FY2022 ALMA/45m/ASTE Users Meeting

ACA Spectrometer
Shun Ishii, Jihyun Kang, Yusuke Aso, Hiroshi Nagai
on behalf of the ACA Spectrometer team
2022-12-21

2022/12/21

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ACA Spectrometer (ACASPEC)• New backend for the Total Power array from an EA Development Program• Development is led by KASI in collaboration with NAOJCSV TeamEngineering Team

2022/12/21

Jongsoo Kim (PI)Manabu Watanabe

Makoto Shizugami

Shun Ishii

Jihyun Kang

Jongsuk Hong

Scott Zang

Susumu Nakayama

Hiroshi Nagai

Yusuke Aso2

ACA Spectrometer (ACASPEC)• Replace the functionality of the ACA Correlator for the TP array• Target to offer from Cycle 10Current Configuration
ArraysCorrelators
2022/12/21

12 m

64-input Correlator(Baseline)

7m

Total PowerACA Correlator
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ACA Spectrometer (ACASPEC)• Replace the functionality of the ACA Correlator for the TP array• Target to offer from Cycle 10→ All arrays will be independent!
New Configuration
ArraysCorrelators
2022/12/21

12 m

7m

Total Power

64-input Correlator(Baseline)

ACA Correlator

ACA Spectrometer5

Expected Benefit• Operational Advantage:• The TP array will be operated independently from the 7m array/the ACA
correlator, which increases the observing efficiency of the TP array.

• Better spectral dynamic range:• The spectral dynamic range can be improved up to 10000:1 by increasing thenumber of bits to 32-bits for FFT/multiplication. (the ACACORR uses 16-bits
for FFT and 4-bits for multiplication).

• Expandability:• The ACASPEC is a GUP Spectrometer. Thanks to the software-based
development and native parallel processing of GPU, the ACASPEC has
excellent scalability to basebands, wider bandwidths, or complex processingin the WSU and further upgrades near future.

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Functionality and Architecture• The ACASPEC will

• Provide auto-correlation data streams from the four TP antennas• Calculate cross-antenna correlation for calibration observations (ACASPEC is also a small correlator)• Digital Spectrometer based on the Graphical Processing Unit (GPU) technology• Computing capacity is rapidly growing• All the processing is done in the software• GPU has advantages on• Parallel processing• Pipeline processing• Expandability• Currently being widely used formany backends of radio telescopes :2022/12/21• VEGAS at GBT• PolariS at NRO45m (Kameno et al. 2014 )• LOFAR etc.

NVIDIA TITAN V, GPU board
selected for the ACASPEC

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System of the ACASPEC: ASMs and ASC
ACA Spectrometer
Control (ASC)controls ASMs,
receives data from
ASMs, and sends
BDF to Archive

Science Data (ASDM)
GPUs

Production DRXPs
GPUs

Chassis Fans

x4
Chassis Fans

2022/12/21

ACA Spectrometer Module (ASM)
processes a BB pair signal from 4
TP antennas, corresponding to aquadrant in the correlator

Photo of a module of the ACASPEC

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Past and Future MilestonesActivity this year
Concept Preliminary
Design Design
Review Review

Critical DesignandManufacturing
Review

Preliminary
Acceptance
In-House
Review

Installation in Commissioning
and Sciencethe ALMA
Verification
SiteObsmode
Review

ScienceOperations

2016
2022/12/21

2017

2019

2021

2022
Feb.

2022
Apr.-Aug.

2022
Nov.
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Commissioning and Science Verification (CSV)

20 specifications/requirements have been identified and validated:• Basic capability as the backend of the TP array:•Number of antenna, Bandwidth, Spectral setups, polarization, Frequency Profile Synthesis• Performance:•Linearity, dynamic range, stability• End-to-End testing•2022/12/21

Generation and execution of SB, Data archiving with correct format, Manual and pipeline processing

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CSV Result: First light of auto-correlation• The first light was archived on 202202-22 using the SiO(J=2–1) maser line
at 86.243 GHz toward Orion KL.
• This confirmed that all the signal paths
from the antenna to the archive are
well connected and processed.

2022/12/21

Test data12

CSV Result: Consistency with the ACA Correlator• Spectral setups and their consistency
within the ACASPEC and with theACACORR were verified for thecombinations of the polarization, theresolution, and the averaging factor• The consistency of the Jy/K factor
was also confirmed.
• ACASPEC: 42.0 ± 1.1• ACACORR: 42.0 ± 1.3• The result indicates that the ACASPEC
has enough linearity performance• The linearity was also validated using
Trx and Tsys spectra.
2022/12/21

Test data

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CSV result: Spectral dynamic range• The spectral dynamic range has been verified. The achieved noise rms is 8.6 mK for thepeak intensity of 92.1 K, and thus the resultant S/N is ∼ 11000, achieving the goal.
CO(J=2-1) in Orion KL

Test data

Test data

Baseline ranges for calculating the rms
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CSV Result: CASA SD Pipeline processing• CASA Single-Dish pipeline can process the data taken by the ACASPEC for SBs of thestandard OTF mapping mode and the TP spectral scan mode
• The intensity in the ACASPEC data agrees
well with that of the ACACORR data.

Test data

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Summary• The ACA Spectrometer is the new backend for the TP array• It is expected the ACASPEC will increase the observing efficiency ofthe TP array• ACASPEC was installed on the ALMA site in February• Commissioning and Science Verification has been carried out using
the on-site environment.
• We successfully verified almost all test items, including end-to-end
testing and ALMA single-dish pipeline processing, without blockers.
• Final implementation in the ALMA subsystems is ongoing toward
offering science operations.
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