Long Term Archive. This refers to two types of archives nearline and offline. See Short Term Storage (STS), Nearline archive, Online storage, Offline archive, and Everything Online (EOL).
The Long Term Accumulator sits after the correlator, and accumulates (coadds) the 1 ms output from the correlator if needed for multiples of the basic 16 ms accumulation period. The fundamental dump rate of the correlator is given by the integer number of accumulator periods (1 or more) that elapse during the time that it takes to read the full correlator output. Note that the LTA itself is accumulating the next set of data while the ``current'' set of outputs are read to the bus.