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

2. 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

3. 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”.

4. 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

5. 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

6. 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

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

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

9. 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”.

10. 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.

11. 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.

12. 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.

13. Target positioning sensor during initial installation

14. 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.

15. Lower hemisphere of NIF target chamber showing final optics assemblies installed

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

17. 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

18. 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

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

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

21. 1 x 1 PEPC in lab

22. Beamlet PEPC

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

24. PEPC prototype during developmental testing

25. PEPC during mock assembly (note aluminum surrogates for optics)

26. PEPC line replaceable unit on precision optical alignment fixture

27. PEPC line replaceable unit on precision optical alignment fixture

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

33. PEPC vacuum system (gas cell removed)

34. 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

35. Back-up Slides

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

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

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

39. 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

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

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

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

43. 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

44. 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.

45. View of amplifier slabs from within the NIF beamline