what specific gas is used?
Helium
Gas tungsten arc welding
 Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld metals with high heat conductivity, such as copper and aluminum.
what is gas tungsten arc welding? It is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. is there a gas used in this welding process? Yes, shielding gas
wiki:24342419
Gas tungsten arc welding [SEP] Shielding gas
When used with alternating current, argon shielding results in high weld quality and good appearance. Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld metals with high heat conductivity, such as copper and aluminum. A significant disadvantage is the difficulty of striking an arc with helium gas, and the decreased weld quality associated with a varying arc length. Argon-helium mixtures are also frequently utilized in GTAW, since they can increase control of the heat input while maintaining the benefits of using argon. Normally, the mixtures are made with primarily helium (often about 75% or higher) and a balance of argon.