Vertical Displacement Event (VDE)

A tall, elongated plasma is vertically unstable and can drift into the wall — a VDE. Kronos holds κ = 2.56 with a control margin of 2.02.

What

Loss of vertical position control

Cause

Elongated plasmas are vertically unstable

Kronos shaping

κ = 2.56

Control margin

2.02 at the floor (S69)

A vertical displacement event (VDE) is what happens when a tokamak loses control of the plasma's up-down position and it drifts into the wall. Elongation is the culprit: a tall, D-shaped plasma carries more current and pressure (a good thing), but it is inherently vertically unstable and must be held in place by active feedback and passive conducting structures.

Kronos MetroVolt runs a strongly shaped plasma at κ = 2.56, so vertical control is a first-order design problem. The deposited analyses (S24, rerun at final size as S69) give a corrected vertical-control margin of 2.02 at the floor — comfortably above unity — using outboard passive plates plus active feedback. A VDE is also one pathway into a full disruption, which is why the margin is tracked carefully.