7 research outputs found
Comments on "Volume ignition of mixed fuel" by H. Ruhl and G. Korn (Marvel Fusion, Munich)
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 . 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.Comment: 6 pages, 1 figur
Comments to Marvel Fusions Mixed Fuels Reactor Concept
Nanostructured solid boron-hydrogen compounds have been suggested as target
and fuel for laser fusion, offering improved laser-plasma coupling, avoiding
cryogenic fuel handling and fuel pre-compression and ultimately allowing a
transit from DT- to aneutronic pB- fusion power production. We describe the
scaling of the different energy loss channels ({\alpha}-particle escape,
bremsstrahlung, hydrodynamic expansion work, electron heat conduction) with
mixed fuel composition using partial inverse gains (Q's) which allow a simple
superposition of losses. This highlights in particular the negative synergy
between these loss-channels for such mixed fuels: the dominance of
bremsstrahlung over fusion power at low temperatures forces a shift of
operation to higher ones, where the plasma gets more transparent to
{\alpha}-particles, and hydrodynamic and heat conduction losses increase
strongly. The use of mixed fuels therefore does not eliminate the need for
strong precompression of the fuel: in fact, it renders achieving burning plasma
conditions much more difficult, if not impossible. A recent suggestion to use
tamping of the fuel by cladding with a heavy metal would only reduce
hydrodynamic expansion losses significantly if the cladding could cover most of
the fuel surface, in competition with access to laser radiation. But even if
tamping were perfect, this would not reduce the remaining three loss channels -
in fact it would have a negative effect on burn propagation, as the escaping
energy would not heat surrounding fuel, but only the cladding material.Comment: 19 pages, 9 figures; affiliation of authors added in revised versio
Numerical study of tearing mode seeding in tokamak X-point plasma
A detailed understanding of island seeding is crucial to avoid (N)TMs and
their negative consequences like confinement degradation and disruptions. In
the present work, we investigate the growth of 2/1 islands in response to
magnetic perturbations. Although we use externally applied perturbations
produced by resonant magnetic perturbation (RMP) coils for this study, results
are directly transferable to island seeding by other MHD instabilities creating
a resonant magnetic field component at the rational surface. Experimental
results for 2/1 island penetration from ASDEX Upgrade are presented extending
previous studies. Simulations are based on an ASDEX Upgrade L-mode discharge
with low collisionality and active RMP coils. Our numerical studies are
performed with the 3D, two fluid, non-linear MHD code JOREK. All three phases
of mode seeding observed in the experiment are also seen in the simulations:
first a weak response phase characterized by large perpendicular electron flow
velocities followed by a fast growth of the magnetic island size accompanied by
a reduction of the perpendicular electron velocity, and finally the saturation
to a fully formed island state with perpendicular electron velocity close to
zero. Thresholds for mode penetration are observed in the plasma rotation as
well as in the RMP coil current. A hysteresis of the island size and electron
perpendicular velocity is observed between the ramping up and down of the RMP
amplitude consistent with an analytically predicted bifurcation. The transition
from dominant kink/bending to tearing parity during the penetration is
investigated