Authors: Adele Payman (Caltech), Paul Bellan (Caltech)

The Caltech jet experiment produces a 50 – 100 µs pulsed plasma that models an astrophysical jet. X-ray camera photographs show 6 keV X-rays associated with the appearance of kink and Rayleigh-Taylor instabilities that constrict and eventually break the jet. The X-rays are thought to originate from electrons that are accelerated to high energies by an inductive voltage spike when the jet breaks. To validate this inductive-acceleration theory, a probe has been developed to directly measure the flux of energetic electrons. The probe is placed outside the jet and consists of a metal plate that collects electrons from the plasma. The current through the probe is measured with a Rogowski coil and is typically 1.2 – 1.5 kA (about 1% of the total discharge current) when the plate is grounded to the vacuum chamber. In this grounded configuration the large collected current masks any transients associated with 6 keV electrons. In future experiments the low-energy electrons that constitute the bulk current will be screened out by negatively biasing the plate beyond the 2 eV average electron energy of the plasma. A circuit is currently being developed for this purpose. The current measurements will be correlated with visual observations of X-ray emissions and the jet’s evolving structure to yield insights into the mechanisms that produce energetic X-ray bursts in analogous astrophysical environments.