Neutralized-Transport Experiment

The Neutralized-Transport Experiment, or NTX, will address many key scientific issues of final focus and neutralized transport in a fusion chamber.  Numerical simulations indicate that the focal spot of a beam on a fusion target is sensitive to aberrations in the final magnetic lenses, the velocity spread within a beam, charge-neutralization processes in the chamber, and in particular, the beam perveance, loosely defined as the ratio of the edge potential of a beam to its kinetic energy.  In NTX, a low-voltage and low-current beam with an adjustable perveance will be used to test final-focus optics and charge neutralization physics, providing the first experimental validation of the computer codes and significantly enhancing the science base for later final-focus designs.  The parameters of the experiment are chosen to ensure that physics observed on NTX will model a full-scale transport system as accurately as possible.

As currently conceived, the injector from the existing MBE-4 source will inject a 400 keV beam of singly charged potassium ions into a magnetic lattice and plasma-filled drift section.  The  source can produce a current up to 75 mA, so that the maximum perveance is 10-3, almost an order of magnitude larger than that expected for a fusion driver.  After careful source characterization,  we will study the effects of geometric aberrations in the final-focus magnets as a function of beam perveance and convergence angle, and we will test the feasibility of octupole corrections.  This part of the experimental program will also provide a test of nonintercepting beam diagnostics.  In the second phase of the experiment, we will assess beam neutralization by a plasma injected into the beam line and study beam stripping by low-pressure gases in the drift section.  A final set of experiments will test beam neutralization by a plasma injected near the end of the drift section, mocking up the photoionized plasma produced by X-rays emitted by a heated fusion target.

The design of NTX components was begun in FY01, and we expect that construction will be completed  in FY02.  The  pregram of investigating final-focus questions and neutralized transport will be carried out during the two following years.

For comments or questions contact or  Work described here was supported by the Office of Fusion Energy at the U.S. Department of Energy under contracts  DE-AC03-76SF00098 and W-7405-ENG-48.  This document was last revised June, 2002.