17th HAPL Meeting

1
NRL J. Sethian M. Myers S. Obenschain J.
Giuliani J. Dubinger M. Wolford
Commonwealth Tech F. Hegeler M. Friedman T.
Albert J. Parish R. Jones P. Howard RSI P.
Burns R. Lehmberg S. Searles W. Webster SAIC R.
Jaynes A. Mangassarian PLEX M. McGeoch APP S.
Glidden H. Sanders Georgia Tech S.
Abdel-Khalik D. Sadowski K. Schoonover
Electra (KrF) Laser Development
17th HAPL Meeting Washington, DC October 30,
2007 Naval Research Laboratory Plasma Physics
Division Washington, DC Presented by M.
Wolford Work supported by DOE/NNSA/DP
2
Summary Since December HAPL Meeting

• Angularly Multiplexed Electra Laser System
• 452 J Single Shot
• 1.585 kJ, 5 shots _at_ 5 Hz for 1 second
• Less expensive solid state switch based on
  commercial product (APP). Plex LLC has tested in
  3 stage Marx 1M shots _at_ 5 Hz. Demo 89
  efficiency.
• Georgia Tech has designed and bench tested Jet
  Foil Cooling Technique (Scalable, less power
  consumption)
• Cathode Rep-Rate Durability
• Averaged 270 J for 16,619 shots _at_ 2.5 Hz over two
  hour period
• Far Less Debris with Silica Coating on Cordierite
  
• No Debris with All Carbon Cathode after 4000
  shots _at_ 2.5 Hz

3
Completed Electra Laser System
LPX
Pre-AMP
Main AMP
4
Angularly Multiplex Preamplifier 25 J Output
Beam 1
INPUT
Beam 2
PD 2
PD1
Beamsplitter
Calorimeter
LPX
PLCC
f 6 m Lens
Photodiode Combo
Cylindrical Optics
5
452 J Single Shot Yield
Calorimeter Array
Output Beams 15 x 15 cm2
Split Each Beam into 3
Split Beam
Big 33 x 33 cm2
Main Amp 30 x 30 cm2
1
2
PRE AMP
OSC
Small 18 x 18 cm2
6
Total Yield 1.585 kJ in One Second 5 Hz Burst
Energy Drops Due To Pre-Amplifier (Phase
Aberrations) Pre-Amplifier Recirculator (
Designed)
PHOTODIODE
7
On going Improvements in Laser System
See Laser Posters J. Giuliani et al. KrF Laser
Amplification in the MultiStage Electra Facility
For Code Comparison R. Lehmberg Pulse Shaping
and Energy Storage Capabilities in Angularly
Multiplexed KrF Laser Amplifiers M. Wolford et
al. Optical System and staging of the Electra
KrF laser facility
Pre-Amp Recirculator Allow rep-rate runs, improve
beam quality Improved Coupling Timing, Pre-Amp
to Main Amp More energy into main amp More
diagnostics for KrF Code Comparison Strip
Cathode for Pre-Amp 25 more energy deposited in
the Laser Gas
8
We have made advances with existing durable
switches that will be less expensive, and will
come close to efficiency
PREVIOUS
NEW ADVANCE
LASER GATED SWITCH High Efficiency But,
potentially more expensive requires further
development
S33 Solid State (45 kV) Switch Applied Pulsed
Power, Ithaca, NY
USE EXISTING Specs 30 kA/usec, gtgt 108
shots Tested to 50 kA/usec PLEX LLC has
demonstrated 96 kA/usec _at_ 40 kV with SMA
PLEX LLC
9
PLEX corporation has built a 3 stage Marx using
modified APP switches and magnetic
assistDemonstrated 1 M shots _at_ 5 Hz
3 stage Marx
Rep-rate/duration 106 _at_ 5 Hz 105 _at_ 10 Hz
dI/dt 60 kA/us Voltage 60 kV Pulse length 320
nsec Total Current 7 kA Switch efficiency
89 Circuit efficiency 84
We will build a 12 stage e-beam system to
demonstrate all solid state, durable architecture
PLEX Corporation
10
"Jet" foil cooling technique developed by Georgia
Tech Keeps foil (uniformly) cool Scalable to
large apertures Low power consumption (minimal
efficiency penalty) Should not mess up the focal
profile
e-beam side
foil
TOP VIEW
Rib
tube
Jet
Gas Side
11
Jet Foil Cooling Technique Successfully
Demonstrated on Bench
12
HypothesisFoil is lifetime not limited by
thermal managementDebris from Cordierite
honeycomb Causes Foil Failure
Evidence of Debris
13
Silica Coated (Far Less Debris) Cordierite
Improvement
Average 270 J _at_ 2.5 Hz Over Two Hour Time Period
14
All Carbon Cathode Shows Potential for Greater
Durability (4000 shots _at_ 2.5 Hz No Debris, No
Foil Damage, 50x lower vacuum)
See Poster M. Myers M. Friedman Development
of a Large Area, Durable Electron Emitter For
High Average Power KrF Lasers
15
Summary Since December HAPL Meeting

• Angularly Multiplexed Electra Laser System
• 452 J Single Shot
• 1.585 kJ, 5 shots _at_ 5 Hz for 1 second
• Less expensive solid state switch based on
  commercial product (APP). Plex LLC has tested in
  3 stage Marx 1M shots _at_ 5 Hz. Demo 89
  efficiency.
• Georgia Tech has designed and bench tested Jet
  Foil Cooling Technique (Scalable, less power
  consumption)
• Cathode Rep-Rate Durability
• Averaged 270 J for 16,619 shots _at_ 2.5 Hz over two
  hour period
• Far Less Debris with Silica Coating on Cordierite
  
• No Debris with All Carbon Cathode after 4000
  shots _at_ 2.5 Hz