LENR reactors need magnetic confinement
In my opinion, the fundamental nature of the Rossi effect is based on magnetism. The catalytic particle that produces the reaction is magnetic in nature. This particle is produced by heat pumping and EMF stimulation. The nature of this Exotic Neutral Particle (ENP)is reflected by the behaviour of the E-Cat itself and reflect how the E-Cat operates.
The ENP can exist at low energy pumping where the energy coming into the particle is equal to the energy leaving the particle. This is similar to the way Rossi keeps his reactor under control. Too much external energy pumping will result in the E-Cat going critical.
The same process of over pumping happens with the ENP. Overpumping brings it to the stage where it becomes self-sufficient requiring no additional EMF input. The energized ENP can get EMF from the environment around it not requiring external heat or EMF simulation to be applied.
The same is true for the E-Cat. When the E-Cat is subcritical, it requires heat and EMF stimulation to be applied. But when it is "over stimulated" it begins to meltdown since it has become independent from externally applied stimulation.
The ENP can live as long as it can catalyze energy production from the material around it. The ENP can live for days on its own as it brings in energy from the environment to sustain its internal LENR reaction processes.
Magnetic confinement increases efficiency of the reaction. Such confinement saves the externally applied energy that produced the ENP from being wasted.
The ENP can leave the reactor if the material that makes up the reactor enclosure is transparent to the optical and magnetic nature of the ENP. This might be why electrolytic cells have difficulty in sustaining powerful LENR reactions. In this case, the ENPs escape the glass beaker reactor enclosure and all the input energy that was pumped into the ENP is wasted to the environment. outside the electrolytic cell.
If the cell is made of material that can contain the ENP both optically and magnetically, the reactor will be efficent. Alumina is antiferromagnetic and will confine magnetic particles that try to escape the reactor shell. Another method of ENP confinement that Rossi might use is a solenoidal confinement coil that keeps the ENPs away from the reactor walls and in the center axis of the reactor.