Hibachi Window Development

1
C. Gentile1 R. Parsells1, J. Butler 2, L.
Ciebiera 1, H. M. Fan 1, R. J. Hawryluk 1, F.
Hegeler 1, P. Heitzenroeder 1, C. Jun 1, L. P.
Ku 1, M. Kalish 1,S. Langish 1, M. Myers2, S.
Raftopoulos 1, J.D. Sethian 2, M. Viola 1 (1)
Princeton University PPPL (2) Naval Research
Laboratory
HIBACHI WINDOW DEVELOPMENT
Diamond Foil withTitanium Ribs
Theory
Abstract A silicon (Si) based electron beam
transmission window with a 2 µm nanocrystal
diamond foil and titanium ribs is to be produced
for use in a KrF laser system in support of
inertial fusion energy technology. The window
separates the lasing medium from an electron beam
source while allowing the electron beam to pass
through. The window must meet requirements set
by the characteristics of the laser and must be
able to withstand the hostile environment
presented by the lasing medium and electron beam
source. Empirical tests for the window are
designed to simulate the actual environment it
will operate in. Various design changes are
considered to enhance the structural integrity of
the windows and relieve stresses at the edges due
to thermal expansion. This work is supported by
the Naval Research Laboratory (NRL) in
collaboration with the Princeton Plasma Physics
Laboratory (PPPL).

Laser Gas Recirculation
Laser Input
Pulsed Power System
Electron Beam
Laser Cell
Electron Transmission Window (Hibachi)
Laser Output
Output Optics
Key Components of a KrF Excimer Laser
Electra Laser Parameters
To maximize fatigue life, various heat rejection
methods are considered
The electron transmission window in the Electra
KrF laser must allow greater than 80 beam energy
transmission while withstanding a harsh
environment that includes fluorine gas, 5 Hz
cyclic pressure (?PABS ? 2.0 to
2.5 atm), and thermal load.

• Etched Micro-channels

Properties Silicon (SCS)
Nanocrystalline Diamond
Single crystal silicon provided with a 2 µm
nanocrystal diamond foil may provide for a robust
window with high transmission and good thermal
properties.
Yield Strength 7000 MPa 53000 MPa
Youngs Modulus 190 GPa 7000 GPa
Thermal Conductivity 157 w/m C 2,000 w/m C
Thermal Expansion 2.33 E-06 / C 1.0 E-06 / C
Conductive Heat Transfer is achieved through the
pumping of water through channels within the
support frame.
Forced Convection allows for laser gas flow
across the entire hibachi surface area. Cryogenic
coolant is pumped through etched micro-channels
within the rib structures.

• Motivation
• "Theoretical and experimental studies of KrF
  laser systems." Naval Research Laboratory Broad
  Agency Announcement No. 01-2000, BAA 45
• Single-crystal silicon . . . advanced micro
  fabrication technology . . . high-precision
  high-strength high-reliability mechanical
  material . . . Youngs modulus of silicon . . .
  has a value approaching that of stainless steel .
  . . tough, hard, corrosion-resistant, thin-film
  coatings such as CVD . . . prevent direct contact
  of the silicon to fluorine gas Petersen,
  Proceedings of the IEEE, Vol 70, No. 5 (1982)

Empirical Testing
Thermoelectric Cooling Concept - Incorporating
the Peltier effect to move heat from the bulk
section of the window to the edges. The hibachi
frame will serve as a sink for facilitating heat
rejection.
Evaporative Cooling Concept - Prior to each
pulse, low vapor liquid will be sprayed uniformly
on the surface of the Si windows. Flow tubes
within the support ribs of the hibachi frame will
deliver this coolant to the spray nozzles.
Multiple hemispherical configuration
Single window25 pane configuration
Single hemispherical configuration
A pressure cycling apparatus was designed to
mechanically model the KrF Laser System. A low
vacuum environment is applied to the etched
region of the window. An initial pressure of
approximately 1.3 to 2 atm (absolute) is placed
on the other surface and cycled at 5 rev/sec.
Silicon coated with nanocrystalline diamond foil
Convex side faces KrFAr gas
Single foil (cryo-spray) cooling concept
A diamond foil configured (pre-etched) window
configured foil during a routine pressure
deflection test under static differential
pressure.
Cryo Panel
With Diamond Foil and Titanium ribs
Pivot
Cooling Tube
With Diamond Foil
Diamond foil on silicon wafer at 5 mtorr