Speaker: Dr. Jongsoo Kim
Director of Radio Division
Korea Astronomy and Space Science Institute (KASI)
The ALMA is an acronym of the Atacama Large Millimeter/submillimeter Array. The ALMA is composed of 66 antennas and located at the Atacama desert in Chile with the height of 5000m from the sea level. The construction of the ALMA is completed in 2013 and the ALMA has produced astonishing science results. At the focal point of the ALMA antennas there are two correlators, which calculate correlation of every pair of the ALMA antennas. KASI and NAOJ (National Astronomical Observatory of Japan) started an upgrade project of the ACA (Atacama Compact Array) correlator based on GPU (Graphical Processing Unit) technology.
In my talk I will introduce the development of a spectrometer for the ALMA TP (Total Power) array, which is composed of four antennas. The main function of the spectrometer is to get power spectra from time-series data using FFT (fast Fourier transform). Each antenna generates eight 4 Gsamples/s data streams with 3 bits/samples, which are then transported through optical fibers to the PCIe slots of a spectrometer (a GPU server). The total amount of data from one antenna is 96Gb/s. The data streams are sent to GPU memory. In a GPU the sampling bit of data streams is converted to 32 bits/sample and then they are FFTed. The power spectra are accumulated in the GPU, sent to CPU memory, and then sent to a control computer. As test purpose, the GPU spectrometer was installed at one of the KVN (Korea VLBI Network) sites and Nobeyama 45m, and it successfully produced power spectra from astronomical objects.