Page 398 - High Power Laser Handbook

366 So l i d - S t at e La s e r s The National Ignition Facility Laser 367

25
Top quad Bottom quad
B314 B313 B312 B315 B316 B317
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B311 B318
Output 1ω energy (kJ) 15

10

5

0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Injected energy (Joules) Injected energy (Joules)
Figure 14.5 Comparison of modeled (dashed and solid lines) and measured (open
and solid points) energies for eight shots on NIF’s first operational bundle (Bundle 31:
beamlines 311 through 318). The output energy is measured by the full-aperture
calorimeters.

14.4.1 Energetics and the Laser Performance Operations
Model Calibration Results
Figure 14.5 shows the comparison between modeled performance
using LPOM and energy measurements for eight shots on the first
bundle of the NIF laser. In this figure, output 1ω energy refers to
the energy measured at the output of the main laser with the full-
aperture calorimeters. The OSP was calibrated to these calorimeters.
The injected energy is inferred from the ISP measurements, the known
four-way ILS beam split ratios, and the known transmission from the
ISP to the injection at the TSF. LPOM’s predictions differ from the
measurements by no more than 1.2 percent, demonstrating that
LPOM can be used to set the desired energy from each beamline
accurately over an extended range of operations.
The laser 1ω output energy is required to be reproducible to
within 2 percent root mean square (rms) from shot to shot for proper
ignition target performance. To test this performance criterion, the
19.2-kJ shot in Fig. 14.5 was repeated three times. After the first shot,
no adjustments were made to either the injected pulse shape or the
injected energy. As Table 14.1 shows, agreement with the target
energy, the rms spread in total energy among the four shots, and the
standard deviation of the eight beamline energies in each shot were
all better than 1 percent. The estimated error in the 19.2-kJ energy
measurement is 1.4 percent, or 0.27 kJ. This error estimate is a root
sum of squares (rss) of the observed random component (1.3 percent)
and the known systematic uncertainty (0.42 percent) of the calibration
standard from the National Institute of Standards and Technology
(NIST) that was used in calibrating NIF’s calorimeters.