetrate the core plasma of the NCST more effectively with a lower toroidal mode number, indicating that resonant ions can absorb the wave energy efficiently. Furthermore, it is found that as the minority ion H concentration is increased, a noticeable decline in the left-handed electric field adjacent to the ion cyclotron resonance layer is observed. Optimal heating efficiency is attained when maintaining a minority ion H concentration within the range 5%–10%. The minority ion velocity distribution was simulated to estimate the tail temperature of minority-ICRH, which is expected to exceed 10 keV. The difference in the power efficiency with different plasma compositions [Ar(H) and D(H)] was also simulated. When the H-ion cyclotron resonance layer is located at the core plasma, the power-absorption fraction of H in Ar(H) plasma surpasses that of D and H combined in D(H) plasma under identical conditions. These simulations provide a crucial foundation and theoretical reference not only for NCST but also for other spherical tokamaks conducting ICRH experiments.

Bio‐inspired synthesis of bio‐hydroxyapatite/synthetic hydroxyapatite hybrid nanosystems

AbstractThe current study focuses on the synthesizing of novel hybrid nanosystems of bio‐hydroxyapatite (BioHAp)/synthetic‐hydroxyapatite (HAp‐Syn). Bio‐HAp was defatted, deproteinized, and then sonicated to obtain nanoparticles (nBioHAp). Hybrid nanosystems (HNS) were synthesized by wet chemical precipitation using nBioHAp as nucleation sites and applying four different precipitation times of 45, 90, 135, and 180 min. X‐ray diffraction (XRD) showed that the patterns of the nBioHAp and HAp‐Syn samples have broadened diffraction peaks due to simultaneous elastic and inelastic scattering. Their crystallite size is about 25 nm, while the hybrid nanosystems have a size between 35 and 40 nm. Fourier‐transform infrared spectroscopy (FT‐IR) revealed the main groups associated with hydroxyapatite (PO32−, OH−, and CO32−), and the nanometer character of the crystals was demonstrated by studying the full width at half maximum (FWHM) of the spectra. Scanning electron microscopy (SEM) revealed the differences between the morphologies of nBioHAp and HAp‐Syn. The shape of HNS resembled that of biogenic HAp, which was confirmed by transmission electron microscopy (TEM). Inductively coupled plasma spectroscopy (ICP‐OES) and energy dispersive X‐ray spectroscopy (EDS) were used to confirm the elemental composition of Mg, Na, K, and Zn as minority ions.

Effects of Cold Plasma on the Mode Conversion From Fast Magnetosonic Wave to Electromagnetic Ion Cyclotron Wave in the Inner Plasmasphere

AbstractPrevious studies show that fast magnetosonic (MS) wave with frequency of tens of Hz may propagate to low L‐shells (L < 2.0) in the inner plasmasphere and mode convert to electromagnetic ion cyclotron (EMIC) wave where its wave frequency is close to the local crossover‐cutoff‐resonance frequency triplet through different propagation paths. In this study, we investigate how this mode conversion process may depend on the ion composition and electron density by full‐wave simulation with various plasma density profiles and initial wave normal angles (WNAs) of incoming MS wave from magnetic equator and a higher latitude of 15°. We find that critical fraction of minority ion (He+ or M/Q = 2 ion − D+ or He++) exists during the mode conversion, over which the conversion from MS wave to H+ band right‐handedly polarized EMIC wave starts to become negligible. This critical fraction decreases with the incident WNA of MS wave from equator. The efficiency of this conversion process also decreases with the electron density. As incoming MS is from higher latitudes off equator, optimal fraction of minority ion exists, with which the efficiency of conversion from MS wave to H+ band left‐handedly polarized EMIC wave reaches a maximum. Moreover, this maximum conversion efficiency varies with the incident WNA and may approach 100% with WNA close to 90° at the magnetic latitude of 15°. We also find that localized wave structure may be formed when the converted H+ band EMIC wave is trapped between local H+ − D+(He++) bi‐ion resonance frequency and D+(He++) − He+ left‐handed polarization cut‐off frequency with a small M/Q = 2 ion fraction and a relatively larger He+ fraction as incoming MS wave is near equator.

Obtention and characterization of nano bio-hydroxyapatite particles by combined hydrothermal alkaline and ultrasonic wet milling methods

This article deals with the extraction, recovery, and characterization of nano bio-hydroxyapatite particles (nBio-HAp) from pig bones obtained by hydrothermal alkaline treatment in combination with an ultrasonic wet milling process. Pig bone powder was defatted and deproteinized with an 1 N potassium hydroxide (KOH) aqueous solution for 24 h with stirring at 90 °C, followed by ultrasonic treatment pulsed at 100 W (Pulse-cycle: 70%) for 10, 20, 30, and 60 min. Fourier Transform Infrared spectroscopy (FT-IR) showed that the alkaline treatment removed the organic compounds from the mineral matrix. Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) showed that the particle size decreased with increasing duration of ultrasound, indicating the mechanism of erosion and fragmentation of micro agglomerates into nanoparticles. The X-ray patterns showed that none of the methods used to clean and extract the nanoparticles (ultrasound) damaged the Bio-HAp nanocrystals. Full Width at Half Maximum (FWHM) and crystallite size proved that they have a size between 22 and 27 nm, which was confirmed by Transmission Electron Microscopy (TEM) in the form of platelets and bacilli. Inductively coupled plasma (ICP) showed the presence of Mg, Na, K, and Zn as minority ions and that the isolation processes of Bio-HAp nanoparticles do not affect their trace element concentrations.

Influence of ICRF-NBI synergy on fast ion distribution and plasma performance in second harmonic heating experiments with deuterium NBI at EAST

Ion Cyclotron Range of Frequencies (ICRF) heating and Neutral Beam Injection (NBI) can have synergy due to the acceleration of NBI beam ions by ICRF wave fields at their harmonics. To understand the influence of ICRF-NBI synergy on fast ion distribution and plasma performance, dedicated experiments and TRANSP simulations have been carried out on EAST. The simulation results are consistent with the experimental results. They show that the ICRF-NBI synergy not only accelerates the NBI beam ions with energy lower than 80 keV to energy larger than 300 keV, but also generates fusion neutrons with energy larger than 3 MeV. Moreover, ICRF-NBI synergy improves the plasma performance by increasing the poloidal beta, plasma stored energy, core ion temperature, total neutron yield and kinetic pressure. In a typical H-mode plasma with 1.0 MW NBI and 1.5 MW ICRF power, it was observed that ICRF-NBI synergy increases the poloidal beta, plasma stored energy, core ion temperature and neutron yield by ∼35%, 33%, 22% and 80%, respectively. Various parameter scans show that the ICRF-NBI synergetic effects can be enhanced by decreasing the minority ion concentration or the distance between the harmonic resonance and magnetic axis, or by increasing the ICRF heating power or NBI beam energy. Consequently, this leads to a generation of fast ions with higher energy. For instance, the maximum energy of the fast ion tail increases from 300 to 600 keV as n(H) decreases from 5% to 0.1%.

Mechanism for Collective Energy Transfer from Neutral Beam-Injected Ions to Fusion-Born Alpha Particles on Cyclotron Timescales in a Plasma

Helium ash alpha particles at ∼100 keV in magnetically confined fusion plasmas may have the same Larmor radius, as well as cyclotron frequency, as the energetic beam-injected deuterons that heat the plasma. While the velocity-space distribution of the helium ash is monotonically decreasing, that of the energetic deuterons is a delta function in the edge plasma. Here we identify, by means of first principles particle-in-cell computations, a new physical process by which Larmor radius matching enables collective gyroresonant energy transfer between these two colocated minority energetic ion populations, embedded in majority thermal plasma. This newly identified nonlinear phenomenon rests on similar underlying physics to widely observed ion cyclotron emission from suprathermal minority ion populations.

Mesoscale structural gradients in human tooth enamel

The outstanding mechanical and chemical properties of dental enamel emerge from its complex hierarchical architecture. An accurate, detailed multiscale model of the structure and composition of enamel is important for understanding lesion formation in tooth decay (dental caries), enamel development (amelogenesis) and associated pathologies (e.g., amelogenesis imperfecta or molar hypomineralization), and minimally invasive dentistry. Although features at length scales smaller than 100 nm (individual crystallites) and greater than 50 µm (multiple rods) are well understood, competing field of view and sampling considerations have hindered exploration of mesoscale features, i.e., at the level of single enamel rods and the interrod enamel (1 to 10 µm). Here, we combine synchrotron X-ray diffraction at submicrometer resolution, analysis of crystallite orientation distribution, and unsupervised machine learning to show that crystallographic parameters differ between rod head and rod tail/interrod enamel. This variation strongly suggests that crystallites in different microarchitectural domains also differ in their composition. Thus, we use a dilute linear model to predict the concentrations of minority ions in hydroxylapatite (Mg2+ and CO32-/Na+) that plausibly explain the observed lattice parameter variations. While differences within samples are highly significant and of similar magnitude, absolute values and the sign of the effect for some crystallographic parameters show interindividual variation that warrants further investigation. By revealing additional complexity at the rod/interrod level of human enamel and leaving open the possibility of modulation across larger length scales, these results inform future investigations into mechanisms governing amelogenesis and introduce another feature to consider when modeling the mechanical and chemical performance of enamel.

Numerical Investigation of the Ion Cyclotron Resonance Heating (ICRH) Physics in DTT

An extensive linear analysis of the ICRH propagation and absorption in DTT full heating scenario has been performed by means of three advanced numerical tools: DISEMAG, FELICE and TORIC. The numerical codes solve respectively the full dispersion relation in the complex domain of the wavenumber (DISEMAG) and the integro-differential equation that accounts for the correct evaluation of the ICRH power absorption in a slab plasma (FELICE) and in the tokamak equilibrium configuration (TORIC). Moreover, by incorporating the antenna conceptual design, as released by the engineering design team, in FELICE and TORIC, the power spectrum, radiated by the antenna (3 straps) and coupled to the plasma, has been evaluated in the case of 60 and 90 MHz (3He and H minority heating respectively). By extensively using the abovementioned suite of codes, and after establishing the plasma target (fixing tokamak dimensions, density, temperatures, plasma current, magnetic field, isotopic composition, etc.), and the antenna characteristics (number, dimension, pitch, and radial position of the straps, antenna size, etc.), the power absorption on the various species (electrons, majority and minority ions) has been calculated as function of the minority concentration, parallel wavenumber, frequency, harmonic resonant layer, etc.. Comparison between the codes DISEMAG and TORIC in evaluating the absorption on electrons and minority ions has also been performed and shows a good agreement of the results. A new ion heating scheme based on three ions mixture has also been proposed in DTT.

Study of ion cyclotron range of frequencies heating characteristics in deuterium plasma in the Large Helical Device

The characteristics of ion cyclotron range of frequencies (ICRF) minority ion heating with a hydrogen minority and deuterium majority plasma were studied by ICRF modulation injection experiments in the Large Helical Device (LHD). In recent experiments with deuterium plasma, no significant increase in the neutron emission rate due to ICRF second harmonic deuteron heating was observed. Therefore, in this study, the neutron emission rate was used to refer to the information regarding the thermal ion component. Like the results of the observations of the heating efficiencies at various minority proton ratios, the experimental results showed good agreement with the simple model simulation of ICRF wave absorption. During these experiments, the accelerated minority hydrogen ions were observed by neutral particle analyzers. The counting rates of the energetic particles were higher in the lines of sight passing through the helical ripple than across the magnetic axis, and the counting rate decreased as the minority hydrogen ion ratio increased. The dependence of the minority hydrogen ion ratio on the density of the energetic ions was consistent with the experimentally observed heating efficiencies and simulations. The heating efficiency of ICRF minority ion heating could be well explained by simple model simulation in the LHD deuterium experiment.

Numerical study on the loss of fast ions produced by minority ion cyclotron resonance heating in EAST

The classical prompt loss of fast ions produced by minority ion cyclotron resonance heating (ICRH) is studied by a guiding center orbit following code in the Experimental Advanced Superconducting Tokamak (EAST). It is found that the loss of fast ions produced by ICRH mainly appears in both ends of the resonance layer, while the loss of fast ions in the middle resonance layer is very small. The dominant fast loss comes from trapped ions, rather than from passing ions. Controlling the location of resonance layer at the plasma core may be more beneficial to the EAST tokamak ICRH. In addition, the loss distribution of fast ions is studied. The results show that the fast ions are mainly lost near the midplane in the poloidal direction, but almost uniformly in the toroidal direction. Moreover, we investigate the dependence of fast ion loss on the ICRH power. The simulation results show that the loss fraction of fast ions in both ends of the resonance region increases with the ion cyclotron range of frequencies (ICRF) power, but barely affects the loss of fast ions in the middle region.

Removal of tritium from vacuum vessel by RF heated plasmas in LHD

The tritium removal from the vacuum vessel is one of the key issues for the realization of a fusion reactor. As in situ tritium removal techniques from the plasma facing materials, helium glow discharge wall conditioning (GDWC) and RF heated plasma due to electron cyclotron wall conditioning (ECWC) and ion cyclotron wall conditioning (ICWC) are applied with Large Helical Device (LHD) which remains tritium produced by deuterium plasma experiment. As the result, it suggests that ICWC could remove the tritium more efficiently than the ECWC and the GDWC. In the ICWC operation, the high energy particles induced by the minority ion heating mode as the standard ICRF heating operation may play an important role in tritium removal from the plasma-facing materials due to the particle’s bombardment.

European transport simulator modeling of JET-ILW baseline plasmas: predictive code validation and DTE2 predictions

The European transport simulator is a fusion machine simulator useful for making predictions of high-performance fusion plasmas, in particular for DT reactors. Recent developments introducing self-consistent simulations of combined RF + NBI heating schemes in which majority, minority and beam ions are simultaneously heated is documented. The predictive simulations are first validated by comparison with the experimental data on a DD JET baseline plasma. In order to prepare the next JET DTE2 experimental campaign, extrapolations of fusion performance on DT plasma from DD plasma are made with a particular focus on ion cyclotron resonance heating (ICRH) computation. Traditional ion cyclotron range of frequency heating models do not permit the study of Coulomb collisional interaction of various ion species simultaneously including neutral beam injection ions, and generally forces one to consider only minority populations. Accounting for multi-population interaction is made possible here by solving coupled sets of Fokker–Planck equations for all ion species adopting the non-linear collision operator for arbitrary distribution functions, accounting for effects, such as the self-collisions of majority (or large minority) populations. To answer the question whether H minority scheme or 3He minority ICRH scheme is better for boosting the DT fusion performance, minority concentration scans are produced.

Physicochemical properties of 3D bovine natural scaffolds as a function of the anterior-posterior, lateral and superior-inferior directions

Bovine trabecular bone (BTB) is a hydroxyapatite (HAp) source for bone regeneration due to its high metabolic activity inside the human body. In this work, the physicochemical properties of BTB raw, defatted-deproteinized, and incinerate (580 °C) cubic pieces (1 × 1 × 1 cm) were analyzed as a function of the anatomical directions. In these natural scaffolds, Inductively Coupled Plasma (ICP) showed the presence of Na, Mg, Zn, and K as minority ions. Scanning Electron Microscopy (SEM) shows that BTB is anisotropic, and X-ray patterns showed hydroxyapatite nanocrystals with preferred orientation in the superior-inferior axis. Micro–Computed Tomography allowed 3D reconstruction of a BTB cube and calculate the areal bone mineral density (aBMD) in Pixel/cm2, which is around 70%. aBMD exhibits an inversely proportional behavior to the porosity of the samples. BTB cubes present higher Young's modulus for the Z-direction than the X- and Y-direction, regardless of their pretreatment. This finding confirms that the mechanical properties of the scaffolds are governed by the crystalline structure, morphology, and spatial distribution of the hydroxyapatite nanocrystals. Infrared analysis showed the presence of carbonate.

Power deposition of H minority heating with a new compact ICRF antenna in KSTAR

The new compact ICRH antenna (CIA) with low electric field and conjugate-T has been installed in KSTAR. It is essential for studying the effect on the KSTAR plasma of H minority heating as a main ICRH scheme. The TRANSP-TORIC code has been adopted for analyzing the ICRH effect. The calculation using TRANSP-TORIC has been conducted with an additional 1 MW of ICRH power to the KSTAR operation at B0 = 2.0 T. About 75% of the ICRH power has coupled to the H minority heating, and most of the power of H minority heating has contributed to the energy of D majority ions and electrons. The deposited profile of the minority heating power varies with the concentration rate of the H minority ions and shows the possibility of producing energetic particles which appears to the increasing energy of D majority ions. The power of the H minority heating has good coupling to the majority ions in the broad range of 5 < n// < 35, including n// of the newly installed CIA in KSTAR.

Numerical investigation of a new ICRF heating scenario in D-T plasma on CFETR

For a fusion device, plasma pre-heating is required before the self-sustaining burning-state reactions of deuterium (D) and tritium (T) commence. Plasma heating with waves in the ion-cyclotron range of frequencies (ICRF) is effective in tokamaks. A new three-ion ICRF heating scheme for plasmas in the Chinese Fusion Engineering Test Reactor (CFETR) that require an increase in the bulk ion temperature via heating the lithium impurities in the D–T plasmas, was studied numerically. Our simulations show that the radio-frequency wave power is strongly absorbed by very few 7Li ions with concentrations of 0.01%–0.2% in a suitable mixture of D–T plasmas, the enhanced minority ion heating is related to that the 7Li fundamental resonance layer is very close to the two mode conversion layers. In adjusting the mixtures over a wide range of composition, an oscillatory behaviour in the 7Li absorption efficiency arises because of interference. Moreover, from estimates of the 7Li ion tail energy, most of the tail energy of the minority ions is found to be transferred to background ions via collisions. Compared with the routine (3He)-D–T scheme, the ICRF power is absorbed more effectively by the 7Li ions in the (7Li)-D–T heating scenario, and after the Fokker–Planck equations were solved, a large fraction of bulk ion heating was evident in the (7Li)-D–T heating scenario. The new three-ion scenario may therefore be an attractive proposition for bulk ion heating during the activated phase of the reactor.

High frequency Alfvén eigenmodes detected with ion-cyclotron-emission diagnostics during NBI and ICRF heated plasmas on the ASDEX Upgrade tokamak

The paper presents the first reported observation of high frequency Alfvén eigenmode excitation on the ASDEX Upgrade tokamak. The mode is driven in a novel way using radio frequency (RF) wave acceleration of either beam-injected deuterium ions or thermal He-3 minority ions in a three-ion heating scenario. In the case of beam ion acceleration, the instability only appears during deuteron acceleration at the third beam ion cyclotron harmonic (wave frequency ω = 3ΩD where ΩD is the deuterium cyclotron frequency), as the mode is not detected during the more commonly used second harmonic/minority heating scenario or in the absence of beam-injected ions. The mode frequency is around 0.6–0.7ΩD, where ΩD is evaluated in the low-field side plasma edge, and tracks the magnetic field B and the edge plasma electron density ne via the Alfvénic relation ω ∼ B ne −1/2. The mode does not appear as a single frequency wave but as a bundle of closely spaced (in frequency) sub-modes. When the parallel beam ion velocity component is increased, the sub-mode frequency spacing is observed to decrease, possibly due to a change in the eigenmode structure. Under certain conditions, typically in discharges with a relatively low plasma current, IP < 0.7 MA, the mode appears to be driven directly by sub-Alfvénic deuterium beam ions. Absolute measurements of the mode amplitude show that at least 1% of the beam-injected power is transferred non-collisionally to the instability. While this is too low for practical alpha-channeling applications, discharges are planned with the aim of increasing the level of power transferred non-collisionally between fast ions and the instability.

Sawtooth control with modulated ICRH in JET-ILW H-mode plasmas

Sawtooth pacing with modulated ion-cyclotron resonance heating (ICRH) has been demonstrated to be very efficient in JET-ILW L-mode plasmas (Lerche et al 2017 Nucl. Fusion 57 036027, Lennholm et al 2017 Fusion Eng. Des. 123 535–40), where the main heat source in the plasma centre is provided by the RF accelerated minority ions. In H-mode plasmas with substantial neutral beam injection power, this technique is more challenging since the fast beam particles have a stabilizing effect on the sawteeth, making it more difficult to trigger a sawtooth crash by removing the additional fast particle sources induced by ICRH inside the q = 1 surface. New results from JET-ILW experiments, showing that this technique can also be used in high power H-modes with considerable success will be presented, with focus on the sawtooth triggering efficiency at different pacing frequencies and plasma parameters, both during the flat-top phase of the discharges and during the H-mode exit and plasma termination.