Source Exit Research Articles

Probabilistic model for predicting fire casualties in an urban traffic tunnel

Fire accidents could result in severe casualties in an urban traffic tunnel due to the concentration of users and narrow space. However, fire casualties could not be easily predicted due to the complicated evacuation environment and uncertainty in personnel distribution. This paper proposes a probabilistic model to predict the fire casualties in an urban traffic tunnel with only natural ventilation, considering the effects of the thermal and carbon monoxide distribution, in addition to the arrangement of various vehicles. First, the general framework of the probabilistic model was put forward and the methods to analyze the fire scenario, evacuation process, casualty criteria, and probability curve were introduced in details. Then, a case study based on a three-lane traffic tunnel was conducted, and the effects of maximum heat release rate on probabilistic curve of fire casualties were discussed. The results showed that the fire casualty increased with the maximum heat release rate. Besides this, when the distance between fire source and evacuation exit was reduced to 150 m, the impact of maximum heat release rate would decrease significantly. This study made notable contributions toward evaluating the personnel loss in tunnel fire and laid a foundation for assessing and improving the resilience of tunnel.

Discoloration of RF antenna coil surface after long-term operation of J-PARC ion source

In J-PARC (Japan Proton Accelerator Research Complex) center, the continuous operation period of the Radio Frequency (RF) negative hydrogen ion (H−) source equipped with the internal RF antenna coil is extended step by step in these 6–7 years for the goal to supply stable beam during the entire period of J-PARC user operation each year. In 2022, the continuous ion source operation for 4,001 hours (5.5 months) was achieved with 60 mA H− beam current at the ion source exit, 25 Hz repetition, mainly 500 μs beam pulse width, and 25 kW RF power injection. As the lifetime of the RF ion source is mainly limited by the deterioration of the enamel coating on the RF antenna coil, a detailed evaluation of the antenna surface is required to ensure the feasibility of the further extension of the operation period. In the present study, surface discoloration on the RF antenna coil observed after 5 months of operation is investigated by the application of a digital microscope and SEM/EDS analyses. The EDS analyses show that depositions of the sputtered stainless steel elements and the injected cesium are the most possible candidates for impurities on the enamel coating. The dimension measurements of the RF antenna thickness before and after the long-term operation also support the assumption that the discoloration is due to the deposited elements and hence insulation of the RF antenna coil by enamel coating is maintained. Possible mechanisms leading to antenna deterioration starting from element depositions on the antenna coating are also discussed in the summary part of this manuscript.

Mathematical modeling of the ion extraction system of a radio-frequency ion source

In order to ensure space debris removal from the near-Earth space, the world scientific community is developing various technical means potentially capable of transporting the spent spacecraft to disposal orbits. The so-called Ion Beam Shepherd is among them. According to this method, in order to transfer momentum efficiently from an ion beam generated by a radio-frequency ion source mounted on board a service spacecraft, it is necessary to ensure the generation of an ion beam with the minimum divergence angle. In order to provide generation of a highly collimated ion beam for a system of contactless removal of technogenic space debris, an ion extraction system was modeled with the aim to study the influence of its geometric parameters on the angle of ion beam divergence at the ion source exit plane. Based on the preliminary study, a model of 28 full factorial experiment was developed for two types of electrodes in an ion extraction system. The regression coefficients have been defined that allow, without performing a large array of numerical studies, to assess the influence of various geometric parameters on the ion beam divergence angle.

Orthovoltage X-Ray Irradiator for Preclinical FLASH Studies

Flash radiotherapy, the delivery of high radiation dose (> 10 Gy) at ultrahigh dose rates (> 37 Gy/s), has been shown to reduce significantly normal tissue toxicity compared to conventional irradiation, while maintaining tumor control probability at similar level. Great excitement has since ensued about the transformative potential of FLASH radiotherapy. At present, important FLASH research employs complex accelerator technologies of limited accessibilities. Here, we study the feasibility of a novel self-shielded x-ray irradiation cabinet system, as an enabling technology to enhance the preclinical research capabilities of the radiation research community.The proposed system employs two commercially available high capacity 150 kVp fluoroscopy x-ray sources, RAD-44 or G-1592 tubes, with rotating anode technology in a parallel-opposed arrangement. Simulation was performed using a simulation toolkit. Simulated dosimetric properties of the x-ray beam for both FLASH and conventional dose-rate irradiations were characterized in terms of output, uniformity and symmetry as a function of SSD, beam current, exposure time, and external filters. Dose and dose rate from a single kV x-ray fluoroscopy source at various depths in solid water phantom were verified with measurements using radiographic films.The parallel-opposed x-ray sources can deliver doses up to 67 Gy to a 20-mm thick water equivalent medium at FLASH dose-rates of 40 - 240 Gy/s. A uniform depth dose rate within ± 5% deviation is achieved over 8-12 mm in central region of the phantom. Conventional dose-rate irradiation (≤ 0.1 Gy/s) can also be achieved by reducing the tube current and increasing the distance between the phantom and tubes. Either the RAD-44 or G-1592 x-ray source can be used to deliver FLASH and conventional dose-rate irradiations with the field larger than 25 mm and up to 200 mm in length, respectively. These field dimensions are well suitable for small animal and cell culture irradiations. For FLASH irradiation using parallel-opposed source arrangement, entrance and exit doses can be increased by 30% compared to the dose at the phantom center. Beam angling can be employed to reduce the high surface doses by minimizing the beams overlap at the phantom surfaces. For a 10 × 10 mm2 field, for example, 26degree beam angle from vertical axis reduces the entrance dose by 39%, while maintaining FLASH dose rate of 118 Gy/s spanning in 8 mm thickness.It is feasible to achieve FLASH dose rate irradiation with kV x-rays using rotating anode x-ray sources in the parallel-opposed arrangement. The system is amendable to self-shielding and readily deployable. Availability of both FLASH and conventional dose rate irradiations in the same platform enables effective comparative research. A cabinet FLASH irradiation system will greatly enhance research in the regular laboratory setting to elucidate the important biological mechanism of the FLASH effect.

Direct experimental comparison of krypton and xenon discharge properties in the magnetic nozzle of a helicon plasma source

Helicon plasma sources currently represent an active field of research in the domain of low-temperature plasmas due to several interesting characteristics for in-space propulsion applications. This work reports direct comparison of krypton and xenon plasma properties through spatially resolved measurements performed in the near-field plume of a sub-kilowatt-class 13.56 MHz helicon source. The set of developed and employed intrusive diagnostics is comprehensively described. The magnetic components of the plasma rf field are inferred using a 3D B-dot probe along the reactor axial direction with and without the externally applied DC magnetic field. Plasma floating potential fluctuations are measured using a capacitive probe to draw design requirements for a rf-compensated Langmuir probe. The latter is used to perform axial and radial measurements of plasma density, electron temperature, and plasma potential. A four-grids retarding potential analyzer is used to infer the ion kinetic energy downstream the source exit. The effect of magnetic field magnitude on ions and electrons properties is especially investigated.

Study of smoke back-layering length with different longitudinal fire locations in inclined tunnels under natural ventilation

To investigate the vehicle fire hazard at different locations in inclined tunnels, the effect of longitudinal fire locations on smoke behavior characteristics induced by inclined tunnel fires was proposed by simulation and theoretical analysis. A series of tunnel models with slope of 4% was conducted by Fire Dynamics Simulator (FDS) software for fire simulation, in which three fire scenarios were considered corresponding to the variation of fire location, upstream length and downstream length respectively. The results show that smoke back-layering length drops progressively with increasing of downstream length, and upstream inlet airflow velocity is linearly positively correlated with downstream length, while the upstream length has a limited impact on smoke movement. A new prediction equation of the dimensionless smoke back-layering length account for downstream length and tunnel slope was established, through the addition of height difference between fire source and downstream exit. The established correlation shows that the dimensionless smoke back-layering length is logarithmically related to cubic power of downstream length, and the predicted results agreed well with simulated data as tunnel slope from 3.5% to 7.5%. The results can provide beneficial suggestion in ventilation system design and emergency evacuation for inclined tunnels.

Experimental study on flame pulsation behavior of external venting facade fire ejected from opening of a compartment

The present study investigated experimentally the flame pulsation magnitude (ratio of maximum flame height to mean flame height; ratio of mean flame height to continuous flame height) and flame pulsation frequency of the external venting facade fire (EVF) ejected from opening of a compartment. Experiments were conducted by employing three model-scale fire compartments with an opening and a vertical facade wall. Fifteen different opening geometries were considered. For the flame pulsation magnitude of EVF, results showed that the ratio of maximum flame height to the mean flame height was about 1.30, while the ratio of mean flame height to continuous flame height was about 1.60; both of them were independent of opening geometries and heat release rates. The flame pulsation frequency of EVF increased with increasing of heat release rate, meanwhile decreased with increasing of opening size (or namely opening characteristic lengths: ℓ1= (AH1/2)2/5; ℓ2= (AH2)1/4). The measured flame pulsation frequency of EVF showed to be much lower than the predicted values by previous classic models developed for free buoyant diffusion flames, which is due to physically the inherent special exit condition (with initial horizontal convection flow of heat) at the opening for EVF. A new formula was proposed for the flame pulsation frequency of EVF in terms of a non-dimensional function between Strouhal number (St) and Froude number (Fr), using Vf∝gZf as the characteristic flame uprising velocity and ℓ1= (AH1/2)2/5 as the characteristic length of the source exit convection flow condition at the opening. The flame pulsation frequency showed to be well represented by the proposed formula. These new observations and the proposed formula provide essential knowledge for the characterization of flame pulsation behavior of external venting facade fire (EVF) ejected through the opening of a compartment.

Modification of momentum flux lost to a radial wall of a helicon source by neutral injection

The profiles of the axial and radial momentum fluxes lost to the radial wall are experimentally investigated in a helicon source by using a momentum vector measurement instrument, where two gas injection configurations from the upstream of the source tube and from the downstream open source exit are tested. It is observed that the axial position of the maximum density is shifted to the source exit side for the downstream gas injection, compared with the upstream one. The measurement shows that the axial momentum flux transferred to the radial wall for the upstream gas injection is larger than that for the downstream gas injection, indicating that the axially accelerated ions are lost to the source wall. It is demonstrated that the loss of the axial momentum can be reduced by injecting the neutral gas near the open source exit, i.e., for the downstream gas injection.

Atom beam emersion from hot cavity laser ion sources

Ion sources exploiting laser resonance ionization offer efficient and element-selective radioactive ion beam production at the leading isotope separation on-line facilities worldwide. Most commonly, laser resonance ionization takes place inside a resistively heated atomizer tube directly coupled to the production target, where the element of interest is evaporated and provided as atomic vapor. While naturally the majority of atoms is ionized inside this hot cavity, a fraction of the neutrals effuses towards the high voltage beam extraction system of the subsequent mass separator.We report on several systematic investigations on this phenomenon regarding its significance and implications on the operation of resonance ionization laser ion sources. Experiments suggest a less sharply directed atom cone than expected from theoretical model, up to a lateral opening angle of 45°. Inside the tubular volume defined by the laser beam diameter around the central axis behind the source exit, more than 90% of potentially ionizable atoms are found within the first 2 cm. Geometrical constraints for the construction of devices based on ionization in the effusing atom beam directly downstream of the hot cavity are derived, and causes for cross-mass beam contamination are identified. Counter measures using laser repetition rate synchronized beam gating by fast electrostatic beam deflection to overcome these problems are presented.

Enhancement of downstream plasma density by a stepped-diameter radiofrequency plasma source under a static magnetic field for a compact sputtering reactor

A stepped-diameter insulator source cavity is employed to a radiofrequency (RF) plasma source for development of a sputtering reactor, where an inner diameter near the open source exit is enlarged compared with the upstream diameter and convergent-divergent magnetic field is applied near the source exit to inhibit the plasma loss to the wall by separating the plasma from the wall. Furthermore argon gas is introduced at the interface between the different diameter regions; a high plasma density of ∼5 × 1017 m−3 can be obtained at ∼50 mm downstream of the source exit for an RF power of about 100 W. To enhance the sputtering performance, a permanent magnet is installed behind the target located downstream of the source and a target current can be increased. The results on the plasma density and a deposition rate of Cu film on a substrate are compared for different source cavities and gas injection locations, which confirm the validity of the stepped-diameter source cavity on the performance improvement of the sputtering reactor.

Independent assessment of source transit time for the BEBIG SagiNova® high dose rate brachytherapy afterloader

Introduction: The dwell time and transit time components contribute to the overall delivered dose to patients in high dose rate (HDR) brachytherapy treatments. The transit time results from source entry and exit as well as source movements between dwell positions. It depends on various parameters such as the source speed profile, source indexer distance to dwell position, and step size. Usually brachytherapy treatment planning systems do not apply a correction for transit time and the afterloader unit itself adjusts the final dwell times taking account of the transit time. The independent verification of transit time for each HDR afterloader is recommended before clinical use. Some published reports have used a video camera and/or stopwatch to perform this task. To the best of our knowledge, there is no published report of transit time measurement for the recently released BEBIG SagiNova® HDR afterloader unit. The goal of this study is to independently evaluate the corrected source transit time of this afterloader unit without using a video camera or stopwatch. Materials and Methods: The assessed unit was a newly installed SagiNova® 60Co HDR afteroloader (software version 1.2.4; Eckert & Ziegler BEBIG GmbH). A dosimetric method was used. The measurements were performed using a previously commissioned PTW source check4п (type 33005) well- type ionization chamber and UNIDOS E® electrometer. A 30 cm plastic needle and a 100 cm transfer tube were used to accurately place the source at the point of maximum response (‘sweet spot’) of the well chamber. Plans were generated using SagiPlan version 2.0 to irradiate the well chamber for dwell times of 3, 5, 10, 15, 20, 30, 40, 60, and 120 s. All the measurements were repeated three times. The transit time following its correction by the afterloader software were assessed using the ESTRO-recommended approach of obtaining transit time correction factors and another strategy established for teletherapy sources. The results obtained using the two strategies were also compared. Results: For the measured setup, the transit time was 0.7 s using both methods. The mean ESTRO transit time correction factor was 0.93 (range 0.88 to 0.99 for dwell times of 3 to 120 s). Conclusion: This work demonstrates an accurate dosimetry-based method to measure source transit time during the commissioning step of HDR BT afteroloaders, using a practical approach and available standard equipment. It also shows the consistency of the results between the two dosimetric methods of obtaining source transit time. The results suggest that the afterloader software correction does not completely eliminate this effect, which results in slightly longer irradiation times.

Bonding, structural properties and thermal stability of low damage RF (N2) plasma treated diamond (100) surfaces studied by XPS, LEED, and TPD

In this work, we investigate the interaction of N2 radio frequency (RF) plasma with single crystal diamond (100) surface. This study shows that a low-level damaged nitrogen terminated diamond (100) surface may be produced using a bent plasma source and a grounded mesh electrode placed at the source exit. Optical emission spectroscopy (OES) was used to characterize the species present in the plasma. The chemical, structural and thermal stability of the N-terminated diamond (100) surface were investigated in-situ by X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and low energy electron diffraction (LEED). OES showed that increasing the flow rate and operating pressure could decrease the ratio of charged-to-neutral nitrogen particles. From XPS results it is determined that the adsorbed nitrogen to the diamond surface may occupy a number of bonding configurations and that the damage to the surface upon nitridation, as reflected in the C(1s) peak shape analysis, can be minimized. From annealing experiments, it was found that some of the incorporated nitrogen onto the diamond surface is stable upon annealing to 1000 °C. LEED results show that upon a short RF (N2) plasma exposure time a (1 × 1) pattern was observed which was preserved upon annealing to 1000 °C suggesting that a thermally stable and ordered nitrogen terminated surface was formed. The TPD spectrum shows two low-temperature N2 desorption peaks that are associated to weakly bonded nitrogen chemisorbed species to the diamond surface at 210 and 560 °C.

Generation of Noble and Refractory Metals Plasma Jets by Electrothermal Discharge for Surface Deposition Applications

Arc-dominated capillary discharges generate high-density plasmas from the ablation of the material of the inner lining sleeve, where ablation is determined by the radiant energy transport in such electrothermal (ET) plasma devices. Properties of sleeve material are an important factor on the generated plasma in ET devices. The 1-D time-dependent NC State University ET plasma code ETFLOW provides simulation of the capillary discharge and predicts the plasma parameters along the capillary axis. Of interest are the plasma parameters at the exit of the capillary which include temperature, pressure, velocity, heat flux and total ablated mass ejected from the source. The experimental discharge current was used in the code, and the plasma parameters at the source exit were calculated. Six materials were tested, namely, titanium, chromium, copper, silver, platinum, and gold. The code results show that the plasma temperature is between 2.4 and 2.57 eV for all tested materials. The lower heat of sublimation of gold and silver leads to increase the total ablated mass, density, electrical conductivity, and the exit pressure combined with reduction of the plasma bulk velocity. The gold has the highest ablated mass while titanium has the lowest values. The total ablated mass of copper material is about 168 mg, which is in a good agreement with previous experimental results.

High Current Audio Frequency (Ion/Electron) Source

Simple technique is used for production of high ion / electron current from an Audio Frequency (AF) (10 – 50 kHz) discharge source. Small size plasma bottle (ϕ = 30 mm, L = 35 mm) with capacitive electrode of AF antenna immersed inside it. The source is working at high discharge pressure ~ 0.2 Torr., without the need of high vacuum system. The extraction system is concentric hemisphere electrodes which allow self-beam focusing by adjusting the beam minimum size and its position from the source exit. The ion species used are nitrogen and argon, the discharge power (100 – 500 W) and the extraction voltage is (100 – 600 V). The AF discharge shows a high discharge cross-section of ionization at certain frequency of the AF supply. The behavior of the AF discharge acts similar to the D.C. discharge explained by known Paschen's curve. The maximum extracted Ar electrons and ions currents are 10 and 2.4 mA respectively, while for Nitrogen are 12.5 and 2.7 mA. Beam simulation by SIMION program shows a good agreement with the analytical study of the hemi-sphere electrodes extraction system.

Filtering peripheral high temperature electrons in a cylindrical rf-driven plasmas by an axisymmetric radial magnetic field

High temperature electrons generated near a radial wall of a cylindrical source tube in a radiofrequency (rf) inductively-coupled plasma is filtered by an axisymmetric radial magnetic field formed near the source exit by locating annular permanent magnets, where the axial magnetic field strength in the radially central region is fairly uniform inside the source tube and is close to zero near the source exit. The source is operated at 3 mTorr in argon and the rf antenna is powered by a 13.56 MHz and 400 W rf generator. Measurement of electron energy probability functions shows the presence of the peripheral high temperature electrons inside the source, while the temperature of the peripheral electrons downstream of the source is observed to be reduced.

Characterization of an electrothermal plasma source for fusion transient simulations

The realization of fusion energy requires materials that can withstand high heat and particle fluxes at the plasma material interface. In this work, an electrothermal (ET) plasma source has been designed as a transient heat flux source for a linear plasma material interaction device. An ET plasma source operates in the ablative arc regime driven by a DC capacitive discharge. The current channel width is defined by the 4 mm bore of a boron nitride liner. At large plasma currents, the arc impacts the liner wall, leading to high particle and heat fluxes to the liner material, which subsequently ablates and ionizes. This results in a high density plasma with a large unidirectional bulk flow out of the source exit. The pulse length for the ET source has been optimized using a pulse forming network to have durations of 1 and 2 ms. The peak currents and maximum source energies seen in this system are 1.9 kA and 1.2 kJ for the 2 ms pulse and 3.2 kA and 2.1 kJ for the 1 ms pulse, respectively. This work is a proof of the principal project to show that an ET source produces electron densities and heat fluxes comparable to those anticipated in transient events in large future magnetic confinement fusion devices. Heat flux, plasma temperature, and plasma density were determined for each shot using infrared imaging and optical spectroscopy techniques. This paper will discuss the assumptions, methods, and results of the experiments.

Thermodynamic analysis of organic Rankine cycle used for flue gases from biogas combustion

This study elaborates an investigation on organic Rankine cycle (ORC) for integration with a sewage plant for generation of power and district heating purposes. Flue gases from combustion of biogas is considered as heat source. Initially, design constraints of the cycle i.e. pump exit temperature, source exit temperature, cooling fluid exit temperature, and flue gases exit temperature are applied to check the ORC applicability. Furthermore, fifteen sets of working conditions with combinations of evaporation pressure, source temperature, and pinch point condition are passed through a step by step energetic and exergetic analysis. Seven best set of working conditions are shortlisted to examine the thermal efficiency of the cycle for combined heat and power (CHP) generation. In addition, the research also highlights the importance of biogas technology with respect to environment. The results show that the maximum work output of 156.4 kW is produced at source temperature of 345 °C, evaporation pressure of 36 bar, and pinch point of 5 °C at evaporator and 10 °C at condenser. This research demonstrates that biogas-fired ORC systems depicts an efficient solution for domestic scale power generation applications in rural areas.

Human health risk evaluation of a microwave-driven atmospheric plasma jet as medical device

PurposeThe aim of this study was the characterisation of a microwave-driven atmospheric plasma jet (APJ) dedicated for medical applications. The scientific focus includes harmless sterilization of surfaces and therapeutic treatments in dentistry. MethodesThe plasma was investigated with respect to potential health risks for human beings, which could occur especially by the gas temperature, heat flow, patient leakage current, UV emission and ozone emission from the plasma jet, according to DIN SPEC 91315:2014-06 (General requirements for plasma sources in medicine) [1]. ResultsThe results of the experiments indicate a high potential of the plasma jet to be used as a medical device exhibiting low gas temperatures up to 34 °C. The calculated leakage currents are mostly below the 10 μA threshold. The limiting UV exposure duration for the APJ with a calculated maximum effective irradiance of 2.6 μW/cm2 is around 19 min, based on the exposure limits of the international commission on non-ionizing radiation protection guidelines (ICNIRP) [2]. A significant ozone concentration was observed mainly in the axial effluent gas flow. Ozone concentration strongly decreases with increasing distance from the plasma source exit nozzle. ConclusionThe investigated APJ exhibits physical properties that might not constitute health risks to humans, e.g. during treatment in dentistry. Thus, the APJ shows a high potential for application as a device in dental therapy.

Laboratory Observation of a Plasma-Flow-State Transition from Diverging to Stretching a Magnetic Nozzle.

An axial magnetic field induced by a plasma flow in a divergent magnetic nozzle is measured when injecting the plasma flow from a radio frequency (rf) plasma source located upstream of the nozzle. The source is operated with a pulsed rf power of 5kW, and the high density plasma flow is sustained only for the initial ∼100 μsec of the discharge. The measurement shows a decrease in the axial magnetic field near the source exit, whereas an increase in the field is detected at the downstream side of the magnetic nozzle. These results demonstrate a spatial transition of the plasma-flow state from diverging to stretching the magnetic nozzle, where the importance of both the Alfvén and ion Mach numbers is shown.

Extraction of ions and electrons from audio frequency plasma source

Herein, the extraction of high ion / electron current from an audio frequency (AF) nitrogen gas discharge (10 – 100 kHz) is studied and investigated. This system is featured by its small size (L= 20 cm and inner diameter = 3.4 cm) and its capacitive discharge electrodes inside the tube and its high discharge pressure ∼ 0.3 Torr, without the need of high vacuum system or magnetic fields. The extraction system of ion/electron current from the plasma is a very simple electrode that allows self-beam focusing by adjusting its position from the source exit. The working discharge conditions were applied at a frequency from 10 to 100 kHz, power from 50 – 500 W and the gap distance between the plasma meniscus surface and the extractor electrode extending from 3 to 13 mm. The extracted ion/ electron current is found mainly dependent on the discharge power, the extraction gap width and the frequency of the audio supply. SIMION 3D program version 7.0 package is used to generate a simulation of ion trajectories as a reference to compare and to optimize the experimental extraction beam from the present audio frequency plasma source using identical operational conditions. The focal point as well the beam diameter at the collector area is deduced. The simulations showed a respectable agreement with the experimental results all together provide the optimizing basis of the extraction electrode construction and its parameters for beam production.