Power-balance laboratory · D–D / D–T / D–³He
Every fusion concept is an energy ledger: joules invested in fast ions or hot plasma against joules returned by fusion. FusionSim runs that ledger live for three machines — the electrostatic fusor you can build in a garage, the gridless orbit trap that swaps the fusor's grid for a planetary orbit, and the pulsed field-reversed configuration that is the most credible bet for small-scale net electricity. Move the sliders. Watch where every joule goes.
Each row shows a device's fusion gain (filled dot: fusion energy out per unit of energy put into the plasma or beam) against the gain it would need for net electricity given its own recovery scheme (open ring). The fusor and orbit-trap rows assume a 40%-efficient thermal plant bolted on; the FRC's finish line moves with your recovery-efficiency slider — that is the whole trick.
Ions fall through the cathode voltage and recirculate until something eats them: a grid wire, a charge-exchange collision with background gas, or Coulomb upscattering. Fusion has to happen before that — and the odds per pass are about one in ten billion.
The whole machine: a spherical shell held at ground, a centimeter-scale wire cage at tens of kilovolts negative, and dilute deuterium gas. Ions born in the gas fall inward, overshoot the center, and oscillate through the core — the pink "star" — until a grid wire or a charge-exchange collision claims them. Elegance is the appeal; the grid and the gas are the verdict.
Presets
Machine
Grid interception deposits the ion's full energy as heat on the wires; charge exchange hands the energy to a fast neutral that hits the wall. Not modeled (both make reality slightly worse): power carried away by secondary electrons and X-rays, and the modest fusion contribution of fast neutrals after charge exchange.
Compress a field-reversed plasmoid, burn for milliseconds, expand, and push the energy back into the circuit as electricity. Because the pulse is over before the plasma fully thermalizes or radiates away, marginal fusion gain can still mean net electricity — if recovery efficiency is extraordinary. This is Helion's wager, reduced to its arithmetic.
One pulse, left to right in time: plasmoids formed at both ends are electromagnetically fired inward, merge at the center, and are squeezed by the compression coil until fusion conditions hold for a few milliseconds. The fusion-heated plasmoid then expands against the field, pushing flux — and current — back through the same coil into the capacitor bank. The coil is both the piston and the generator; there is no turbine anywhere.
Presets
Fuel
Pulse
The vertical marker is the energy you paid for the pulse. If the two electricity segments together reach past it, the machine is a power plant; if not, it is a very expensive capacitor heater. Note how the marker chases the bar as recovery efficiency changes — breakeven here is a property of the circuit, not just the plasma.
Bench 1's verdict was the grid and the gas. This bench deletes the grid: a bare charged spike sits at the center, and an ion given enough sideways momentum orbits it like a comet — never touching metal. One test ion's equation of motion is integrated live below for your settings. The questions that decide the concept: how deep is the well, how long does the ion recirculate, and what finally claims it?
The actual integrated trajectory, not a cartoon. In a perfect spherical well the orbit is a closed Kepler ellipse that would repeat forever; in the cylindrical (Orbitron-style) well it precesses into a rosette. Either way nothing solid stands in the ion's path — so the losses move elsewhere: a charge-exchange collision with background gas, the slow drift of the periapsis into the spike, or Coulomb upscatter.
Presets
Well geometry
Trap
Past a certain pressure every added gas molecule is a fusion target and an ion thief in equal measure, and the neutron rate stops rising: that plateau is the ceiling of any gridless trap as a neutron source at fixed voltage and current. The thin curves re-run the same orbit at half and double the well voltage — raising the voltage, not the pressure, is the only way up.
Fusion reactivity climbs three to four orders of magnitude between 5 and 50 keV. D–T is ~100× easier than D–D at fusor-relevant energies — which is why any marginal concept gets evaluated on D–T first — while D–³He only wakes up above ~40 keV but pays out almost entirely in charged particles that direct recovery can capture.