  Systematic variation of the pre-disruption core electron temperature (Te)
from 1 to 12 keV using an internal transport barrier scenario reveals a
dramatic increase in the production of seed runaway electrons (REs), ultimately
accessing near-complete conversion of the pre-disruption current into sub-MeV
RE current. Injected Ar pellets are observed to ablate more intensely and
promptly as Te rises. At high Te, the observed ablation exceeds predictions
from published thermal ablation models. Simultaneously, the thermal quench (TQ)
is observed to significantly shorten with increasing Te -- a surprising result.
While the reason for the shorter TQ is not yet understood, candidate mechanisms
include: insufficiently accurate thermal ablation models, enhanced ablation
driven by the seed RE population, or significant parallel heat transport along
stochastic fields. Kinetic modeling that self-consistently treats the plasma
cooling via radiation, the induced electric field, and the formation of the
seed RE is performed. Including the combined effect of the inherent dependence
of hot-tail RE seeding on Te together with the shortened TQ, modeling recovers
the progression towards near-complete conversion of the pre-disruption current
to RE current as Te rises. Measurement of the HXR spectrum during the early
current quench (CQ) reveals a trend of decreasing energy with pre-disruption
Te. At the very highest Te ($\approx$ 12 keV), $\approx$ 100% conversion of the
thermal current to runaway current is found. The energy of this peculiar RE
beam is inferred to be sub-MeV as it emits vanishingly few MeV hard X-rays
(HXRs). These measurements demonstrate novel TQ dynamics as Te is varied and
illustrate the limitations of treating the RE seed formation problem without
considering the inter-related dependencies of the pellet ablation, radiative
energy loss, and resultant variations of the TQ duration.
