Sokar's particle accelerator
From The Stargate Omnipedia
Advanced device the Goa'uld System Lord Sokar used to transmit an image of himself through the Earth Stargate to the opposite side of the iris. He hoped to use it to then slowly heat up the barrier until it was destroyed, allowing him access to Apophis, who was recently captured and lying strapped to a bed in the infirmary, dying.
KEY EPISODE
Serpent's Song - Sokar fires his particle accelerator at Earth's Stargate in the hopes of retrieving Apophis for himself.