Electron-ion Pair Research Articles

Dosimetric saturation effect study and correction calculation method of ionization chamber at ultra-high dose rate (FLASH)

Backgroundand Purpose: FLASH radiotherapy has aroused strong interest among researchers, but how to monitor dose in real time and lack of generally accepted ion correction model are one of the challenges. This study is based on previous research work, the dosimetric verification of FLASH ionization chamber was performed using a 200 keV electron beam irradiation platform at an ultra-high dose rate. At the same time, the finite element program is written to analyze and calculate the ion correction factor. In addition, the results are compared with the calculation results of Boag model. MethodsIn this study, the pressure of the sensitive volume in the detector was adjusted to 16 mbar for the purpose of dosimetry of dose rates in excess of 100 Gy/s. In order to monitor the response of the detector, the beam frequency and pulse width were adjusted accordingly. However, due to the saturation effect of the ionization chamber, the processes of electron ion pair drift, attachment, recombination and diffusion in the sensitive volume were modelled on the basis of the relevant physical principles. Finally, the correction factor was calculated by the finite element analysis. ResultsThe experimental results demonstrate that the FLASH ionization chamber is capable of meeting the requirements of dose measurement and beam monitoring of the electron beam at ultra-high dose rates. Furthermore, the analytical model is able to more accurately describe the saturation effect and calculate the correction factor. ConclusionIn this paper, the method of reducing air pressure is employed for the purpose of monitoring the dose of ultra-high dose rate. Simultaneously, the finite element method was employed to analyze the physical process of electron–ion pairs within the chamber and to calculate the ion correction factor analytically. A comparison with the Boag model indicates that the proposed approach is effective. However, the results exhibit a certain degree of divergence from experimental outcomes. This discrepancy may be attributed to the influence of the input parameters, which require further calibration to enhance the accuracy and the robustness of the model.

Cathode shape dependence of gas ionization chamber on electron collection in ΔE − E telescope ERDA

Our ΔE − E telescope elastic recoil detection analysis (ERDA) system employed a gas ionization chamber (GIC), which consisted of a U-shaped cathode, Frisch grid, and anode. The cathode shape was designed to downsize the electrodes. The difference of performance between the U-shaped and planar shaped cathodes, however, has not been studied well, yet. Therefore, we quantitatively evaluated the influence using the U-shaped cathode on ΔE − E telescope ERDA. The performances of U-shaped and planar shaped cathodes were compared from the viewpoint of a recoil counting loss due to the stagnation inducing a recombination of ion–electron pairs, and the electron uptake by the Frisch grid. No significant difference occurs between the two cathodes from the viewpoint of O recoil yields. The inhomogeneous electric field formed by the U-shaped cathode, however, induced the electron collection suppression, which leads to an attenuation of ΔE pulse heights. In our ERDA condition, the lateral straggling of recoils is suppressed due to their high energy, so that the attenuation of ΔE pulse heights is not severe and does not impair the reliability of ΔE − E telescope ERDA. These results show that the U-shaped cathode can also be used safely for ΔE − E telescope ERDA, and that GICs have a flexibility in the electrode shape, which is useful to make GICs more compact.

Performance of new CO2 based mixture in CMS Improved Resistive Plate Chambers in HL-LHC environment

Resistive Plate Chamber (RPCs) detectors in the Compact Muon Solenoid operate with a gas mixture composed of 95.2% of C2H2F4, which provides a high number of ion-electron pairs, 4.5% of iC4H10, which ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4 is known to be a Greenhouse gas with a global warming potential (GWP) of 1430. Consequently, several ECO-friendly alternatives to C2H2F4 have been investigated in recent years. In this context, a short-mid term approach for the upcoming years of Large Hadron Collider (LHC) operation could be to focus on reducing the GWP of the RPC gas mixture by replacing C2H2F4 with CO2. The studies are conducted at the CERN Gamma Irradiation Facility in the North Area of the Super Proton Synchrotron (SPS), where a 13.6 TBq radiation source and a muon beam from SPS mimic the conditions of Phase-II (i.e. High-Luminosity (HL)) of the LHC. This paper presents the performance of a 1.4 mm gap RPC with three different CO2 based mixtures (30 and 40% of CO2; 0.5 and 1% of SF6) under high gamma background conditions with the perspectives for the longevity campaign.

Unraveling the Photoionization Dynamics of Indole in Aqueous and Ethanol Solutions.

The photoionization dynamics of indole, the ultraviolet-B chromophore of tryptophan, were explored in water and ethanol using ultrafast transient absorption spectroscopy with 292, 268, and 200 nm excitation. By studying the femtosecond-to-nanosecond dynamics of indole in two different solvents, a new photophysical model has been generated that explains many previously unsolved facets of indole's complex solution phase photochemistry. Photoionization is only an active pathway for indole in aqueous solution, leading to a reduction in the fluorescence quantum yield in water-rich environments, which is frequently used in biophysical experiments as a key signature of the protein-folded state. Photoionization of indole in aqueous solution was observed for all three pump wavelengths but via two different mechanisms. For 200 nm excitation, electrons are ballistically ejected directly into the bulk solvent. Conversely, 292 and 268 nm excitation populates an admixture of two 1ππ* states, which form a dynamic equilibrium with a tightly bound indole cation and electron-ion pair. The ion pair dissociates on a nanosecond time scale, generating separated solvated electrons and indole cations. The charged species serve as important precursors to triplet indole production and greatly enhance the overall intersystem crossing rate. Our proposed photophysical model for indole in aqueous solution is the most appropriate for describing photoinduced dynamics of tryptophan in polypeptide sequences; tryptophan in aqueous pH 7 solution is zwitterionic, unlike in peptides, and resultantly has a competitive excited state proton transfer pathway that quenches the tryptophan fluorescence.

Influence of different particle injection methods on plasma sheath with strong production of negative ion in one-dimensional PIC simulation

Particle injection is necessary to maintain the plasma source term in particle-in-cell (PIC) simulation. There are two commonly used particle injection methods, namely, a) constant flux injection, in which a fixed number of ion-electron pairs are injected each time step, and b) pair re-injection, in which the number of ion-electron pairs injected is according to the number of positive ions removed. Different injection methods may bring big difference to the simulation results. Therefore, the appropriate particle injection method must be selected according to the object and purpose of simulation to obtain the correct result. In this paper, a 1D3V (one dimension in space and three dimensions in velocity space) PIC model is used to analyze the evolution of plasma in the formation of space charge limited (SCL) sheath and reverse sheath with the condition of surface production, and the differences of the two particle injection methods are compared. It is found that the simulation result with pair re-injection does not match experiment result.

Electrochemically Controlled Hydrogels with Electrotunable Permeability and Uniaxial Actuation.

The unique properties of hydrogels enable the design of life-like soft intelligent systems. However, stimuli-responsive hydrogels still suffer from limited actuation control. Direct electronic control of electronically conductive hydrogels can solve this challenge and allow direct integration with modern electronic systems. An electrochemically controlled nanowire composite hydrogel with high in-plane conductivity that stimulates a uniaxial electrochemical osmotic expansion is demonstrated. This materials system allows precisely controlled shape-morphing at only -1V, where capacitive charging of the hydrogel bulk leads to a large uniaxial expansion of up to 300%, caused by the ingress of ≈700 water molecules per electron-ion pair. The material retains its state when turned off, which is ideal for electrotunable membranes as the inherent coupling between the expansion and mesoporosity enables electronic control of permeability for adaptive separation, fractionation, and distribution. Used as electrochemical osmotic hydrogel actuators, they achieve an electroactive pressure of up to 0.7MPa (1.4MPa vs dry) and a work density of ≈150kJm-3 (2MJm-3 vs dry). This new materials system paves the way to integrate actuation, sensing, and controlled permeation into advanced soft intelligent systems.

Electron beam impact parameters for the creation of excited species in N2 gas

The number of electron–ion pairs and the distribution of excited species created by the passage of an intense electron beam in a gas are important parameters for many applications. The previously published values for molecular nitrogen rely on a differential ionization cross section that uses a number of fitting parameters and excitation cross sections determined from analytical fitting functions [S. P. Slinker, A. W. Ali, and R. D. Taylor, J. Appl. Phys. 67, 679 (1990)]. Slinker used cross section fits to solve the Boltzmann equation which was then used to compute the important beam-impact parameters. In this work, it is shown that an alternative approach based on the continuous slowing down approximation (CSDA) can be used to compute the energy expended per electron-ion pair and the distribution of excited gas species. This method results in an integral equation that can be solved iteratively and converges rapidly. The binary-encounter Bethe (BEB) differential ionization cross section is used [Y. K. Kim and M. E. Rudd, Phys. Rev. A 50, 3954 (1994); W. Hwang, Y.-K. Kim and M. E. Rudd, J. Chem. Phys. 104, 2956 (1996)]. The BEB model naturally extends to relativistic energies and has no free parameters. This makes the BEB considerably easier to use than previous models based on fitting parameters. The BEB model requires orbital constants obtained from quantum chemistry calculations. To demonstrate the technique, the electron-beam impact parameters are computed for nitrogen gas. The tabulated low-energy excitation cross sections are extended to relativistic energies using Bethe's asymptotic value for the inelastic cross sections [M. Inokuti, Rev. Mod. Phys. 43, 297 (1971)]. It is shown that the results for the energy expended per electron–ion pair as well as the distribution of excited states agree with published experimental values and are similar to previously published theoretical results.

Performance studies of RPC detectors operated with C2H2F4 and CO2 gas mixtures

Resistive Plate Chambers detectors are largely employed at the CERN LHC experiments thanks to their excellent trigger performances and contained costs. They are operated with a gas mixture made of 90%–95% of C2H2F4, that provides a high number of ion–electron pairs, about 5% of i-C4H10, that ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4is known to be a Greenhouse gas, with a global warming potential (GWP) of 1430. CERN has identified several strategies to reduce the consumption of greenhouse gas emissions from particle detectors at LHC experiments. One research line is focused on the study of alternatives to C2H2F4. In this context, a conservative approach for the next years of LHC operation could be to focus on reducing the GWP of the RPC gas mixture by only adding CO2 and not using new gases, whose effects on detector long-term operation have to be studied. The RPC performance with standard gas mixture with the addition of 30%–50% of CO2 (and SF6 concentration between 0.3 and 0.9%) were studied both in laboratory set-up and at the CERN Gamma Irradiation Facility in presence of muon beam and gamma background radiation. Encouraging results were obtained showing that the addition of CO2 to the standard gas mixture can represent a mid-term solution to reduce emissions and lower operational costs by keeping stable detector performance and safe long-term operation.

Concept of power absorbed and lost per electron in surface-wave plasma columns and its contribution to the advanced understanding and modeling of microwave discharges.

Microwave (MW) sustained discharges have distinct advantages over other existing types of discharges in terms of the specific understanding they can provide regarding discharge phenomena and mechanisms. First, only electrons can pick up energy from the discharge E-field since ions cannot respond to rapid oscillations above ≈100 MHz. A second remarkable feature of MW discharges is that their plasma sheath is stationary, unlike in radiofrequency (rf) discharges. Furthermore, the sheath voltage is low, so that the electron energy expended to sustain them can be ignored as a first approximation. These characteristics favored the development of the concept of power per electron, which involves determining the respective roles of the power absorbed per electron θ_{A} and the power lost on a per-electron basis θ_{L} in the equilibrium relationship between them. This led to establishing the following: (i) In the equilibrium relation of the power per electron (θ_{A}=θ_{L}), the power lost has precedence over the power absorbed, the latter simply adjusting to compensate for the losses. (ii) The value of the power absorbed θ_{A}, when conforming to compensate for the losses, determines the intensity of the high-frequency E-field in the discharge, the maintenance field, construing it as an internal parameter (as opposed to an operator-set). (iii) Ensuring a smaller volume within which power is absorbed (resulting from E-field confinement) compared to the loss volume (plasma) is a way to achieve higher maintenance E-field intensity, thus higher atomic (molecular) excitation and ionization rates, as is the case, for example, with microdischarges. (iv) In pulsed-operated discharges, the E-field intensity is maximum at the very beginning of the pulse and then decreases, eventually reaching stationarity as the pulse time elapses. (v) A significant and more comprehensive similarity law is procured than for direct-current (dc) discharges. (vi) The power per electron concept is valid for all MW discharges. In the case of dc and rf discharges, where ions are also accelerated in the E-field, θ_{A} is no longer proportional to the E-field intensity: θ_{A} is then the power necessary to maintain an electron-ion pair in the discharge. It can be used, taking into account the operating conditions (field frequency, gas nature and pressure, and discharge vessel properties), to optimize the power consumed for a given plasma-driven process.

A study of thermodynamics of mixing for Al[formula omitted]Zn[formula omitted] liquid binary alloy

Thermodynamics of mixing, namely, the energy of mixing (ΔF), enthalpy of mixing (ΔQ) and entropy of mixing (ΔS) for Al1−xZnx liquid binary alloys are calculated theoretically by using the electronic theory of metals (ETM) along with the perturbative approach and the statistical mechanics at T=1000 K. The electron-ion and ion-ion effective pair interactions, vital for any microscopic study, are described by a local pseudopotential. The results of our calculations for energy of mixing, however, agree very well with the available experimental data. In the case of entropy of mixing and the enthalpy of mixing agreement with experimental data is found to be good. We offer a prescription to lessen the discrepancy between theory and experiment in the case of enthalpy of mixing and entropy of mixing, and this project will be undertaken as our future work.

Effect of electron energy distributions on the electron density in nitrogen inductively coupled plasmas

The effect of the electron energy distribution function (EEDF) on the behavior of the electron density (n e) is investigated under various gas pressures of nitrogen (N2) in inductively coupled plasma (ICP) operated at low and high input powers. A Langmuir probe is used to measure the EEDFs and electron densities, and the antenna coil current is measured to obtain the absorbed power in the plasma (P abs). At gas pressures above 2.67 Pa (20 mTorr) and 2500 W, P abs increases continually with increasing the gas pressure, but the electron density slightly decreases. In this case, the EEDF has a Maxwellian distribution with a high-energy tail. On the other hand, at 300 W, P abs decreases slightly with increasing gas pressure, but the electron density dramatically decreases, and the EEDF evolves from a bi-Maxwellian to a non-Maxwellian distribution with substantially highly depleted high-energetic part (high-energy tail). To analyze the difference in the behavior of the decrease rate in electron density, the total energy loss per electron–ion pair lost (ε T) is measured through the probe diagnostics, and the measured electron density is compared with the calculated electron density from the global model. An additional experiment is performed in Ar plasma under the same discharge conditions as N2 plasma to compare the EEDF effect. This study provides experimental evidence that the EEDF has a decisive effect on the behavior of the electron density in plasmas.

A novel technique for the measurement of the avalanche fluctuations of a GEM stack using a gating foil

We have developed a novel technique for the measurement of the size of avalanche fluctuations of gaseous detectors using a gating device (gating foil) prepared for the time projection chamber in the international linear collider experiment (ILD-TPC). In addition to the gating function, the gating foil is capable of controlling the average fraction of drift electrons detected after gas amplification. The signal charge width and shape (skewness) for electron–ion pairs created by a pulsed UV laser as a function of the transmission rate of the gating foil can be used to determine the relative variance of gas gain for single electrons. We present the measurement principle and the result obtained using a stack of gas electron multipliers (GEMs) operated in a gas mixture of Ar-CF4(3%)-isobutane(2%) at atmospheric pressure. Also discussed is the influence of the avalanche fluctuations on the spatial resolution of the ILD-TPC.

Overview of C-2W: high temperature, steady-state beam-driven field-reversed configuration plasmas

TAE Technologies, Inc. (TAE) is pursuing an alternative approach to magnetically confined fusion, which relies on field-reversed configuration (FRC) plasmas composed of mostly energetic and well-confined particles by means of a state-of-the-art tunable energy neutral-beam (NB) injector system. TAE’s current experimental device, C-2W (also called ‘Norman’), is the world’s largest compact-toroid device and has made significant progress in FRC performance, producing record breaking, high temperature (electron temperature, T e > 500 eV; total electron and ion temperature, T tot > 3 keV) advanced beam-driven FRC plasmas, dominated by injected fast particles and sustained in steady-state for up to 30 ms, which is limited by NB pulse duration. C-2W produces significantly better FRC performance than the preceding C-2U experiment, in part due to Google’s machine-learning framework for experimental optimization, which has contributed to the discovery of a new operational regime where novel settings for the formation section and the confinement region yield consistently reproducible, hot, and stable plasmas. An active plasma control system has been developed and utilized in C-2W to produce consistent FRC performance as well as for reliable machine operations using magnets, electrodes, gas injection, and tunable NBs. The active control system has demonstrated stabilization of FRC axial instability. Overall FRC performance is well correlated with NBs and edge-biasing system, where higher total plasma energy is obtained by increasing both NB injection power and applied-voltage on biasing electrodes. C-2W divertors have demonstrated a good electron heat confinement on open-field-lines using strong magnetic mirror fields as well as expanding the magnetic field in the divertors (expansion ratio > 30); the energy lost per electron ion pair, η e ∼ 6–8, is achieved, which is close to the ideal theoretical minimum.

Plasma parameters in very high frequency argon plasmas mixed with nitrogen at atmospheric pressure

A recently reported procedure [Yoshida et al., J. Appl. Phys. 128, 133303 (2020)] for estimating plasma parameters in atmospheric-pressure (AP) Ar plasma has been extended to be applicable for Ar-N2 AP plasma. Amplitudes of current density and voltage between the electrodes and power absorbed in the plasma have been obtained by three-dimensional computer simulation of the whole system. The only needed input parameters for the simulation are input power and capacitance gaps in the matching unit. Using an inhomogeneous plasma model and a power balance relation, the central electron density (n0) and the collisional energy loss per electron–ion pair created (ɛc) have been estimated. In this study, to estimate the average electron temperature (Te), ɛc as a function of Te has been calculated from the cross-sectional data set on electron impact reactions in the range applicable for the present plasma condition. In the low Te range (<1 eV) where ɛc has not been well reported, we have calculated ɛc(Te) as a function of N2 concentration in Ar taking the vibrational and rotational excitations of N2 molecules into account. From the experiments and analyses of Ar-N2 AP plasma generation, it is found that n0 decreases drastically with increasing N2 concentration while Te increases slightly. Also, it is found that n0 increases with increasing input power (P) such as n0∝P1.9 while Te increases gradually. Based on the N2 concentration and input power dependences of Te and n0, some guidelines for selecting effective AP plasma nitridation conditions have been discussed.

Experimental investigation on optimal plasma generation in inductively coupled plasma

Total energy loss per ion–electron pair lost (εT) is investigated to optimize the plasma generation at various RF powers and gas pressures in an argon inductively coupled plasma (ICP). The ion densities and electron temperatures are measured to obtain εT at the plasma–sheath edge. At a fixed RF power, the obtained εT has a minimum at a certain electron temperature, and at this condition, an optimal plasma generation is achieved according to a global model. Since the electron temperature is a function of the gas pressure, at that certain gas pressure the energy loss in the plasma is minimized and plasma is generated most efficiently. Interestingly, the electron temperature at which εT becomes the minimum decreases as the RF power increases. This is explained by multistep ionization and the electron density dependence of the density of the excited states. Measured εT is compared with the calculated result from the global model that includes multistep ionization, and these are consistent with each other.

Plasma Treatment and Seed Quality Advancement: A Review

Plasma also called as ‘fourth state of matter’ encompasses ionized gas, atoms, free molecules, radicals and free electrons. Considering its discovery in late 19th century plasma is extensively used as low pressure or high pressure plasmas in many applications commercially such as microelectronic technology, textile industry, organic waste management etc. When a gas is passed through an electric field in a plasma chamber, three types of collisions are known to take place in it particularly, excitation, ionization and deposition that provide plasma its characteristic glow, ion-electron pair, reactive species respectively. Plasma treatment of different object can change their chemical and physical properties. In Seed Science and Research, many seed quality enhancement techniques are used to improve seed quality in crop plants such as, seed priming, fortification, solid matrix priming, chemical treatment, hardening etc. Plasma treatment of seeds is a unique tool that utilizes an ionized gas to modify the physical and chemical properties seed viz., wettability, porosity, water absorption, activity of antioxidant enzymes. It can also decontaminate the seed surface off micro flora and convert hydrophobic seeds to hydrophilic. It also enhances soluble sugar content, protein content and causes a reduction in lipid peroxidation. Thus plasma treatment in turn improves seed germination rate, seedling characteristics, seed physical quality and seed health.

A new ionization network and radiation transport module in pluto

ABSTRACT We introduce a new general-purpose time-dependent ionization network (IN) and a radiation transport (RT) module for the magnetohydrodynamic (MHD) code pluto. Our IN is reliable for temperatures ranging from 5 × 103 to 3 × 108 K and includes all ionization states of H, He, C, N, O, Ne, Mg, Si, S, and Fe, making it suitable for studying a variety of astrophysical scenarios. Radiation loss for each ion–electron pair is calculated using cloudy-17 data on the fly. Photoionization and charge exchange are the main processes contributing to chemical heating. The IN is fully coupled to the RT module over a large range of opacities at different frequencies. The RT module employs a method of short characteristics assuming spherical symmetry. The radiation module requires the assumption of spherical symmetry, while the IN is compatible with full 3D. We also include a simple prescription for dust opacity, grain destruction, and the dust contribution to radiation pressure. We present numerical tests to show the reliability and limitations of the new modules. We also present a post-processing tool to calculate projected column densities and emission spectra.

Fabrication and Characterization of Gaseous Detector for the identification of High Energy Particles.

There is a vast range of gases which get ionized, produce electron-ion pairs, on the passage of high energy charged particles. Such gases are extensively used in experiments such as LHC, Belle-II, RHIC, DAFNE, etc which produce high energy particles. Panjab University established a detector assembly and characterization laboratory dedicated to gaseous detectors such as Resistive Plate Chamber (RPC) and Gas Electron Multiplier (GEM) for the LHC experiment. Here, we present the recent work on the fabrication and characterizations of the GEM detector at Panjab University.

Plasma parameters in very high frequency helium and argon plasmas at atmospheric pressure

A simple procedure has been proposed to estimate atmospheric-pressure (AP) plasma parameters based on the electric field simulation of a very-high-frequency plasma system including the impedance matching unit. The capacitively coupled plasma is generated between metal electrodes with a narrow gap, where the standard Langmuir probe method cannot be applied. The amplitudes of current density (J0) and voltage (V0) between the electrodes are determined by the three-dimensional computer simulation of the system in the impedance matched state using two experimental parameters (i.e., the separations between two parallel-plate capacitors) in the matching unit. Approximate analytical solutions relating the central electron density (n0) and the sheath thickness to J0 and V0 are derived based on a simplified inhomogeneous plasma model with collisional sheaths. The average electron temperature Te is estimated using a power balance relation between the total powers absorbed and lost in the ionizing plasma. The results on power dependences of n0 and Te show reasonable agreement with the predictions by the particle and power balance relations. In the case of AP plasma of Ar or He mixed with impurity or process gas molecules, it is impossible to determine Te. However, n0 can be obtained and the collisional energy loss per electron–ion pair creation (ɛc) can be estimated, which brings certain information on the change of plasma chemistry. Since the proposed procedure is simple and non-intrusive, it might become a useful tool for discussing AP plasma properties in process developments.

Measurements of axial energy loss from magnetic mirror trap

The work represents a next step in studies of longitudinal energy losses from linear magnetic plasma confinement devices. The paper describes the experimental technique that has been developed and used to measure the absolute values of longitudinal particle and energy density fluxes from an open magnetic mirror trap. Using this technique, it was possible to measure and account for the secondary electron emission coefficient from plasma-facing end plate, and perform a comparison with the existing theory of energy confinement in open traps. It is shown that the average energy transported by an ion-electron pair leaving the trap is close to theoretically predicted minimum value of 6–8 electron temperatures. As confirmed by the measured dependencies, this conclusion is valid in a broad range of parameters and the threshold value of the magnetic expansion ratio does not exceed its theoretically predicted minimum of .