  LHD inward-shifted configurations are unstable to resistive MHD
pressure-gradient-driven modes. Sawtooth like activity was observed during LHD
operation. The main drivers are the unstable modes $1/2$ and $1/3$ in the
middle and inner plasma region which limit the plasma confinement efficiency of
LHD advanced operation scenarios. The aim of the present research is to study
the hard MHD limit of $1/2$ sawtooth like activity, not observed yet in LHD
operation, and to predict its effects on the device performance. Previous
investigations pointed out this system relaxation can be an internal disruption
[J. Varela et al, internal disruptions and sawtooth like activity in LHD, 38 th
EPS Conference on Plasma Physics, 2011, P5.077]. In the present work, we
simulate an internal disruption; we study the equilibria properties before and
after the disruptive process, its effects on the plasma confinement efficiency
during each disruptive phase, the relation between the $n/m = 1/2$ hard MHD
events and the soft MHD events and how to avoid or reduce their adverse
effects. The simulation conclusions point out that the large stochastic region
in the middle plasma strongly deforms and tears the flux surfaces when the
pressure gradient increases above the hard MHD limit. If the instability
reaches the inner plasma, the iota profiles will be perturbed near the plasma
core and three magnetic islands can appear near the magnetic axis. If the
instability is strong enough to link the stochastic regions in the middle
plasma (around the half minor radius $\rho$) and the plasma core ($\rho <
0.25$), an internal disruption is driven.
