what is the reaction called when you touch a plasma sphere

The reaction is usually called electrical discharge or plasma discharge. When you touch a plasma sphere, your body acts like a conductor, so the glowing filaments are drawn toward your finger and concentrate there.

What you’re seeing

Inside the sphere, ionized gas forms visible plasma filaments. When your hand touches the glass, it changes the electric field and gives the discharge an easier path, so the arcs “follow” your touch.

Simple way to say it

People often describe it as:

• “The plasma follows your finger.”
• “The arcs are attracted to your hand.”
• “You’re redirecting the discharge.”

Safety note

It usually feels harmless in normal use, but people with pacemakers or similar medical devices are often advised not to touch plasma globes.

TL;DR: It’s not a special named “reaction” in the chemistry sense; it’s an electric discharge responding to your body’s conductivity.