  We demonstrate the robust operation of a gallium arsenide tunable-barrier
single-electron pump operating with 1 part-per-million accuracy at a
temperature of $1.3$~K and a pumping frequency of $500$~MHz. The accuracy of
current quantisation is investigated as a function of multiple control
parameters, and robust plateaus are seen as a function of three control gate
voltages and RF drive power. The electron capture is found to be in the
decay-cascade, rather than the thermally-broadened regime. The observation of
robust plateaus at an elevated temperature which does not require expensive
refrigeration is an important step towards validating tunable-barrier pumps as
practical current standards.
