G. Derylo

Focal plane detectors for Dark Energy Camera (DECam)

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.

0.250mm-thick CCD packaging for the Dark Energy Survey Camera array

The Dark Energy Survey Camera focal plane array will consist of 62 2k x 4k CCDs with a pixel size of 15 microns and a silicon thickness of 250 microns for use at wavelengths between 400 and 1000 nm. Bare CCD die will be received from the Lawrence Berkeley National Laboratory (LBNL). At the Fermi National Accelerator Laboratory, the bare die will be packaged into a custom back-side-illuminated module design. Cold probe data from LBNL will be used to select the CCDs to be packaged. The module design utilizes an aluminum nitride readout board and spacer and an Invar foot. A module flatness of 3 microns over small (1 sqcm) areas and less than 10 microns over neighboring areas on a CCD are required for uniform images over the focal plane. A confocal chromatic inspection system is being developed to precisely measure flatness over a grid up to 300 x 300 mm. This system will be utilized to inspect not only room-temperature modules, but also cold individual modules and partial arrays through flat dewar windows.

CCD testing and characterization for Dark Energy Survey

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.

Cooling the Dark Energy Camera CCD array using a closed-loop, two-phase liquid nitrogen 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 Survey CCD imager design

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 described.

Automated characterization of CCD detectors for DECam

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.

Commissioning and Initial Performance of the Dark Energy Camera Liquid Nitrogen Cooling System

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.

DECam Integration Tests on Telescope Simulator

Abstract The Dark Energy Survey (DES) is a next generation optical survey aimed at measuring the expansion history of the universe using four probes: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the survey, the DES Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera which will be mounted at the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory. DES will survey 5000 square degrees of the southern galactic cap in 5 filters (g, r, i, z, Y). DECam will be comprised of 74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. Construction of DECam is nearing completion. In order to verify that the camera meets technical specifications for DES and to reduce the time required to commission the instrument, we have constructed a full sized telescope simulator and performed full system testing and integration prior to shipping. To complete this comprehensive test phase we have simulated a DES observing run in which we have collected 4 nights worth of data. We report on the results of these unique tests performed for the DECam and its impact on the experiments progress.

Surface cleaning of CCD imagers using an electrostatic dissipative formulation of first contact polymer

We describe the results obtained cleaning the surface of DECam CCD detectors with a new electrostatic dissipative formulation of First ContactTM polymer from Photonic Cleaning Technologies. We demonstrate that cleaning with this new product is possible without ESD damage to the sensors and without degradation of the antireflective coating used to optimize the optical performance of the detector. We show that First ContactTM is more effective for cleaning a CCD than the commonly used acetone swab.