Probing Runaway Electrons with Nanoparticle Plasma Jet

The injection of C$_{60}$/C nanoparticle plasma jet (NPPJ) into tokamak plasma during a major disruption has the potential to probe the runaway electrons (REs) during different phases of their dynamics and diagnose them through spectroscopy of C ions visible/UV lines. A C$_{60}$/C NPPJ of $\sim75$ mg, high-density ($>$10$^{23}$ m$^{-3}$), hyper-velocity ($>$4 km/s), and uniquely fast response-to-delivery time ($\sim1$ ms) has been demonstrated on a test bed. It can rapidly and deeply deliver enough mass to increase electron density to $\sim2.4\times10^{21}$ m$^{-3}$, $\sim60$ times larger than typical DIII-D pre-disruption value. We will present the results of our investigations on: 1) C$_{60}$ fragmentation and gradual release of C atoms along C$_{60}$ NPPJ penetration path through the RE carrying residual cold plasma, 2) estimation of photon emissivity coefficient for the lines of the C ions, and 3) simulation of C$_{60}$/C PJ penetration to the RE beam location in equivalent conditions to the characteristic $\sim1$ T B-field of DIII-D. The capabilities of this injection technique provide a unique possibility in understanding and controlling the RE beam, which is a critical problem for ITER.