This 2005 presentation on using nuclear fusion for propulsion in space within 20 years of the start of a development program mentions John Slough’s work and the graphics match what is being used by Helion Energy.
Star Thrust experiment page (1000 to 1 million ISP) This work was in the 1990s. Helion Energy development of a Field Reversed Configuration would also enable Star Thrust propulsion development.
Most fusion confinement concepts are unsuited for space power production due to their large size and complexity, and are non-ideal for propulsion due to the use of D-T fuel which releases most of its energy in the form of high energy neutrons. A notable exception to these restraints is provided by the Field Reversed Configuration (FRC) which is a simple elongated current ring confined in a modest field solenoidal magnet, as sketched above. FRCs lack any significant toroidal field, which results in a compact high b plasma that is suitable for burning advanced aneutronic fuels. (Synchrotron radiation would limit ignition of high temperature aneutronic fuels in the low b environment of most confinement geometries.) The linear geometry and magnetic separatrix are a natural attribute for propulsive applications.
FRTP startup technology is well developed, but is too bulky and heavy for space applications. In recognition of this, NASA is supporting a very high power, but short duration, RMF startup experiment called STX (Star Thrust Experiment). STX will study the RMF formation and sustainment of hot (100s eV) mid-sized FRCs, where the classical skin depth of the RMF is much less then the radius of the FRC. Penetration of the RMF has been demonstrated under such circumstances due to the collisionless Hall effect. In the laboratory frame of reference, the RMF works by pulling the electrons around azimuthally while leaving the ions behind, whereas in the electron frame, the RMF appears at rest due to synchronous rotation. This is accomplished by selecting the RMF frequency and amplitude such that the electrons are magnetized with respect to the rotating field and the ions are not). It is also necessary that the electrons be highly collisionless in order to experience synchronous rotation, and thus allow RMF penetration.
The STX vacuum chamber consists of a 40 cm diameter by 3 m long quartz tube. Two high Q (400) tank circuits will produce the required .01T .5MHz RMF at the tens of megawatts level for .2 msec. In addition to an ion Alfven heater and axial discharge, these high power tank circuits will be responsible for ionizing and heating the plasma past the radiation barrier, and thus will have the capability of briefly attaining power outputs in the hundreds of megawatts, levels common to FRTPs. Additional IGBT circuits (solid state) will sustain the RMF for a longer duration at lower power levels. STX is presently under construction. The experimental design, power supply performance and preliminary ionization and heating data, along with FRC RMF theory, will be presented.