Gyroradius & ρ*

Charged particles spiral with a gyroradius set by field and temperature. Its normalized value ρ* governs how experiments scale to a reactor.

Gyroradius

Radius of a particle's spiral around a field line

Smaller when

Field is stronger

ρ*

Gyroradius ÷ machine size (dimensionless)

Kronos G1

ρ* within 1.7× of the full plant

A charged particle in a magnetic field spirals around the field line with a gyroradius (or Larmor radius) set by its energy and the field strength — stronger fields mean tighter spirals. Because a high-field machine like Kronos MetroVolt has small gyroradii, particles are held closer to their field lines, which is part of why high field improves confinement.

What matters for scaling is the normalized gyroradius, ρ* — the gyroradius divided by the machine size. Two plasmas with the same ρ* (and other dimensionless parameters) behave similarly regardless of absolute size, which is how a smaller experiment can predict a reactor. Kronos designed its G1 confinement testbed to sit within 1.7× of the full plant's ρ*, so its confinement results transfer meaningfully to the commercial machine.