The Astral helm is a Protoss device used to enhance psionic power for training and long distance communication.
During training, the Helm creates a type of psychic virtual reality to help users practice and focus their skills without damaging the surroundings. Multiple safeguards are in place to avoid users from being trapped in the reality should something unforeseen arise (Young Justice: Failsafe).
For interstellar contact, an Astral helm serves as a psionic beacon to allow the user's astral form to move through limitless dimensions without getting lost (Stargate: Long-range communication stone). Users can also connect with multiple minds at once to relay information in combat or emergencies (Marvel: Cerebro; Naruto: Chakra Transmission Communication Device). This proves to be essential as most of the Protoss are scattered across the Koprulu Sector.