Content uploaded by Lloyd Chauncey Brown
Author content
All content in this area was uploaded by Lloyd Chauncey Brown on Dec 28, 2013
Content may be subject to copyright.
GA–A22714
THE DESIGN OF THE OMEGA CRYOGENIC
TARGET SYSTEM
by
D.T. GOODIN, N.B. ALEXANDER, I. ANTEBY, W.A. BAUGH,
G.E. BESENBRUCH, K.K. BOLINE, L.C. BROWN, W. EGLI,
J.F. FOLLIN, C.R. GIBSON, E.H. HOFFMANN, W. LEE, L. LUND,
J.E. NASISE, A. NOBILE, K.R. SCHULTZ, and R. STEMKE
NOVEMBER 1997
DISCLAIMER
This report was prepared as an account of work sponsored by an agency of the United States
Government. Neither the United States Government nor any agency thereof, nor any of their
employees, makes any warranty, express or implied, or assumes any legal liability or
responsibility for the accuracy, completeness, or usefulness of any information, apparatus,
produce, or process disclosed, or represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial product, process, or service by trade name,
trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or any agency thereof. The views
and opinions of authors expressed herein do not necessarily state or reflect those of the United
States Government or any agency thereof.
GA–A22714
THE DESIGN OF THE OMEGA CRYOGENIC
TARGET SYSTEM
by
D.T. GOODIN, N.B. ALEXANDER, I. ANTEBY,
†
W.A. BAUGH,
G.E. BESENBRUCH, K.K. BOLINE, L.C. BROWN, W. EGLI,
J.F. FOLLIN, C.R. GIBSON, E.H. HOFFMANN, W. LEE, L. LUND,
‡
J.E. NASISE,
◊
A. NOBILE,
◊
K.R. SCHULTZ, and R. STEMKE
†
Negev Nuclear Research Center
‡
Laboratory for Laser Energetics, University of Rochester
◊
Los Alamos National Laboratory
This is a preprint of a paper to be presented at the 17th IEEE/NPSS
Symposium on Fusion Engineering, October 6–11, 1997, San Diego,
California and to be published in the
Proceedings
.
Work supported by
the U.S. Department of Energy
under Contract No. DE-AC03-95SF20732
GA PROJECT 3748
NOVEMBER 1997
GENERAL ATOMICS REPORT GA-A22714 1
The Design Of The OMEGA Cryogenic Target System
*
D.T. Goodin,
a
N.B. Alexander,
a
I. Anteby,
b
W.A. Baugh,
a
G.E. Besenbruch,
a
K.K. Boline,
a
L.C. Brown,
a
W. Egli,
a
J. F. Follin,
a
C.R. Gibson,
a
E.H. Hoffmann,
a
W. Lee
a
, L. Lund,
c
J.E. Nasise,
d
A. Nobile,
d
K.R. Schultz,
a
and R. Stemke
a
a
General Atomics, P.O. Box 85608, San Diego, California 92186-9784
b
Negev Nuclear Research Center, Israel
c
Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14623-1299
d
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
Abstract — General Atomics is designing and building the
OMEGA Cryogenic Target System (Fig. 1) for the University
of Rochester’s Laboratory for Laser Energetics. The purpose
of this system is to deliver millimeter sized polymer shell
targets to the center of the target chamber for inertial
confinement fusion experiments. Prior to insertion, these
targets are filled to pressures as high as 1500 atm with
hydrogen isotopes (DT), the gas is cryogenically condensed,
and the condensed material is layered to form a uniform
inner shell. GA has demonstrated the successful filling with
D
2
of plastic targets to 1100 atm, cooling, and cold transport
utilizing prototype equipment. In addition to proving the
viability of the proposed fill process, the prototypes have led
to significant equipment simplifications and process
improvements for the University of Rochester system.
1. INTRODUCTION
Inertial Confinement Fusion (ICF) [1] is supported by the
U.S. Department of Energy Office of Inertial Fusion as a
part of the U.S. DOE “science-based stockpile
stewardship” program. The temperatures and pressures
achieved in inertial fusion are similar to those produced in
a nuclear weapon.
A major purpose of the ICF program is to provide these
conditions for research and maintenance studies without
the need for actual nuclear testing. A long term application
of inertial fusion is fusion energy for electric power and
other energy applications.
The University of Rochester’s Laboratory for Laser
Energetics (UR/LLE) is a major facility conducting implo-
sion experiments and basic physics experiments in support
of the national Inertial Confinement Fusion program. A
major goal of this program is to achieve the conditions for
fusion ignition. To reach sufficient density to approach
ignition conditions with reasonable laser power requires
cryogenic targets with uniform fuel layer thickness and
density, and a smooth inner surface finish. UR/LLE will
do experiments on the OMEGA laser to study implosion
of cryogenic targets. Cryogenic targets require specialized
UPPER PYLON
TARGET
TANK
CHARACTERIZATION
STATION
LOWER PYLON
MOVING
CRYOSTAT
LA CAVE
MOVING
CRYOSTAT
ELEVATOR
NOVING CRYOSTAT
TRANSPORT CART
FILL STATION
Glovebox
ROOM 157
PRESENT
LLE TRITIUM
FILLING
DIAPHRAGM
COMPRESSOR
GLOVEBOX
Fig. 1. OMEGA cryogenic target system and the OMEGA target chamber.
*
Work supported by U.S. Department of Energy under Contract No. DE-AC03-95SF20732.
2 GENERAL ATOMICS REPORT GA-A22714
systems to fill, layer, and characterize targets, and then
insert, align and protect them in the target chamber.
General Atomics is designing and building the OMEGA
Cryogenic Target System (OCTS, Fig. 1). The cryogenic
target delivery system being built for the OMEGA laser
will also benefit the National Ignition Facility (NIF) being
constructed at Lawrence Livermore National Laboratory,
since the same technologies are applicable.
A prototype fill station and cold transfer cryostat have
been designed, constructed, and operated at General
Atomics with D
2
to demonstrate the fill process and to
provide input to the final design. The prototype system
definitively demonstrated the feasibility of high pressure
filling, cooling, and transporting of cryogenic polymer
targets with the UR/LLE C-mount design [2]. Based on
the prototype testing and a strong emphasis on design
simplicity, the cryogenic target process and equipment
have changed significantly from the original conceptual
design [3,4]. The remainder of this paper describes the
final OCTS equipment and process design.
2. FUNCTIONS AND ESSENTIAL FEATURES
The OCTS fills hollow ICF target shells with DT fuel at
290–400 K to pressures up to 1500 atm and then cools
them from the fill temperature to approximately 20 K to
condense the fuel. Pressure gradients across the shell must
be carefully controlled during the fill/cool sequence (to as
little as 0.2 atm, depending on the shell thickness). The
targets containing the condensed DT are then layered [5]
to develop a uniform layer (<2% variation) of DT between
10 and 100 µm thick on the inner surface. The layered
target is then cooled and held at a precise temperature
(+ 0.025 K) in the vicinity of 18 K, characterized to
measure the DT ice layer thickness, the uniformity and the
smoothness of the inner ice surface, and then inserted into
the OMEGA chamber. In the chamber it is positioned
within 5 µm at chamber center where a final pre-shot
verification will take place. The protective shroud is
removed just before the target is shot. The shroud must be
removed fast enough to prevent thermal degradation of the
target prior to the laser shot (<100 ms) and without
significantly disturbing the positioning of the target.
3. OCTS PROCESS OVERVIEW
This section provides an overview of the entire process,
while the sections below provide additional details on the
equipment design. Fig. 1 shows an overview of the OCTS
system as it will be configured at the UR/LLE.
The target filling equipment is located within the tritium
laboratory. A cryogenic DT intensifier is used to supply
low pressure tritium (~125 atm) to a diaphragm intensifier
that increases the pressure up to 1500 atm. The DT
mixture is routed to a high pressure Permeation Cell where
the diffusion filling process takes place. The Permeation
Cell is contained within a Fill/Transfer Cryostat (FTS) to
provide for cooling after the fill. The targets are mounted
utilizing a convoluted wire (to avoid the laser beams
during a shot) and suspended by three spider silk strands.
The targets are filled in one operation, four in a rack, and
then separated within the FTS for transfer to the Moving
Cryostat (MC).
The MC is contained within a Moving Cryostat Transport
Cart and receives the filled, cryogenic target from the FTS.
The MC maintains the cryogenic target environment as the
target is moved to the area beneath the target chamber, and
within the target chamber before the shot. The MCTC
attaches to the target chamber Lower Pylon, providing a
vacuum seal, and the MC moves from the cart to chamber
center. The MC’s thermal shroud is attached to a linear
motor (Shroud Puller) positioned overhead in the Upper
Pylon.
Immediately before the shot, the Shroud Puller is used to
remove the MC thermal shroud, exposing the cryogenic
target to the chamber for the laser shot.
4. PRESSURIZATION SYSTEM
The diaphragm intensifier design is based on a similar
compressor utilized at the Weapons Engineering Tritium
Facility at Los Alamos National Laboratory. The three-
layer diaphragm position is precisely controlled by
pressurized oil on one side from a hydraulic syringe pump,
controlled in turn by a reducing gear and stepper motor.
The tritium is separated from the oil by three diaphragms.
The center one of the three diaphragms is etched on each
side to allow any oil or DT leaking through the outer
diaphragms to be channeled to leak detectors. The
pressurization sequence is computer controlled through the
stepper motor, and allows for active pressure control
during cooling if needed to maintain a very low pressure
gradient across the filled shell.
The intensifiers, the high pressure Permeation Cell, and
the cryostat containing it, are all located within a
secondary enclosure (glovebox) to control the spread of
tritium contamination from routine operations and to
provide additional release barriers in the event of
accidental tritium release.
5. FILL/TRANSFER CRYOSTAT
Fig. 2 shows a sideview of the FTS. The FTS is a cryostat
consisting of an insulated three-layer dome and a cooled
base. The dome has a permanent vacuum insulation space
and is removed as one piece, for ease of maintenance of
underlying components in the Glovebox. The FTS base
has two parallel plates with an integral liquid nitrogen
bath. The FTS has an associated Cooling Module which
contains the cryocoolers and heat exchange gas system.
GENERAL ATOMICS REPORT GA-A22714 3
Permeation Cell
Inserter
Fig. 2 Side view of FTS showing inserter and permeation cell.
The FTS has an insertion system which positions a target
rack containing up to four mounted targets within the
permeation cell. The target rack is manually loaded onto
the insertion system through a vacuum lock. The high
pressure Permeation Cell is closed with a rotating breech-
lock and sealed by a helium gas actuated diaphragm. After
filling and cooling of targets, excess DT is removed from
the Permeation Cell by evacuating it through the inlet line.
The FTS also contains a precision remote manipulator
(Fig. 3) that removes individual filled (cryogenic) targets
from the target rack and places them onto the moving
cryostat (Fig. 4, as described below). The outermost line in
Fig. 3 indicates the limits of the Glovebox containing the
FTS.
6. MOVING CRYOSTAT
The moving cryostat (MC), and its support system, the
moving cryostat transport cart (MCTC, Fig. 5), attaches to
the lower FTS port (shown outside of the Glovebox in
Fig. 3). The vacuum isolation gate valves are then opened
and the MCTC and FTS inner vacuums are connected. An
internal lift system is used to raise the MC from its
transport position in the MCTC to the interior of the FTS.
The MC thermal shroud is removed by a manipulator
inside the FTS dome. The Target Manipulator then
removes a single filled, cryogenic target from the target
rack and places it into the MC, followed by replacement of
the thermal shroud. The MC is then lowered back into the
Target Manipulator
MC/MCTC
Port
Glovebox
Boundary
Fig. 3. Side view of FTS showing target manipulator.
MCTC, detached from the FTS, and transported to the area
under the Target Chamber (La Cave). The MCTC, which
weighs approximately 4000 lbs, is supported by four air
casters during its journey to La Cave. Power and air are
supplied via umbilicals from the building facilities.
In the MC thermal shroud, the filled cryogenic target is
located within a highly isothermal layering sphere at
~18 K. In this isothermal environment, heat energy from
the beta decay of the tritium results in a redistribution of
the DT into a uniform layer on the inner surface of the
shell.
After layering, the target is characterized by a convergent
beam interferometer through windows in the thermal
Fig. 4. Moving cryostat schematic view (~48 in. Tall).
4 GENERAL ATOMICS REPORT GA-A22714
Umbilical
Spooler
52"
Instrumentation
16" Gate
Value
Aircaster
(Typ. of 4)
46"
16" Gate
Value
Moving
Cryostat
Elevator
Rail
Aircaster
(Typ. of 4)
Umbilical
Spooler
Fig. 5. Moving cryostat transport cart (MCTC).
shrouds, and the MCTC is attached to the Lower Pylon.
The MC is pushed with a rigid chain approximately 20 ft.
to tank center where it is lacked into place. Sighting
through the windows, positioning signals are provided to
place the target at the shot position (+ 5 µm) using fine
positioning motors in the MC. A final check of the target
layer is performed at tank center.
7. SHROUD PULLER
Immediately before the shot, the Shroud Puller is used to
remove the Moving Cryostat thermal shroud, exposing the
cryogenic target to the chamber for the laser shot. The
shroud must be removed fast enough to prevent thermal
degradation of the target prior to the shot. A linear motor
is utilized to achieve the accelerations needed. The Upper
Pylon is independently supported in order to decouple the
shroud retraction force from the target chamber. After the
shroud is removed, a target existence detection system is
used to verify that the target remains in position. This
precludes damage to the optics which would occur if the
shot were to take place with no target.
8. CONCLUSIONS
Based on testing with the prototype equipment, the
cryogenic target process and equipment have changed
significantly from the original conceptual design [2,3].
Equipment has been relocated into one tritium laboratory,
the number of process steps has been reduced by process
simplification, and the equipment has been optimized for
ease of maintenance and from an operational and human
factors viewpoint.
The DT Fill and Transfer functions are now located in one
Glovebox in the tritium laboratory, keeping all major
tritium inventories in one work area. An entire transfer
cryostat system has been eliminated by combining the
functions of previously separate subsystems into one
cryostat (the FTS). The FTS was redesigned based on a
similar cryostat in use at Los Alamos National Laboratory.
The one piece dome simplifies the maintenance operations
greatly, and eliminates the need for indium (cryogenic)
seals. High pressure cryovalves have been replaced with
one room temperature valve, reducing the penetrations
into the vessel and simplifying maintenance. The high
pressure DT cell has been simplified, using an integral
actuator that eliminates a separate cryogenic wrench, and
reduces the operational steps significantly.
Overall, these changes have resulted in a streamlined
process that will decrease cycle times and reduce
operational costs. The final design is nearing completion
and construction is underway for completion of
installation of the OCTS at UR/LLE in FY99.
REFERENCES
[1] J.D. Lindl, et al., Physics Today 45 33 (1992).
[2] D.T. Goodin, et al., “Testing of the cryogenic target
handling system for the OMEGA laser,” Proc. 19th
Symposium on Fusion Technology, Lisbon Portugal,
(1996).
[3] R.L. Fagaly, et al., “High pressure fill system for the
OMEGA Upgrade ICF laser,” Proc. 5th Topical
Meeting on Tritium Technology in Fission Fusion,
and Isotopic Applications, Lake Maggiore, Italy,
(1995).
[4] R.L. Fagaly, et al., Proc. 10th Target Fabrication
Specialists Meeting, Taos, New Mexico, Department
of Energy Doc. No. LA-UR-95-2938 (1995) 223.
[5] J.K. Hoffer, et al., “Forming a ‘perfectly’ uniform
shell of solid DT fusion fuel by the beta layering
process,” Proc. 14th International Conference on
Plasma Physics and Controlled Nuclear Fusion,
Würzburg, Germany, September 1992.
