APEX (Advanced Power EXtraction) is a study to identify and explore novel, possibly revolutionary, concepts for fusion chamber technology that may substantially improve the attractiveness of fusion energy systems. The study is being carried out by a multi-institutional team led by Mohamed Abdou of UCLA. An Interim Report has recently been issued, "On the Exploration of Innovative Concepts for Fusion Chamber Technology" (UCLA-ENG-99-206, November 1999).

In the first phase of the study, a set of goals for chamber technology were adopted to calibrate new ideas and to measure progress. These goals include: (1) high power density capability with neutron wall loads greater than 10 Megawatts per square meter and surface heat flux greater than 2 Megawatts per square meter, (2) high power conversion efficiency (greater than 40%), (3) high availability (i.e., low failure rate and fast maintenance), and (4) simple technological and material constraints.

A number of promising ideas have emerged from the study, which will need extensive further research and development. They fall into two categories. The first category seeks to totally eliminate the solid "bare" first wall of the fusion chamber. The most promising ideas in this category are flowing liquid first wall variations. The liquid wall idea evolved during the APEX study into a number of concepts that have some common features but also have widely different issues and merits. These concepts differ according to (1) the type of working fluid, (2) the thickness of the liquid flow, and (3) the type of restraining force used to control the liquid flow. The second category of ideas focuses on extending the capabilities, particularly the power density and temperature limits, of solid first walls. A promising example is the use of high temperature refractory alloys (e.g., tungsten) in the first wall, together with an innovative heat transfer and heat transport scheme based on the vaporization of lithium.

The APEX team has already initiated Phase 2 of the study, which will focus on more detailed exploration of liquid walls and cooling of solid walls by lithium vaporization. For further information, contact Mohamed Abdou (abdou@fusion.ucla.edu).