The Visible Tunable Filter Instrument (VTF) is a 2D imaging spectropolarimeter for high spatial and spectral resolution solar observations in the visible light. Integration into the world largest solar telescope, the 4m aperture Daniel K. Inouye Solar Telescope (DKIST) started in January 2024. In this paper we present an overview over the complete software infrastructure designed and developed for this instrument. In particular the Instrument Control Software (ICS), the Instrument Performance Calculator (IPC) which is a graphical tool enabling scientist to explore instrument performance and create executable observing configurations. Furthermore, real-time monitoring plugins were implemented to verify data acquisition and instrument performance. The main part of the infrastructure is the ICS package which provides the interface between the operator, the instrument and the observatory. It is based on the Common Services Framework (CSF) provided by DKIST and is based on an object-oriented design and written in JAVA. The interface to the operator is given by the engineering GUI that allows the user to monitor and control all system drives and sensors. All observation and calibration tasks can be configured and started from this GUI. The interface to the instrument is realized by a DKIST framework compatible OPC/UA layer developed for this instrument which interfaces to a Beckhoff Programmable Logic Controller (PLC) that manages the real-time requirements of the instrument. All real-time and synchronization requirements are implemented using the DKIST timing and synchronization system (TRADS) based on the precision time protocol (PTP) that allows timing accuracy well below microseconds. Furthermore, the ICS interfaces to the Camera System Software (CSS) and Data Handling System (DHS), where VTF delivers up to 2400 MB/s or roughly 9 TB/hour when used in spectropolarimetric imaging mode.
The Daniel K. Inouye Solar Telescope, with its 4m aperture, is the largest telescope for observations of the Sun, and is currently in its Operations Commissioning Phase. During this phase of the project, the five DKIST first light instruments, the Visible Broadband Imager (VBI), the Visible Spectro-Polarimeter (ViSP), the Diffraction-Limited Near-Infrared Spectro-Polarimeter (DL-NIRSP), the Cryogenic Near-Infrared Spectro-Polarimeter (Cryo-NIRSP) and the Visible Tunable Filter (VTF) are used in selected modes to acquire scientific data. We provide an overview of the DKIST instrumentation system and its inherent flexibility. We further report on lessons learned during commissioning, and present sample data products.
The Visible Tunable Filter Instrument (VTF) is a 2D imaging spectropolarimeter for high spatial and spectral resolution solar observations in the visible light. It will be operated at the world’s largest solar telescope, the 4m aperture Daniel K. Inouye Solar Telescope (DKIST) in Maui, Hawaii, USA. The VTF is designed and constructed by the Leibniz-Institut f¨ur Sonnenphysik (KIS) with support from the Istituto ricerche solari Aldo e Cele Dacc`o (IRSOL), the Max-Planck-Institut f¨ur Sonnensystemforschung (MPS) and the National Solar Observatory (NSO). KIS started integrating and commissioning the VTF at the DKIST in January 2024. VTF is based on two large Fabry-P´erot etalons (FPIs) acting as spectral filters. The field of view of 1 arcmin combined with a spectral accuracy well below 1 picometer leads to a clear aperture (CA) of 250 mm, an allowed cavity error smaller than 3 nm RMS over the CA, a microroughness below 0.4 nm RMS and a required cavity stability of ±100 pm over one hour. Therefore, the world’s largest tunable etalons for imaging applications had to be built. With these etalons, VTF will be able to drive solar science for the next decades. In this paper we describe the overall design and specifications of the VTF-FPIs. The first etalon was completely assembled and commissioned in the lab in 2023. We present the main characteristics as measured in the laboratory and demonstrate the dynamic response probed by the integrated metrology system.
The visible tunable filter is an imaging spectropolarimeter for solar observations in visible light. The instrument consists of several Fabry–Pérot interferometers (FPIs), a polarization modulator, and a prefilter. It will be one of the first light instruments for the Daniel K. Inouye Solar Telescope (DKIST) on Haleakaláa, Maui, Hawaii. We have developed simulation algorithms to describe the instrument and its impact on scientific observations. Our aim is to study the expected measurement accuracy and to test calibration algorithms. A well-known problem is the surface quality of the glass plates for each FPI. We developed algorithms to describe the influence of a surface microroughness, reflectivity, and figure errors of the individual FPI plates, and the expected total photon flux for scientific data acquisition. This tool is used to derive the limits for manufacturing processes to achieve the measurement accuracy required for science observations with DKIST.
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