HETDEX VIRUS

Overview

The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) instrument is being built at Texas A&M University in collaboration with University of Texas–Austin. VIRUS is the instrument that enables observations for the Hobby-Eberly Telescope Dark Energy Experiment HETDEX project, an experiment designed to learn more about Dark Energy–a mysterious force in our Universe that astronomers are only now beginning to be able to describe.

Virus Telescope
Figure 1: The Hobby-Eberly Telescope with up to 192 spectrographs.

The VIRUS instrument consists of up to 192 identical fiber-fed integral field optical spectrographs. VIRUS provides a unique challenge in astronomical instrumentation: each of the 192 instruments must be identical and each component must be interchangeable amongst every other spectrograph in order to ease assembly and maintenance of the instrument. The spectrographs will be assembled production-line-stye, and will be optically aligned and tested at Texas A&M before being shipped to McDonald Observatory to be installed on the Hobby-Eberly Telescope.

Virus Spectrograph
Figure 2: Section-view drawing of a pair of VIRUS spectrographs. The fiber head is shown on the right. Light from the fibers enters the instrument and is collimated by the oblong spherical collimator mirrors (upper center left). The light is reflected by a folding flat located around the fiber feed (center right), and into the grating (lower center left) which is mounted in front of the vacuum Schmidt cameras (left).
Virus IFU
Figure 3: Picture of an IFU input head assembly in a preliminary plug plate using the first nine fiber bundles, featuring some 4000 individual fibers, which will feed 18 VIRUS-spectrographs.
Virus Spectrograph
VIRUS Staff in Summer 2011 with a partially assembled spectrograph.

This material is based upon work supported by the National Science Foundation under Grant Number 0928636. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

For more information about VIRUS, please see our Publications section.

VIRUS Collimators

The Visual Integral-Field Replicable Unit Spectrograph (VIRUS) instrument is a baseline array of 150 identical fiber fed optical spectrographs designed to support observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). 130 VIRUS collimator sub-assemblies have been assembled in a production line and are now complete. Here we review the design choices and assembly practices used to produce a suite of identical low-cost spectrographs in a timely fashion using primarily unskilled labor.

Virus Telescope
The VIRUS spectrograph pairs will be mounted inside two climate-controlled enclosures located on either side of the telescope.
Section-view drawing of a pair of VIRUS spectrographs.
One complete collimator with all optics installed. Additional completed collimators (with their protective covers installed) may be seen in the background.
Installation fixture used to install the folding flat into the head plate. Two pairs of mirrors are installed into two head plates in one setup. The fold mirrors are precisely positioned with respect to the head plates using a Faro coordinate measuring machine (CMM) arm having a measurement accuracy of ~25 microns and are held in place with metal shims while RTV is applied around the edges of the mirror.
Collimator mirrors are installed in the instrument using an Invar mounting puck that is bonded to the back of the mirror. The puck is precisely located with respect to the edges of the mirror using an alignment fixture.


VPH gratings are optically aligned in their cell during installation using a laser (left). Internal baffles of the grating housings are installed using a fixture (right). The grating cell is later installed on top of the housing.




Collimator subassemblies were pre-assembled and stored before the final collimator assembly. Shown here are the base plates (left) and side, top, and bottom plates (right). Each of these components has multiple alignment and attachment features to facilitate the final assembly. Collimator mounting plates with attached Invar metering rods can be seen on the top rack of the carts.


In the end, the final mating of collimator subassemblies into a complete collimator unit was accomplished relatively quickly, with the final thirty pairs of collimators being assembled in just over two weeks in December 2013. The record assembly time of fifteen minutes to complete one pair of collimators is shared by the team of Nagasawa and Li.


Once the final collimator assembly is complete no further optical alignment is required at this stage. The completed collimators are fitted with a plastic cover that remains with the collimators once installed on the telescope, protected from dust with plastic wrap, and finally packaged and shipped to UT-Austin for integration with the VIRUS cameras and final optical alignment.

VIRUS Enclosures

The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) instrument will be installed at the Hobby-Eberly Telescope in the near future. The instrument will be housed in two enclosures that are mounted adjacent to the telescope, via the VIRUS Support Structure (VSS). The enclosures have been designed to support and protect the instrument, to enable servicing of the instrument, and to cool the instrument appropriately while not adversely affecting the dome environment. The system uses simple HVAC air handling techniques in conjunction with thermoelectric and standard glycol heat exchangers to provide efficient heat removal. The enclosures also provide power and data transfer to and from each VIRUS unit, liquid nitrogen cooling to the detectors, and environmental monitoring of the instrument and dome environments.

  • A rendering of the HET with the VSS, enclosures, and IFUs.

  • The VSS and enclosures without HET for clarity.

  • The first VIRUS enclosure being stacked at Texas A&M University.

  • A model of the enclosure with the added annex.

  • A model of the enclosure mounting rails that will hold the VIRUS units.

  • The VIRUS unit will sit on the v-groove and angle iron.

  • Enclosure door design installed on the enclosure prototype to test the amount of pressure it can hold.

  • Seal selected for the enclosure door.

  • The thermoelectric cooler used in the enclosure HVAC system.

  • The VIRUS electronics box airflow adapter sitting on a mock electronics box.

  • The adapter on a production electronics box in the enclosure, attached to the flexible hosing and duct work.

Illustration of the two HVAC zones. The blue area on the right is for the enclosure which houses the VIRUS units, and the yellow area is for the enclosure annex which holds the VIRUS electronics equipment and enclosure cooling system.
Temperatures of the air inside and out of the closed loop test system. The bump in internal temperature starts when the 220W heat is activated.
Differential temperatures of the air inside and out of the closed loop test system. The bump in internal temperature starts when the 220W heat is activated. This shows that for the test loop, it was able to track the temperatures within 0.1°C.