Applications of Vacuum Technology in the NIF Laser System John Hitchcock Pete Biltoft LLNL UCRL-PRES-219314

Agenda National Ignition Facility (NIF) missions Overview of the NIF Movies Description of N Vacuum Systems Target Chamber Spatial Filters Plasma Electrode Pockels Cell Diagnostic Vacuum Systems Summary

Stockpile stewardship Development of laser fusion as an energy source Missions: The NIF laser system is being built to support important national security and research activities Stockpile stewardship Development of laser fusion as an energy source Astrophysics Use any search engine & search for “NIF”.

The NIF laser would not be possible without the ready availability of stock and custom vacuum hardware Vacuum pumps Roughing & high vacuum (turbos, cryos) Vacuum gauges Hot and cold cathode ion gauges, rough vacuum gauges, capacitance manometers Valves Large 36” electro pneumatic gate valves to KF-25 manual valves Feedthroughs Electrical, mechanical and fluid

NIF Vacuum Volumes System Volume (liters) Quantity Total Volume (liters) NIF Target Chamber 750,000 1 Cavity Spatial Filters 44,000 24 1,056,000 Transport Spatial Filters 94,000 2,256,000 PDS 52,300 TARPOS 7,000 TASPOS DANTE 380 DIM's 1,700 2 3,400 FFLEX 60 ARC (Not Installed Yet) 100,000 PEPC 65 48 3,120 SXI 300 PAM VRT-1 18 864 PAM VRT-2 VRT #1 192 3,456 VRT #2 4 VRT #3 96 1,728 538 4,242,664

The NIF target chamber routinely achieves a pressure of < 5 x 10-6 Torr using a combination of roughing pumps, turbo pumps and cryo pumps

The NIF target chamber contains ports for beamlines, laser diagnostics, vacuum pumps and gauges

Alignment of the target is accomplished with a precision system called TASPOS

View inside NIF target chamber showing target positioner and workers on manlift inside the vessel The target positioner holds the target to a positional tolerance of +/- 6.8 microns. This positional tolerance can be thought of in the folloiwing way. Imagine a cantilever rod extends (without intermediate support) from Livermore CA to SanFrancisco. The corresponding positional tolerance would be approximately 1”.

One quad of optics in the final optics assembly as seen from inside the target chamber. Stainless steel first wall panels surround the optics First wall panels added to the interior surface of the NIF target chamber did not significantly increase the time reqired to evacuate the vessel from atmospheric pressure to 5 e-6 Torr. ~ 360 uniquely shaped 409 stainless steel panels were installed. 409 stainless steel was selected based upon its reduced neutron activation compared with other stainless alloys such as 316 and 304.

Installation of the final optics assemblies onto the NIF target chamber required skilled workers following stringent cleanliness protocols Each of the 48 final optics assemblies (FOAs) are required to deliver frequency-converted laser light to target chamber center. Each FOA contains a final optics cassette including debris shields that serve to protect expensive optics from damage caused by radiation and particles.

The target positioning system (TASPOS) includes a vacuum vessel with flexible track inside. The Diagnostic insertion module is used to position a diagnostic into the NIF target chamber. Despite a large amount of polymer insulated cabling, the NIF target chamber vacuum system meets base pressure requirements with the DIMs deployed.

Target positioning sensor during initial installation

Target positioner inside TARPOS vacuum vessel Tarpos boom is carbon fiber with a flame sprayed aluminum coating. This coating serves two purposes: Protects the carbon fiber from radiation 2) Conducts electrical chargethat would have built up during a NIF shot.

Lower hemisphere of NIF target chamber showing final optics assemblies installed

Target positioning system vacuum vessel during installation onto the NIF target chamber

NIF spatial filters require one of the largest clean-room rated vacuum systems in the world 2300 tons of vessels 10–5 torr vacuum MIL STD 1246C level 100 — A/10 cleanliness CSF End Vessel (2x) TSF End Vessel (2x) 23.5m 60 m TSF Beam Tubes CSF Center Vessel TSF Center Vessel

Transport spatial filter vessels being installed Transport spatial filter vessels being installed. These vessels are evacuated to a pressure of ~ 5 x 10-5 Torr using turbo pumps

The transport spatial filter vessels occupy a significant portion of each of the two laser bays

Upper hemisphere of NIF target chamber showing beamlines and final optics assemblies

1 x 1 PEPC in lab

Beamlet PEPC

Prototype of the Plasma Electrode Pockels Cell (PEPC) line replaceable unit (LRU) during testing

PEPC prototype during developmental testing

PEPC during mock assembly (note aluminum surrogates for optics)

PEPC line replaceable unit on precision optical alignment fixture

PEPC line replaceable unit on precision optical alignment fixture

Utilities including foreline vacuum pump line supporting the Plasma electrode Pockels cell enter the LRU from the interface flange

PEPC vacuum system (gas cell removed)

Summary: The NIF laser system would not be possible without the technology and hardware provided by vacuum equipment manufacturers Some of the specific components of the NIF laser that rely on vacuum equipment include: Vacuum relay telescopes in the preamplifier modules Spatial filters Amplifier flashlamps Plasma Electrode Pockels Cell Final Optics Assembly Target chamber and target diagnostics Precision Diagnostic System

Back-up Slides

Implosions conducted on NIF will be compared with computational models to optimize fusion experiments

The first attempt at fusion will be made in 2010 using the indirect drive fusion process

All 192 beams of the NIF laser will be focused onto a very small target

The target assembly for direct drive is held at 19 K +/- a few mK using a two-stage GM cryo-cooler similar to those developed for cryo pumps

In~ 2012 the NIF laser will be reconfigured for direct drive fusion

The NIF beamline contains several key elements that rely upon creation of stable vacuum environments

As a laser pulse moves through the NIF beamline it passes through a variety of optics and environments

The lasing media for the NIF main amplifiers is neodymium-doped glass The lasing media for the NIF main amplifiers is neodymium-doped glass. Vacuum chucks are used to lift and position these slabs into LRUs

Power lines that support operation of the main amplifier flashlamps Power lines that support operation of the main amplifier flashlamps. Each of the ~7000 flashlamp tubes is ~ 6 feet long and has an internal static vacuum. Flashlamps are expected to last > 20,000 shots.

View of amplifier slabs from within the NIF beamline