M. Narula

Overview of the ALPS Program

Abstract The US Advanced Limiter-divertor Plasma-facing Systems (ALPS) program is developing the science of liquid metal surface divertors for near and long term tokamaks. These systems may help solve the demanding heat removal, particle removal, and erosion issues of fusion plasma/surface interactions. ALPS combines tokamak experiments, lab experiments, and modeling. We are designing both static and flowing liquid lithium divertors for the National Spherical Torus Experiment (NSTX) at Princeton. We are also studying tin, gallium, and tin-lithium systems. Results to date are extensive and generally encouraging, e.g., showing: 1) good tokamak performance with a liquid Li limiter, 2) high D pumping in Li and non-zero He/Li pumping, 3) well-characterized temperature-dependent liquid metal surface composition and sputter yield data, 4) predicted stable low-recycle improved-plasma NSTX-Li performance, 5) high temperature capability Sn or Ga potential with reduced ELM & disruption response concerns. In the MHD area, analysis predicts good NSTX static Li performance, with dynamic systems being evaluated.

A Study of Liquid Metal Film Flow, Under Fusion Relevant Magnetic Fields

Abstract The use of flowing liquid metal streams or “liquid walls” as a plasma contact surface is a very attractive option and has received considerable attention over the past several years both in the plasma physics and fusion engineering programs. A key issue for the feasibility of flowing liquid metal plasma facing component (PFC) systems, lies in their magnetohydrodynamic (MHD) behavior. The spatially varying magnetic field environment, typical of a fusion device can lead to serious flow disrupting MHD forces that hinder the development of a smooth and controllable flow needed for PFC applications. The present study builds up on the ongoing research effort at UCLA, directed towards providing qualitative and quantitative data on liquid metal free surface flow behavior under fusion relevant magnetic fields, to aid in better understanding of flowing liquid metal PFC systems.

TOWARD AN INTEGRATED SIMULATION PREDICTIVE CAPABILITY FOR FUSION PLASMA CHAMBER SYSTEMS

Abstract The fusion environment is inherently complex, in which an adequate understanding of response from a plasma chamber system requires integrated (and in some areas coupled) analysis across multiple disciplines (neutronics, thermo-fluids, structural mechanics, electromagnetism etc). An integrated simulation predictive capability, which utilizes a computer based single CAD geometric model where a detailed simulation of the multi-physics phenomena occurring in a fusion plasma chamber system is performed, is under development and is described in this paper.

Development Status of the Helium-Cooled Porous Tungsten Heat Exchanger Concept

The development status of a helium cooled refractory metal heat exchanger (HX) concept using tungsten foam for enhanced heat transfer is presented. The HX design is based on azimuthal flow of helium through the foam sandwiched between two concentric tungsten tubes. This concept holds the promise for an efficient and low pressure-drop HX concept for plasma facing components, such as divertors. A prototypical flat-top HX-tube is being manufactured for testing at the high heat flux testing facility at SNL. Concept design optimization requires knowledge of the enhanced heat transfer coefficients due to the foam structure. Solid models of representative metal foams were developed for use in CFD analysis. Initial CFD results show improved heat transfer between the heated wall to the coolant. For a 1-mm thick foam with a specific density of 12% and a pore density of 65 PPI an average heat transfer coefficients of 40 000 W/m2-K was estimated, along with a pressure drop of ~60 kPa. For a 10 MW/m2 surface heat load and an inlet helium temperature of 600degC at a pressure of 4 MPa, maximum structural temperatures were estimated to be 1060degC. This preliminary design has a maximum combined primary plus secondary von Mises stress of less than 600 MPa.

Finite Element Stress Analysis OF ITER Module 13

Of the 18 module designs in ITER, the US is responsible for three. Each of these modules will be designed to meet requirements established by the ITER international organization (ITER IO). Finite element analysis (FEA) is being utilized to ensure that the module designs are in compliance with the strength requirements established by ITER IO. The strength requirements are defined in terms of maximum allowable stress and strain conditions under loading scenarios determined by ITER IO. These allowable conditions are based on material properties and the expected frequency of the specific loading condition being investigated. This paper presents the FEA approach applied to the design of Module 13. The thermally induced stress distributions caused by ITER operating conditions and internal pressure of cooling fluid were presented. Stresses caused by electromagnetic forces on the module were also presented if available. The stress levels under these conditions were compared to the allowable limits defined by the ITER IO.

ASSESSMENT OF THE QUALIFICATION TEST OF THE FIRST WALL QUALIFICATION MOCKUP

Understanding the manner in which the First Wall Qualification Mockup (FWQM) responds structurally to simulated ITER conditions is important to the establishment of a reliable first wall. This paper provides a thermal and structural response analysis for the first round of qualification tests performed at Sandia National Laboratories. The results display the stresses and strains created in the FWQM as a result of the thermal expansion that occurred when subjected to cyclic heat flux under simulated ITER normal and MARFE conditions. From this structural response, further insight may be gained into the likelihood of fatigue failure of the Beryllium//CuCrZr interface once the first wall is in operation in ITER. While fully determining the reliability of this joint is beyond the scope of this study, some suggestions are made as to how this topic might be addressed with further research. Also investigated are the thermal patterns seen during testing that indicated slight variation from the intended test parameters. It is shown that these disparities from the ideal test parameters do not significantly affect the qualification of the FWQM.

Thermo-fluid Exploratory Design Analysis for ITER FW/Shield Module 7

This paper describes the thermo-fluid analysis for the preliminary designs of the first wall (FW) panel and shield block (SB) for ITER shield module 7. This effort forms a part of the conceptual design activity for US ITER components. The key approach used here is design by analysis, whereby various exploratory designs undergo rigorous thermo-fluid analysis to ascertain that the design allows for an adequate coolant distribution under the existing surface and volumetric heating environment, so that the maximum temperatures are under the design limit. The principal code being used for the thermo-fluid analysis is CFdesign, which is a finite element code with a direct interface to the CAD program CATIA. Several enhancements to the code allow an export of temperatures, pressures and convective heat transfer coefficients to other finite element programs for stress analysis. The temperature and flow distribution as well as the pressure drop information of near exact CATIA fabrication models has been obtained from the various analyses. The effect of special design features like radial flow drivers in the shield block coolant tubes and tee vanes in the coolant headers, in enhancing the overall cooling of the shield block is emphasized.

Exploring liquid metal PFC concepts: Dynamics of fast flowing lithium films under fusion relevant magnetic fields

The use of fast flowing lithium streams for protection of the divertor surface in a magnetic fusion device is a very attractive option for effective particle pumping and surface heat removal. The divertor magnetic field environment tends to create strong flow disrupting magnetohydrodynamic (MHD) forces, which pose a major challenge in establishing a smooth and controllable flow. In this paper the 3D incompressible, multi-material MHD free surface code, HIMAG, developed by HyPerComp Inc. in collaboration with UCLA has been applied to model several problems of interest which are pivotal in understanding the basic MHD behavior of fast flowing lithium streams on rectangular electrically conducting substrates. The parameters used in the numerical studies conform to the outboard divertor region of the NSTX machine at Princeton