Greater Energy Deposition Research Articles

Ignition enhancement of liquid kerosene by a novel high-energy spark igniter in scramjet combustor at Mach 4 flight condition

Spark ignition system is the most widely used method in the combustor. However, it is generally considered unsuitable for scramjet engines due to the shortage of ignition energy. This study firstly presents a novel long electrode distance high-energy spark igniter (LHSI), which significantly increases the energy deposition of spark by simultaneously improving the energy storage and discharge efficiency. The discharge and ignition characteristics of LHSI were investigated based on the discharge waveforms and high-speed photography. The results show that the discharge efficiency of LHSI can reach 62.4% with the single-pulse stored energy of 100 J while that of conventional high-energy spark igniter (HSI) is only 28.2%. The ignition process produced by such a high-energy spark is firstly reported in a scramjet combustor. An initial flame kernel with a larger size and higher combustion intensity can be produced, which is capable of igniting the cavity with proper local equivalence ratio rapidly and reliably. Compared with HSI, the ignition process of LHSI is more active and the ignition limit can be obviously extended. A novel tail flame ignition mode is observed. It can be concluded that the spark ignition with greater energy deposition is worthy to be further studied in scramjet.

Production of runaway electrons and x-rays during streamer inception phase

Streamers play a key role in the formation and propagation of lightning channels. In nature streamers rarely appear alone. Their ensemble behavior is very complex and challenging to describe. For instance, the intricate dynamics within the streamer zone of negative lightning leaders give rise to space stems, which help advance the stepped-leader. Another example is how the increasing morphological complexity of sprites can lead to higher sprite current and greater energy deposition in the mesosphere. Insights into the complex dynamics of a streamer corona can be obtained from laboratory experiments that allow us to control the conditions of streamer formation. Based on simultaneous nanosecond-temporal-resolution photography, and measurements of voltage, current, and x-ray emissions, we report the characteristics of negative laboratory streamers in 88 kPa of atmosphere. The streamers are produced at peak voltages of 62.2 ± 3.8 kV in a point-to-plane discharge gap of 6 cm. While all discharges were driven to the same peak voltage, the discharges occurred at different stages of the relatively slow voltage rise (177 ns), allowing us to study discharge properties as a function of onset voltage. The onset voltage ranged between 24 and 67 kV, but x-ray emissions were observed to only occur above 53 kV, with x-ray burst energies scaling quadratically with voltage. The average delay between the current pulse and x-ray emission was found to be 3.5 ± 0.5 ns, indicating that runaway electrons are produced during the streamer inception phase or no later than the transition stage, when the inception cloud is breaking into streamer filaments. During this short time span, runaway electrons can traverse the gap, hit the ground plate and produce bremsstrahlung x-ray photons. However, streamers themselves cannot traverse more than 3.5 mm across the gap, which supports the idea that runaway electron production is not associated to streamer connection to the ground electrode.

Review of pool boiling critical heat flux (CHF) and heater rod design for CHF experiments in TREAT

Preventing the occurrence of a departure from nucleate boiling (DNB) event is an important aspect of nuclear safety in pressurized water reactors (PWRs). This phenomenon is partially governed by the cladding-to-coolant heat transfer under transient irradiation conditions, such as during a reactivity-initiated accident (RIA). Currently, there are large uncertainties about cladding-to-coolant heat transfer under these rapid transient conditions. This effort aims to elucidate the mechanisms of CHF under in-pile fast transient irradiation conditions using the Transient Reactor Test (TREAT) facility. These experiments will be carried out under pool boiling conditions, within experimental capsules that will be inserted into the TREAT reactor. A heater rodlet made from stainless steel 304 with tailored natural boron content will be usedin these experiment capsules to induce CHF when submitted to a TREAT power pulse. We will investigate the impacts of the presence of an oxide layer, radiation-induced surface activation (RISA), heat transfer time constant, and rapid surface heating effects on the CHF phenomenon.We review the parameters with significant effects governing the predictions of pool boiling CHF. Only CHF influencing parameters that are highly important, among them coolant subcooling and pressure, as well as oxide layer thickness, RISA, and rapid heating effects were included in this literature assessment.Preliminary neutronics and thermal hydraulic results from the design of the experimental apparatus are also presented in this paper. To aid in the modeling approach, the energy deposition and occurrence of CHF were identified as the most crucial key Figures of Merit (FoMs).In the heater rod design, boron concentrations between 0.1 and 2.09 wt% were considered. Further, a self-shielding study was performed to determine whether an instrumented borated tube could be used in place of a solid borated rod. This study determined that the inner region of the rod can be excluded or instrumented without heat generation penalties. Lastly, a thermal-hydraulics sensitivity study determined the lowest limiting boron concentration needed to induce CHF in water with different degrees of subcooling. Additionally, the value of CHF is known to increase during a rapid transient. Therefore, a CHF multiplier sensitivity study determined what multipliers would inhibit CHF for varying degrees of subcooling of two chosen power coupling factors (PCFs). The current borated tube rodlet geometry configuration achieved a maximum CHF multiplier value of 7.8 using a 1400 MJ power pulse in TREAT. Although this was the power pulse with the greatest energy deposition considered for this study, the TREAT facility is capable of pulses up to ~2500 MJ. This provides a significant margin in energy capacity that was not included within the scope of the calculations carried out to date.The application of the heater rod design was successfully demonstrated in initial experiments in December 2019. The results of these experiments will be explored in future publications.

Phase I/II Trial Evaluating Carbon Ion Radiotherapy for Salvaging Treatment of Locally Recurrent Nasopharyngeal Carcinoma.

Background: Radiation therapy is the mainstay strategy for the treatment of nasopharyngeal cancer (NPC). Intensity-modulated X-ray therapy (IMXT) alone is the current standard for stage I and II NPC. For stage III and IV A/B diseases, concurrent chemotherapy should be provided in addition to IMXT. However, optimal treatment for locally recurrent NPC after previous definitive dose of radiotherapy is lacking. Various techniques including brachytherapy, IMXT, stereotactic radiosurgery or radiotherapy (SRS or SBRT) have been used in the management of locally recurrent NPC. Due to the inherent limitation of these techniques, i.e., limited range of irradiation or over-irradiation to surrounding normal tissues, moderate efficacy has been observed at the cost of severe toxicities. Carbon ion radiotherapy (CIRT) offers potential physical and biological advantages over photon and proton radiotherapy. Due to the inverted dose profile of particle beams and their greater energy deposition within the Bragg peak, precise dose delivery to the target volume(s) without exposing the surrounding organs at risk to extra doses is possible. In addition, CIRT provides an increased relative biological effectiveness (RBE) as compared to photon and proton radiotherapy. Such advantages may translate to improved outcomes after irradiation in terms of disease control in radio-resistant and previously treated, recurrent malignancies. It is therefore reasonable to postulate that recurrent NPC after high-dose radiotherapy could be more resistant to re-irradiation using photons. Reports on the treatment of radio-resistant malignancies in the head and neck region such as melanoma, sarcoma, and adenoid cystic carcinoma (ACC) have demonstrated superior local control rates from CIRT as compared to photon irradiation. Thus patients with recurrent NPC are likely to benefit from the enhanced biological effectiveness of carbon ions. As effective retreatment strategy is lacking for locally recurrent NPC, carbon ion radiation therapy offers an ideal alternate to conventional X-ray irradiation.Methods and Design: The recommended dose of re-irradiation using CIRT for locally recurrent NPC will be determined in the dose-escalating phase (Phase I) of the study. Efficacy in terms of local progression-free survival (LPFS) and overall survival (OS) will be studied in the second phase of the study. Increasing doses of CIRT using raster scanning technology from 55GyE (22×2.5 GyE) to 65 GyE (26× 2.5 GyE) will be delivered in the Phase I part of the study. The primary endpoint of the Phase I part of the study is acute and sub-acute toxicities; the primary endpoint in the Phase II part is local progression-free survival and overall survival. Using the historical 2-year OS rate of 50% in locally recurrent NPC patients treated with photon or proton, we hypothesize that CIRT can improve the 2-year OS rate to 70%.Discussion: The utilization of conventional radiation techniques including IMXT, brachytherapy, or stereotactic radiation therapy provides moderate efficacy in the treatment of locally recurrent NPC due to the limitations in dose distribution and biological effectiveness. Improved outcome in terms of treatment-induced toxicity, LC, LPFS, and OS are expected using CIRT due to the physical and biological characteristics of carbon ion beam. However, the recommended dose of CIRT used in re-irradiation for the local NPC focus remain to be determined. The recommended dose as well as the efficacy of CIRT in the treatment of locally recurrent NPC will be evaluated in the present trial.

Effect of soft metal gasket contacts on contact resistance, energy deposition, and plasma expansion profile in a wire array Z pinch

Soft metal gaskets (indium and silver) were used to reduce contact resistance between the wire and the electrode in an aluminum wire Z pinch by more than an order of magnitude over the best weighted contact case. Clamping a gasket over a Z-pinch wire compresses the wire to the electrode with a greater normal force than possible with wire weights. Average contact resistance was reduced from the range of 100-3000 Omega (depending on wire weight mass) to 1-10 Omega with soft metal gaskets. Single wire experiments (13 microm Al 5056) on a 16 kA, 100 kV Marx bank showed an increase in light emission (97%) and emission volume (100%) of the plasma for the reduced contact resistance cases. The measured increases in plasma volume and light emission indicate greater energy deposition in the ablated wire. Additionally, dual-wire experiments showed plasma edge effects were significantly decreased in the soft metal gasket contact case. The average height of the edge effects was reduced by 51% and the width of the edge effects was increased by 40%, thus the gasket contact case provided greater axial uniformity in the plasma expansion profile of an individual wire.

MR imaging of epilepsy: State of the art at 1.5 T and potential of 3 T

ABSTRACT Shortly after being introduced in the nineteen eighties, magnetic resonance imaging (MRI) became a key tool for the investigation of patients with epilepsy, due to its ability to acquire high quality images. The strength of the magnetic field of a scanner is measured in tesla (T). This review addresses the clinical and research potential in epilepsy of MR imaging at 1.5 T and 3 T. A typical clinical scanning protocol at 1.5 T for a patient with refractory epilepsy may include T1‐ and T2‐weighted imaging, fluid‐attenuated inversion recovery (FLAIR) imaging, and a 3D volume acquisition sequence. A research protocol may add quantification of structural imaging, such as volumetric assessment and T2‐relaxometry, together with functional measures, such as MR‐spectroscopy, functional MRI and diffusion weighted sequences. MR‐spectroscopy assesses the metabolites of the seizure focus and other brain areas. Functional MRI allows localisation of cognitive and sensori‐motor function and the ability to assess the spatial relationship of these functions to the seizure focus. Whereas these techniques can be performed at 1.5 T, particularly MR‐spectroscopy and functional MRI benefit from increased magnetic field‐strength. Higher magnetic field‐strength is associated with a higher signal‐to‐noise ratio (SNR). The increased SNR can allow shorter imaging times for a given resolution, higher resolution for a given imaging time, or combination of both. The use of higher magnetic field‐strengths is therefore indicated for the (fast) imaging of ill subjects, for long protocols, including structural, metabolic and functional imaging, and for novel applications, such as continuous EEG recording and functional MRI for the detection of the seizure focus. Disadvantages of MR imaging in epilepsy at a high field‐strength of 3 T and above are, apart from engineering and technical challenges, the greater energy deposition into tissue and increased susceptibility to artefacts. So far, magnets of 3 T and above have been used mainly for research applications, however the benefits of high field‐strength for MR spectroscopy and functional MRI, and the usefulness of these techniques for the investigation of epilepsy patients are obvious incentives for the use of 3 T systems in routine clinical investigations. [Published with neuroimaging sequences.]

Effects of heavy gases on the tandem mass spectra of peptide ions in the quadrupole ion trap

Heavy gases (xenon, argon, krypton, methane) have been used to improve the performance of the quadrupole ion trap when performing collision-induced dissociation on peptides. MS/MS spectra reveal that increased amounts of internal energy can be deposited into peptide ions and more structural information can be obtained. Specifically, the pulsed introduction of the heavy gases (as reported previously by Doroshenko, V. M.; Cotter, R. J. Anal. Chem. 1996, 68, 463) provides greater energy deposition without the deleterious effects that static pressures of heavy gas have on spectra. Internal energy deposition as indicated by a qualitative evaluation of MS/MS spectra shows pulsed introduction of heavy gases enables ions to obtain more internal energy than possible by using static pressures of the same heavy gases. A linear correlation is observed between the percentage of heavy gas added and the ratio of product ions used to reflect internal energy deposition. Results here also show that upon pulsed introduction of heavy gases, empirical optimization of a single frequency resonant excitation signal is no longer needed to obtain good MS/MS spectrometry efficiency. The presence of many low mass-to-charge ratio ions and the absence of side chain cleavages in the MS/MS spectra of peptides suggests that the propensity for consecutive fragmentations is increased with the pulsed introduction of heavy gases. In addition, by varying the delay time between introduction of the gas and application of the resonant excitation signal, the amount of fragmentation observed in MS/MS spectra can be changed.