Roman Samulyak

Target studies with BNL E951 at the AGS

We report initial results of exposing low-Z solid and high-Z liquid targets to 150-ns, 4/spl times/10/sup 12/ proton pulses with spot sizes on the order of 1 to 2 mm. The energy deposition density approached 100 J/g. Diagnostics included fiberoptic strain sensors on the solid target and high-speed photography of the liquid targets. This work is part of the R&D program of the Neutrino Factory and Muon Collider Collaboration.

Trimming swept volumes

Abstract The trimming problem for swept volumes — concerning the excision of points ostensibly on the boundary that actually lie in the swept volume interior — is investigated in detail. Building upon several techniques that have appeared in the literature, efficient methods for both local and global trimming of swept volume are developed. These methods are shown to be computationally cost effective when combined with the sweep-envelope differential equation algorithm for the approximate calculation and graphical rendering of swept volumes for quite general objects and sweeps. Examples are presented to demonstrate the efficacy of the trimming strategies.

AN EMBEDDED BOUNDARY METHOD FOR ELLIPTIC AND PARABOLIC PROBLEMS WITH INTERFACES AND APPLICATION TO MULTI-MATERIAL SYSTEMS WITH PHASE TRANSITIONS

Abstract The embedded boundary method for solving elliptic and parabolic problems in geometrically complex domains using Cartesian meshes by Johansen and Colella (1998, J. Comput. Phys. 147, 60) has been extended for elliptic and parabolic problems with interior boundaries or interfaces of discontinuities of material properties or solutions. Second order accuracy is achieved in space and time for both stationary and moving interface problems. The method is conservative for elliptic and parabolic problems with fixed interfaces. Based on this method, a front tracking algorithm for the Stefan problem has been developed. The accuracy of the method is measured through comparison with exact solution to a two-dimensional Stefan problem. The algorithm has been used for the study of melting and solidification problems.

Spherically symmetric simulation of plasma liner driven magnetoinertial fusion

Spherically symmetric simulations of the implosion of plasma liners and compression of plasma targets in the concept of the plasma jet driven magnetoinertial fusion have been performed using the method of front tracking. The cases of single deuterium and xenon liners and double layer deuterium-xenon liners compressing various deuterium-tritium targets have been investigated, optimized for maximum fusion energy gains, and compared with theoretical predictions and scaling laws of [P. Parks, Phys. Plasmas 15, 062506 (2008)]. In agreement with the theory, the fusion gain was significantly below unity for deuterium-tritium targets compressed by Mach 60 deuterium liners. The most optimal setup for a given chamber size contained a target with the initial radius of 20 cm compressed by a 10 cm thick, Mach 60 xenon liner, achieving a fusion energy gain of 10 with 10 GJ fusion yield. Simulations also showed that composite deuterium-xenon liners reduce the energy gain due to lower target compression rates. The effect of heating of targets by alpha particles on the fusion energy gain has also been investigated.

A magnetohydrodynamic simulation of pellet ablation in the electrostatic approximation

A magnetohydrodynamic numerical model for hydrogenic pellet ablation in the electrostatic approximation has been developed based on the method of front tracking. The main features of the model are the explicit tracking of interfaces that separate the solid pellet from the ablated gas and the cold, dense and weakly ionized ablation cloud from the highly conducting fusion plasma, a surface ablation model, a kinetic model for the electron heat flux and an equation of state accounting for atomic processes in the ablation cloud. The interaction of the pellet ablation flow with the magnetic field including the J ×B Lorentz force is studied here systematically for the first time. The model has also been validated through the comparison with the semi-analytic Transonic Flow model and previous purely hydrodynamic simulations. Contrary to prevailing expectations, the ablation rate is reduced only slightly when the geometry is changed from spherically symmetric to axially symmetric, in the case of purely hydrodynamic models. However, in the magnetohydrodynamic simulations the J ×B force funnels the flow into an extended plasma shield, which intercepts the incident plasma heat flux and reduces the ablation rate, depending on the rise time of heat flux seen by the pellet. Shorter ‘warm-up’ times lead to narrower ablation channels, stronger shielding and reduced ablation rates. This new feature implies that pellets traversing strong plasma gradients, as in the edge pedestal region of the ITER plasma, could have significantly lower ablation rates if injected at higher velocity.

Direct Numerical Simulation of Bubbly Flows and Application to Cavitation Mitigation

The direct numerical simulation (DNS) method has been used to the study of the linear and shock wave propagation in bubbly fluids and the estimation of the efficiency of the cavitation mitigation in the container of the Spallation Neutron Source liquid mercury target. The DNS method for bubbly flows is based on the front tracking technique developed for free surface flows. Our front tracking hydrodynamic simulation code FronTier is capable of tracking and resolving topological changes of a large number of interfaces in two- and three-dimensional spaces. Both the bubbles and the fluid are compressible. In the application to the cavitation mitigation by bubble injection in the SNS, the collapse pressure of cavitation bubbles was calculated by solving the Keller equation with the liquid pressure obtained from the DNS of the bubbly flows. Simulations of the propagation of linear and shock waves in bubbly fluids have been performed, and a good agreement with theoretical predictions and experiments has been achieved. The validated DNS method for bubbly flows has been applied to the cavitation mitigation estimation in the SNS. The pressure wave propagation in the pure and the bubbly mercury has been simulated, and the collapse pressure of cavitation bubbles has been calculated. The efficiency of the cavitation mitigation by bubble injection has been estimated. The DNS method for bubbly flows has been validated through comparison of simulations with theory and experiments. The use of layers of nondissolvable gas bubbles as a pressure mitigation technique to reduce the cavitation erosion has been confirmed. DOI: 10.1115/1.2720477

Numerical Simulation of Hydro- and Magnetohydrodynamic Processes in the Muon Collider Target

We have developed numerical methods and performed numerical simulations of the proposed Muon Collider target. The target will be designed as a pulsed jet of mercury interacting with strong proton beams in a 20 Tesla magnetic field. A numerical approach based on the method of front tracking for numerical simulation of magnetohydrodynamic flows in discontinuous media was implemented in FronTier, a hydrodynamics code with free interface support. The FronTier-MHD code was used to study the evolution of the mercury jet in the target magnet system. To model accurately the interaction of the mercury target with proton pulses, a realistic equation of state for mercury was created in a wide temperature - pressure domain. The mercury target - proton pulse interaction was simulated during 120 microseconds. Simulations predict that the mercury target will be broken into a set of droplets with velocities in the range 20-60 m/sec.

A numerical algorithm for MHD of free surface flows at low magnetic Reynolds numbers

We have developed a numerical algorithm and computational software for the study of magnetohydrodynamics (MHD) of free surface flows at low magnetic Reynolds numbers. The governing system of equations is a coupled hyperbolic-elliptic system in moving and geometrically complex domains. The numerical algorithm employs the method of front tracking and the Riemann problem for material interfaces, second order Godunov-type hyperbolic solvers, and the embedded boundary method for the elliptic problem in complex domains. The numerical algorithm has been implemented as an MHD extension of FronTier, a hydrodynamic code with free interface support. The code is applicable for numerical simulations of free surface flows of conductive liquids or weakly ionized plasmas. The code has been validated through the comparison of numerical simulations of a liquid metal jet in a non-uniform magnetic field with experiments and theory. Simulations of the Muon Collider/Neutrino Factory target have also been discussed.

A High-Power Target Experiment

We describe an experiment designed as a proof-of-principle test for a target system capable of converting a 4-MW proton beam into a high-intensity muon beam suitable for incorporation into either a neutrino factory complex or a muon collider. The target system is based on exposing a free mercury jet to an intense proton beam in the presence of a high-strength solenoidal magnetic field.

An R&D program for targetry and capture at a neutrino factory and muon collider source

The need for intense muon beams for muon colliders and for neutrino factories based on muon storage rings leads to a concept of 1-4 MW proton beams incident on a moving target that is inside a 20-T solenoid magnet, with a mercury jet as a preferred example. Novel technical issues for such a system include disruption of the mercury jet by the proton beam and distortion of the jet on entering the solenoid, as well as more conventional issues of materials lifetime and handling of activated materials in an intense radiation environment. As part of the R&D program of the Neutrino Factory and Muon Collider Collaboration, an R&D eort related to