L-H transition

Model for the L-H transition

The L-H and H-L transition time can be either set from the namelist, or calculated from power threshold.

  • To impose the L-H transition time from the namelist:

NMODEL_L2H_TRANS = 0

TIME_L2H = 0.0d0 ! time (s) of transition from L mode to H mode

TIME_H2L = 0.0d0 ! time (s) of transition from H mode to L mode

  • To calculate the L-H transition time from power threshold:

NMODEL_L2H_TRANS = 1

There are two options for the calculation of the L-H power threshold, which can be selected with LPED(1)

  • LPED(1) = 1

      • LPED(1) = 2 ! Martin scaling

TRANSP assumes that the plasma is in H-mode when the power across the separatrix exceeds the power threshold for the L-H transition.

The input variable CPED(8) can be used to adjust the power threshold, so the plasma is in H-mode if

Ploss > CPED(8) x Pth

NOTE: the variable CPED(6) set the minimum time at which a L-H transition is allowed, thus

CPED(6) = t1 means: "do not allow H-mode before this time"

The power threshold for the H-mode back transition is decreased inside TRANSP by a factor 1.25 to account for hysteresis effects.

To avoid too large and fast variations in the profiles across the L-H transition and help with convergence, the following control variable limits the time rate of the boundary conditions.

This is independent of whether the L-H transition is calculated in TRANSP and profiles are predicted, or the density and temperature profiles are input to TRANSP.

TAU_LH_TRANS_X2 = 0.005d0

This parameter sets the minimum time (s) for factor of 2 change in the boundary condition parameters. The same parameter is used also to limits excursions due to large variations in the input data also when the plasma is in L-mode.

NOTE: all the above parameters can be changed in time during the simulation, by adding at the bottom of the TRANSP namelist the following lines:

~update_time = <time1>

<1st update of parameters>

~update_time = <time2>

<2nd update of parameters>

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