Setting Laser Beam Energetics

The Energetics tab is used to specify the laser beam power (in TW).

For the laser beam power, VISRAD currently supports specifying either:

• a constant (time-independent) power
• variable, time-dependent powers
• a standard laser pulse profile for the laser facility*

To specify time-dependent parameters, check the Variable box, and enter values into the time-dependent two-column tables. A multiplier can be applied to the table values to facilitate parameter studies. The multiplier is applied at the bottom of the two-column table dialog.

When selecting a standard laser pulse profile for the facility, the total energy of the beam (integrated over the time-dependent power profile) can be specified. When doing this, the time-dependent power is normalized such that the total energy in the beam is equal to the specified value.

* Data files for available pulse shapes are contained in the "/data/laser_pulse_shapes" folder distributed with each VISRAD release. Initially, only a limited number of pulse shapes for OMEGA will be included. Additional pulse shapes will be added as they become available.

Blue, Green, and Red Cone Powers for NIF Laser Beams

For the NIF laser beam system, each laser beam is modeled using 3 cones: Blue (B), Green (G), and Red (R). In this case, one of four models can be used to specify the power in each cone. For each model, either the Total or Blue cone power is specified using the approach described above. The red and green cone power specification depends on the model used:

• None: All power is in the blue cone.
• Absolute Power: The power for the red and green cones are specified in TW (P_R(t) and P_G(t)).
• Fraction of Total Beam Power: The fraction of power in the red and green cones is specified (f_R(t) and f_G(t) specified, where f_i(t) = P_i(t)/P_TOT(t)).
• Relative to Blue Cone Power: The red and green powers are specified relative to the blue power value (R_R(t) and R_G(t) specified, where R_i(t) = P_i(t)/P_B(t)).

The total power in the four models, in terms of the quantities specified, is given by:

• None: P_TOT(t) = P_B(t).
• Absolute Power: P_TOT(t) = P_B(t) + P_G(t) + P_R(t).
• Fraction of Total Beam Power: P_TOT(t) = (f_B(t) + f_G(t) + f_R(t)) * P_TOT(t), where f_B(t) = 1 - f_G(t) - f_R(t).
• Relative to Blue Cone Power: P_TOT(t) = P_B(t) * ( 1 + R_G(t) + R_R(t)).

Except for the Fraction of Total Beam Power model, where P_TOT(t) is specified, the blue cone power is specified by the user.

The time-dependent powers for one or more beams, or for the individual RGB cones, are readily plotted by right-clicking on beams in the Laser Beams List, and selecting the Plot Power vs. Time menu item.

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