Energy Confinement Time (τ_E)
τ_E measures how long a plasma holds its heat. Confinement scalings and the required H98 = 2.28 multiplier are expressed against it.
- Symbol
- τ_E
- Meaning
- Energy content ÷ heating power
- Kronos requirement
- H98 = 2.28 over IPB98(y,2) (Mode D; 2.38 banking)
- Measured at
- the G1 confinement testbed
Energy confinement time (τ_E) is the single most important performance number in magnetic fusion: it is the plasma's stored energy divided by the power needed to sustain it — in effect, how long the bottle holds its heat before it leaks out. Longer τ_E means the plasma stays hot with less input, pushing the machine over the Lawson threshold.
Because τ_E cannot be predicted from first principles alone, the field uses empirical scalings — the standard being IPB98(y,2). Performance is then quoted as a multiplier, H98, over that scaling. Kronos MetroVolt requires H98 = 2.28 on a profile basis at the Mode-D baseline (2.38 on the banking leg), which the negative-triangularity confinement is expected to deliver.