Hello Julian,
I'll do my very best to provide you with a satisfactory answer. If you would like for me to go into more detail on any specific point or if I need to explain something more coherently, please let me know.
To start off, I think I need to provide a little background information. An EVO is a toroidal cluster of electrons and much heavier positive ions (anything from hydrogen to xenon) swirling in opposite directions that has achieved a variable level of geometric and energetic stability. The electrons typically move along the outer surface of the torus and the positive ions are located in the interior. The type of EVOs Kenneth Shoulders created form whenever an adequate quantity of electrons are bunched together, and, usually in motion. The motion of the electrons (along with whatever positive ions are present) create a magnetic field that starts to induce these particles into forming loops. These are Bostick's vortex filaments - coils of electrons and positive ions. In Kenneth Shoulders typical systems, the fast high voltage pulse applied to a sharp tip of wire is sufficient to produce an "ecton" explosion at the narrow end. The charged electrons, protons, and other ions obtain enough kinetic motion, which translates into magnetic field intensity, to not only form filaments but to reconnect at their ends forming toroids. In a typical "hot fusion" big science spheromak generator, external magnetic fields are used (for example permanent magnets or solenoids) to assist in the reconnection. One point worth noting here is that these larger spheromak shaped toroids are generally far less energy dense than the small high density charge clusters of Kenneth Shoulders. As a rule, smaller plasmoids are more energy AND mass dense per unit volume.
Now, the next bit of background information I need to provide is the phenomenon of Surface Plasmon Polaritons. I found them very mysterious until a couple of months ago I spent some time getting to the bottom of what they really were. Basically, the first word, surface, means they are centered at the interface of a conductive metal and a dielectric (water, air, vacuum). The second word, plasmon, describes collective undulations of electrons that can bob up and down like waves at such a dielectric interface - sort of like ripples of water on the surface of a pond. Now, the third word is critical: polaritons. This world represents the combination of a plasmon (ripple of electrons on a surface with associated magnetic and electric fields) with a trigger of some kind that excites them: like a rock thrown on the surface of the pond. However, with SPPs, the triggers are not rocks but namely charged particle impacts (electrons, protons, and ions) and photons. If any of these impact the metal-dielectric interface, ripples of electrics will roll across the surface. The reason for charged particles to cause this is obvious: their charge will manipulate the plasmons (undulations of electrons). However, it's the magnetic and electric fields of the photon that produce undulations as well. I'll go into this further in a minute, but I should say here that EVOs are probably the equivalent of shooting a .45 caliber bullet into the pond: they contain charged particles that spray out in all directions upon destruction and produce a wide variety of photons: radio frequency, x-rays, etc.
Normally, these undulations are fairly weak and dampen quickly as they spread out in a 360 degree pattern from the point of a charged particle or photon impact. But here is where things get fascinating: surface structures and features can immensely magnify the gentle ripples into powerful spikes. And this is highly engineerable: mainstream labs are coming up with all sorts of nano-structures that produce specific, often resonant, effects. A surface protrusion (imagine a little bump sticking up) will create a powerful upwards oscillation of the electrons composing the plasmon undulation. Imagine an ice pick of electrons projecting upwards. The opposite structure, a pit, can create a different formation. Additionally, a powerful surface plasmon polariton can form between different sized nano-particles, for example, a large spherical particle and one of much smaller diameter. Finally, I've read the most powerful amplification comes from intersecting cracks on a surface, at the center of a Y or X shaped crack.
(Side note: the electric field amplification effect on a sharp tipped cathode is due to a surface plasmon polariton process creating the conditions for a powerful outburst that forms the EVO.)
Now, before we move to how these form in LENR systems, we need to talk about why we even want them: how they induce nuclear reactions. They can do so via multiple routes. For one, for a small input EVOs, including the heavy ions they contain, can be accelerated to high speeds; the protons they contain can hit targets with MeV of energy. This could produce traditional thermonuclear fusion upon impact. Additionally, there are multiple conditions in which nuclear reactions can happen inside of EVOs/Spheromaks before impact on a target, often when the EVO is being compressed. The high velocity flows in their structure can be disrupted and high speed ions can collide. This can produce particle emissions that spray out (electrons always seem to be shooting out of EVOs which was proven with Shoulders Electron Pin Hole Camera) including copious x-rays. Upon hitting a target, when an EVO destroys itself, even more powerful particles and x-rays are emitted. These can induce Surface Plasmon Polaritons. Now, what's interesting, is that there are researchers who claim that the production of SPPs on a hydrogenated material can induce nuclear reactions both by production of "heavy electrons" that can borrow through the electron shells of atoms and induce nuclear reactions (sort of like muon induced fusion) and the release of "slow neutrons" with a wide "cross section" that allows them to perhaps induce isotopic shifting. Basically, there are a lot of ways both EVOs and SPPs (which I consider to be quasi-EVOs or quasi spheromaks) can induce nuclear effects.
In an electrolytic system, the most likely method by which EVOs would be produced is by fracto-emission. As the Pd becomes highly loaded, very brittle hydride layers can form. If temperature, pressure, or perhaps even cell voltage is changed, I expect that cracks can form when mechanical stress causes fractures in the lattice. When such a fracture happens, electrons can be emitted. Fracto-emission is a common process: if you crack open a rock with a sledge hammer you can sometimes see sparks popping out. Also, during and after earthquakes, ball lightning and strange lights are often seen. Kenneth Shoulders thought that the electrons emitted from hydride layers can form EVOs. Basically, this is likely a form of charge separation, similar to how you can generate x-rays from pulling on a reel of packaging tape. There's a potential difference that develops that can lead to a discharge.
Once an EVO is discharged from one wall of the fracture, it could slam into the other side, and induce nuclear reactions via any of the methods mentioned above. If the reaction is powerful enough, additional damage could be inflicted on the lattice which would result in more fracto-emission. You could end up with cycles of SPPs traveling along amplifying surface features and EVOs jumping from wall to wall creating a self-sustained reaction.
There's a really good article I read a few years ago about a team that cryogenically froze metal hydrides (titanium hydride if I remember correctly) and then quickly brought it back up to room temperature. They recorded neutrons and other emissions that were likely due to thermal stresses resulting in fractures. I don't think they used the term EVO, but I think they may have mentioned fracto-emission.
Edward Storms has actually posted a theory about how cracks might be the NAE of LENR systems. Shoulders actually claimed that he was probably on the top of the list of all the LENR researchers he knew (he mentions this in the interview with John Hutchison). I'm very confident that fracto-emission and SPP effects (amplifying electric fields to create regions of high charge density) are the reason that cracks are a likely NAE. In fact, there are characteristic EVO "boreholes" in SEM photographs of electrode samples from electrolytic systems. There are such photographs in Shoulders papers that are published online.
When it comes to gas phase system, like Rossi's systems, I'm convinced the production and utilization of EVOs is his true catalyst. Every step of the way, he has incorporated features into his systems that would produce the conditions for EVO production. I could go on and on about this, but I've covered most of it in my earlier posts. But just a few of several EVO generation methods are his direct electrical discharges through his carbonyl (spikey) fuel, radio frequency generators, three phase rotating magnetic fields, etc. These EVOs may induce LENR before they even strike due to the electrons they spray out and x-rays that are generated. Upon impact, they can induce nuclear reactions directly via a number of different routes OR simply produce SPPs that may induce nuclear reactions.
I consider ASTOUNDED states (Atypical Spheromak Triggering Of Unambiguous Nuclear Derived Energy Discharges) to be the equivalent of a twelve gauge shotgun in home defense. Such a weapon is probably overkill (a puny little .22 revolver can kill someone with a well placed shot), but you are virtually guaranteed a one shot kill. It may not be as elegant as using a precisely tuned laser to generate SPPs for LENR, but the results are powerful and the excess heat will be plain as day.
I hope this helps. I've been spending countless hours every day reading papers for the past few months ever since I started to connect the dots between EVOs, LENR, various free energy devices, and other exotic technologies. Right now, I've been up for a very long time so I'm a little groggy. If there are any points you want to discuss please let me know. I'm happy to communicate with anyone who wants to talk about these issues.