1. SWCam Project Status
October 3, 2012
Gordon Stacey 1

2. Instrument Development Plan
Call made from the CCAT Project Office for proposals to design first light instruments for CCAT in the fall of 2011.
Proposals due on February 17, 2012
The idea is to bring designs up to the level appropriate for a preliminary design review by July of 2013
Subject to approval, instruments must be ready for a late 2017 deployment.
Total study period budget was targeted at ~ $1.3 million.
30 April 2012
CCAT Board Meeting – Toronto, Canada

3. Evolution of Development Plan
Four Proposals submitted to the Project Office
SWCam – short wavelength camera
LWCam – long wavelength camera
X-Spec – direct detection spectrometer
CHAI – heterodyne spectrometer
Plan was to down-select from these to fit within the tight instrument development budget.
Recommendations of the Project Office were presented to the CCAT Board in April 2012
After much conversation, it was decided to accept all four proposals
Deemed too early for down-select
Budget cap raised, but requests were made for trimmings
Actual development cycle had been reduced from 18 months to about 15
Thought process for final selection includes down-select made at PDR, with likely assignment of “first light” and “second light status”
30 April 2012
CCAT Board Meeting – Toronto, Canada

4. CCAT Board Meeting – Toronto, Canada
SWCam: As Proposed
Primary Observing bands:
350 μm, 450 μm and possibly 200 μm
7 sub-arrays, each sub-array 88x88 pixels
Pixel size base-lined at 1 mm at f/#-2.86
 pix = /D at 350 m
 each sub-camera captures a 4.4’4.4’ (square) FoV
Total 54,208 pixels
Total equivalent FoV = 13.1’ diameter
Technology: MKID arrays, with TES backup
30 April 2012
CCAT Board Meeting – Toronto, Canada

5. SWCam Optical Layout Focal plane split into sub-cameras:
Keeps off-axis aberrations acceptable
Minimizes issues with windows/fore-optics
Opens up real estate for focal planes
“Solves” field curvature problem

6. SWCam Optical Layout Seven sub-cameras, each with 7744 pixels
Seven sets of optics – silicon baseline with HDPE backup
Six identical, with central exception
Closed cycle refrigerators

7. SWCam Detectors Microwave kinetic inductance detectors (MKIDS)
TiN based absorber- resonator
Lab demonstration at 200 um with low background
“MAKO” demonstration camera to deployed on the CSO in late 2012
Backup Technology is TES-based bolometers.

8. Evolution Over the Summer
Going in premise:
We wish to build an observatory that is very versatile.
The science cases often involve observations with more than one instrument.
With a 1 FoV, we can envision simultaneous operation of two instuments, e.g. SWCam and LWCam
Fig. 3. Simulated 4 hour exposures using ATACamera on SPT at 350 (left) and 850 (right) m. The 5 circled sources are > 5  detections at 850 m that are not detected at 350 m – these are the high redshift galaxies that we seek. There are m drop-outs in the image.

9. CCAT Image Plane Field of View is 2.8 m in diameter
Focal plane is very curved
SWCam
LWCam

10. First Step: Detailed Optical Modeling
We had picked an f/# = pixel size plate scale to:
Be on the sweet spot with point source detection limit ~ 0.8 to 1.6 f/#
Compromise between mapping speed (which asks for a larger pixel size) and beam size (which asks for a limits pixel size)
Also, larger pixel scale makes it easier to be background limited.
Pixel size in units of f/#

11. Off-Axis Performance for SWCam
Focused on even Meniscus/Plano-Convex configuration as proposal with even aspheric surfaces
Tried tilting and displacing lenses
Found good performance for ~ 0.07 to 0.08 (96 pixel radius) circular FoV cameras both on-axis, and 0.08off-axis
However , a 0.16 off-axis camera has a restricted FoV ~ 0.04
Can be improved by tilting focal plane and adding a third lens

12. Radial Spot Diagrams: Center Camera
Circle has diameter of first null of Airy pattern

13. Radial Spot Diagrams: 0.08  off-Axis Camera
Circle has diameter of first null of Airy pattern

14. Radial Spot Diagrams: 0.16  off-Axis Camera
Circle has diameter of first null of Airy pattern

15. Ensquared Energy: on-Axis Camera –Radial Cut

16. Ensquared Energy: 0.08 deg. Off-Axis Camera

17. Ensquared Energy: 0.16 deg. Off-Axis Camera

18. On-Axis Camera might grow to 0.038 FoV
0.08 off-axis Camera barely works for 0.07 FoV
0.16 Off-Axis Camera restricted to 0.04 FoV

19. The Crux SWCam can be made to perform off-axis, but:
Will need tilted focal planes and 3 lens system
Every camera will need to be different
We HAVE to have any 200 um module on-axis
LWCam needs to have telecentric optics due to antenna coupled MKIDs
Means arrays cannot be tilted, so that despite the longer wavelengths, they are not much more forgiving to off-axis optics

20. Solutions Make both instruments suffer
Switch between SWCam and LWCam using tertiary
But… this means non-simultaneous observing
Logjam broken by realizing that simultaneous observing doesn’t buy much
Time to confusion vastly different  only ~ 10% loss in efficiency due to non-simultaneity
But, must tilt dewars significantly

21. CCAT Board Meeting – Toronto, Canada
30 April 2012
CCAT Board Meeting – Toronto, Canada

22. CCAT Board Meeting – Toronto, Canada
30 April 2012
CCAT Board Meeting – Toronto, Canada

23. CCAT Board Meeting – Toronto, Canada
30 April 2012
CCAT Board Meeting – Toronto, Canada

24. CCAT Board Meeting – Toronto, Canada
30 April 2012
CCAT Board Meeting – Toronto, Canada

25. New Dewar Parameters At Nasmyth focus, plate scale is 2.78 m/
A 0.08 radius f.o.v. then corresponds to a lens diameter of cm – make 25 cm
Minimum clearance between lenses =2.5 cm
3 lenses on a line means 3*25+5 = 80 cm
10 cm for shields means 100 cm.

26. New Camera Parameters A 0.08 = 288”radius  to 96 pixel radius
Total pixel count/camera = 7235 if circular array
Total for 7 cameras = 5064
Practicalities: Arrays being developed are 27  16 = 432 pixels on 1 mm pitch.
18 arrays per camera fill a nearly circular FoV with 7776 pixels each, or 5443 totol

27. 288” FoV

28. Near Term Work Finalize optics: Joe Adams 3-6 weeks
Finalize dewar design: Steve Parshley
Detector progress: Darren Dowell
Lens A/R coating: Mike Niemack/Jason Glenn/German Cortes
Software including data acquisition and reduction
Readout electronics: Ganesh Rajagopalan