Supersonic Molecular Beam Research Articles

Characteristics of edge temperature ring oscillation during the stationary improved confinement mode in EAST

The I-mode is a natural edge localized mode (ELM)-free regime with H-mode-like improved energy confinement and L-mode-like particle confinement, making it an attractive scenario for future tokamak-based fusion reactors. A kind of low-frequency oscillation has been widely observed, with a frequency between stationary zonal flow and geodesic-acoustic mode (GAM) zonal flow. In EAST, most stationary I-mode shots have such a mode, called edge temperature ring oscillation (ETRO). This mode probably plays an important role in development and maintenance of the I-mode , while investigations are needed to clarify the differences between ETRO and similar mode low-frequency oscillation in other devices, such as limit cycle oscillation (LCO). In this paper, the properties of ETRO are described in detail, including the structure of its magnetic components, its radial propagation characteristics, statistics of its central frequency, a linear analysis of the alternating transition turbulences and a comparison with GAM and LCO. Although some similarities can be found between ETRO and both GAM and LCO, the main features are not identical. ETRO is probably a novel type of finite frequency zonal flow or pressure gradient-induced drift that is unique to the I-mode. It is found that modest fueling can reduce ETRO intensity while maintaining I-mode confinement, suggesting that supersonic molecular beam injection could be used as an effective tool to control ETRO.

Fast saliva analysis by GC-MS with Cold EI and Open Probe Fast GC-MS with Cold EI for the detection of cannabis usage.

Saliva is a body fluid that is much easier to collect and analyze than blood. Thus, saliva analysis for the detection of delta 9-tetrahydrocannabinol (delta 9-THC) can serve as a tool for law enforcement agents to detect cannabis consumption by drivers. Fast saliva analysis for the presence of delta 9-THC and/or cannabidiol (CBD) is described with both gas chromatography-mass spectrometry (GC-MS) with Cold electron ionization (EI) with good separation and in 10min and/or with Open Probe Fast GC-MS with Cold EI in under 1 min full analysis cycle time. Saliva was taken directly from donors' tongues on a thin glass rod that was used "as is" for analysis. The saliva was thermally desorbed with a modified ChromatoProbe device inside the gas chromatograph (GC) injector and in an Open Probe (Agilent name QuickProbe) for its sub-1-min analysis. Cold EI is based on coupling of the GC and mass spectrometer (MS) with a supersonic molecular beam and on EI of vibrationally cold sample molecules during their flight through a contact-free ion source (thereby named Cold EI). A revised type of Open Probe Fast GC-MS on the bench is also described. Our saliva analysis was characterized by: Saliva can be collected in the field and transported to the lab for analyses "as is" without any sample preparation. Easy detection of cannabis consumption from cigarettes and/or other cannabis products. Distinction between the isomers delta 9-THC and CBD. Ultra-fast analysis in under 1 min using Open Probe Fast GC-MS with Cold EI.

Design and characterization of an optical-fiber-coupled laser-induced desorption source for gas-phase dynamics experiments.

Preparation of neutral non-volatile molecules intact in the gas phase for mass spectrometry or chemical dynamics experiments remains a challenge for many classes of molecules. Here, we report the design and characterization of a fiber-coupled laser-based thermal desorption source capable of preparing intact neutral molecules at high molecular densities in the gas phase for use in velocity-map imaging experiments. Within this source, the sample is deposited onto a thin tantalum foil. Irradiation of the foil from the reverse side by a focused laser beam leads to highly localized heating of the sample, resulting in desorption of a plume of molecules into the gas phase. The fiber-coupled design simplifies the alignment of the desorption laser beam, and the ability to rotate the foil relative to the fixed laser beam allows the sample to be continually refreshed under vacuum. We use 118nm photoionization of three test molecules-uracil, adenine, and phenylalanine-to characterize the source and to demonstrate various aspects of its performance. These include the dependence of the velocity-map imaging performance on the size of the interaction region and the dependence of the laser-induced desorption source emission on desorption laser power and heating time. Signal levels recorded in these measurements are comparable to those we typically obtain in similar experiments using a pulsed supersonic molecular beam, and we, therefore, believe that the source has considerable potential for use in a wide range of chemical dynamics and other experiments.

Shielded ionisation discharge (SID) probe for spatiotemporal profiling of pulsed molecular beam.

Intense pulsed supersonic molecular beams are used in many applications such as tokamak fueling, edge plasma diagnostics, ion beam profile monitors, laser cluster experiments, chemical kinetics, etc. Measurement of absolute density is required to optimize beam sources used in these experiments. Absolute density measurement of a continuous molecular beam is challenging due to its small size and rarefied flow, which makes it even more difficult for a pulsed molecular beam due to its transient nature. In this work, we demonstrate a novel probe to measure the spatiotemporal evolution of the absolute number density of a pulsed supersonic molecular beam. The probe is named the Shielded Ionization Discharge probe. It measures density using localized discharge within the molecular beam created by the thermionic emission of electrons from a hot filament. We describe the design, calibration, and characterization of the developed probe. The performance of the probe is demonstrated by measuring the spatial and temporal profiles of a pulsed supersonic molecular beam of 1.5ms duration.

Development of dual-path multi-pass Thomson scattering system in GAMMA 10/PDX

A dual-path Thomson scattering (DPTS) system was developed to measure electron temperature and density in a GAMMA 10/PDX central cell (CC) and an end cell (EC). The DPTS comprises CC Thomson scattering system (CC-TS) and an EC Thomson scattering system (EC-TS). In the CC-TS, we developed a multipass system to improve the signal intensities and time resolution. In the EC-TS, a double-pass system was developed as a preliminary step in developing a multipass system. In a previous EC-TS, the optical components for the double-pass configuration were placed in a vacuum vessel. To reduce the influence of stray light and facilitate alignment, a hole for the double-pass laser path was made on the partition wall in the vacuum chamber such that the probe laser could be extracted into the atmosphere and the double-path configuration could be easily adjusted. We applied DPTS to detached plasma experiments and successfully measured the core and edge electron temperatures and densities with the detached plasma experiments with the additional application of supersonic molecular beam injection and central electron cyclotron heating in the core plasma to simultaneously introduce intermittent particle flux.

CH3Cl Dissociation, CH3 abstraction, and Cl adsorption from the dissociative scattering of supersonic CH3Cl on Cu(111) and Cu(410)

To study the elementary steps in the Rochow-Müller process, we bombarded Cu(111) and Cu(410) with 0.7–1.9 eV supersonic molecular beams (SSMB) of CH3Cl. We then identified the corresponding adsorbed species using X-ray photoemission spectroscopy (XPS) in conjunction with synchrotron radiation (SR). We found Cl as the dominant adsorbed species (much higher than that of adsorbed carbonaceous species) coming from the dissociative scattering of CH3Cl. We also found that the threshold kinetic energy of the reaction depends on the crystal surface orientation.

State-resolved studies of CO2 sticking to CO2 ice.

Internal vibrations may affect the adsorption, scattering, and reactions of molecules impinging onto a surface. The energy of the ν 3 antisymmetric stretch vibration of CO2 slightly exceeds the desorption energy of CO2 bound to CO2 ice. We use supersonic molecular beam techniques and rovibrationally state-resolved excitation to determine whether this vibration affects condensation of gas phase CO2 to its ice. We detect sticking and CO2 ice formation using RAIRS and quantify the sticking probability using the King and Wells method with modulation of the vibrational excitation and Fourier transform based detection. We find that the influence of this vibration on the structure of the formed ice and on the sticking probability is negligible under our conditions. Based on our detection limit, we quantify the weighted average sticking probability at approximately 0.9 and the difference between the state-resolved and weighted average sticking probability as below 0.03%.

Experimental study on the characteristics of supersonic molecular beam injection

Experimental study on the characteristics of supersonic molecular beam injection

An efficient preparation of HD+ molecular ions in an ion trap by REMPI

We report a method of efficiently generating ultracold hydrogen molecular ions HD+ in a segmented linear ion trap. HD+ ions are created by [2+1′] resonance-enhanced multiphoton ionization (REMPI) of an HD supersonic molecular beam, and sympathetically cooled by laser-cooled Be+ ions. The HD+ ions are generated species-selectively using 201 nm and 395 nm pulse lasers with energies of 0.08 mJ (5.1 × 106 W/cm2) and 1.5 mJ (9.5 × 107 W/cm2) respectively. The average loading rate of 4.3(2) HD+ ions per second in the ion trap is determined by comparing the experimental images with the simulated images of Be+-HD+ bi-component Coulomb crystals. This method paves a way to produce the state-selected HD+ ions, which can improve the signal strengths of the selected rovibrational transitions of HD+ ions.

Controlled Carboxylic Acid-Functionalized Silicon Nitride Surfaces through Supersonic Molecular Beam Deposition.

The functionalization of inorganic surfaces by organic functional molecules is a viable and promising method towards the realization of novel classes of biosensing devices. The proper comprehension of the chemical properties of the interface, as well as of the number of active binding sites for bioreceptor molecules are characteristics that will determine the interaction of the sensor with the analyte, and thus its final efficiency. We present a new and reliable surface functionalization route based on supersonic molecular beam deposition (SuMBD) using 2,6-naphthalene dicarboxylic acid as a bi-functional molecular linker on the chemically inert silicon nitride surface to further allow for stable and homogeneous attachment of biomolecules. The kinetically activated binding of the molecular layer to silicon nitride and the growth as a function of deposition time was studied by X-ray photoelectron spectroscopy, and the properties of films with different thicknesses were investigated by optical and vibrational spectroscopies. After subsequent attachment of a biological probe, fluorescence analysis was used to estimate the molecular layer's surface density. The successful functionalization of silicon nitride surface via SuMBD and the detailed growth and interface analysis paves the way for reliably attaching bioreceptor molecules onto the silicon nitride surface.

The stable conformations and vibronic and cation spectroscopy of 2-ethoxybenzonitrile

Ethoxy-substituted benzene has several stable conformations as the single bond in the ethoxy group is capable of internal rotation. Ethoxybenzonitrile may has more conformers due to different orientations of ethoxy with respect to the CN group. In this paper, the potential energy surface (PES) of 2-ethoxybenzonitrile in the ground state was calculated at the level of B3LYP/cc-pvdz, and five different molecular conformers were found on the PES. Only the most stable conformer I (trans) was observed in the supersonic molecular beam experiments. The resonance enhanced multiphoton ionization (REMPI) and mass analyzed threshold ionization (MATI) spectra of 2-ethoxybenzonitrile were measured and Franck-Condon simulations were performed, and the theoretical results are in good agreement with the experimental measurements. The similar molecular structures in S0, S1, and D0 states imply the large Franck-Condon factors. The vibronic structures in S1 and D0 states were analyzed in detail and the vibronic features were assigned. The MATI spectra follow well the propensity rule Δν = 0, indicating that the molecular structures of the cationic and excited states are similar. Most of the observed vibrations are associated with the ring in-plane distortion. The band origin of the S1←S0 transition and the accurate adiabatic ionization energy of 2-ethoxybenzonitrile are determined for the first time to be 34 092 ± 2 and 69 796 ± 5 cm−1, respectively.

An innovative approach to the improved radiating divertor concept by supersonic molecular beam injection on HL-2A

The ‘puff-and-pump’ radiating divertor condition is a promising approach for the reduction of excessive thermal power loading on the divertor targets. The divertor supersonic molecular beam injection (SMBI) system installed on HL-2A strongly enhances the capacity of the divertor heat load control. This system has a faster time response than the divertor gas puffing (GP) system. Divertor heat load control capacity has been compared between these two techniques by experiments on HL-2A and simulations. Experimental results suggest that the divertor SMBI system reduces the divertor heat flux peak to a lower level with less time delay than that for the divertor GP system, owing to a higher injection rate and particle velocity. Simulations by SOLPS demonstrate that a high injection rate shortens the function time which is defined by the time interval between the arrival of the particles at the divertor plasma edge and the reduction of divertor electron temperature. High velocity of SMBI injected neutral gas particle also shortens the particle flight time to arrive at the edge. Less flight time and function time lead to a faster response of the divertor SMBI system compared to the divertor GP system. In addition, simulations by EMC3-EIRENE also suggest that, compared to the GP system, stronger heat load reduction of the SMBI system can also be caused by deeper deposition of gas source owing to its higher particle velocity.

Particle pump-out induced by trapped electron mode turbulence in electron cyclotron heated plasmas on XuanLong-50 spherical torus

Particle pump-out effects induced by low-frequency (<200 kHz) density fluctuations were observed in solely electron cyclotron wave (ECW)-heated plasmas on the spherical torus XuanLong-50 (EXL-50) without a central solenoid. The intensity of the relative density fluctuations increases with increasing ECW power and decays when the ECW is turned off while sustaining the plasma current. The electron densities are maintained relatively high and steady when the density fluctuations are completely absent, indicating that the outward transport of electrons is dominated by the particle pump-out effect of the ECW. The density fluctuations are modulated by a supersonic molecular beam injection pulse and the modulation amplitude decreases with increasing electron density at the same ECW injection power and decreasing ECW power at the same electron density, respectively. Analysis revealed that a critical value of electron temperature gradient (ETG) triggers the density fluctuations, and the intensity of the relative density fluctuations is positively correlated with the ETG and approximately inversely proportional to the effective collision frequency. With plasma parameters similar to those of EXL-50 experiments, the HD7 code simulations demonstrate that trapped electron mode (TEM) turbulence can be excited by ETG higher than the critical value observed in the experiment. In addition, the dependence of the mode growth rate (supposed to be proportional to the saturation level of fluctuations in quasi-linear theory) and the measured intensity of the density fluctuations is comparable. The simulated outward particle flux integrated over the poloidal wave number spectrum is significant and proportional to ETG. These observations demonstrate that the density fluctuation is TEM turbulence, which is driven by ETG and induces particle pump-out when the electron density/effective electron collision frequency is low. The potential relevance of this work with the controls of plasma profiles, impurities, helium ash, and heat transport in future reactors of similar low effective collision frequency is also discussed.

Sensitivity comparison of gas chromatography-mass spectrometry with Cold EI and standard EI.

Gas chromatography-mass spectrometry (GC-MS) with Cold EI is based on interfacing GC and MS with supersonic molecular beams (SMBs) along with electron ionization of vibrationally cold sample compounds in SMB in a fly-through ion source (hence the name Cold EI). Cold EI improves all the central performance aspects of GC-MS, and in this paper, we focus on its improvement of signal-to-noise ratio (S/N) and limits of detection (LODs). We found that the harder the compound for analysis with standard EI, the greater the Cold EI gain in S/N and LOD. The lower LOD and higher S/N of Cold EI emerge from a few reasons: (a) similar ionization yield as standard EI, (b) enhanced abundance of molecular ions, (c) elimination of vacuum background noise, (d) elimination of ion source-related peak tailing and degradation, (e) ability to lower the elution temperatures via the use of high column flow rates, and (f) greater range of thermally labile and low-volatility compounds that can be analyzed. We demonstrate the superior S/N and lower LOD of Cold EI versus standard EI in a range of compounds, from the simple-to-analyze octafluoronaphthalene all the way to reserpine and an organo-metallic compound that cannot be analyzed by standard EI. These compounds include methyl stearate, cholesterol, n-C32 H66 , large polycyclic aromatic hydrocarbons, dioctyl phthalates, diundecyl phthalate, pentachlorophenol, benzidine, lambda-cyhalothrin, and methidathion. The significantly lower Cold EI LODs that can be over 1000 times better than in standard EI further result in far superior response linearity and greater measurement dynamic range.

A coupled NS-DSMC method applied to supersonic molecular beam and experimental validation

In this paper, experimental and numerical studies are conducted on supersonic molecular beam injection (SMBI) for fusion devices based on steady-state assumption. To explore the characteristics of SMBI from continuous to rarefied flow, the flow information is predicted by solving the Navier-Stokes (NS) equation based CFD method and direct simulation Monte Carlo (DSMC) method. To verify the coupled NS-DSMC method, a flow measurement apparatus platform is designed and constructed. A moveable full-range vacuum gauge with Pitot probe in the vacuum chamber is employed to measure the spatial distribution of the beam pressure signal. The simulation results are converted into Pitot pressure, corrected for rarefaction effect and compared with the experimental data. It is observed that the experimental results are consistent with the simulation results. This study provides technical support for the accurate prediction of SMBI flow characteristics and optimization of the SMBI systems.

Coherent mode induced by supersonic molecular beam injection in EAST Ohmic plasmas

A coherent mode (CM) induced by the supersonic molecular beam injection (SMBI) was observed in Ohmic plasmas of EAST tokamak. The CM existed in the spectra of the electron temperature fluctuation and density fluctuation, but not in the spectrum of Mirnov fluctuation. The radial location of the CM was about 10 cm inside the separatrix (normalized minor radius ). In most cases, the CM has multiple discrete frequencies between with an interval of ∼1 kHz. Occasionally, there is only one dominant frequency. The poloidal scale of the CM (poloidal wavenumber , poloidal mode number ) is between that of typical ion turbulence and macroscopic magnetohydrodynamic activities. Statistical analysis results suggest that the onset of the CM requires a high temperature gradient and a relatively low density gradient. Furthermore, the transport analysis shows that the SMBI-caused perturbation propagates inward faster in plasmas with stronger CM, which implies that the CM might be correlated to a high local transport level. However, the impact of the CM on macroscopic plasma parameters including stored energy, energy confinement time, and SMBI-caused mean density fluctuation is too weak to be found in comparison with the random fluctuation and the measurement errors, which suggests that the CM does not have a clear influence on the global confinement.

The versatile fueling systems of WEST

New fueling systems have been designed for WEST, a full tungsten wall tokamak with divertor configuration. They consist of standard gas injection, supersonic molecular beam injection and pellets injection systems, each being able to fuel continuously the plasma discharge up to a duration of 1000s. A massive gas injection system is also implemented to mitigate the impact of disruptions and runaway electrons. The standard gas system consists of 4 independent lines allowing the injection of up to 4 different gas species during a plasma discharge through 11 injections areas, 4 of them being located in the divertors and in the private flux region. The pellet injection system is able to inject up to 10 pellets per second through 4 tracks: one on the low field side, and the other 3 on the high field side. The supersonic molecular beam injection system consists of 3 injectors located close to the midplane, two on the high field side and one on the low field side. On trigger, the massive gas injection system can deliver in a single puff up 800 Pa.m3 of noble gas in order to stop the plasma discharge. All the fueling systems have been characterized and can be used routinely on plasma.

Adsorption dynamics of O2 on Cu(111): a supersonic molecular beam study.

We have studied the adsorption of O2 on Cu(111) using supersonic molecular beam techniques. For incident energies ranging between 100 and 400 meV, we have determined the sticking probability as a function of angle of incidence, surface temperature, and coverage. Initial sticking probabilities range from near 0 to 0.85 with an onset near 100 meV, making Cu(111) considerably less reactive than Cu(110) and Cu(100). Normal energy scaling applies and reactivity increases appreciably over the entire range of surface temperatures from 90 to 670 K. A strictly linearly decreasing coverage dependence on sticking precludes adsorption and dissociation via an extrinsic or long-lived mobile precursor state. We cannot exclude that sticking also occurs molecularly at the lowest surface temperatures. However, all tell tales from our experiments suggest that sticking is predominantly direct and dissociative. Comparison to earlier data shows implications for the relative reactivity of Cu(111) vs. Cu/Ru(0001) overlayers.

A combined spectroscopic and computational investigation on the solvent-to-chromophore excited-state proton transfer in the 2,2'-pyridylbenzimidazole-methanol complex.

This article demonstrates experimental proof of excited state 'solvent-to-chromophore' proton transfer (ESPT) in the isolated gas phase PBI (2,2'-pyridylbenzimidazole)-CH3OH complex, aided by computational calculations. The binary complexes of PBI with CH3OH/CH3OD were produced in a supersonic jet-cooled molecular beam and the energy barrier of the photo-excited process was determined using resonant two-colour two-photon ionization spectroscopy (R2PI). The ESPT process in the PBI-CH3OH complex was confirmed by the disappearance of the Franck-Condon active vibrational transitions above 000 + 390 cm-1. In the PBI-CH3OD complex, the reappearance of the Franck-Condon transitions till 000 + 800 cm-1 confirmed the elevation of the ESPT barrier upon isotopic substitution due to the lowering of the zero-point vibrational energy. The ESPT energy barrier in PBI-CH3OH was bracketed as 410 ± 20 cm-1 (4.91 ± 0.23 kJ mol-1) by comparing the spectra of PBI-CH3OH and PBI-CH3OD. The solvent-to-chromophore proton transfer was confirmed based on the significantly decreased quantum tunnelling of the solvent proton in the PBI-CH3OD complex. The computational investigation resulted in an energy barrier of 6.0 kJ mol-1 for the ESPT reaction in the PBI-CH3OH complex, showing excellent agreement with the experimental value. Overall, the excited state reaction progressed through an intersection of ππ* and nπ* states before being deactivated to the ground state via internal conversion. The present investigation reveals a novel reaction pathway for the deactivation mechanism of the photo-excited N-containing biomolecules in the presence of protic-solvents.

Preliminary study of supersonic molecular beam injection in Thailand Tokamak-1 using 3D fluid model

Successful operation of a tokamak relies on effective and appropriate methods of plasma fueling. The development plan of Thailand Tokamak-1 (TT-1) will employ the supersonic molecular beam injection (SMBI) which delivers the fueling gas more effectively and deeper than the gas puffing method. In this work, we study the effect of SMBI on the plasma transport of TT-1 plasma by using 3D fluid simulation. The model includes the continuity equation, energy balance equation, momentum equation, continuity of fuel equation, and momentum of fuel. BOUT++ is then used to solve these equations by a finite difference method with the field-aligned coordinates in the edge region. The simulation shows that when hydrogen fuel gas is by the SMBI method from the low-field side into the plasma with a speed of 1000 m/s, the electron density in the edge locally rises as a result of the dissociation and ionization. The ion and electron temperatures then drop. After that, the density spread over the whole plasma volume within about 10 ms. When the injection speed increases, it results in a deeper penetration length of the fuel deposition.