Interesting and well presented video, but....
Mentioning vacuum tubes is appropriate as they are all about manipulating plasmas.
The grid transparency issue is a major issue in fusors, but it is not the only issue. A typical glow discharge fusor might top out with a grid transparency of ~ 95%. This means an ion could travel back and forth through the grid about 20 times. Depending on the size of the machine it may need a grid transparency of at least 99.99%, or allow for ~ 10,000 passe sof the typical ion. If the machine is very big, perhaps a kilometer in diameter, the number of passes required is decreased proportionately. So, at least theoretically a typical gridded fusor could reach break even. But only if this grid transparency to ions is the only consideration. You also, have to account for what is happening to the electrons. Also, the effects of non fusing collisions-Coulomb collisions that scatter the charged particles and drive them to Maxwellian energy distributions. The average ion energy/ temperature may be trapped in the grid induced potential well, but up scattered ions will escape,.. And of course the electrons are essentially one pass participants. The Elmore Tuck and Watson version of the fusor reversed things. Electrons are trapped in a potential well from a grid (anode) placed near the edge of the machine. Wishfully, the electrons are electrostatically (potential well ) trapped, and as they converge towards the center they would form a virtual central cathode to then trap ions. The problem again was the grid transparency (to electrons this time. Also, any ions that reached the radius of the anode would then be accelerated (repelled) to the wall. This could not be avoided as the ions thermalized- a certain percentage would always be energetic enough to escape in this manner, as would some of the electrons.
This is starting to move in the direction of the Polywell concept.
The first consideration is to use excess electrons. This produces a deeper potential well, perhaps approaching the strength of the electron injection energy. The electron injection energy can come from two sources. A peripheral anode grid -like in ETW or WB6, or from high energy electron guns outside the grid (in this case the grid (magnet cans) is at ground.
The grid transparency is addressed by not having the electrons pass the grid once trapped, at least that was the plan. This is done by having magnetic shielding. Magnetic shielding is not perfect though. Charged particles penitrate through magnetic fields much like gas diffuses across a room. Except it is done in discreet steps dependent on the particle energy, momentum, magnetic field strength and density driven scattering collisions. Through a random walk process the charged particle moves through the B field one gyroradius distance at a time either deeper or shallower with each collision. As a result the charged particles migrate from greater to lower densities till the magnet surface is hit and the KE of the particle is lost - generally as heat. Ions with their greater weight and thus momentum have gyro radii >60 times greater than electrons, so at the same B field strength, and particle energy the ions diffuse through the B field ~ 60 times faster than electrons. This is one reason why tokamaks have to be so large, so that the reaction volume can be maintained long enough against this loss mechanism. A much smaller machine is possible if only the electrons are contained in this manner (magnetically contained). At least until inertial confinement regimes are entered.
The ions have to be decoupled from the magnetic field. Whether the electromagnetic field or an internal plasma generated magnetic field , the ion diffusion- ExB diffusion, through the B field is too fast, energy is lost too fast in smaller machines. Some would say the magnetic insulation is inadequate in small machines. In the Polywell though, the ions are not magnetically contained (for the majority of the ions for the majority of their lifetime). The excess electrons produce a potential well that not only confines the ions at radii less than the influence of the electromagnet B fields, but also serves to accelerate them to useful high energy towards the center of the machine. The picture is not of ions flying (or spiraling in a magnatized plasma) back and forth along a cyclinder till they fuse, but ions flying back and forth towards a spherically defined center. This may allow for greatly increased densities in the core which is mostly good , but is not required. The magnetic field does come into play for ions that are up scattered and travel to radii great enough to reach the electron confining magnetic field. These ions are mostly turned back towards the center with out as great of an ExB penalty, because they are a minority of the ions and their energy and thus gyroradius are smaller.
The electrons are contained magnetically, their energy is initially from the ETW like grid, but subsequently their energy is only due to their inertia. They will cool through bremsstruhlung radiation, etc. and there is no additional energy input. They stay hot long enough to get the job done- hopefully, otherwise other means is needed to reheat the electrons/ plasma- such as microwaves, or hot neutral beam injection (that would seem to play havoc with the electrostatic ion containment). In the WTW machines the electrons would be reheated/ re accelerated whenever they passed outside the anode grid. In WB6 the appreciation for the inadequacy of electron cusp magnetic confinement it was appreciated, Here escaping electrons were stopped and re accelerated back into the machine due to the magrid anode positive charge, much like the ETW. This is fundamentally different in later EMC2 machines that apparently have a grounded magrid. The electrons are accelerated well outside the magrid and injected through the cusps. This does not allow for reheating of escaping electrons as they loop around to another cusp. There are obviously tradeoffs (think WB5 failure), but I remain curious why they have chosen this path.
All of this boils down to several clever tricks utilized in the Polywell to change the game- Minimizes ion concerns with ExB diffusion, eliminates much of the concerns about grid transparency, and of course the essential Wiffleball consideration. The triple product solution involves the short confinement times of cusp magnetic fields, but improved enough that with the corresponding increased density, and ease (hopefully) of heating, the containment of particles and heat is sufficient for net positive fusion energy output..
Other considerations such as edge stability, cool electrons in the core, ion confluence (central focus) are additional advantages that may allow for advanced fuel fusion, not just baseline D-T fusion.
In your cylindrical design, the plasma is magnatized, there will be significant ExB diffusion issues. There can be edge instabilities, macro instabilities, MHD instabilities (which ever term you prefer). Cusp losses may be less with two ring cusps on either end-and there have been cylindrical solenoid designs with end ring magnets to decrease end losses, but they have not been pursued, presumably because they failed theoretically or experimentally.
One experiment that may be similar to what you are thinking of was done by George Miley. I think it was called the dipole arrangement. A ring electromagnet was placed between two end curved cathodes which injected electrons towards the center. The electrons quickly left due to a negative space charge buildup. A anode was placed on the inner surface of the magnet to limit this. Some electron confinement was achieved, but I think it was far below what was hoped for.
https://www.google.com/search?q=George+ ... Cg#imgdii=_
Dan Tibbets