The Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square
degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be
used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. All components of
DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A
summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and
commissioning will be presented.
The Dark Energy Camera and its cooling system has been shipped to Cerro Tololo Inter-American Observatory in Chile
for installation onto the Blanco 4m telescope. Along with the camera, the cooling system has been installed in the Coudé
room at the Blanco Telescope. Final installation of the cooling system and operations on the telescope is planned for the
middle of 2012. Initial commissioning experiences and cooling system performance is described.
The DES project is a 5 year imaging survey of the southern sky using the 4m Blanco Telescope at the Cerro Tololo
International Observatory in Chile. A new wide field camera with a 2.2 degree diameter field of view has been built to
undertake this survey. The alignment of the large lenses for this camera poses a significant challenge as they have to be
aligned to a tolerance of ±50 micrometers. This paper presents the assembly and alignment process of the full optical system along with the test results. Also included is the predicted imaging performance from the as-built system.
The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO. This
instrument is a 3 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k CCDs
and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. The DECam CCD array is
inside the imager vessel. The focal plate is cooled using a closed loop liquid nitrogen system. As part of the development
of the mechanical and cooling design, a full scale prototype imager vessel has been constructed and is now being used
for Multi-CCD readout tests. The cryogenic cooling system and thermal controls are described along with cooling
results from the prototype camera. The cooling system layout on the Blanco telescope in Chile is described.
The Dark Energy Camera (DECam) is the new wide field prime-focus imager for the Blanco 4m telescope at CTIO.
This instrument is a 2.2 sq. deg. camera with a 45 cm diameter focal plane consisting of 62 2k × 4k CCDs and 12 2k × 2k
CCDs and was developed for the Dark Energy Survey that will start operations at CTIO in 2011. DECam includes the
vessel shell, the optical window cell, the CCDs with their readout electronics and vacuum interface, the focal plane
support plate and its mounts, and the cooling system and thermal controls. Assembly of the imager, alignment of the
focal plane and installation of the CCDs are described. During DECam development a full scale prototype was used for
multi-CCD readout tests. This test vessel went through several stages as the CCDs and related hardware progressed
from early prototypes to final production designs.
The Dark Energy Survey Camera (DECam) will be comprised of a mosaic of 74 charge-coupled devices (CCDs). The
Dark Energy Survey (DES) science goals set stringent technical requirements for the CCDs. The CCDs are provided by
LBNL with valuable cold probe data at 233 K, providing an indication of which CCDs are more likely to pass. After
comprehensive testing at 173 K, about half of these qualify as science grade. Testing this large number of CCDs to
determine which best meet the DES requirements is a very time-consuming task. We have developed a multistage
testing program to automatically collect and analyze CCD test data. The test results are reviewed to select those CCDs
that best meet the technical specifications for charge transfer efficiency, linearity, full well capacity, quantum efficiency,
noise, dark current, cross talk, diffusion, and cosmetics.
Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely
red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty
two 4k2k and twelve 2k2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and
a eld of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will
cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from
To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down
for the design of DECam. Among them, the
atness of the focal plane needs to be controlled within a 60-micron
envelope in order to achieve the specied PSF variation limit. It is very challenging to measure the
the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image
based techniques to measure the
atness of the focal plane. By imaging a regular grid of dots on the focal plane,
the CCD oset along the optical axis is converted to the variation the grid spacings at dierent positions on the
focal plane. After extracting the patterns and comparing the change in spacings, we can measure the
to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal
plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the
pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by dierent
CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are
in good agreement with the direct optical measurements.
The Dark Energy Camera is a new prime-focus instrument to be delivered to the Blanco 4-meter telescope at the Cerro
Tololo Inter-American Observatory (CTIO) in 2011. Construction is in-progress at this time at Fermilab. In order to
verify that the camera meets technical specifications for the Dark Energy Survey and to reduce the time required to
commission the instrument while it is on the telescope, we are constructing a "Telescope Simulator" and performing full
system testing prior to shipping to CTIO. This presentation will describe the Telescope Simulator and how we use it to
verify some of the technical specifications.
The Dark Energy Camera is an wide field imager currently
under construction for the Dark Energy Survey.
This instrument will use fully depleted 250 μm thick
CCD detectors selected for their higher quantum efficiency
in the near infrared with respect to thinner devices.
The detectors were developed by LBNL using
high resistivity Si substrate. The full set of scientific
detectors needed for DECam has now been fabricated,
packaged and tested. We present here the results of
the testing and characterization for these devices and
compare these results with the technical requirements
for the Dark Energy Survey.
The Dark Energy Survey Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 520
Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to
perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. Construction of
DECam is well underway. Integration and testing of the major system components has already begun at Fermilab and
the collaborating institutions.
The Dark Energy Survey (DES) will produce high quality images covering over 5000 square degrees of the sky,
with precise photometric redshifts between z = 0.2 to z = 1.3, using g, r, i, z and Y filters. The Dark Energy
Camera (DECam), under construction for this survey, consists of wide field corrector optics and a CCD detector
array that will give a 2.2 square degree field of view. It will be placed at the prime focus of the Blanco 4-meter
telescope at the Cerro Tololo Inter-American Observatory in Chile. The Optical Science Laboratory (OSL) at
University College London (UCL) is undertaking the alignment of the five lenses in the imaging system. These
lenses range in diameter from 0.60 - 0.98 meters. The lenses must be held within tight tolerance limits in order
to meet the DES science requirements. The tolerances are especially driven by the accuracy in the measurement
of the weak lensing signal. This paper details the design for the cells that will hold the lenses and the alignment
procedure for the mounting of the lenses and cells. Also presented is the expected static shear distortion pattern
that will be generated and the impact of this pattern on the weak lensing signal measurement.
DECam is a 520 Mpix, 3 square-deg FOV imager being built for the Blanco 4m Telescope at CTIO. This facility
instrument will be used for the "Dark Energy Survey" of the southern galactic cap. DECam has chosen 250 μm thick
CCDs, developed at LBNL, with good QE in the near IR for the focal plane. In this work we present the characterization
of these detectors done by the DES team, and compare it to the DECam technical requirements. The results demonstrate
that the detectors satisfy the needs for instrument.
We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey.
DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo
International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector,
five filters (g,r,i,z,Y), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of
62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of
view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley
National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms,
and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.
DECam, camera for the Dark Energy Survey (DES), is undergoing general design and component testing.
For an overview see DePoy, et al in these proceedings. For a description of the imager, see Cease, et al in
these proceedings. The CCD instrument will be mounted at the prime focus of the CTIO Blanco 4m
telescope. The instrument temperature will be 173K with a heat load of 113W. In similar applications,
cooling CCD instruments at the prime focus has been accomplished by three general methods. Liquid
nitrogen reservoirs have been constructed to operate in any orientation, pulse tube cryocoolers have been used
when tilt angles are limited and Joule-Thompson or Stirling cryocoolers have been used with smaller heat
loads. Gifford-MacMahon cooling has been used at the Cassegrain but not at the prime focus. For DES, the
combined requirements of high heat load, temperature stability, low vibration, operation in any orientation,
liquid nitrogen cost and limited space available led to the design of a pumped, closed loop, circulating
nitrogen system. At zenith the instrument will be twelve meters above the pump/cryocooler station. This
cooling system expected to have a 10,000 hour maintenance interval. This paper will describe the
engineering basis including the thermal model, unbalanced forces, cooldown time, the single and two-phase
The Dark Energy Survey is planning to use a 3 sq. deg. camera that houses a ~ 0.5m diameter focal plane of 62 2k×4k
CCDs. The camera 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 camera
vessel has been constructed and is now being used for multi-CCD readout tests. Results from this prototype camera are
The DECam instrument, for the 4m Blanco telescope at CTIO, is a 5 lens element wide field camera giving a 2.2 degree
diameter field of view. The lenses are large, with the biggest being 980mm in diameter, and this poses challenges in
mounting and alignment. This paper reports the status of the production of the optics for the DECam wide field imager
Also presented are the design and finite element modelling of the cell design for the 5 lenses of the imager along with the
proposed alignment process.
A description of the plans and infrastructure developed for CCD testing and characterization for the DES focal plane detectors is presented. Examples of the results obtained are shown and discussed in the context of the device requirements for the survey instrument.
The CTIO V. M. Blanco 4-m telescope is to be the host facility for the Dark Energy Survey (DES), a large area optical
survey intended to measure the dark energy equation of state parameter, w, to a precision of ˜ 5%. The survey is
expected to take 5 years and use a new 520 megapixel CCD prime focus imaging system: the Dark Energy Camera
(DECam). In preparation for the arrival of DECam, we plan numerous upgrades to the telescope, including a new
telescope control system optimized for programmed and queued survey observations, modifications to the telescope
itself to improve reliability and performance, extended real-time telemetry of site and facility characteristics, and a
distributed observer interface allowing for on- and off-site observations and real time quality control. These upgrades
are specifically motivated by the scientific goals of the DES but will also improve community use of the telescope.