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 WMSharp@lbl.gov or DPGrote@lbl.gov. 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.