Ablation Drag Research Articles

Abstract 13948: High Intraprocedural Atrial Fibrillation Termination Rate by Large Area Rotor Ablation Combined With Pulmonary Vein Isolation

Introduction: There remains contradictory data about the optimal ablation technique and the type of termination of atrial fibrillation (AF) ablation particularly in patient (pt) with persistent AF. The aim of this study was to determine the type of the termination of persistent AF during combined conventional and rotor ablation. Method: This is a single-center, prospective, observational study enrolled thirty-eight pts (24/63% male, mean age 63 years) with AF (mean left atrial size: 46,2 ± 7 mm), who underwent focal impulse and rotor modulation (FIRM) mapping and large area ablation around the core of the identified rotor(s), followed by conventional pulmonary vein isolation(PVI) using contact force catheter aiming 10-20 gr depending on the location. Two distinctive types of the AF termination were defined: sub-acute termination related to rotor elimination, furthermore acute termination due to PVI. Electric cardioversion (ECV) was executed only in the absence of spontaneous conversion to sinus rhythm (SR). Result: In 10(26%) pts acute AF termination after PVI was observed. In further 12 (31%) pts sub-acute termination of the AF could be observed after the identified rotor ablation. The combined technique of conventional and rotor ablation of pts with persistent AF resulted in 57,8% of termination rate. Spontaneous cardioversion could not be reached in 16 (42%) pts however 15 out of them were converted to SR by ECV. Procedural complication occurred in 3 pts presenting with groin hematoma, in one patient left atrial appendage (LAA) thrombus was revealed by transoesophageal echocardiography performed right after the ablation for guiding the planned LAA closure. Conclusion: Large area rotor ablation drag technique combined with contact force sensing technique results in a high termination rate of persistent AF. More studies are warranted to define the clinical significance and long term success rate of rotor ablation in pts with persistent atrial fibrillation.

Experimental investigation of a small bore plasma armature rail launcher at high current densities

This paper presents experimental results obtained with a small bore (/spl phi/6 mm) plasma armature rail launcher with electrothermal preacceleration. Special attention is focused on rail and insulator ablation for high rail line current densities (up to 100 kA/mm). The measurements indicate that most of the ablated rail material enters the plasma armature in liquid state. Secondary arcing occurred during all experiments and was identified to be the most substantial loss mechanism. Typically the momentum efficiency of the propulsive arcs was in the range of 80%, showing that viscous and ablation drag, which are often stated to be severe velocity limiting effects, may be neglected in the velocity range up to 5 km/s. >

Electromagnetic gun circuit analysis code (EGCAC)

A system engineering code that simulates the performance of a railgun/power supply system is described. The code, named EGCAC (electromagnetic gun circuit analysis code), accounts for many performance degrading effects, including viscous drag on the armature, viscous drag on the gas being pushed in front of the projectile, entrained gas that must be accelerated in front of the projectile, time-dependent rail resistance, armature resistance, system resistance, and ablation drag. EGCAC has been utilized to predict railgun performance up to a velocity of approximately 4 km/s for experiments at several laboratories. The theory of EGCAC is described, and sample calculations are presented. >

Velocity limiting magnetohydrodynamic effects in railgun plasma armatures

The results of a four-year theoretical and experimental research program in railgun armature physics at the University of Tennessee Space Institute are reviewed with an emphasis on understanding how the magnetohydrodynamic (MHD) flowfield and electromagnetic interactions limit the velocity in plasma and hybrid armature railguns. The understanding of the 3D plasma armature flowfield has been developed through a combination of highly instrumented railgun experiments, secondary arc performance models, and 2D MHD calculations. These 2D calculations are only qualitative in nature, but they provide insight into the complex armature flow and indicate that the formation of secondary armatures, ablation drag, and primary armature preparation are interrelated. Experimental evidence suggests that 3D MHD flow effects are very important in controlling these phenomena. >

Experimental comparison of conventional and trans-augmented railguns

A 2.4-m-long, 1-cm-diameter round bore railgun was constructed to perform careful experiments which compared the performance of conventional and transaugmented plasma armature railguns. Conventional railgun experiments were performed over a range of currents to characterize the base performance of the railgun and to provide data for the development of ablation drag and thermal propulsive models. Experiments were then performed for a range of (separately powered) augmentation currents but with railgun currents equal to those used in the conventional experiments. The enhanced performance provided by augmentation was found to be significantly less than predicted by theory, even though the railgun operated without the formation of secondary armatures or restrikes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scaling study for the performance of railgun armatures

A model is developed for investigating the performance of solid, plasma, hybrid, and transitioning armatures as a function of railgun geometry and gun operating conditions. The two figures of merit used in the calculation are the armature efficiency and the maximum velocity. Effects investigated include armature parasitic mass, armature resistance, friction, ablation drag, and, for the hybrid armature, gap growth. The model is applied to study how armature performance scales with projectile mass, or correspondingly bore dimension, and with gun current per unit rail height in the hypervelocity regime from 7 to 15 km/s. The model indicates that armature efficiency generally increases with projectile mass, whereas the maximum velocity for plasma and transitioning armatures is relatively insensitive to projectile mass. Calculations are also performed to determine the sensitivity of the model's predictions to uncertainty in key parameters, such as the ablation entrainment fraction, the skin friction coefficient, and the contact potential.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Armature options for hypervelocity railguns

Models have been developed to study the effects of various performance-degrading mechanisms on the efficiency of railgun armatures. The models have been used to compare three armature options-plasma, hybrid, and transitioning-for the case of a 2.5-gm projectile accelerated to velocities of up to 15 km/s. Effects considered include armature parasitic mass, electrical resistance, viscous drag between the armature and bore, ablation drag due to ohmic and viscous dissipation, and for the hybrid armature, gap growth due to ablation of the solid conductor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the drag effect of a refueling pellet

A refueling pellet is subjected mainly to two kinds of drags: (1) inertial drag caused by the motion of the pellet relative to the surrounding plasma, and (2) ablation drag caused by an uneven ablation rate of the front and the rear surface of the pellet in an inhomogeneous plasma. Computational results showed that for reasonable combinations of pellet size and injection speed, the drag effect is hardly detectable for plasma conditions prevailing in current large tokamaks.