  A superconductor-normal metal-superconductor mesoscopic Josephson junction
has been realized in which the critical current is tuned through normal current
injection using a symmetric electron cooler directly connected to the weak
link. Both enhancement of the critical current by more than a factor of two,
and supercurrent suppression have been achieved by varying the cooler bias.
Furthermore, this transistor-like device demonstrates large current gain
$\sim$20) and low power dissipation.
