Wall Chambers Research Articles

Laser IFE Direct Drive Chamber Concepts with Magnetic Intervention

The High Average Power Laser (HAPL) program is focusing on the development of laser IFE power plants based on lasers, direct-drive targets and dry wall chambers. One key issue is the survival of the chamber wall under the ion threat spectra (representing ˜25% of the yield energy). The possibility of steering the ions away from the chamber to specially-designed dump chambers using magnetic intervention is being investigated. This brings up the intriguing possibility of utilizing a liquid wall to accommodate the ion fluxes in the dump chamber provided the right measures are taken to prevent the liquid from contaminating the main chamber. This paper covers the initial assessment of different magnetic configurations for a laser IFE chamber. Their key characteristics are described; results of the supporting design analyses are summarized; and the major findings and issues are highlighted.

Mapping radiation quality inside photon-irradiated absorbers by means of a twin-chamber method

In photon-beam radiotherapy, the absorbed dose in an irradiated object contains a contribution by energy-degraded photons originating from Compton scatter processes at parts of the treatment head and within the absorber itself. These low-energy spectral components may lead to changes in the response of non-ideally water-equivalent radiation detectors, such as Si diodes and radiographic films, in the water/tissue dose conversion factors and in the relative biological effectiveness (RBE). As a simple means of accounting for these changes in spectral quality, the Monte Carlo calculated fraction of the kerma or absorbed dose contributed by scattered photons with energies not exceeding a certain cut-off value has previously been proposed as a useful parameter. In this paper, we present an equivalent experimental approach, providing a means for the spatial mapping of radiation quality. Its applicability will be demonstrated for the case of 60Co and 6 MV photons. A twin-chamber combination of a Farmer type ionization chamber, equipped with a graphited PMMA outer electrode, and a chamber of the same design, but with an outer electrode made from copper, has been developed. The measured quantity is the signal ratio (SR) of the copper wall and graphited wall chambers. A correlation between the SR and the fraction of the air kerma respectively of the absorbed dose to water, contributed by photons with energies not exceeding 200 keV, has been established at a Theratron 780-C 60Co teletherapy unit and at a Siemens Primus 6 MV linear accelerator. We also describe a two-dimensional version of the twin-chamber method using the PTW 2D-Array 256. Typical trends of parameter SR with depth and off-axis distance in water-equivalent phantoms have been observed. Thereby, a simple experimental method for the space-resolved assessment of the dose fraction attributable to low-energy Compton scattered photons can be presented as an innovative instrument of describing radiation quality in radiotherapy.

Impact Attenuation Characteristics of Thin Walled Collapsible Air Chambers for Use in Protective Helmets

Abstract For the past 40 years, helmets have primarily used expanded polystyrene, vinyl nitrile, and expanded polypropylene foams for impact attenuation. Even though the packaging industry has investigated a variety of structures for impact management, the helmet industry has been slow to adopt these types of innovations. More recently, engineered structures have been developed and introduced for use in the helmet industry. This study was intended to describe the impact characteristics of a thin walled collapsible air chambers designed to be used in sport helmets. This study investigated three structures: rigid walls, a chamber with rigid walls and a vent, and a chamber with rigid walls and no vent. Each structure was impacted with a 5 kg weight at three velocities: 1.9, 2.8, and 3.4 m/s. The three structures were also made using two materials of different stiffnesses. Analysis of the results revealed that the effect of the walls, vent, and material stiffness interacted to produce effective energy management. The results demonstrated that by changing the material stiffness, wall thickness, and vent diameter the performance of the chambers can be engineered to effectively manage different levels of energy.

Spark plasma sintering of zirconium carbide and oxycarbide: Finite element modeling of current density, temperature, and stress distributions

A combined experimental/numerical approach was developed to determine the distribution of current density, temperature, and stress arising within the sample during spark plasma sintering (SPS) treatment of zirconium carbide (ZrCx) or oxycarbide (ZrCxOy). Stress distribution was calculated by using a numerical thermomechanical model, assuming that a slip without mechanical friction exists at the interfaces between the sample and the graphite elements. Heating up to 1950 °C at 100 °C min−1 and a constant applied pressure of 100 MPa were retained as process conditions. Simulated temperature distributions were found to be in excellent agreement with those measured experimentally. The numerical model confirms that, during the zirconium oxycarbide sintering, the temperature measured by the pyrometer on the die surface largely underestimates the actual temperature of the sample. This real temperature is in fact near the optimized sintering temperature for hot-pressed zirconium oxycarbide specimens. It is also shown that high stress gradients existing within the sample are much higher than the thermal ones. The amplitude of the stress gradients was found to be correlated with those of temperature even if they are also influenced by the macroscopic sample properties (coefficient of thermal expansion and elastic modulus). At high temperature, the radial and angular stresses, which are much higher than the vertical applied stress, provide the more significant contribution to the stress-related driving force for densification during the SPS treatment. The heat lost by radiation toward the wall chambers controlled both the thermal and stress gradients.

Development of ion chambers for the measurement of low energy synchrotron radiation

Measurement of radiation fields due to low energy synchrotron radiation (SR) needs special considerations. The photoelectric interactions, which are mainly responsible for signal generation in this case, result in electron emission in a direction nearly perpendicular to the direction of incident photon. A free air ionisation chamber was designed and used for measurement of intensity of SR in the beam line and a methodology has been developed to measure SR fields away from the beam line using large volume ion chambers. Studies with spherical and cylindrical ion chambers in X-ray beams obtained at a tube potential of 15 kV (3 mm Be inherent filtration) showed that the chamber sensitivity at low energy strongly depended on curvature of the chamber wall especially in thick walled chambers. Our studies further showed that large volume thin and plane walled (0.01 mm thick aluminium wall) chambers could be used for measurement of SR fields away from the beam lines, with reasonably good accuracy (±10%) by calibrating them against the free air ion chamber through a similar chamber of smaller dimensions.

Endoscopic Treatment of an Unusual Cause of Biliary Ductal Dilation

Purpose: Benign tumors of the bile duct are rare and occasionally mimic malignancy. We report a case of ampullary adenomyomatous hyperplasia presenting with abdominal pain, abnormal liver tests along with a cystic mass in the duodenum. Methods: A 81 year old lady presented with abdominal discomfort, abnormal liver tests and biliary ductal dilation on imaging. Malignant biliary disease was suspected, given the age and EUS performed. There was a submucosal bulge involving the papilla raising concern for a choledochocele. On tracing the CBD, a stricture was noted leading into a dilated, thick walled chamber involving the papilla, seen as a bulge. Biopsy and FNA revealed no diagnosis. Choledocoscopy was performed and direct biopsy of the stricture obtained. This revealed benign tissue. On a separate occasion, complete endoscopic resection of the bulging tissue was performed, effectively accomplishing an extended ampullectomy. Brushings and biopsies from the distal ducts were also obtained. Final pathology showed adenomyomatous hyperplasia. Duodenal and ampullary mucosa with focally dilated cystic mucosal glands with a prominently thickened muscularis mucosa was seen. There was no dysplasia. Results: Patient symptoms and abnormalities of liver tests resolved completely. Follow up ERCP at 6 months showed wide open CBD/PD and normal ampullary tissue. Conclusion: Adnomyomatous hyperplasia can present as a benign stricture and mimic a neoplasm. Endoscopic resection is feasible and can be curative.Figure: Endoscopic View of the Ampulla.Figure: Cystic Dilation with Proximal Short Stricture.

Acoustic communication in Panthera tigris: A study of tiger vocalization and auditory receptivity revisited

Preliminary findings reported at the 145th meeting of the Society suggested that confrontational tiger roars contain energy in the infrasonic portion of the electromagnetic spectrum. This discovery generally supported the proposition that free ranging individuals may take advantage of this capability to communicate with widely dispersed conspecifics inhabiting large territories in the wild. Preliminary ABR findings indirectly supported this view suggesting that although tigers are most sensitive to acoustic events containing energy in the 0.3 to 0.5 kHz band, they are most likely able to detect acoustic events in the near-infrasonic and infrasonic range based on the assumption that felid audiograms exhibit uniform shapes. In this study, the spectral content of territorial and confrontational roars was analyzed and relevant features of ABR based threshold-frequency curves were considered in relation to the acoustical properties of both roar types. Unlike the confrontational roar, infrasonic energy was not detected in the territorial roar; however, like the confrontational roar, peak acoustic power was detected in a frequency band centered on ̃ 0.3 kHz. In addition, ABR recordings acquired in a double walled sound attenuating chamber recently installed at the Henry Doorly Zoo suggest that acoustic sensitivity is significantly underestimated under "field" conditions.

Experimental investigation of aerosol formation in laser fusion reactor chamber by discharge method

Liquid wall chambers are one of the most critical technologies in inertial fusion energy (IFE) plants. The critical problem for the liquid wall IFE chamber is the chamber clearance after laser shots. This paper presents preliminary results from an experimental simulation of ablation processes induced by alpha-particle heating.

Vacuum system design of the third generation synchrotron radiation source PETRA III

Within the next two years the 2.3 km long storage ring PETRA will be rebuild into one of the most brilliant x-ray sources worldwide (PETRA III). The large bending radius and the use of damping wigglers allow to achieve small beam emittances and extremely brilliant x-ray beams. In this paper we describe the design and the expected performance of the vacuum system for the storage ring. It consists of standard arc sections, an experimental octant which is equipped with undulators and several straight sections that include the damping wigglers. Because of the long length of the storage ring a cost effective solution had to be found. Besides the requirement to quickly provide acceptable residual gas pressures the technical challenges of the system include the provision of high thermal stability with respect to magnets and BPM's, and the design of thin walled insertion device chambers as well as high power synchrotron radiation absorbers.

Mass Production Methods for Fabrication of Inertial Fusion Targets

The High Average Power Laser (HAPL) Program is a national program to develop Inertial Fusion Energy with lasers (http://aries.ucsd.edu/HAPL/), direct drive targets and solid wall chambers. General Atomics is currently constructing and will operate a Mass Production Layering Experiment (MPLX) System. The MPLX System will demonstrate the filling and layering of approximately 700 plastic spherical targets (4 mm diameter plastic shells) simultaneously in a fluidized bed as a batch process in less than a day. In addition the system will be able to characterize a single deuterium filled and layered cryogenically-cooled target. This paper details hardware being developed and tested for the building of this system.

06/02238 Modeling convective drying of ventilated wall chambers in building enclosures: Davidovic, D. et al. International Journal of Thermal Sciences, 2006, 45, (2), 180–189.

06/02238 Modeling convective drying of ventilated wall chambers in building enclosures: Davidovic, D. et al. International Journal of Thermal Sciences, 2006, 45, (2), 180–189.

An Integrated Geophysical and Archaeological Investigation of the Emperor Qin Shi Huang Mausoleum

Integrated geophysical methods that included high-precision gravity, magnetic, electrical resistivity tomography, radioactive radon, and ground-penetrating radar surveys were used to investigate the underground palace of China’s first Emperor, Qin Shi Huang, his Mausoleum, and its appurtenant structures (i.e., pits and tombs). Successful identification of the underground palace’s distribution, as well as a thin-compacted wall and coffin chambers in the burial mound, as interpreted from analysis of the geophysical data, was corroborated by subsequent excavation. The effectiveness of the integrated procedures was also demonstrated on the known auxiliary pits and tombs adjacent to the main buried palace structure. These results are the most significant recent discoveries at the Emperor Qin Shi Huang Mausoleum, as well as the general mausoleum architecture in the Qin dynasty.

Method for detecting the disconnection of an extracorporeal device using a patient's endogenous electrical voltages

Tubing (especially venous) disconnections using pumped devices cause significant hemorrhage, and current monitoring techniques are imperfect because they rely on intraluminal pressure changes. We devised a passive detection method based on a patient's electrical voltages being transmitted via blood tubing to our alarm circuit. As the arterial and venous access sites are in close proximity, the signals are nearly identical during connection, and markedly different with disconnection. We built a prototype and tested it in vitro with saline and during hemodialysis treatments (n=7). The connection status is determined by examining the difference between endogenous voltages in the blood tubing from and to the patient, and when it exceeds a threshold an alarm condition is triggered. We tested for possible confounding by an electrical shunt through the dialyzer and determined that pathway had an impedance approximately three times (>350 kOmega) that of the tubing to the patient. As the roller blood-pump periodically occluded the tubing, the resultant intermittent very high impedance prevented that potential shunting problem and improved the sensitivity of our device. Disconnections were detectable at various bloodline sites (needles, sampling ports, drip chambers). Thus, the circuit's sensors can be placed remotely at the dialysis machine, with electrical continuity to blood made by inexpensive conductive elements at the tubing wall or drip chambers. Appropriate threshold and noise-eliminating circuitry, as well as alarm states that alert the staff and stop the blood pump, make our prototype a promising low-cost safety enhancement.

Conceptual design of laser fusion reactor KOYO-fast – Concepts of reactor system and laser driver

We have carried out the design studies of KOYO-Fast laser fusion power plant, using fast ignition cone targets, DPSSL lasers, and LiPb liquid wall chambers. Using fast ignition targets, we could design a middle sized 300 MWe reactor module, with 200 MJ fusion pulse energy and 4 Hz rep-rates, and 1200MWe modular power plants with 4 reactor modules and a 16 Hz laser driver. The liquid wall chambers with free surface cascade flows are proposed for cooling surface quickly enough to a 4 Hz pulse operation. We examined the potential ofYb-YAG ceramic lasers operated at 150 ∼ 225 K for both implosion and heating laser systems required for a 16-Hz repetition and 8 % total efficiency.

Threats, design limits and design windows for laser IFE dry wall chambers

The High Average Power Laser (HAPL) program is carrying out a coordinated effort to develop inertial fusion energy based on lasers, direct-drive targets and a dry wall chamber. The dry wall must accommodate the ion and photon threat spectra from the fusion micro-explosion over its required lifetime. This paper summarizes the current HAPL strategy on the armor/first wall configuration based on tungsten and ferritic steel as preferred armor and structural materials, respectively. The thermal performance of an example fully dense tungsten armor configuration on a ferritic steel first wall is described showing the basis for separating the high energy accommodation function of the armor from the structural function of the first wall. Example design operating windows for the armor, first wall and blanket are presented based on different requirements and constraints. The possibility of utilizing an engineered porous armor is discussed. Key chamber wall and armor issues are summarized.

Modeling convective drying of ventilated wall chambers in building enclosures

In North America, residential enclosure walls are often built with provision for natural convection and, therefore, provide potential for ventilation drying within the wall. At present, our knowledge of the drying process in the wall systems is limited. The drying process is driven by very low airflow rates with complex flow patterns through the narrow and irregular wall cavities, resulting mostly in unstable ventilation driven by natural convection. Different venting strategies coupled with the stochastic nature of driving forces for ventilation contribute to the complexity of the drying process. Both the physical and the mathematical modeling of wall cavity convective drying are challenging. However, it is difficult to accurately predict the convective drying rates in wall cavities at any time during the year. Nevertheless, the convective drying process is probably one of the key mechanisms for mold suppression in residential walls in the US, and therefore, needs to be fully understood and quantified. An equation is developed to estimate the convective moisture transport in screened and ventilated wall systems. The intent was to develop a simple equation for practical design applications. The equation represents a solution of the two-dimensional moisture transport equation, solved for steady state conditions assuming laminar flow with a uniform velocity field in the wall cavity. The results derived from the simple equation were compared to measured data obtained in the Building Enclosure Test Laboratory (BeTL) at the Pennsylvania State University (PSU). The comparison showed that the simple equation can accurately predict the convective drying rates. The results are highly sensitive to the environmental conditions in the immediate vicinity of the wet wall surfaces. This equation could be used in engineering practice to provide an estimate of convective drying rates in the ventilated chamber of rain-screened and ventilated wall systems. Future validation with on-site experiments is necessary.

Update on Progress and Current Research in the Development of Heavy Ion Fusion

Since the completion of the Robust Point Design (RPD) for a heavy ion fusion power plant, progress has been made in addressing key issues and some possible new directions have emerged. Work has continued on thick liquid wall chambers, which are particularly well suited to heavy ion fusion since they allow compact chambers minimizing the standoff for the final focus magnets and thus improving beam focusing on target. Work has continued on HIF indirect-drive targets in an attempt to allow larger spot sizes than the ~2 mm spots required by the baseline target in the RPD. A promising approach is the use of shine shields at both ends of the hohlraum, which allows beams to fill the entire 5-mm-radius target. This larger spot size target design opens the door to other driver and focusing schemes. Work has started exploring a modular driver approach in which many individual accelerators provide the total beam energy on target as opposed to the single accelerator with many (~100) individual beamlets threading common induction cores. Neutralized drift compression and plasma channel focusing are being studied as a way to deliver these high current beams to target. We have also started investigating new chamber designs that would be compatible with this focusing scheme, in particular designs using a vortex flow configuration to establish the thick liquid wall. This paper highlights progress since the last Technology of Fusion Energy (TOFE) Conference.

On the noise transmission and control for a cylindrical chamber core composite structure

The vibroacoustic properties, sound transmission behavior, and noise transmission control of a novel chamber core composite cylinder are studied. An approximate uniform shell model of the sandwich cylindrical chamber core structure is developed to aid in the calculation of the ring frequency and external critical frequency. Acoustic modal parameters are analytically and experimentally obtained. The structural modal parameters are identified from measured data. The coupling between structural and acoustic modes is investigated. The sound transmission into the cylindrical chamber core is experimentally characterized, where the stiffness-, cavity resonance-, mass-, and coincidence-controlled zones are identified. Finally, the addition of fills to the wall chambers of the chamber core is investigated as a part of passive control study, which also serves to corroborate the model development.

The design, construction and performance of a variable collimator for epithermal neutron capture therapy beams

A patient collimator for the fission converter based epithermal neutron beam (FCB) at the Massachusetts Institute of Technology Research Reactor (MITR-II) was built for clinical trials of boron neutron capture therapy (BNCT). A design was optimized by Monte Carlo simulations of the entire beam line and incorporates a modular construction for easy modifications in the future. The device was formed in-house by casting a mixture of lead spheres (7.6 mm diameter) in epoxy resin loaded with either 140 mg cm−3 of boron carbide or 210 mg cm−3 of lithium fluoride (95% enriched in 6Li). The cone shaped collimator allows easy field placement anywhere on the patient and is equipped with a laser indicator of central axis, beam's eye view optics and circular apertures of 80, 100, 120 and 160 mm diameter. Beam profiles and the collateral dose in a half-body phantom were measured for the 160 mm field using fission counters, activation foils as well as tissue equivalent (A-150) and graphite walled ionization chambers. Leakage radiation through the collimator contributes less than 10% to the total collateral dose up to 0.15 m beyond the edge of the aperture and becomes relatively more prominent with lateral displacement. The measured whole body dose equivalent of 24 ± 2 mSv per Gy of therapeutic dose is comparable to doses received during conventional therapy and is due principally (60–80%) to thermal neutron capture reactions with boron. These findings, together with the dose distributions for the primary beam, demonstrate the suitability of this patient collimator for BNCT.

Fusion energy with lasers, direct drive targets, and dry wall chambers

A coordinated, focused effort is underway to develop Laser Inertial Fusion Energy. The key components are developed in concert with one another and the science and engineering issues are addressed concurrently. Recent advances include: target designs have been evaluated that show it could be possible to achieve the high gains (>100) needed for a practical fusion system.These designs feature a low-density CH foam that is wicked with solid DT and over-coated with a thin high-Z layer. These results have been verified with three independent one-dimensional codes, and are now being evaluated with two- and three-dimensional codes. Two types of lasers are under development: Krypton Fluoride (KrF) gas lasers and Diode Pumped Solid State Lasers (DPSSL). Both have recently achieved repetitive ‘first light’, and both have made progress in meeting the fusion energy requirements for durability, efficiency, and cost. This paper also presents the advances in development of chamber operating windows (target survival plus no wall erosion), final optics (aluminium at grazing incidence has high reflectivity and exceeds the required laser damage threshold), target fabrication (demonstration of smooth DT ice layers grown over foams, batch production of foam shells, and appropriate high-Z overcoats), and target injection (new facility for target injection and tracking studies).