  In the most recent note on Marvel Fusion's concept for a laser driven pB
reactor without compression, Ruhl and Korn consider the volumetric energy
balance of fusion reactions vs. bremsstrahlung losses in a mixed fuel (DT and
pB) environment and claim the satisfaction of this necessary "ideal ignition"
condition. Their results are based, however, on improper assumptions about the
deposition of fusion energy in the plasma. Correcting for them, we show that
the quoted composition of their fuel (a solid boron composite, binding high
concentrations of D, T and p) would actually preclude ignition due to the high
bremsstrahlung losses associated with the presence of boron. To facilitate
ignition, Ruhl and Korn also consider the reduction of the bremsstrahlung
losses by confining the radiation in the optically thin fuel region by high Z
walls. They suggest to preload this region with radiation so that the radiation
temperature equals approximately that of the plasma constituents $T_{r} \approx
T_{e} \approx T_{i}$. We show that in this set-up the radiation energy -
neglected in these considerations - would, however, vastly exceed the thermal
energy of the plasma and actually dominate the ignition energy requirements.
