The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the
Thirty Meter Telescope (TMT). It combines a diffraction limited imager and an
integral field spectrograph. This paper focuses on the electrical system of
IRIS. With an instrument of the size and complexity of IRIS we face several
electrical challenges. Many of the major controllers must be located directly
on the cryostat to reduce cable lengths, and others require multiple bulkheads
and must pass through a large cable wrap. Cooling and vibration due to the
rotation of the instrument are also major challenges. We will present our
selection of cables and connectors for both room temperature and cryogenic
environments, packaging in the various cabinets and enclosures, and techniques
for complex bulkheads including for large detectors at the cryostat wall

Chisholm, Eric

Dunn, Jennifer

Greffe, Timothee

Hardy, Tim

Johnson, Chris

Larkin, James

Magnone, Ken

Suzuki, Ryuji

Trapp, A. C.

English

arXiv

The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT). It combines a diffraction limited imager and an integral field spectrograph. This paper focuses on the electrical system of IRIS. With an instrument of the size and complexity of IRIS we face several electrical challenges. Many of the major controllers must be located directly on the cryostat to reduce cable lengths, and others require multiple bulkheads and must pass through a large cable wrap. Cooling and vibration due to the rotation of the instrument are also major challenges. We will present our selection of cables and connectors for both room temperature and cryogenic environments, packaging in the various cabinets and enclosures, and techniques for complex bulkheads including for large detectors at the cryostat wall.Peer reviewed: YesNRC publication: Ye

NRC Publications Archive

The infrared imaging spectrograph (IRIS) for TMT: electronics-cable architecture

The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT). It combines a diffraction limited imager and an integral field spectrograph. This paper focuses on the electrical system of IRIS. With an instrument of the size and complexity of IRIS we face several electrical challenges. Many of the major controllers must be located directly on the cryostat to reduce cable lengths, and others require multiple bulkheads and must pass through a large cable wrap. Cooling and vibration due to the rotation of the instrument are also major challenges. We will present our selection of cables and connectors for both room temperature and cryogenic environments, packaging in the various cabinets and enclosures, and techniques for complex bulkheads including for large detectors at the cryostat wall

Magnone, Kenneth

Caltech Authors - Main

PROCEEDINGS OF SPIE
SPIEDigitalLibrary.org/conference-proceedings-of-spie
The infrared imaging spectrograph
(IRIS) for TMT: electronics-cable
architecture
A. C. Trapp, James  Larkin, Ken  Magnone, Timothee
Greffe, Tim  Hardy, et al.
A. C. Trapp, James  Larkin, Ken  Magnone, Timothee  Greffe, Tim  Hardy,
Jennifer  Dunn, Eric  Chisholm, Chris  Johnson, Ryuji  Suzuki, "The infrared
imaging spectrograph (IRIS) for TMT: electronics-cable architecture," Proc.
SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII,
10702A1 (23 July 2018); doi: 10.1117/12.2313978
Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas,
United States
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The infrared imaging spectrograph (IRIS) for TMT:
electronics-cable architecture
A.C. Trappa, James Larkina, Ken Magnonea, Timothee Greffeb, Tim Hardyc, Jennifer Dunnc,
Eric Chisholmd, Chris Johnsona, and Ryuji Suzukie
aUCLA Department of Physics and Astronomy, 430 Portola Plaza, Los Angeles, CA, USA
bCaltech, 1216 E California Blvd, Pasadena, CA 91125
cNRC Herzberg Astronomy and Astrophysics Research Centre
dTMT, 100 West Walnut Street, Pasadena, CA, 91124
eNAOJ, Osawa, Mitaka, Tokyo, Japan
ABSTRACT
The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT).
It combines a diffraction limited imager and an integral field spectrograph. This paper focuses on the electrical
system of IRIS. With an instrument of the size and complexity of IRIS we face several electrical challenges.
Many of the major controllers must be located directly on the cryostat to reduce cable lengths, and others
require multiple bulkheads and must pass through a large cable wrap. Cooling and vibration due to the rotation
of the instrument are also major challenges. We will present our selection of cables and connectors for both room
temperature and cryogenic environments, packaging in the various cabinets and enclosures, and techniques for
complex bulkheads including for large detectors at the cryostat wall.
Keywords: ELT: TMT, TMT: IRIS, Cable Architecture, Electronics Diagrams, SPIE Proceedings
1. INTRODUCTION
The InfraRed Imaging Spectrograph (IRIS1) is a first-generation instrument for the Thirty Meter Telescope
(TMT2). A combination of the On-Instrument Wave Front Sensor (OIWFS3) and the TMT adaptive optics
system NFIRAOS4 will allow IRIS to reach the diffraction limit of TMT at wavelengths longer than 1 micron.
IRIS combines an imager and an integral field spectrograph operating between 0.8 to 2.5 microns. The imager is
composed of four 4K by 4K Teledyne detectors (Hawaii 4RG) with 4 mas pixels and a combined 34 x 34 arcsec2
field of view. The integral field spectrograph takes ∼ 10, 000 spectra simultaneously with spectral resolution
R ∼ 4000 to R ∼ 8000 on four spatial scales from 4 mas to 50 mas with fields of view of 0.46 x 0.51 arcsec2
to 2.2 x 4.6 arcsec2 respectively. The science applications of IRIS span from our own Solar System to the most
distant galaxies in the Universe.
IRIS is a large cryogenic cylinder 2 meters in diameter, 3.1 meters in height, with a total mounted mass of
∼ 5400 kg. It is suspended from underside of TMT’s adaptive optics system NFIRAOS. IRIS will spin about
its vertical axis to correct for field rotation. Most IRIS control electronics will be housed in a climate-controlled
cabinet (called the nasmyth cabinet) on a platform below IRIS. Cables exit the nasmyth cabinet and go through
a cable wrap, then up to a bulkhead attached to the underside of the cryostat. From there, the cables penetrate
IRIS via multiple bulkheads on the sides of the cryostat (see Fig. 1). Detector controllers are mounted on the
sides of the cryostat in CO2 gas cooled enclosures. In section 2, we discuss some of the architectural challenges of
IRIS with regards to the electronics system, section 3 briefly discusses the nasmyth cabinets as well as connectors
and cables we plan to use, and section 4 discusses some of the actions we plan to take in the near future.
2. ARCHITECTURAL CHALLENGES
A spinning, multi-ton object with over 50 cable attachments poses some design problems, many of which have
been solved for smaller or simpler instruments. Integrating these solutions and coming up with new ones for
such a large instrument is a challenge.
Ground-based and Airborne Instrumentation for Astronomy VII, edited by Christopher J. Evans, Luc Simard, Hideki Takami, 
Proc. of SPIE Vol. 10702, 10702A1 · © 2018 SPIE · CCC code: 0277-786X/18/$18 · doi: 10.1117/12.2313978
Proc. of SPIE Vol. 10702  10702A1-1
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Figure 1. IRIS is mounted to the underbelly of TMTs AO system NFIRAOS by the IRIS support structure. After exiting
NFIRAOS, light passes through the On Instrument Wave Front Sensor (OIWFS), which allows for tip-tilt, focus, and
plate scale corrections, and finally through a window into the science cryostat, which has both an imaging and integral
field spectrometer mode. The cable wrap sits below the cryostat on the nasmyth platform, and connects to the nasmyth
cabinets (not shown here). The current design also includes a bulkhead around the bottom rim of the cryostat (not shown
here) which acts as a cable break for easier installation of the instrument. Also not shown here are the detector control
boxes (see Fig. 2) which will be mounted on the sides of the cryostat.
2.1 Cryostat Rotation
The instrument remains vertical for all observations, but must rotate about the vertical axis to correct for field
rotation. Fig. 1 shows the limited space for the cable wrap and hoses. The cable wrap must be very complex and
efficient for two reasons: (i) The radii of curvature of many cables in the wrap are near the radius of the cable
wrap itself, and (ii) nearly all available space in the wrap will be filled due to the large number of cables. The
Figure 2. An example of an ARC box; similar enclosures will be attached to the side of the science cryostat and will
house detector control electronics.
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Næsrnyth
Cabinet
sE7
OIWFS
|
L
Cable
Wrap
Cryostat
Bulkhead
Rotator
Science Cryostat
Cold Shield SpectLeach
Controller
Imager
Imager
laZehr
Lneaagli
Controller
wrap must be designed to impart minimal torque on the cryostat, as precision rotation is required, and minimal
vibration can be conducted to the cryostat or AO system.
2.2 Cryostat-Mounted Controllers
Due to the long cable distance between the instrument cryostat and nasmyth cabinet, the Astronomical Research
Cameras (ARC5) controller system for the imager, spectrograph, and OIWFS must be placed directly on the
cryostat or OIWFS in their own cooled enclosures. Mounting control electronics directly to the cryostat also
reduces the amount of control cabling through the wrap, but at the same time, these boxes must be cooled via
insulated CO2 gas coolant lines that take up room in the wrap. Fig. 2 shows an image of the type of box to be
mounted to the side of the science cryostat. The science detectors are connected directly to the control boxes
via a ∼ 1 meter ribbon cable. The boxes will contain amplifiers and analog-to-digital converters, as well as bias
control, clocking, and other control electronics. This scheme is believed to slightly out-perform a cryogenic ASIC
in terms of noise, and the complicated read-out patterns planned for the detector will be easier to implement
with custom electronics.
Figure 3. A high-level schematic diagram of Fig. 1 showing the large number of cable connections required to control
IRIS, as well as their paths from the nasmyth cabinets to the cryostat, rotator, or OIWFS.
Proc. of SPIE Vol. 10702  10702A1-3
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ewe 99.
a -b-
Cabinet wall
-c-
Dewar bottom
n H
SOO. PM
Cable Leads: 25
Used Leads: 24
Gauge: 24
MIL Connector:
Shell -Model: 17 -26
Contacts#gauge: 26020
-d-
Dewar wall
[r
i 999P.
Cold shield
e f
Breakout Board
c
4
Slicer
Lb
Figure 4. The average cable goes through 5-6 cable breaks on its way from the electronics cabinet, through the cable
wrap, and into the science cryostat. Cables will be labeled for ease of organization and installation. For example, all
cables between the cryostat wall and cold shield will have “d” in their designation, cables going through the cable wrap
will have “b” in their designation, etc.
2.3 Cable Number/Length
Fig. 3 shows the large amount of cables (∼ 50) between the nasmyth cabinet and the cryostat/OIWFS. On top
of large numbers, the average cable goes through 5-6 cable breaks on its way (see Fig. 4), bringing the number
of individually fabricated cables to ∼ 300. The production and installation of this many long, heavy cables will
be a challenge; the connections at cable breaks must be simple to assemble and disassemble on-site, and must
be robust and repeatable. Simple steps like efficient naming schemes for cables will increase ease of organization
and installation.
3. HARDWARE
3.1 Nasmyth Cabinets
A large amount of control electronics are housed nearby the cryostat in three 19-inch rack cabinets, called nasmyth
cabinets; each will control one of the OIWFS, Imager, and Spectrograph. Each cabinet has its own temperature
monitor and glycol cooling unit for environment control. Fig. 5 shows the layout of various components in the
nasmyth cabinets. Sometimes a component will be racked by itself, like the “Spectrograph Lakeshore 336” in
the “Middle Cabinet”, and sometimes components will be grouped in a custom box and racked together, like
the “Rotary and Linear...Pressure Controller” in the “Middle Cabinet”. Fig 6 shows the architecture and type
of connections between the various components of the “Middle Cabinet” in Fig. 5.
3.2 Cables and Connectors
Military-style connectors are used in most non-cryogenic connections. They are durable enough to withstand the
torques of the cable wrap, and can be keyed such that erroneous connections are impossible. AirBorn connectors
are used for most cryogenic connections. They are simple to fabricate, and connect/disconnect easily; they also
maintain good connections when cooled to cryogenic temperatures.
Twisted/shielded pair cables will be used outside the cryostat. These cables provide shielding against EM
interference as well as a high level of customizability in numbers of wires and wire gauges. Inside the cryostat,
we will use constantan cables because of their performance at cryogenic temperatures.
4. FUTURE WORK
We must determine the exact lengths, cable types, and connector specifications for each cable. The design of the
CO2 gas coolant system is still preliminary. Coolant pipes typically place more stringent constraints on cable
architecture because of increased bend radius, diameter, and mass per meter.
Proc. of SPIE Vol. 10702  10702A1-4
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38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
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22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
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Left Cabinet Middle Cabinet Right Cabinet
[.1
CSRO Safety PLC - 4U
v a
+/ -12 VDC Power Supplies for ARC
Controllers - 3U
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-2U
24 VDC power Supply - 2U I
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Controllers -3U
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Rotary and Linear Motor Control
with Power Supplies + Imager
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Drivers - 3U
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8 8
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Terminal Server - 2U
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Digiport Terminal Server -2U Imager Target Computer -2U
Imager Target Computer -2U
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O Detector
9 9
Imager Target Computer -2U
CSRO Network Switch - 1U
IRIS Rack Computer - 2U
8 8
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13 Imager Network Switch - lU
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8
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Eaton IPC3402- NET -Pear Cont. - 1U
IRIS$ Eaton IPC3402- NET -Pwr Cont. - lU Eaton IPC3402- NET -Pwr Cont. - lU
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Lytron AS06- 16G01BD -
Cooling Unit -3U
á Et i
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Lytron AS06- 16GO1BD -
Cooling Unit - 3U
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Lytron AS06- 16GO1BD -
Cooling Unit - 3U
e e
ACKNOWLEDGMENTS
The TMT Project gratefully acknowledges the support of the TMT collaborating institutions. They are the
California Institute of Technology, the University of California, the National Astronomical Observatory of Japan,
the National Astronomical Observatories of China and their consortium partners, the Department of Science and
Technology of India and their supported institutes, and the National Research Council of Canada. This work
was supported as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation, the
Ontario Ministry of Research and Innovation, the Natural Sciences and Engineering Research Council of Canada,
the British Columbia Knowledge Development Fund, the Association of Canadian Universities for Research in
Figure 5. The layout for the electrical control components in the nasmyth cabinets located on the nasmyth platform (the
same platform the cable wrap is located on; see Fig. 1). There will be three cabinets, one devoted to each of the OIWFS,
the spectrograph, and the imager. Sometimes a component will be racked by itself, like the “Spectrograph Lakeshore
336” in the “Middle Cabinet”, and sometimes components will be grouped in a custom box and racked together, like the
“Rotary and Linear...Pressure Controller” in the “Middle Cabinet”. Yellow items are OIWFS, cable wrap, and rotator
components; orange are spectrograph components; blue are imager components; and green are cabinet environment
control, power, and communication.
Proc. of SPIE Vol. 10702  10702A1-5
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Spectro
Network
Switch
EtheEnet Input
Rack Computer
Ethernet Input ;
1=2 34
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7
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Glycol Cooling
Unit
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-7 Ethernet Input 2
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Switches: Lenslet mask slide, Grating turret
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Spect Detector Heater
Spect Detector Control Sensors
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Output
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Power
Temperature Sensing and Heaters
Ethemet
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Fiber Optic
Misc. Power and Control
Glycol
Spect Leach Power
Figure 6. The architecture and type of connections between the various components of the “Middle Cabinet” in Fig. 5.
Orange components are science cryostat control electronics, and green are cabinet environment control, power, and
communication.
Astronomy (ACURA), the Association of Universities for Research in Astronomy (AURA), the U.S. National
Science Foundation, the National Institutes of Natural Sciences of Japan, and the Department of Atomic Energy
of India.
REFERENCES
[1] Larkin, J. E., Wright, S. A., Chisholm, E. M., Andersen, D., Dekany, R. G., Dunn, J. S., Ellerbroek, B. L.,
Hayano, Y., Kupke, R., Moore, A. M., Phillips, A. C., Simard, L., Smith, R. M., Suzuki, R., Trapp, A.,
Walth, G., Weber, R., Wincentsen, J. E., Weiss, J. L., and Zhang, K., “The infrared imaging spectrograph
(iris) for tmt: Instrument overview,” Proceedings of the SPIE 10702 (2018).
[2] Sanders, G. H., “The thirty meter telescope (tmt): An international observatory,” Journal of Astrophysics
and Astronomy 34, 81–86 (2013).
[3] Dunn, J., Reshetov, V., Atwood, J., Pazder, J., Wooff, B., Loop, D., Saddlemyer, L., Moore, A. M., and
Proc. of SPIE Vol. 10702  10702A1-6
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Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Larkin, J. E., “On-instrument wavefront sensor design for the tmt infrared imaging spectrograph (iris) up-
date,” Proceedings of the SPIE 9147 (2014).
[4] Herriot, Glenand Andersen, D. A. J., Boyer, C., Byrnes, P., Caputa, K., Ellerbroek, B., Gilles, L., Hill, A.,
Ljusic, Z., Pazder, J., Rosensteiner, M., Smith, M., Spano, P., Szeto, K., Vran, J.-P., Wevers, I., Wang, L.,
and Wooff, R., “Nfiraos: first facility ao system for the thirty meter telescope,” Proceedings of the SPIE 9148
(2014).
[5] “Astronomical Research Cameras, Inc..” Website http://www.astro-cam.com. (Accessed: 20 July, 2018).
Proc. of SPIE Vol. 10702  10702A1-7
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PROCEEDINGS OF SPIE
SPIEDigitalLibrary.org/conference-proceedings-of-spie
The infrared imaging spectrograph
(IRIS) for TMT: electronics-cable
architecture
A. C. Trapp, James  Larkin, Ken  Magnone, Timothee
Greffe, Tim  Hardy, et al.
A. C. Trapp, James  Larkin, Ken  Magnone, Timothee  Greffe, Tim  Hardy,
Jennifer  Dunn, Eric  Chisholm, Chris  Johnson, Ryuji  Suzuki, "The infrared
imaging spectrograph (IRIS) for TMT: electronics-cable architecture," Proc.
SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII,
10702A1 (23 July 2018); doi: 10.1117/12.2313978
Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas,
United States
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 1/2/2019  Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
The infrared imaging spectrograph (IRIS) for TMT:
electronics-cable architecture
A.C. Trappa, James Larkina, Ken Magnonea, Timothee Greffeb, Tim Hardyc, Jennifer Dunnc,
Eric Chisholmd, Chris Johnsona, and Ryuji Suzukie
aUCLA Department of Physics and Astronomy, 430 Portola Plaza, Los Angeles, CA, USA
bCaltech, 1216 E California Blvd, Pasadena, CA 91125
cNRC Herzberg Astronomy and Astrophysics Research Centre
dTMT, 100 West Walnut Street, Pasadena, CA, 91124
eNAOJ, Osawa, Mitaka, Tokyo, Japan
ABSTRACT
The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT).
It combines a diffraction limited imager and an integral field spectrograph. This paper focuses on the electrical
system of IRIS. With an instrument of the size and complexity of IRIS we face several electrical challenges.
Many of the major controllers must be located directly on the cryostat to reduce cable lengths, and others
require multiple bulkheads and must pass through a large cable wrap. Cooling and vibration due to the rotation
of the instrument are also major challenges. We will present our selection of cables and connectors for both room
temperature and cryogenic environments, packaging in the various cabinets and enclosures, and techniques for
complex bulkheads including for large detectors at the cryostat wall.
Keywords: ELT: TMT, TMT: IRIS, Cable Architecture, Electronics Diagrams, SPIE Proceedings
1. INTRODUCTION
The InfraRed Imaging Spectrograph (IRIS1) is a first-generation instrument for the Thirty Meter Telescope
(TMT2). A combination of the On-Instrument Wave Front Sensor (OIWFS3) and the TMT adaptive optics
system NFIRAOS4 will allow IRIS to reach the diffraction limit of TMT at wavelengths longer than 1 micron.
IRIS combines an imager and an integral field spectrograph operating between 0.8 to 2.5 microns. The imager is
composed of four 4K by 4K Teledyne detectors (Hawaii 4RG) with 4 mas pixels and a combined 34 x 34 arcsec2
field of view. The integral field spectrograph takes ∼ 10, 000 spectra simultaneously with spectral resolution
R ∼ 4000 to R ∼ 8000 on four spatial scales from 4 mas to 50 mas with fields of view of 0.46 x 0.51 arcsec2
to 2.2 x 4.6 arcsec2 respectively. The science applications of IRIS span from our own Solar System to the most
distant galaxies in the Universe.
IRIS is a large cryogenic cylinder 2 meters in diameter, 3.1 meters in height, with a total mounted mass of
∼ 5400 kg. It is suspended from underside of TMT’s adaptive optics system NFIRAOS. IRIS will spin about
its vertical axis to correct for field rotation. Most IRIS control electronics will be housed in a climate-controlled
cabinet (called the nasmyth cabinet) on a platform below IRIS. Cables exit the nasmyth cabinet and go through
a cable wrap, then up to a bulkhead attached to the underside of the cryostat. From there, the cables penetrate
IRIS via multiple bulkheads on the sides of the cryostat (see Fig. 1). Detector controllers are mounted on the
sides of the cryostat in CO2 gas cooled enclosures. In section 2, we discuss some of the architectural challenges of
IRIS with regards to the electronics system, section 3 briefly discusses the nasmyth cabinets as well as connectors
and cables we plan to use, and section 4 discusses some of the actions we plan to take in the near future.
2. ARCHITECTURAL CHALLENGES
A spinning, multi-ton object with over 50 cable attachments poses some design problems, many of which have
been solved for smaller or simpler instruments. Integrating these solutions and coming up with new ones for
such a large instrument is a challenge.
Ground-based and Airborne Instrumentation for Astronomy VII, edited by Christopher J. Evans, Luc Simard, Hideki Takami, 
Proc. of SPIE Vol. 10702, 10702A1 · © 2018 SPIE · CCC code: 0277-786X/18/$18 · doi: 10.1117/12.2313978
Proc. of SPIE Vol. 10702  10702A1-1
Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 1/2/2019
Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Figure 1. IRIS is mounted to the underbelly of TMTs AO system NFIRAOS by the IRIS support structure. After exiting
NFIRAOS, light passes through the On Instrument Wave Front Sensor (OIWFS), which allows for tip-tilt, focus, and
plate scale corrections, and finally through a window into the science cryostat, which has both an imaging and integral
field spectrometer mode. The cable wrap sits below the cryostat on the nasmyth platform, and connects to the nasmyth
cabinets (not shown here). The current design also includes a bulkhead around the bottom rim of the cryostat (not shown
here) which acts as a cable break for easier installation of the instrument. Also not shown here are the detector control
boxes (see Fig. 2) which will be mounted on the sides of the cryostat.
2.1 Cryostat Rotation
The instrument remains vertical for all observations, but must rotate about the vertical axis to correct for field
rotation. Fig. 1 shows the limited space for the cable wrap and hoses. The cable wrap must be very complex and
efficient for two reasons: (i) The radii of curvature of many cables in the wrap are near the radius of the cable
wrap itself, and (ii) nearly all available space in the wrap will be filled due to the large number of cables. The
Figure 2. An example of an ARC box; similar enclosures will be attached to the side of the science cryostat and will
house detector control electronics.
Proc. of SPIE Vol. 10702  10702A1-2
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Næsrnyth
Cabinet
sE7
OIWFS
|
L
Cable
Wrap
Cryostat
Bulkhead
Rotator
Science Cryostat
Cold Shield SpectLeach
Controller
Imager
Imager
laZehr
Lneaagli
Controller
wrap must be designed to impart minimal torque on the cryostat, as precision rotation is required, and minimal
vibration can be conducted to the cryostat or AO system.
2.2 Cryostat-Mounted Controllers
Due to the long cable distance between the instrument cryostat and nasmyth cabinet, the Astronomical Research
Cameras (ARC5) controller system for the imager, spectrograph, and OIWFS must be placed directly on the
cryostat or OIWFS in their own cooled enclosures. Mounting control electronics directly to the cryostat also
reduces the amount of control cabling through the wrap, but at the same time, these boxes must be cooled via
insulated CO2 gas coolant lines that take up room in the wrap. Fig. 2 shows an image of the type of box to be
mounted to the side of the science cryostat. The science detectors are connected directly to the control boxes
via a ∼ 1 meter ribbon cable. The boxes will contain amplifiers and analog-to-digital converters, as well as bias
control, clocking, and other control electronics. This scheme is believed to slightly out-perform a cryogenic ASIC
in terms of noise, and the complicated read-out patterns planned for the detector will be easier to implement
with custom electronics.
Figure 3. A high-level schematic diagram of Fig. 1 showing the large number of cable connections required to control
IRIS, as well as their paths from the nasmyth cabinets to the cryostat, rotator, or OIWFS.
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ewe 99.
a -b-
Cabinet wall
-c-
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Figure 4. The average cable goes through 5-6 cable breaks on its way from the electronics cabinet, through the cable
wrap, and into the science cryostat. Cables will be labeled for ease of organization and installation. For example, all
cables between the cryostat wall and cold shield will have “d” in their designation, cables going through the cable wrap
will have “b” in their designation, etc.
2.3 Cable Number/Length
Fig. 3 shows the large amount of cables (∼ 50) between the nasmyth cabinet and the cryostat/OIWFS. On top
of large numbers, the average cable goes through 5-6 cable breaks on its way (see Fig. 4), bringing the number
of individually fabricated cables to ∼ 300. The production and installation of this many long, heavy cables will
be a challenge; the connections at cable breaks must be simple to assemble and disassemble on-site, and must
be robust and repeatable. Simple steps like efficient naming schemes for cables will increase ease of organization
and installation.
3. HARDWARE
3.1 Nasmyth Cabinets
A large amount of control electronics are housed nearby the cryostat in three 19-inch rack cabinets, called nasmyth
cabinets; each will control one of the OIWFS, Imager, and Spectrograph. Each cabinet has its own temperature
monitor and glycol cooling unit for environment control. Fig. 5 shows the layout of various components in the
nasmyth cabinets. Sometimes a component will be racked by itself, like the “Spectrograph Lakeshore 336” in
the “Middle Cabinet”, and sometimes components will be grouped in a custom box and racked together, like
the “Rotary and Linear...Pressure Controller” in the “Middle Cabinet”. Fig 6 shows the architecture and type
of connections between the various components of the “Middle Cabinet” in Fig. 5.
3.2 Cables and Connectors
Military-style connectors are used in most non-cryogenic connections. They are durable enough to withstand the
torques of the cable wrap, and can be keyed such that erroneous connections are impossible. AirBorn connectors
are used for most cryogenic connections. They are simple to fabricate, and connect/disconnect easily; they also
maintain good connections when cooled to cryogenic temperatures.
Twisted/shielded pair cables will be used outside the cryostat. These cables provide shielding against EM
interference as well as a high level of customizability in numbers of wires and wire gauges. Inside the cryostat,
we will use constantan cables because of their performance at cryogenic temperatures.
4. FUTURE WORK
We must determine the exact lengths, cable types, and connector specifications for each cable. The design of the
CO2 gas coolant system is still preliminary. Coolant pipes typically place more stringent constraints on cable
architecture because of increased bend radius, diameter, and mass per meter.
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38
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ACKNOWLEDGMENTS
The TMT Project gratefully acknowledges the support of the TMT collaborating institutions. They are the
California Institute of Technology, the University of California, the National Astronomical Observatory of Japan,
the National Astronomical Observatories of China and their consortium partners, the Department of Science and
Technology of India and their supported institutes, and the National Research Council of Canada. This work
was supported as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation, the
Ontario Ministry of Research and Innovation, the Natural Sciences and Engineering Research Council of Canada,
the British Columbia Knowledge Development Fund, the Association of Canadian Universities for Research in
Figure 5. The layout for the electrical control components in the nasmyth cabinets located on the nasmyth platform (the
same platform the cable wrap is located on; see Fig. 1). There will be three cabinets, one devoted to each of the OIWFS,
the spectrograph, and the imager. Sometimes a component will be racked by itself, like the “Spectrograph Lakeshore
336” in the “Middle Cabinet”, and sometimes components will be grouped in a custom box and racked together, like the
“Rotary and Linear...Pressure Controller” in the “Middle Cabinet”. Yellow items are OIWFS, cable wrap, and rotator
components; orange are spectrograph components; blue are imager components; and green are cabinet environment
control, power, and communication.
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Spectro
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Figure 6. The architecture and type of connections between the various components of the “Middle Cabinet” in Fig. 5.
Orange components are science cryostat control electronics, and green are cabinet environment control, power, and
communication.
Astronomy (ACURA), the Association of Universities for Research in Astronomy (AURA), the U.S. National
Science Foundation, the National Institutes of Natural Sciences of Japan, and the Department of Atomic Energy
of India.
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[1] Larkin, J. E., Wright, S. A., Chisholm, E. M., Andersen, D., Dekany, R. G., Dunn, J. S., Ellerbroek, B. L.,
Hayano, Y., Kupke, R., Moore, A. M., Phillips, A. C., Simard, L., Smith, R. M., Suzuki, R., Trapp, A.,
Walth, G., Weber, R., Wincentsen, J. E., Weiss, J. L., and Zhang, K., “The infrared imaging spectrograph
(iris) for tmt: Instrument overview,” Proceedings of the SPIE 10702 (2018).
[2] Sanders, G. H., “The thirty meter telescope (tmt): An international observatory,” Journal of Astrophysics
and Astronomy 34, 81–86 (2013).
[3] Dunn, J., Reshetov, V., Atwood, J., Pazder, J., Wooff, B., Loop, D., Saddlemyer, L., Moore, A. M., and
Proc. of SPIE Vol. 10702  10702A1-6
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Larkin, J. E., “On-instrument wavefront sensor design for the tmt infrared imaging spectrograph (iris) up-
date,” Proceedings of the SPIE 9147 (2014).
[4] Herriot, Glenand Andersen, D. A. J., Boyer, C., Byrnes, P., Caputa, K., Ellerbroek, B., Gilles, L., Hill, A.,
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and Wooff, R., “Nfiraos: first facility ao system for the thirty meter telescope,” Proceedings of the SPIE 9148
(2014).
[5] “Astronomical Research Cameras, Inc..” Website http://www.astro-cam.com. (Accessed: 20 July, 2018).
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Larkin

Dunn

Herriot

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The infrared imaging spectrograph (IRIS) for TMT: electronics-cable
  architecture

The infrared imaging spectrograph (IRIS) for TMT: electronics-cable architecture

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