Namakanui (“Big-Eyes”) is a heterodyne receiver unit making use of the ALMA “insert” concept for a dewar that can hold three single-receiver inserts. These inserts are used singly when observing (i.e. only one at a time). This configuration mirrors that of the Greenland Telescope (GLT) instrumentation.
The three heterodyne receiver inserts will focus on 86, 230 and 345 GHz, and will be named ʻAla‘ihi (“Squirrelfish”), ʻŪʻū (“Soldierfish”) and ʻĀweoweo (“Big Eye”) respectively. The 86 GHz insert is a dual polarization, 1-sideband mixer. The 230 and 345 GHz inserts have dual polarization 2-sideband mixers, producing four Intermediate Frequencies (IFs) with bandwidths of 4 – 12 GHz each (although this may be restricted to 4 – 8 GHz initially). Aweoweo (345 GHz) will be capable of supporting IFs in the 5 – 9 GHz range. Please note that, at present, the ACSIS IF system only supports IFs of 4 – 7.3 GHz.
The 230 and 345 GHz mixers are identical to those used by ALMA. More technical details on the 230 GHz mixer are available here. The most recent public user information on these receivers is given in Sections 4.2.4 and 4.2.5 of the ALMA Technical Handbook. Due to each insert having a separate optical path (TMU position), only one receiver/frequency range can be used at any one time.
Namakanui Commissioning Roadmap
The inserts for 86 and 345 GHz are already in hand, and work on the optics for these is ongoing. The dewar and 230 GHz mixers have been ordered and their delivery has been scheduled.
The Namakanui commissioning plan specifies that ASIAA assemble and test the system during the fall, and then deliver the receiver for telescope integration and testing. The current priority of the Namakanui commissioning roadmap is U‘u (230 GHz), with the aim of initial commissioning completion during the summer of 2019.
To this end, the JCMT semester 19A Call for Proposals invites prospective users of U‘u to submit PI proposals on a “Shared Risk” basis. The accessible U‘u frequency range is currently anticipated to be 212 – 274 GHz. Use of ACSIS with the new 230 GHz mixer during the 19A shared risk period means that the bandwidth and resolution configurations available are currently expected to be the same as for RxA3m. The standard heterodyne observing modes expected to be available for U‘u shared risk observing are Stare, Jiggle and Raster. For more details on these observing modes, please see this page. Anticipated instrument capabilities and overall system performance have been incorporated into the JCMT Heterodyne Integration Time Calculator.