  In this work we numerically study a self-guiding process in which ionization
plays a dominant role and analyze its effect on high-order harmonic generation
(HHG) in gases. Although this type of self-guiding --- termed as plasma-core
induced self-guiding in previous works --- limits the achievable cut-off by
regulating the intensity of the laser beam, it provides favorable conditions
for phase matching, which is indispensable for high-flux gas high-harmonic
sources. To underline the role of self-guiding in efficient HHG, we investigate
the time-dependent phase matching conditions in the guided beam and show how
the spatio-temporally constant fundamental intensity contributes to the
constructive build-up of the harmonic field in a broad photon-energy range up
to the provided cut-off.
