  With the advent of neoclassically optimised stellarators, optimising
stellarators for turbulent transport is an important next step. The reduction
of ion-temperature-gradient-driven turbulence has been achieved via shaping of
the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence
is adressed in the present paper. Recent analytical and numerical findings
suggest TEMs are stabilised when a large fraction of trapped particles
experiences favourable bounce-averaged curvature. This is the case for example
in Wendelstein 7-X [C.D. Beidler $\textit{et al}$ Fusion Technology $\bf{17}$,
148 (1990)] and other Helias-type stellarators. Using this knowledge, a proxy
function was designed to estimate the TEM dynamics, allowing optimal
configurations for TEM stability to be determined with the STELLOPT [D.A. Spong
$\textit{et al}$ Nucl. Fusion $\bf{41}$, 711 (2001)] code without extensive
turbulence simulations. A first proof-of-principle optimised equilibrium
stemming from the TEM-dominated stellarator experiment HSX [F.S.B. Anderson
$\textit{et al}$, Fusion Technol. $\bf{27}$, 273 (1995)] is presented for which
a reduction of the linear growth rates is achieved over a broad range of the
operational parameter space. As an important consequence of this property, the
turbulent heat flux levels are reduced compared with the initial configuration.
