Tokamak Plasma Confinement (2D)

What the 2D view shows

The poloidal cross-section of an ITER-class tokamak (R = 6.2 m, a = 2 m, elongation 1.7, triangularity 0.33) with nested flux surfaces coloured by temperature, the surfaces where the safety factor q is 3/2, 2 and 3, and the alpha particles that heat the plasma. The four graphs are views the 3D hall cannot give: the Lawson triple-product plane, a power-balance time series, the density/current operating map and the q profile.

Equations (same module as the 3D page)

• Energy balance dW/dt = Paux + Pα - Prad - W/τE, with stored energy W = 3 n T V (n = n_e = n_i).
• Fusion power Pfus = (n/2)² <σv> Ef V, E_f = 17.6 MeV, alpha share 3.5/17.6; Bosch-Hale D-T reactivity <σv>(T).
• Confinement τE = H98 · 0.0562 Ip0.93 Bt0.15 P-0.69 n0.41 M0.19 R1.97 ε0.58 κ0.78 (IPB98(y,2)); L-mode uses 0.55 of it until P exceeds the L-H threshold (Martin scaling).
• Lawson: n τE = 12 T / (<σv> Ef (1/5 + 1/Q)), Q = P_fus/P_heat.
• Limits: Greenwald density nG = Ip/(πa²), kink limit q₉₅ > 2, normalised beta β_N < 3.5.

Honest simplifications

Zero-dimensional volume averages: no profiles or transport code, fixed Z_eff, no helium ash, ELMs or sawteeth. The flux-surface shading and q profile are illustrative shapes scaled to the volume averages. Plasma time is compressed by the speed slider. Limits are empirical boundaries; crossing one for about 1.4 s plasma time triggers the disruption animation. This is an educational model of a generic machine and is not affiliated with any project.

What to try

• Load ITER-like baseline and watch Q settle near 8.
• Turn auxiliary heating off in Ignition attempt: does it self-sustain?
• Raise density past the orange Greenwald line in the operating map.
• Drop Bt to 2.6 T with 15 MA: q95 falls below 2.