The Dark Energy Survey CCD Vessel Design

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The Dark Energy Survey CCD Vessel Design H.
Cease, G. Derylo, R.L. Schmitt, A. Stefanik
(FNAL) V. Guarino (ANL), V. Simaitis (UIUC)
The Dark Energy Survey is planning to use a 3 sq.
deg. camera that houses an 0.5m diameter focal
plane of 62 2kx4k CCDs and 8 2k x 2k focus,
alignment and guide CCDs . The CCD vessel
including the optical window cell, focal plate,
focal plate mounts, cooling system and thermal
controls is described. As part of the development
of the mechanical and cooling design, a full
scale prototype vessel has been constructed and
is being commissioned for multi-CCD readout
tests. Results from this prototype multi-CCD
vessel are also described.
Focal Plane Assembly
Support Ring Mount G-10 Electrical Isolation
12 Copper Braids for Cooling
CCD Packaging (see poster by Tom Diehl)
Bipod Support Ring
Focal Plate Supports Ti 6Al-4V Bipods
CCDs on the Focal Plane 62 2kx4k Image CCDs 8
2kxk2 CCDs for guiding, focus and
lateral alignment
Focal Plate Bipod Mount
Focal Plate Material Aluminum Tooling Plate 35 mm
x 525 mm diameter
CCD Vessel and Thermal Model
Multi-CCD Test Vessel Prototype Vessel
Dewar Window FEA
Focal Plate Assembly FEA
20 C, Bipod Support Ring
Blue -97.7 C
Next Steps Readout multiple CCDs and Measure
Focal Plate Flatness Cold
All cold fingers set to -100 C At back of focal
plate
Red -98.5 C
C5 Lens Temperature gradients Red 20 C and
Blue -8 C
Displacements about 13 microns.
Temps on front of focal plate
Focal Plate Flat within 4 microns
Von Mises Stresses Lens center 1.6 MPa.
Under the O-rings 3 MPa. Fused Silica Yield
Strength of is 48 MPa. A safety factor of 10 is
required
VIB
Window Blank
Schematic Plumbing Route
Multi-CCD Vessel with one 2Kx4K mock device
LN2 Reservoir and Pump
Prime Focus Imager and Corrector
Instrument Control Crates
Vacuum Interface Board Electronic Readout Feed
Thru
Electronic Readout Crates
LN2 Cooling System Tube Heat Exchanger to copper
block with copper spreader bars 120 Watt, Dewar
Total Thermal Load
CCD Array
Vacuum Components On back of vessel
Corrector Assembly
5th Lens and Dewar Window
Dewar Window