Ion Enhancement Research Articles

Three-dimensional structure of radiative cooling in impurity seeded plasmas in the Large Helical Device

• Three-dimensionally localization of radiative cooling due to nitrogen seeding for divertor detachment was detected experimentally. • Principal component analysis was applied to two-dimensional radiation images. • A radiation feature in nitrogen seeding was extracted as a principal component. • EMC3-EIRENE code suggested the ionization enhancement at one of the divertor legs. • The extracted feature along the magnetic field lines which pass through the divertor leg. Three-dimensionally localization of radiative cooling due to nitrogen (N 2 ) seeding for divertor detachment was detected experimentally. Since the localization along some magnetic field lines induces toroidal asymmetry of heat load reduction on divertor plates, it should be avoided for fusion reactors. The three-dimensionally localized structure was extracted using Principal Component Analysis (PCA) from two-dimensional radiation images measured with an InfraRed imaging Video Bolometer (IRVB). By applying PCA to 34 images each in N 2 seeded plasmas with toroidally-asymmetric heat load reduction and in neon (Ne) seeded plasmas with toroidally-symmetric heat load reduction, a radiation feature in N 2 seeded plasmas was found as one of the principal components (PC). The three-dimensional transport code EMC3-EIRENE indicated that the ionization in one of the divertor legs is enhanced in nitrogen seeding compared with Ne seeding due to the difference in the first ionization energy. The magnetic field lines from the divertor leg were along the extracted radiation structure and were terminated by the divertor where the heat load decreased due to the N 2 seeding. These results indicate that three-dimensionally localized structure of radiative cooling was detected experimentally.

Investigation of the multielectron dynamics of CO in intense laser fields by the effective potential analysis of natural orbitals

We simulated the multielectron dynamics of CO in multicolor pulses of a near-IR fundamental ω and harmonics up to 4ω by using the multiconfiguration time-dependent Hartree-Fock method. The dynamics were analyzed in terms of effective potentials that govern the time evolution of molecular orbitals. The effective potential for the highest occupied orbital has a hump barrier responsible for anisotropic ionization of CO and the shape of a hump significantly changes at different internuclear distances. The electronic response became nonadiabatic when a 4ω-field was included, resulting in the enhancement in ionization and the extension of the high-order harmonic generation cutoff.

The principle of minimal power

This article is devoted to the memory of Yuri P Raizer, who passed away in 2021. He left a noticeable trace in gas discharge physics. The principle of minimal power (the state that requires minimal power is most probable) is thoroughly used in his books. Although the fundamental laws of physics do not imply this ad hoc principle, a detailed analysis of underlying phenomena can often reveal why nature prefers this path. Raizer illustrated this principle for plasma stratification, formation of electrode spots, discharge constriction, the shape of an arc channel, etc. We argue that the nonlinearity of equations describing gas discharges can often justify the realization of a plasma state maintained at minimal electric power. This nonlinearity appears because small groups of energetic electrons often control the ionization processes. The number of these electrons depends strongly on the ratio of the electric field to gas density, E/N. Under certain conditions, the ionization rate can also depend nonlinearly on electron density due to stepwise ionization and Coulomb collisions. We use the principle of minimal power to illustrate some of Raizer’s contributions to gas discharge physics from a single point of view. We demonstrate that nonlinearity of ionization processes in gas discharges can substantiate this principle for plasma stratification. However, striations of s, p, and r types in neon could exist with minimal or no ionization enhancement. This reminds us of Raizer’s warning that applying the minimal power principle could lead to erroneous predictions, and a proper theory is required in each case to justify its use. ‘The phenomenon of striations satisfies the principle of minimal power’ – Yuri Raizer

Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study, a coaxial transmission line resonator is constructed, which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon, nitrogen, or even air, respectively. Although the different kinds of working gas induce the different discharge performance, their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods, and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 1018 m−3. The tail region of plasma jets all contain a large number of active particles, like NO, O, emitted photons, etc, but without O3. The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields, the ionization wave propulsion, and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets. The parameters of plasma jet could be modulated by adjusting microwave power, modulation pulse parameters (modulation frequency and duty ratio), gas type and its flow rate, according to the requirements of application scenarios.

Peptidyl-Resin Substrates as a Tool in the Analysis of Caspase Activity.

Caspases, proteolytic enzymes belonging to the group of cysteine proteases, play a crucial role in apoptosis. Understanding their activity and substrate specificity is extremely important. Fluorescence-based approaches, including fluorogenic substrates, are generally used to confirm cleavage preferences. Here we present a new method of substrate specificity and activity analysis based on the application of fix-charge tagged peptides located on the resin. The proteolysis of peptide bond on the resin, occurring even with low efficiency, results in the formation of N-terminal fragments of model peptide containing ionization enhancers in the form of quaternary ammonium groups, allowing for ultrasensitive and reliable analysis by LC-MS/MS. The possibility of application of the proposed solution was tested through the analysis of substrate specificity and activity of caspase 3 or 7. The obtained results confirm the known substrate specificity of executioner caspases. Our solution also allowed us to observe that caspases can hydrolyze peptides shorter than those presented to date in the scientific literature.

The effect of anode axial position on the performance of a miniaturized cylindrical Hall thruster with a cusp-type magnetic field

A 200 W cylindrical Hall thruster with a cusp-type magnetic field was proposed, manifesting convergent plume and high specific impulse. In this paper, a series of ring-shaped anodes are designed and the influence of anode axial position on the performance of CHT with a cusp-type magnetic field is studied. The experimental results indicate that the thruster keeps stable operation at the condition of 140–270 W discharge power. When the anode moves axially towards the upstream cusp field, the thrust enhances from 6.5 mN to 7.6 mN and specific impulse enhances from 1658 s to 1939 s significantly. These improvements of thruster performance should be attributed to the enhancement of current utilization, propellant utilization and acceleration efficiency. According to the analyses on the discharge characteristics, it is revealed that as the anode moves upstream, the electron transport path could be extended, the magnetic field in this extended path could impede electron cross-field transport and facilitate the ionization intensity, yielding to the enhancement of current utilization and propellant utilization efficiency. Moreover, along with this enhancement of upstream ionization at the given anode flow rate, the main ionization region is thought to move upstream and then separate more apparently from the acceleration region, which has been demonstrated by the narrowing of ion energy distribution function shape. This change in acceleration region could decrease the ion energy loss and enhance acceleration efficiency. This work is beneficial for optimizing the electrode structure of thruster and recognize the ionization and acceleration process under the cusp magnetic field.

Tests of a New Solar Flare Model Against D and E Region Ionosphere Data

AbstractWe present results from a suite of models designed to simulate solar flare effects on the D and E region of the ionosphere. This suite includes models of the solar spectrum, the ionosphere and of HF radiowave propagation. A central component of this system is the development of photoelectron ionization enhancement factors with higher energy resolution in the soft X‐ray spectral region that can be used to supplement existing ionization schemes currently implemented in upper atmospheric general circulation models. We tested this photoelectron model in the NCAR Thermosphere‐Ionosphere‐Mesosphere‐ Electrodynamics General Circulation Model (TIME‐GCM) and in a photochemical model of the D region. In both cases, we compared predicted flare response using two different input solar flare spectra. One is the Flare Irradiance Spectral Model (FISM) and the other is a physics based model called NRLFLARE. Our predictions for the E region were compared with incoherent scatter radar data and suggest that enhanced flux in the 1–2 nm spectral region, as indicated by NRLFLARE, is important for reproducing the observations. For the D region, we combined our theoretical results for the X1.3 flare of 7 September 2017 with ray tracing calculations that suggest 20–40 db of 6.4 MHz absorption. This agrees with previously published observations and model estimates, all of which suggest greater HF absorption than the operational D region absorption prediction model (swpc.noaa.gov/products/d‐region‐absorption‐predictions‐d‐rap). Finally, our theoretical comparison with previously published empirical models derived from very low frequency data was less clear due, in part, to large differences between the different empirical models.

Asymmetric Dissociative Tunneling Ionization of Tetrafluoromethane in ω - 2ω Intense Laser Fields.

Dissociative ionization of tetrafluoromethane (CF4) in linearly polarized ω-2ω ultrashort intense laser fields (1.4 × 1014 W/cm2, 800 and 400 nm) has been investigated by three-dimensional momentum ion imaging. The spatial distribution of produced by CF4 → + F + e− exhibited a clear asymmetry with respect to the laser polarization direction. The degree of the asymmetry varies by the relative phase of the ω and 2ω laser fields, showing that 1) the breaking of the four equivalent C-F bonds can be manipulated by the laser pulse shape and 2) the C-F bond directed along the larger amplitude side of the ω-2ω electric fields tends to be broken. Weak-field asymptotic theory (WFAT) shows that the tunneling ionization from the 4t 2 second highest-occupied molecular orbital (HOMO-1) surpasses that from the 1t 1 HOMO. This predicts the enhancement of the tunneling ionization with electric fields pointing from F to C, in the direction opposite to that observed for the asymmetric fragment ejection. Possible mechanisms involved in the asymmetric dissociative ionization, such as post-ionization interactions, are discussed.

Self-discharge by Streaming Cosmic Rays

A new nonthermal phenomenon caused by streaming cosmic rays (CRs) in the universe is proposed. The streaming CRs drive the return current of thermal electrons to compensate for the CR current. Then, electric fields are induced by the resistivity of the return current. It is shown that the resistive electric fields can accelerate secondary electrons generated by the streaming CRs. This is the self-discharge by streaming CRs. In this work, the self-discharge condition and the condition for runaway acceleration of secondary electrons are presented. The self-discharge creates high-energy secondary electrons, resulting in enhancements of ionization and nonthermal emission including the Kα emission line of neutral iron. After the self-discharge, the return current of thermal electrons is replaced by the electric current of secondary electrons. Since some generation and amplification of magnetic fields are driven by the return current of thermal electrons, the self-discharge can significantly influence them.

Solar and interplanetary events that drove two CIR-related geomagnetic storms of 1 June 2013 and 7 October 2015, and their ionospheric responses at the American and African equatorial ionization Anomaly regions

This study investigates the sequence of solar and interplanetary events that drove the 1 June 2013 and October 2015 geomagnetic storms and how the American (68°–78oE) and African (32°–42oE) Equatorial Ionization Anomaly (EIA) regions responded to them. We constructed the EIA structures by using Total Electron Content (TEC) and ionospheric irregularities derived from Global Navigation Satellite System (GNSS) receivers along with the study locations. We also analyzed disturbed time ionospheric electric field and model data alongside the GNSS data. The 1 June 2013 geomagnetic storm was driven by a combination of a weak CME and HSSs from solar coronal holes, while the 7 October 2015 storm was solely driven by HSSs. Storm-time hemispherical asymmetry in ionospheric TEC and irregularities distributions was consistently observed. Storm with minimum SYM-H value at day-side locations caused enhancement in plasma ionization and pole-ward movement of EIA crests, while storm with minimum SYM-H value at night-side locations caused reduction in plasma ionization and equator-ward movement of EIA crests. The phase of responses of the ionosphere to geomagnetic storms depends on the local time of storm’s onset and local time of the storm’s main phase minimum which also determine the orientation of Prompt Penetration Electric Field (PPEF). At storm’s onset time in the low latitude regions, the main storm-induced electric field is PPEF. Daytime eastward PPEF intensified plasma fountain to increase the EIA crests locations, while nighttime westward PPEF reversed plasma fountain to cause equator-ward collapse of the EIA crests. However, around the storm’s recovery phase, under southward turning of IMF Bz, depending on their orientations, PPEF and Disturbed Dynamo Electric Field (DDEF) collectively influenced low latitude ionosphere. Eastward PPEF at the Pre-Reversal Enhancement (PRE) time enhanced irregularities generation, while westward DDEF at PRE time inhibited irregularities generation. The season of storm’s occurrence is also a factor that dictates ionospheric response to a storm, for instance, the 7 October storm (SYM-H −124 nT) influenced the ionosphere more than the 1 June storm (SYM-H −137 nT). Both storms had long recovery phase. On pre-storm days, we observed stronger and well-developed EIA crests over the American sector than over the African sector.

Coupling Simulation on Two-dimensional Axisymmetric Beaming Propulsion System

A two-dimensional (2D) axisymmetric fluid modeling for plasma dynamics was coupled with an electromagnetic wave propagation to capture the electromagnetic wave and plasma structures on the microwave-driven in-tube accelerator (MITA) concept. The electromagnetic wave injected into a waveguide was focused on at the vehicle’s rear side through reflection processes by the front mirror and the waveguide. An overcritical plasma was created at the high-intensity electric field region because of enhancement of an electron-impact ionization. The incident microwave was reflected by the plasma with overcritical density and a standing wave was induced in front of the dense plasma because the reflected wave overlapped with the incident microwave. In addition to wave enhancement by standing process, the strong electric field region was obtained at edges of the overcritical plasma because of wave diffraction, which can affect a shock wave strength and thrust performance of the MITA.

Thermal relic of self-interacting dark matter with retarded decay of mediator

The existence of a light mediator is beneficial to some phenomena in astroparticle physics, such as the core-cusp problem and diversity problem. It can decouple from Standard Model to avoid direct detection constraints, generally realized by retard decay of the mediator. Their out-of-equilibrium decay process changes the dark matter (DM) freeze-out via temperature discrepancy. This type of hidden sector (HS) typically requires a precision calculation of the freeze-out process considering HS temperature evolution and the thermal average of the cross-section. If the mediator is light sufficiently, we can not ignore the s-wave radiative bound state formation process from the perspective of CMB ionization and Sommerfeld enhancement. We put large mass splitting between DM and mediator, different temperature evolution on the same theoretical footing, discussing the implication for DM relic density in this HS. We study this model and illustrate its property by considering the general Higgs-portal dark matter scenario, which includes all the relevant constraints and signals. It shows that the combination of BBN and CMB constraint favors the not-too-hot HS, rinf< 102, for the positive cubic interaction of mediator scenario. On the other hand, the negative cubic interaction is ruled out except for our proposed blind spot scenario.

Dual Electrospray Ionization Enhancement of Proteins Enabled by DMSO Supercharging Reagent.

Supercharging reagents assist protein ionization by producing higher charge states and increasing signal intensities, thus improving sensitivity. Described here is an approach to employ a dual-spray ionization source with DMSO as a supercharging reagent to expand in-source supercharging. Under denaturing conditions, dual-source supercharging enhances ionization up to an order of magnitude for proteins of various properties and sizes, but the effect is not uniform. Efficient mixing of solutions from two nebulizing plumes was observed, which allowed sufficient transfer of supercharging molecules to a protein. The described method and proposed mechanism require at least 2.5% of DMSO to produce visible enhancement.

Enhanced field emission of CuO nanowires by aluminum coating for volatile organic compound detection

This work reports-a novel ionization gas sensor assembled by the building blocks of CuO nanowires coated with a thin layer of aluminum. The superficial aluminum is then partially oxidized to alumina forming an Al2O3/Al/CuO hybrid nanocomposite. It is revealed that this nanocomposite enables the discharge of volatile organic compound at ppm level at an ultralow ionization voltage (several tens of volts) with high stability. Typical organic gases, including toluene, acetone, isopropanol, and methanol can be identified by this sensor with the specific threshold voltages in the cleanroom. In addition, the concentration of isopropanol gas has also been detected at a low limit down to 5 ppm. The gas sensing mechanism is due to the variation of voltages that are required to ionize a specific gas as the fingerprint. Based on the comparative discharge experiments along with the energy band analysis, the high enhancement of gas ionization is attributed to the optimized low work function and intermediate energy interlayer in combination with the tip effect of Al2O3, Al, and CuO. This work may pave a new way for the design of the similar material system to advance ionization gas sensing.

Analysis of Fragmentation Pathways of Peptide Modified with Quaternary Ammonium and Phosphonium Group as Ionization Enhancers.

Peptide modification by a quaternary ammonium group containing a permanent positive charge is a promising method of increasing the ionization efficiency of the analyzed compounds, making ultra-sensitive detection even at the attomolar level possible. Charge-derivatized peptides may undergo both charge remote (ChR) and charge-directed (ChD) fragmentation. A series of model peptide conjugates derivatized with N,N,N-triethyloammonium (TEA), 1-azoniabicyclo[2.2.2]octane (ABCO), 2,4,6-triphenylopyridinium (TPP) and tris(2,4,6-trimetoxyphenylo)phosphonium (TMPP) groups were analyzed by their fragmentation pathways both in collision-induced dissociation (CID) and electron-capture dissociation (ECD) mode. The effect of the fixed-charge tag type and peptide sequence on the fragmentation pathways was investigated. We found that the aspartic acid effect plays a crucial role in the CID fragmentation of TPP and TEA peptide conjugates whereas it was not resolved for the peptides derivatized with the phosphonium group. ECD spectra are mostly dominated by cn ions. ECD fragmentation of TMPP-modified peptides results in the formation of intense fragments derived from this fixed-charge tag, which may serve as reporter ion.

A Forward-Thinking Approach to Addressing the New Synthetic Opioid 2-Benzylbenzimidazole Nitazene Analogs by Liquid Chromatography-Tandem Quadrupole Mass Spectrometry (LC-QQQ-MS).

Novel psychoactive substances (NPS) continue to represent a threat to public health and safety. The number of new drugs in the latest emergent synthetic opioid class—the 2-benzylbenzimidazole analogs—also called the nitazenes—has begun to dominate the current new synthetic opioid (NSO) subclass of NPS. We describe a liquid chromatography–tandem quadrupole mass spectrometry method for the quantification of nine analogs and/or metabolites of drugs in this series: isotonitazene, metonitazene, protonitazene, etonitazene, clonitazene, flunitazene, N-desethyl isotonitazene, 5-amino isotonitazene and 4ʹ-hydroxy nitazene in human whole blood, urine, and tissue. Samples were prepared for analysis using a basic liquid–liquid extraction. Chromatographic separation was achieved using a C-18 analytical column. Multiple reaction monitoring mode was used for detection. The calibration range for the analytes was 0.5–50 ng/mL (except for 5-amino isotonitazene, which was 1.0–50 ng/mL). The limit of detection was 0.1 ng/mL, and the limit of quantitation was 0.5 ng/mL. The method had no carryover or interferences. Ionization enhancement was observed but did not affect quantitation. All analytes passed the method validation assessment. Authentic human samples suspected of containing NSOs were obtained from a medical examiner and coroner offices, as well as partnering forensic toxicology laboratories. Isotonitazene was confirmed in 92 blood samples, and its metabolites were confirmed across various matrices. Metonitazene (n = 35), flunitazene (n = 5), protonitazene (n = 3), etodesnitazene (n = 2) and butonitazene (n = 1) were also detected in cases. These newly emerging 2-benzylbenzimidazole analogs were commonly found in combination with NPS benzodiazepines and opioids (e.g., flualprazolam, fentanyl). Nitazene analogs are potent esoteric drugs that may not be identified during routine toxicological screening, and specialized assays based on sensitive instrumentation are needed to accurately characterize these NSOs.

Tracking the Ionization Site in Neutral Molecules.

When a diatomic molecule is exposed to intense light, the valence electron may tunnel from a higher potential (corresponding to an upfield atom) due to the suppressed internuclear barrier. This process is known as ionization enhancement and is a key mechanism in strong field ionization of molecules. Alternatively, the bound electron wave function can evolve adiabatically in the laser field, resulting in ionization from the downfield atom. Here, we introduce a method to quantify the relative contribution of these two processes. Applying this method to experimentally measured electron momenta distributions following strong field ionization of N_{2} with infrared laser light, we find approximately a 2∶1 ratio of electrons ionized from a downfield atom, relative to upfield. This suggests that the bound state wave function largely adapts adiabatically to the changing laser field, although the nonadiabatic process of ionization enhancement still contributes even in neutral molecules. Our method can be applied to any diatomic neutral molecule to better understand the evolution of the initially bound electron wave packet and hence the nature of the molecular ionization process.

Direct Connection Between Auroral Oval Streamers/Flow Channels and Equatorward Traveling Ionospheric Disturbances

We use simultaneous auroral imaging, radar flows, and total electron content (TEC) measurements over Alaska to examine whether there is a direct connection of large-scale traveling ionospheric disturbances (LSTIDs) to auroral streamers and associated flow channels having significant ground magnetic decreases. Observations from seven nights with clearly observable flow channels and/or auroral streamers were selected for analysis. Auroral observations allow identification of streamers, and TEC observations detect ionization enhancements associated with streamer electron precipitation. Radar observations allow direct detection of flow channels. The TEC observations show direct connection of streamers to TIDs propagating equatorward from the equatorward boundary of the auroral oval. The TIDs are also distinguished from the streamers to which they connect by their wave-like TEC fluctuations moving more slowly equatorward than the TEC enhancements from streamer electron precipitation. TIDs previously observed propagating equatorward from the auroral oval have been identified as LSTIDs. Thus, the TIDs here are likely LSTIDs, but we lack sufficient TEC coverage necessary to demonstrate that they are indeed large scale. Furthermore, each of our events shows TID’s connection to groups of a few streamers and flow channels over a period in the order of 15 min and a longitude range of ∼15–20°, and not to single streamers. (Groups of streamers are common during substorms. However, it is not currently known if streamers and associated flow channels typically occur in such groups.) We also find evidence that a flow channel must lead to a sufficiently large ionospheric current for it to lead to a detectable LSTID, with a few tens of nT ground magnetic field decreases not being sufficient.

Resonance-induced ionization enhancement and suppression of circular states of the hydrogen atom in strong laser fields

We theoretically investigated the ionization dynamics of a hydrogen atom in circular excited states irradiated by the circularly polarized laser pulses by solving the time-dependent $\mathrm{Schr}\stackrel{\ifmmode \ddot{}\else \&#34;{}\fi{}}{\mathrm{o}}\mathrm{dinger}$ equation. We calculated the ionization yields of the two excited states which are corotating and counter-rotating with respect to the laser fields as a function of the laser frequency. For the corotating excited state, our results show an obvious ionization suppression when the laser frequency is beyond the one-photon ionization threshold, and it is followed by a strong ionization enhancement when the laser frequency further increases. These ionization suppressions and enhancements are absent for the counter-rotating excited state. By tracing the ionization process, we found that resonance between the initial state and a lower-energy state occurs at the frequency of the ionization enhancement. Ionization from this lower-energy state is responsible for this ionization enhancement. At the frequency of ionization suppression, Rabi oscillation between the initial and the lower-energy state occurs, which prevents further ionization and thus suppresses the final ionization yield.

Enhancement of electron-impact ionization induced by warm dense environments.

Studies have shown significant discrepancies between the recent experiment [Berg etal., Phys. Rev. Lett. 120, 055002 (2018)PRLTAO10.1103/PhysRevLett.120.055002] and current theoretical calculations on the electron-impact ionization cross section of ions in warm dense magnesium. Here, we present a systematic study the effects of the ionic correlations and free-electron screening on the electron-impact ionization of ions in warm dense matter. The ionic correlation and the free-electron screening effects yield additional Hermitian terms to the calculation of the ionic central-force-field potential, which significantly change the electronic structure compared with that of the isolated ion. In calculating the electron-impact ionization, we describe the impact and ionized electrons using a damped-distorted wave function, which considers the momentum relaxation of free electrons due to collisions with other free electrons and ions. We reproduce the electron-impact ionization process for Mg^{7+} in the solid-density plasma and increase the ionization cross section by one order of magnitude compared with that of the isolated ion, which excellently agrees with the experimental result of Berg etal.