Electron Beam Energy Research Articles

Effects of a 4.3T superconducting wiggler on the electron beam optics and dynamics at NSLS-II

A superconducting wiggler (SCW) with a peak field of 4.3 T has recently been installed at NSLS-II. The wiggler generates a high-flux X-ray beam with a photon energy range from 20 keV to 200 keV for the High Energy Engineering X-ray Scattering beamline. This device induces significant distortions in the electron beam orbit and optics. We have corrected these adverse effects using feed-forward tables. The effects of the SCW on the electron beam emittance, energy spread, and bunch length were calculated and measured. The beam-induced heating of the cryogenic vacuum chamber was also studied. Finally, the superconducting wiggler has been commissioned for user operations.

Optimization of target system for the production of 99Mo via 100Mo(γ,n)99Mo reaction

With an increase of stopping operation of nuclear reactors worldwide, the supply of medical 99Mo becomes difficult and thus many efforts have been made to find an alternative. A process based on an electron linear accelerator (linac) system and a100Mo target via the 100Mo (γ,n)99Mo reaction receives a lot of attention due to the relatively low level of co-produced impurities. This process has been recently developed at the Institute of Modern Physics (IMP) and the Monte Carlo simulation was used to optimize the target system before operating pilot irradiation experiments. First, tungsten and tantalum, as mostly used converter materials, were tested. The yield of 99Mo was evaluated with respect to the converter thickness and the electron beam energy by means of Geant4 simulations. Besides, the specific activity of 99Mo produced from one-stage approach (100Mo target without a converter) and two-stage approach (100Mo target with a converter) was compared when varying the testing conditions. The two-stage approach was selected for the experiment due to the higher specific activity of produced 99Mo at all tested conditions. A target consisting of a 10 mm thickness of the 100Mo tablets and a 2.4 mm thick Ta converter was irradiated for 40 h (50 MeV with 0.2 μA). The Geant4-calculated specific activity of generated 99Mo at the end of bombardment agreed well with the experimental value, which proved high level of accuracy of the Geant4 simulation. In future studies, the Geant4 simulation will be used to optimize the production process when using high power linac system.

Quality assurance for mixed electron-photon beam radiation therapy using treatment log files and MapCHECK.

Mixed photon-electron beam radiotherapy (MBRT) is a technique that combines the use of both photons and electrons in one single treatment plan to exploit their advantageous and complimentary characteristics. Compared to other photon treatment modalities, it has been shown that the MBRT technique contributes to better target coverage and organ-at-risk (OAR) sparing. However, the use of combined photons and electrons in one delivery makes the technique more complex and a well-established quality assurance (QA) protocol for MBRT isessential. To investigate the feasibility of using MapCHECK and log file-dose reconstruction for MBRT plan verification and to recommend a patient-specific quality assurance (PSQA) protocol forMBRT. MBRT plans were robustly optimized for five soft-tissue sarcoma (STS) patients. Each plan comprised step-and-shoot deliveries of a six MV photon beam and a combination of five electron beam energies at an SAD of 100 cm. The plans were delivered to the MapCHECK device with collapsed gantry angle and the 2D dose distributions at the detector depth were measured. To simulate the expected dose distribution delivered to the MapCHECK, a MapCHECK computational phantom was modeled in EGSnrc based on vendor-supplied blueprint information. The dose to the detectors in the model was scored using the DOSXYZnrc user code. The agreement between the measured and the simulated dose distribution was evaluated using 2D gamma analysis with a gamma criterion of 3%/2 mm and a low dose threshold of 10%. One of the plans was selected and delivered with a rotating gantry angle for trajectory log file collection. To evaluate the potential interlinac and intralinac differences, the plan was delivered repeatedly on three linacs. From the collected log files, delivery parameters were retrieved to recalculate the 3D dose distributions in the patient's anatomy with DOSXYZnrc. The recalculated mean dose to the clinical target volume (CTV) and OARs from all deliveries were computed and compared with the planned dose in terms of percentage difference. To validate the accuracy of log file-based QA, the log file-recalculated dose was also compared with filmmeasurement. The agreement of the total dose distribution between the MapCHECK measurement and simulation showed gamma passing rates of above 97% for all five MBRT plans. In the log file-dose recalculation, the difference between the recalculated and the planned dose to the CTV and OARs was below 1% for all deliveries. No significant inter- or intralinac differences were observed. The log file-dose had a gamma passing rate of 98.6% compared to filmmeasurement. Both the MapCHECK measurements and log file-dose recalculations showed excellent agreement with the expected dose distribution. This study demonstrates the potential of using MapCHECK and log files as MBRT QAtools.

Applying fully convolutional networks for beam profile and emittance measurements

The transverse cross-sectional size and emittance are critical beam parameters that characterize the performance of the accelerator and assess the state of the beam. Inspired by the success of machine learning in image processing tasks, we have crafted a bespoke measurement system with a primary focus on accurately determine the transverse cross-sectional size and emittance of the beam. The system utilizes a beam spot detector to convert the beam spot to a light spot image, which is then projected onto the CCD camera through the telecentric lens for the acquisition. The image data collected by the camera is subsequently imported into the EPICS database developed based on ADAravis software. We employ the Gaussian fitting technique on the collected images to accurately calculate the cross-sectional size of the beam. Furthermore, by incorporating the four-level iron scanning method, the lateral emittance of the beam is calculated in a comprehensive manner. To suppress the salt and pepper noise introduced due to the presence of dark current and beam shooting phenomena on the transmission line, we propose a novel fully convolutional neural network (FCN) design with preactivated residual units. The test conducted at HLS-II confirms that the measurement uncertainty of this system is superior to 27.5 μm. Moreover, when operating at an electron beam energy of 800 MeV, the measured emittance of the accelerator is found to be 38.515 nm·rad, a value closely aligning with the theoretical value of 36.2 nm·rad. These compelling results provide strong evidence supporting the reliability of the emittance measurement algorithm, making it suitable for deployment in the forthcoming terahertz accelerator.

Comparison of the Direct Power Consumption for Different Linac Treatment Parameters in External Beam Radiation Therapy

The negative impact of climate change on the environment has led to increasing concern around the world. Relatively little is known about the contribution of radiation oncology systems to carbon emissions. This study measures the energy utilization of Linac-based EBRT for different treatment parameters and techniques, which was then converted to power use (kWh) and ultimately a carbon footprint of various photon treatment approaches. A Varian TrueBeam was evaluated. The direct power consumption was measured using a Fluke 1736 Power Logger, recorded in one-second intervals for one week. Different photon and electron beam energies, dose rates, treatment techniques (3D, IMRT, gated), and imaging types (kV, MV) were evaluated. Clinical treatment plans were reviewed, and average treatment times used to determine kWh. IRB approval was obtained. The Greenhouse Gas Equivalencies Calculator was used to determine kg of CO2. Power draw for 6 MV, 10 MV, and 18 MV at a rep rate of 600 MU/min was 31.6, 32.0, and 27.5 kW, respectively. The power draw for end of range dose rates for 6 MV (60, 600), 6 FFF (400, 1400), 10 FFF (400, 2400), and 6 MeV (100, 1000) were (22.2, 31.6 kW), (23.7, 31.6 kW), (19.6, 32.1 kW), and (22.6, 23.6 kW), respectively. 6 MV open 2D fields, modulated IMRT fields, and gated/beam hold fields had similar power draw at 31.6, 31.7, and 31.9 kW, respectively. Portal MV imaging with 2.5 MV beam was 32.5 kW, while CBCT and kV/kV imaging was ∼11 kW and not distinguishable from baseline power fluctuations. A total of 191 delivered treatment plans were reviewed. Electron plans (n = 8) treatment time was on average 29 sec (16 sec STDEV) per fraction and 635 sec (185 sec STDEV) per course, 2D/3D plans (n = 63) were 77 sec (32 sec STDEV) and 1004 sec (1002 sec STDEV), and IMRT plans (n = 120) were 182 sec (60 sec STDEV) and 5351 sec (2401 sec STDEV), respectively. The kWh per treatment for electron, 2D/3D, and IMRT plans were 0.19, 0.68, and 1.6 kWh, respectively. The CO2 equivalent for electrons, 2D/3D, and IMRT techniques are 0.08, 0.29, and 0.7 kg. There was some variability in the power draw for different energies and different dose rates but was relatively stable around 32 kW. Power consumption for clinical therapy is a result of kW power draw multiplied by duration of beam delivery, which for our patients varied significantly as a function of technique and number of fractions delivered. Reduction in radiation oncology carbon footprint will likely be driven more by number of fractions and type of treatment technique, and length of patient commute, rather than beam energy and dose rate selection.

Assessment of the spatial distribution of low-temperature plasma parameters on plasma-beam installation

At present continue, studies of the interaction of plasma with structural materials of the first wall and divertor of the ITER international experimental fusion reactor on operating tokamaks and simulated plasma facilities. In the research of the interaction of plasma with the surface of candidate materials TNR an important role plasma parameters play. For determination of local values of the main plasma parameters there is a separate field of research – plasma diagnostics. Plasma diagnostics is the determination of local and instantaneous values of main its parameters: concentration and temperature of charged plasma particles, as well as the distribution functions of various plasma components by energies.This works presents the results of a research to the spatial distribution of local parameters (temperature electrons (Te) and plasma concentration (ne)) of a low-temperature plasma on a plasma-beam installation (PBI) with the help a movable Langmuir probe with the following geometrical parameters of the electrode: length – 4 mm; diameter 0.5 mm. The probe sweep was with the help a Keithley 6487 picoammeter. The processing of volt-ampere characteristics (VAC) was carried out by standard methods.To assess the spatial distribution of the above-mentioned parameters of low-temperature plasma, experiments were carried out with the location of the probe at a distance of 5 mm, 9 mm and 11 mm from the center of the plasma beam at different energies of the primary electron beam in the range from 0.5 keV to 5 keV.The experiments results showed a smooth decrease in plasma concentration in the radial direction.

Effects of heat treatment on the microstructure and flexural mechanical properties of carbon fiber reinforced composite cured by electron beam

Carbon fiber (CF)-reinforced composite materials are attracting attention in the automobile and aerospace industries based on their light weight and excellent mechanical properties. Electron beam curing technology is replacing the thermal curing process and can improve productivity by shortening the curing time of CF-reinforced composite materials to minutes. However, the electron beam-cured CF-reinforced composite materials have weak flexural strength. We have found that the deterioration of flexural strength of electron beam-cured CF-reinforced composites can be solved by heat treatment in a vacuum bag prior to the electron beam curing process. Through heat treatment under vacuum, the viscosity of the matrix resin was lowered, and voids between the laminated surfaces of the CF prepregs could be removed. Through this approach, the flexural strength of the electron beam cured composite material reached 1.6 GPa, which was approximately 65% improved compared to the non-heat treated material. In addition, the energy distribution transmitted when the composite material is irradiated with an electron beam was simulated using the Geant4 code. It was confirmed that the nonlinear distribution of energy transmitted to the inside of the specimen according to the electron beam energy should be carefully considered in the design of the product shape and when setting the electron beam irradiation conditions.

Search for heavy Majorana neutrinos in the τ final state at proton-electron colliders

We utilize the lepton number violation signal process p e− → τ+jjj to search for heavy Majorana neutrinos at future proton-electron colliders. The LHeC (FCC-eh) is considered to run with an electron beam energy of 60 GeV, a proton beam energy of 7 (50) TeV and an integrated luminosity of 1 (3) ab−1, and the electron beam is considered to be unpolarized. We apply detector configurations and simulate signal and related standard model background events for both hadronic τh and leptonic τℓ final states, ℓ being a muon. After preselection, multivariate analyses are performed to reject the background. The strategy to reconstruct the heavy neutrino mass is developed and distributions of reconstructed mass are presented. Discovery sensitivities on parameter |VτN|2|VeN|2/(|VτN|2 + |VeN|2) for the heavy neutrino mass between 10 and 3000 GeV are predicted. At the 2-σ significance, the best discovery sensitivity is ∼ 1.2 × 10−5 (5.0 × 10−6) at the LHeC (FCC-eh) when mN ∼ 100 GeV for the hadronic τh final state. Sensitivities for the leptonic τℓ final state are found to be similar to those for the hadronic τh final state for most of the parameter space investigated. We also derive the limits on mixing parameters from electroweak precision data (EWPD) and DELPHI experiment. Assuming |VτN|2 = |VeN|2 = |VℓN|2, sensitivity bounds from the LHeC and FCC-eh experiments are found to be stronger than those from EWPD when mN ≲ 900 GeV, and also stronger than those from DELPHI when mN ≳ 70 GeV. Constraints are also interpreted and compared in the |VτN|2 vs. |VeN|2 plane. Compared with current limits from EWPD, DELPHI, and LHC experiments, future pe experiments can probe large additional regions in the parameter space formed by |VτN|2 and |VeN|2, and thus significantly enhance the discovery potential for a large portion of the |VτN|2 vs. |VeN|2 plane.

In Situ Intrinsic Self-Healing of Low Toxic Cs2 ZnX4 (X=Cl, Br) Metal Halide Nanoparticles.

This study reports on the intrinsic and fast self-healing ability of all inorganic, low-toxic Cs2 ZnX4 (X=Cl, Br) metal halide nanoparticles (NPs) when subjected to local heating by electron beam irradiation in high-resolution transmission electron microscopy (HR-TEM). The local heating induces the creation of nanoshells (NSs) following the template of the corresponding NPs, which are subsequently healed back to their original state within several minutes. Energy dispersive spectroscopy (EDS) and fast Fourier transform (FFT) analysis reveal that the composition, phase, and crystallographic structure of the original NPs are restored during the self-healing process, with a thin crystalline layer observed at the bottom of the NSs acting as the healing template. The inelastic scattering of the electron beam energy generates local heat that causes rapid atomic displacement, resulting in atomic mobility that lowers the density of the material and leads to NSformation. A unique insitu TEM heating stage measurement demonstrates the appearance of identical damage and self-healing to those induced by the electron beam. The NPs exhibit excellent stability under ambient conditions for up to a month, making them suitable for self-healing scintillators and other optoelectronic applications that require atomic-scale stability and healing.

Observations and identifications of extreme ultraviolet spectra of Ca-like to Na-like neodymium ions using an electron beam ion trap

Abstract Extreme ultraviolet spectra from M-shell transitions in highly-charged Ca-like Nd40+ through Na-like Nd49+ ions were measured at the electron beam ion trap (EBIT) facility of the National Institute of Standards and Technology. To produce the ionization stages of interest, the electron beam energies were varied between 3.60 keV and 10.01 keV. A flat-field grazing incidence spectrometer was used to observe the spectra in the wavelength range between 2.67 nm and 17.30 nm. Simulated spectra generated with detailed collisional-radiative modeling of the non-Maxwellian EBIT plasma were used for line identifications. Forty-seven new spectral lines corresponding to electric-dipole and magnetic-dipole transitions were identified. Measurements were compared to the available previously calculated and predicted values.

Compliance Test of Percentage Depth Dose (PDD) Using LINAC Machine Brand Electa Precise against American Association of Physicists in Medicine (AAPM) PDD with Electron Beam Energy Variation at Radiotherapy Installation RSUP Prof. Ngoerah in Denpasar

The purpose of the study was to determine the value of PDD against energy variations in the electron beam using the Elekta Precise Brand LINAC aircraft, and to determine the suitability of the PDD value against energy variations in the electron beam with the standards set by AAPM. PDD value data obtained from the results of research using Sun Nuclear Dosimetry Software (SNC Dosimetry). The results of the study will then be compared with the standard Tolerance value set by AAPM of a maximum of 2%. From the deviation value of each 4 MeV energy is 1.1% - 1.8%, 6 MeV energy is 1.1% - 1.6%, and 8 MeV energy is 1.0% - 1.2%, the deviation error at 4, 6, and 8 MeV energy is in accordance with the tolerance limit set by AAPM which is 2%. So that the Elekta Precise LINAC machine at the Radiotherapy Installation of Prof. Ngoerah Denpasar Hospital is feasible to operate to receive patients.

Atomic-scale modeling of C/N kinetic stability descriptors for PGM-free electrocatalysts at finite temperatures

The durability of platinum group metal-free (PGM-free) electrocatalysts is a major barrier to their usage in polymer electrolyte fuel cell cathodes. C and N removal from active sites may play an important role in the catalyst’s ability to maintain high activity. While C degradation mechanisms are kinetically controlled, previous studies have focused on thermodynamic descriptors. In this work, we develop a temperature-dependent kinetic descriptor of C and N stability using an electron beam-damage model. Our approach considers the electron beam energy threshold (EBET) describing the knock-on displacement of C and N atoms as a stability descriptor for atomic structures. The stability of different sites is calculated to be different showing this approach can discriminate between similar sites with varied configurations. In addition, we provide important insight regarding TEM beam damage of proposed active sites. We calculate 60 keV electrons can damage some proposed active site structures even at room temperature.

Design Study for HybriSCU: A HYBRID NbTi/ReBCO Superconducting Undulator

At the European X-ray Free-Electron Laser (XFEL), the undulator systems group has started in 2020 an R&D project dedicated to the development of innovative superconducting undulator (SCU) coils. SCUs are of great interest for storage rings and free electron lasers (FEL) facilities as they enable to widen the tunability range of the generated photon energy for the same electron beam energy compared with the established technology of the permanent magnet undulators. In this contribution, we present the characterization study and the achievable performance of HybriSCU a graded SCU coil combining two different superconductors: NbTi and high temperature superconductor (HTS) based on Rare-Earth Barium Copper Oxide (ReBCO) tape.

Electron energy dissipation in a magnetotail reconnection region

The four Magnetospheric Multiscale spacecraft encountered a reconnection region in the Earth's magnetospheric tail on 11 July 2017. Previous publications have reported characteristics of the electron diffusion region, including its aspect ratio, the reconnection electric field, plasma wave generation from electron beams in its vicinity, and energetic particles in the Earthward exhaust. This paper reports on the investigation of conversion of electromagnetic energy to electron kinetic energy (by J·E) and the ensuing conversion of electron beam energy to electron thermal energy via the pressure–strain interaction. The main result is that omnidirectional, compressive dissipation of electron energy dominates in the positive J·E region, while incompressive parallel dissipation dominates in the inflow region where J·E is small. The existence of parallel electric fields in the inflow region supports previous suggestions that electron trapping by these fields contributes to the parallel dissipation. All of the results are reproduced quantitatively within a factor of two with a 2.5-D particle-in-cell simulation.

Assessing the Quality of Oxygen Plasma Focused Ion Beam (O-PFIB) Etching on Polypropylene Surfaces Using Secondary Electron Hyperspectral Imaging.

The development of Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) systems has provided significant advances in the processing and characterization of polymers. A fundamental understanding of ion-sample interactions is still missing despite FIB-SEM being routinely applied in microstructural analyses of polymers. This study applies Secondary Electron Hyperspectral Imaging to reveal oxygen and xenon plasma FIB interactions on the surface of a polymer (in this instance, polypropylene). Secondary Electron Hyperspectral Imaging (SEHI) is a technique housed within the SEM chamber that exhibits multiscale surface sensitivity with a high spatial resolution and the ability to identify carbon bonding present using low beam energies without requiring an Ultra High Vacuum (UHV). SEHI is made possible through the use of through-the-lens detectors (TLDs) to provide a low-pass SE collection of low primary electron beam energies and currents. SE images acquired over the same region of interest from different energy ranges are plotted to produce an SE spectrum. The data provided in this study provide evidence of SEHI's ability to be a valuable tool in the characterization of polymer surfaces post-PFIB etching, allowing for insights into both tailoring polymer processing FIB parameters and SEHI's ability to be used to monitor serial FIB polymer surfaces in situ.

Background optimization of powder electron diffraction for implementation of the e-PDF technique and study of the local structure of iron oxide nanocrystals.

The local structural characterization of iron oxide nanoparticles is explored using a total scattering analysis method known as pair distribution function (PDF) (also known as reduced density function) analysis. The PDF profiles are derived from background-corrected powder electron diffraction patterns (the e-PDF technique). Due to the strong Coulombic interaction between the electron beam and the sample, electron diffraction generally leads to multiple scattering, causing redistribution of intensities towards higher scattering angles and an increased background in the diffraction profile. In addition to this, the electron-specimen interaction gives rise to an undesirable inelastic scattering signal that contributes primarily to the background. The present work demonstrates the efficacy of a pre-treatment of the underlying complex background function, which is a combination of both incoherent multiple and inelastic scatterings that cannot be identical for different electron beam energies. Therefore, two different background subtraction approaches are proposed for the electron diffraction patterns acquired at 80 kV and 300 kV beam energies. From the least-square refinement (small-box modelling), both approaches are found to be very promising, leading to a successful implementation of the e-PDF technique to study the local structure of the considered nanomaterial.

Femtosecond Polarization Shaping of Free-Electron Laser Pulses.

We demonstrate the generation of extreme-ultraviolet (XUV) free-electron laser (FEL) pulses with time-dependent polarization. To achieve polarization modulation on a femtosecond timescale, we combine two mutually delayed counterrotating circularly polarized subpulses from two cross-polarized undulators. The polarization profile of the pulses is probed by angle-resolved photoemission and above-threshold ionization of helium; the results agree with solutions of the time-dependent Schrödinger equation. The stability limit of the scheme is mainly set by electron-beam energy fluctuations, however, at a level that will not compromise experiments in the XUV. Our results demonstrate the potential to improve the resolution and element selectivity of methods based on polarization shaping and may lead to the development of new coherent control schemes for probing and manipulating core electrons in matter.

Dosimetric properties of PASSAG polymer gel dosimeter in electron beam radiotherapy using magnetic resonance imaging.

Several physical factors such as photon beam energy, electron beam energy, and dose rate may affect the dosimetric properties of polymer gel dosimeters. The photon beam energy and dose rate dependence of PASSAG gel dosimeter were previously evaluated. This study aims to assess the dosimetric properties of the optimized PASSAG gel samples in various electron beam energies. The optimized PASSAG gel samples are first fabricated and irradiated to various electron energies (5, 7, 10 and 12 MeV). Then, the response (R2) and sensitivity of gel samples are analyzed by magnetic resonance imaging technique at a dose range of 0 to 10 Gy, scanning room temperature range of 15 to 22 °C, and post-irradiation time range of 1 to 30 days. The R2-dose response and sensitivity of gel samples do not change under the evaluated electron beam energies (the differences are less than 5%). Furthermore, a dose resolution range of 11 to 38 cGy is obtained for the gel samples irradiated to different electron beam energies. Moreover, the findings show that the R2-dose response and sensitivity dependence of gel samples on electron beam energy varies over different scanning room temperatures and post-irradiation times. The dosimetric assessment of the optimized PASSAG gel samples provides the promising data for this dosimeter during electron beam radiotherapy.

Electron Energy Spectrometer for MIR-THz FEL Light Source at Chiang Mai University

The linear accelerator system of the PBP-CMU Electron Linac Laboratory has been designed with the aim of generating free-electron lasers (FELs) in the mid-infrared (MIR) and terahertz (THz) regions. The quality of the radiation is strongly dependent on the properties of the electron beam. Among the important beam parameters, the electron beam energy and energy spread are particularly important. To accurately measure the electron beam energy, the first dipole magnet in the bunch compressor system and the downstream screen station are employed as an energy spectrometer. The A Space Charge Tracking Algorithm (ASTRA) software is used for the design and optimization of this system. Simulation results demonstrate that the developed spectrometer is capable of accurately measuring the energy within the 5–25 MeV range. The screen station system is designed and constructed to have the ability to capture a beam size with a resolution of 0.1 mm per pixel. This resolution is achieved with a screen-to-camera distance of 1.2 m, which proves sufficient for precise energy measurement. The systematic error in energy measurement is found to be less than 10%, with a minimum energy spread of 0.4% achievable when the horizontal beam size remains below 3 mm.

Optical properties of N2/Ar plasma generated by electron beams with silicon nitride transmission window at high pressures

In this paper, we report the generation of nitrogen/argon electron beam plasmas with a 0.4 μm-thick silicon nitride transmission window. The measured transmittance of the electron beam is about 92% when the incident energy of electron beam is 40 keV. The optical properties of the electron beam plasma are investigated at high pressures. The luminescence intensity distribution of nitrogen and argon electron beam plasmas shows a good similarity with changing the gas pressure, suggesting that electron beam ionization is independent of background gas. At the same gas pressure, the nitrogen plasma with conical structure has a longer length along the incident direction of the electron beam and a smaller divergence cone angle compared with the argon plasma. In the nitrogen discharge, it is found that the intensities I380.4, I399.7, and I391.4 corresponding to characteristic lines at 380.4, 399.7, and 391.4 nm decrease along the incident direction of the electron beam, which is correlated with the reduction of the electron density along the incident direction of the electron beam. There is no change in the ratio of I399.7 to I380.4, indicating the spatial uniformity of the electron temperature. When the pressure increases, the ionization process induced by primary electron is enhanced, generating more plasma electrons, which is responding to the increase in the characteristic line intensity. At the same time, the neutral particle collision processes are enhanced and the electron temperature decreases with the increase in the pressure, which is believed to contribute to the observed reduction of the I399.7/I380.4 ratio.