I have run a number of simulations on my ECAT model and have found a simple rule of thumb that Rossi or others wanting to replicate his design can use to ensure stable operation. It is possible to violate the rule during a fractional time period when a carefully designed PWM drive is utilized, but the latest test showed that steady drive can be used effectively and that seems to be preferable. It is certainly far simpler to measure a steady state power input system, a point made by the testers.
The core section generates thermal power that is a function of the temperature at which it operates. The actual polynomial series that the ECAT follows for core power production versus temperature is not known to me since that information is an important trade secret. I have asked for that information but the request is not fulfilled. Therefore, my model is currently using a simple second order function that reveals general system behavior. When the true series is discovered I can modify the model quickly to take it into account. Heat is extracted from the core by means of a linear term that represents the convection and conduction pathways. Another term corresponding to radiation is modeled by a forth order dependency. These functions can be modified rapidly as well as additional data becomes available. The relatively high order pathway (4th order) is a major key to stability since it can be adjusted to dominate over lower order core power production terms. The rule of thumb for stable operation is that for all temperatures to which the core is exposed the thermal power leaving the core by the radiation, convection, and conduction paths must always exceed the power generated within the core. This makes sense and seems obvious once you realize that any excess core thermal generation above the amount extracted will cause the internal temperature to rise as the thermal capacity is charged. Positive feedback of this nature then compounds upon itself until some limitation is reached. I expect the limit to be established by destruction of the device, a quasi stable operating point where the radiation finally dominates, or some type of unknown behavior. If destruction does not occur it is likely that the device will becomes latched at some intermediate power output level that is out of control. Radiation is very important for the control since it varies as the forth order of temperature and can allow the thermal exit paths to dominate without much of a battle. This is an excellent reason to design the ECAT type devices so that they radiate a significant portion of their energy from the core at the nominal output power level. The lower order pathways are also important and must be adjusted appropriately to ensure that heat can be extracted rapidly enough during operation within the lower power region to prevent latching. The thermal pathways are most readily adjusted by modifying the geometry of the device and that is likely the reason for the latest long, narrow design. In that case the surface area with its surface treatment will be able to remove enough thermal energy quickly enough to satisfy the stability criteria. The proper balance between radiation and the other two processes needs to be achieved for optimum control and COP. All indications are that a complete system must be engineered by taking into consideration the power functional characteristics of the fuel. The geometry of the device should then be constructed to achieve the power balance discussed above. If either the fuel or the geometry are not correct then stable high COP operation can not be expected. Dave
