4.1 Overview

The DLI facility utilizes two beams of the NIF laser that are delivered into a dedicated DLI vessel, converting the light to 526 nm, and overlapping both beams onto a wide test plane in a large test volume. A layout of the NIF DLI system is shown in Figure 1, which shows NIF beamlines 351 and 352 being directed into CV2 using an insertable pickoff mirror. This allows independent use of beams 351 and 352, so the facility can support a DLI test as a ride-along to main Target Chamber shots without interference. The test area is 31.6 cm x 31.6 cm (1,000 cm2), and the test volume extends forward and back from the test plane (on the order of +400 mm, -780 mm). The two laser beams are polarized orthogonal to each other, and, as a result, do not create an interference pattern at the test plane despite that fact that they are overlapped. Users should note that the test volume is reduced as one moves forward or backward away from the test plane due to the changing overlap of the two beams. This is discussed in more detail in Section 6.3.

The DLI facility design separates the DLI test area from the laser optics and beam transport areas as shown in Figure 1. This separation will ensure that the laser transport optics are protected, kept in a stable environment, and, thus, require minimum maintenance. The laser optics and beam transport area will be maintained at a constant pressure (local atmospheric) to maintain temperature and humidity. Two vacuum windows separate these areas. To ensure integrity of the vacuum window during DLI shots, the system will use two disposable debris shields per beam. Currently, the test area operates at local atmospheric pressure, however, a vacuum capability will be commissioned during FY25 which will provide the option to conduct experiments at vacuum (~10-4 torr). The option to conduct experiments at vacuum will be available no earlier than FY26; for more information, please reach out to the DLI Laser Scientist and Experimental Lead.

This design allows the system to provide the required shot rate and system availability with minimum impact to the NIF workforce. Adequate baffling has been added in the space between the vacuum window at the interface of the laser-transport area and the test-area volume to ensure no potential damage can be caused by light reflected by the test object.

NIF DLI layout next to compressor vessel 1 (CV1) showing component in CV2 for the laser transport and conversion from 1ω to 2ω.
Figure 1. NIF DLI layout next to compressor vessel 1 (CV1) showing component in CV2 for the laser transport and conversion from 1ω to 2ω.