Current results from the Los Alamos CTX spheromak

Continued discharge cleaning, improved vacuum practices, and optimized plasma formation operation have resulted in the CTX experiment achieving 1-ms plasma lifetimes with average temperatures of 20 to 40 eV. The major advance in operation has been the use of 5 to 20 mTorr H2 gas fill. A multipoint Thomson scattering diagnostic with 12 radial positions yields radial profiles of temperature and densities, an example of which is shown. Local ν's can be determined from the measured pressure profile, and average values are typically 15 to 20%. In clean, long-lived discharges the density decreases at a more rapid rate than the magnetic field, until it reaches a value around 2 to 4 x 1013 cm-3 where it remains constant. This is in contrast to the colder, radiation-dominated behavior, and is taken as evidence that the plasma ν is a limit to current operation in CTX