Focal Plane Instruments
There are three key instruments for the new telescope, as described in the following.
Such instruments are increasingly required to have larger FoVs in order to satisfy the camera requirements, along with larger instantaneous bandwidths for heterodyne receivers. In addition, an imaging spectrograph to facilitate ``3D imaging'' of the cosmic large-scale structure has been newly developed. Therefore, prototyping and test of the key instruments are hence strongly required.
Wideband Medium-Resolution Imaging Spectrometer Array
One of the key instruments is a multi-object spectrograph and/or imaging spectrometer, which facilitates multi-pixel broadband spectroscopy at the focal plane. Such instrument is strongly desirable for the blank-field CO/[C II] survey. The Deep Spectroscopic High-redshift Mapper (DESHIMA, Endo et al. 2012) or its scaled-up instrument, tentatively named ``Super-DESHIMA'', as well as the proposed multi-object spectrograph concept, MOSAIC (Baselmans et al.; see http://alma-intweb.mtk.nao.ac.jp/~diono/meetings/ASTE_ALMA_2014/aste-workshop-2014-mosaic.pdf), are potential instruments for that purpose.
DESHIMA is a medium-resolution (R = lambda / d(lambda) ~ 500) spectrometer with integrated on-chip filterbanks exploiting a microwave kinetic inductance device (MKID).
A similar concept of on-chip spectrograph has also been proposed (e.g., Kovacs et al. 2012). DESHIMA is designed to span a range of 326-905 GHz, with a number of spatial pixels N_pix of up to 7. For our future single-dish telescope, we require the capabilities of ``Super-DESHIMA'', which spans 190-420 GHz (or 70-420 GHz, if possible) with N(pix) > 100-300, in order to conduct the CO/[C II] tomography discussed in the ''SCIENCE'' section.
Multi-Chroic Wide-Field Camera
Another key instrument is a wide-field, multi-color continuum camera or multiple-chroic camera, covering 150 to 350 GHz with 3 bands (baseline plan). A maximum of 6 bands from 90 to 420 GHz may be achieved (goal).
Large-format multi-color bolometer arrays have already become operational (e.g., SCUBA2; Holland et al.~2013, Holland et al. 2013) employing transition edge sensors (TES) with time-domain multiplexing. TES arrays with frequency-domain multiplexing are now widely implemented, as highlighted by recent scientific results from the South Pole Telescope (Carlstrom et al. 2011). Multi-chroic TES technology has been intensively studied and developed for cosmic microwave background (CMB) experiments such as Polarbear and LiteBIRD (e.g., Suzuki et al. 2012).
For the ASTE 10-m telescope, a dual-color TES camera has been developed (e.g., Takekoshi et al. 2012, Oshima et al. 2013, Hirota et al. 2013) and commissioning and initial scientific verification were conducted successfully in 2014, at 270 and 350 GHz (N_pix = 169 and 271, respectively). Further commissioning runs with a new calibration device were performed (2016 April to July). An upgrade plan, which will have 881 pixels in total at 350 and 670 GHz, has also been investigated.
MKID technology is also becoming suitable for multicolor wild-field imaging instruments, as demonstrated by NIKA2 on the IRAM 30-m telescope (Calvo et al. 2016). A 600-pixel MKID camera for the Nobeyama 45-m telescope is also under development (Sekimoto et al. 2014). Verification of both the TES and MKID technologies on ASTE (and other telescopes such as LMT and IRAM) will be one of the very important steps toward developments of the wide-field camera required for the proposed next-generation submillimeter-wave telescope.
Multi-Frequency Heterodyne Receiver
Based on the scientific demands for high-spectral-resolution spectroscopy (R > 300,000 or dv <1 km/s, which is currently impossible to achieve with a direct detector spectrograph like DESHIMA), large heterodyne arrays are also unique and indispensable instruments for future large single-dish telescopes; e.g., arrays at 100, 230, 350, and 490 GHz.
An ultra-wideband coherent receiver system is also desirable for some key science cases of the LST, including the unbiased line surveys for exploration of the chemical diversity in protostellar cores, as well as a blind spectroscopic search for absorption lines against the reverse shock of very high-z gamma-ray bursts (Inoue et al. 2007), which shall be conducted immediately after the detection (within a few hours) of a submillimeter transient source.
The considerable expertise has been acquired by the developments of receivers for the NRO 45m, ASTE, and also for the ALMA (e.g., Sekimoto et al. 2008, Uzawa et al. 2009, Asayama et al. 2014), and it can be used for the future developments of the heterodyne instruments.
Although the current intermediate frequency (IF) bandwidth is limited to ~ 10 GHz, a novel idea to drastically widen the instantaneous bandwidths of the heterodyne instruments has been proposed, in which radio-frequency (RF) domain multiplexing of a series of SIS mixers is employed (Kojima et al. 2015).