Hi Gerald, your statement is a little vague to what u r looking 4.
But, i've welded copper before using a rod called Everdure 254; it's a silicone bronze rod.
Most of the heat from the GTAW process should be directed onto the rod and not the base material.
Another rod we use for welding material of 90/10 (90%cu+10%ni) would be an ER70/30 rod.
You can get more info on those products on the web.
Hope this helps.