This is a poloidal cross-section through a tokamak — the slice you get by cutting straight across the doughnut-shaped vessel at one point around the ring, the diagram physicists actually draw on a whiteboard. Nested D-shaped flux surfaces wrap a hot D-T plasma core; ions gyrate in tight Larmor loops around the field lines that thread through the page, drifting slowly outward and occasionally colliding to fuse. It runs the identical Lawson-criterion and Q-factor physics as the 3D outside-view model of this reactor.
Lawson criterion: n·τ·T ≥ 3×10²¹ m⁻³·s·keV
D-T reactivity fit (NRL formulary): ⟨σv⟩(T) = C1·exp(-C2/T^(1/3))·T^(-C3/3)
Fusion power density: P_fus = 0.25·n²·⟨σv⟩·E_fus (E_fus = 17.6 MeV)
Heating power density: P_heat = 3nT/τ Q = P_fus / P_heat
The D+T reaction releases 17.6 MeV per fusion event, split as 3.5 MeV to the helium-4 nucleus and 14.1 MeV to a fast neutron — that neutron would heat a surrounding blanket to generate electricity in a real power plant.
This simulation shows a poloidal cross-section through a tokamak reactor — a face-on slice through the doughnut-shaped vessel at one point around the ring, the diagram physicists actually sketch when explaining magnetic confinement. It runs the same Lawson-criterion, D-T reactivity and Q-factor physics as the 3D companion simulation, so the trade-offs between temperature, density and confinement time are identical; only the viewing geometry and visual language change. Nested flux surfaces wrap the hot plasma core, ions gyrate on true Larmor circles and drift outward as confinement time worsens, and fusion events flash near the core at a rate that tracks the real fusion-power formula.
Comparing the two views side by side is instructive: the 3D model shows the whole torus from outside, orbited with the mouse, while this 2D model shows what a single poloidal slice looks like from the side — nested D-shaped magnetic surfaces, toroidal field markers threading in and out of the page, and a scrolling Lawson-ratio timeline instead of a static bar. Both simulations integrate the identical NRL-formulary reactivity fit underneath.
The 3D version renders the whole torus from outside, with toroidal field coils, a glowing plasma ring and an orbiting camera. This 2D version instead shows a single poloidal cross-section — a face-on slice through the ring — with nested flux surfaces, gyrating D and T ions, fusion flashes and a scrolling Lawson-ratio timeline. Both simulations integrate the identical Lawson-criterion, D-T reactivity and Q-factor equations, so the numeric readouts (nτT product, fusion power, heating power, Q) behave exactly the same way in both.
Use the Temperature slider to set the plasma's ion energy in keV — higher values speed up ion gyration and sharply raise the fusion reaction rate. The Density slider sets how many ions populate the plasma (shown as more dots on the flux surfaces). The Confinement time slider controls how fast ions drift outward across flux surfaces before their energy is lost; shorten it and you will see the drift accelerate and the Lawson-ratio timeline fall. Click Pause to freeze the animation and inspect the timeline, or Reset to reseed the ion population.
Each flash represents a fusion event, and the rate at which flashes appear is scaled directly from the fusion power density formula, 0.25·n²·⟨σv⟩·E_fus, the same expression driving the numeric Fusion power readout. Raising temperature or density increases both the readout and the flash frequency together, so the animation and the numbers never disagree.
A tokamak's magnetic field organizes the plasma into nested, closed surfaces of constant magnetic flux, shaped like a stack of D's when viewed in poloidal cross-section. Charged particles are largely confined to move along these surfaces rather than straight across them, which is the basic mechanism that makes magnetic confinement fusion possible. In the simulation the surfaces are drawn as concentric D-shaped shells, brighter and hotter toward the core.
A charged ion moving through a magnetic field spirals around the local field line in a tight circle called a Larmor orbit, with a radius set by the ion's speed, mass, charge and the local field strength. In this simulation, hotter ions (higher temperature T) gyrate with a visibly larger radius and higher frequency, illustrating how temperature simultaneously drives fusion likelihood and the difficulty of confining fast-moving particles.
Real fusion plasmas leak energy through turbulence, collisions and radiation, which is exactly what the confinement time τ parametrizes: a short τ means energy escapes quickly, a long τ means it is retained. In the simulation, ions drift from inner to outer flux surfaces at a rate proportional to 1/τ and are reseeded near the core once they reach the edge, visualising the constant balance between fusion heating and confinement losses that real reactor designers must win.
The Lawson triple product, the D-T reactivity fit from the NRL plasma formulary, and the fusion/heating power-balance formulae are the same standard relations used in both this 2D model and the 3D companion simulation, so the underlying trade-offs are realistic. The cross-section artwork itself — flux-surface shapes, Larmor gyro-radii and drift rates — is a simplified, illustrative rendering rather than a full magnetohydrodynamic simulation, and effects such as impurities, instabilities and detailed reactor geometry are not modelled.
Deuterium and tritium, two hydrogen isotopes, fuse into helium-4 and a fast neutron, releasing 17.6 MeV per reaction — 3.5 MeV carried by the helium nucleus and 14.1 MeV by the neutron. D-T has the largest fusion cross-section at the lowest achievable temperatures of any fuel combination, which is why both this simulation and virtually every real fusion reactor design target it.
Yes. In 2022 the National Ignition Facility, which uses laser-driven inertial confinement rather than magnetic confinement, produced more fusion energy than the laser energy delivered to the fuel. Magnetic-confinement tokamaks such as JET have produced substantial fusion power for short pulses, and ITER is being built to sustain a Q of about 10.