Tokamak 2D — Poloidal Cross-Section Confinement

☢️ 2D Tokamak

Poloidal cross-section (r–θ plane) of a tokamak. A toroidal field B_φ ∝ 1/R combines with a poloidal field B_θ generated by the plasma current to form helical field lines. Charged particles gyrate and slowly drift outward — too weak a field and they hit the wall.

🎛 Fields

Toroidal field B_φ 5.0 T Plasma current I_p 2.0 MA Poloidal field factor 1.0× Particle count N 50

📐 Diagnostics

Safety factor q

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Larmor r_L

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Cyclotron f_c

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Confinement

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ℹ️ Physics

Safety factor q = rB_φ / RB_θ sets the field-line twist. Pure toroidal field cannot confine — the grad-B and curvature drift push ions and electrons apart; the poloidal field averages this out over each poloidal transit. Drift width scales with the Larmor radius r_L = mv⊥ / eB, so weak fields → wide orbits → particles cross the wall and confinement is lost.