The Ohio State University College of Mathematical & Physical Sciences Department of Astronomy

Attendees: Bruce Atwood, Tom O'Brien, Mark Derwent, Ross Zhelem, Jerry Mason, Ray Gonzalez, Andy Gould, Jason Eastman, Dan Pappalardo, & Rick Pogge.

MODS Optics

SOML is working on the red corrector lens spherical side, we should learn more at the end of the week.

The Blue mirrors (2 camera primaries and 2 collimators) arrived safely from Newport Thin Films Lab last Friday. These were given enhanced Aluminum coatings. Ross and Tom inspected them and they all look pretty good except for a few minor issues:

• The packaging left much to be desired. The mirrors were wrapped in paper that touched the corners of the coated surfaces, and the way they were packed allowed them to move during shipping, abrading the coatings at the contact points on the corners.
• On one mirror a fold of paper was against the coated surface which abraded a spot about 80mm from one edge.
• All optics under very bright illumination clearly show small but barely noticable scratches that appear to be artifacts of their mechanical cleaning process.

The blue corrector lens was mounted in its cell last Friday, but still has its protective film coating pending final mounting of the lens+cell on the MODS1 blue camera. There was a small delay while they reconciled a small disparity between the optical prescription and the camera model. The consequences are small and they're ready to go with camera assembly. Some rework of the dewar brackets is required, with minor impact on the location of the detector boxes, but all of it is straightforward.

The To-Do list for blue camera optics integration:

1. Re-assemble the camera and mount the lens (later this week)
2. Rough alignment of the camera using the laser chief-ray technique.
3. Fine alignment using the CCD and field lens.

MODS Enclosure

Dave Steinbrecher has been working on assembling the phase-2 enclosure model. The hexagon has been reassembled except for corner reinforcement brackets from Indian Creek. The system is ready to start receiving the 6 side panels and being setup into its working configuration for the remaining tests. About 1-2 weeks of work remain. Some rework has been done on the interface brackets to the mounting spheres, mostly to resolve some interference with the collimator tubes.

MODS Mechanisms

Mark and Ray got the first of the camera filter wheels online with the 4-axis and single-axis boxes and have it working with the MicroLYNX microcode. About 2 days of filter wheel work remain, then it is ready to go.

MODS Detectors

No news from Mike Lesser yet on the MODS 4K first-light devices, and Bruce has not yet had a chance to get the MDM4K camera back online yet. The MDM4K CCD is back in its detector mount, but not yet returned to the dewar. The first task ahead is to get that system back online in the student lab (Rick and Jason are tasked with identifying and clearing a table at the north end of the lab to do this).

E2V technologies continues to make progress on the 3x8K devices. A mechanical sample using invar instead of SiC will be sent. They have asked if we are willing to wait about 1 week for this to be given wirebonds, which we need. They've made the first set of wafers and have some rework to do on the metallization. The mechanical sample looks to be on schedule for delivery in early April (~7 weeks).

Phil Covington has received the boards he needs to run the old CCD system with the new digital electronics, should be up and running by month's end.

In the meantime, Bruce's other task is to setup to perform thermal tests on the detector boxes with the black dewar and a temperature sensor package in the mount. One of the old scratched field flatteners will be used in those tests. Should take most of March and part of April to complete.

MODS Electronics

Dan gave a brief presentation on where the outputs for the IMCS quad cells should go. It was prompted by a question from Bruce. I'm going to skip some details and summarize the basic points.

Dan started with "Plan A", what we used in the IMCS testing last year, namely the analog outputs from the quad cell go into WAGO A/D boards in the instrument electronics boxes (IEBs) where they can be commanded to digitize the signals for analysis and subsequent collimator tip/tilt correction by the IMCS software. A downside of this is that it means there will be an electrical path from the IEBs to the detector head electroncis boxes (HEBs), since in operation the quad cell is mounted in the dewar with the CCD detector. This has the considerable potential of causing noise problems in the CCD.

Two other plans ("B" and "C") that Dan presented would be to embed a WAGO fieldbus unit and ADC modules in the HEB proper, which has a number of downsides for packaging, power, etc. that make them non-starters.

"Plan D" would be to construct a custom 4-channel ADC board for the HEB, so it shares the HEB ground plane, and then run an isolated digital I/O line into the WAGO fieldbus controller in the IEB for the quadcell interface. A digital I/O line is already run from the HEB to IEB for shutter control on each channel, so this is not that different of a connection than we already have. The IMCS software would query the ADCs in the HEB via the WAGO digital I/O. Bruce suggested an amendment to Plan D whereby the design of the ADC board should be such that you could operate it temporarily from a separate enclosure while the HEB is being constructed or serviced, mitigating the problem of the IMCS testing being dependent on a working HEB early in the integration process.

The thinking at the end of Dan's very nice presentation was to to proceed with Plan A at least for the early part of integration (we have all the parts in hand), but for Dan, Bruce, and Ray to examine a way to implement Plan D, including cost and effort estimates and report back. While it adds an extra step, controlling the noise in the CCDs in this very sensitive instrument is critical to its scientific performance.