The kappa mechanism is a fancy name for how liquid can change into a gas when it gets really hot.
Imagine you have a cup of water. When it's cold, the water is a liquid and stays in the cup. But when you heat it up, like when you put it in the microwave, the water starts getting hotter and hotter.
As the water gets hotter, the particles inside it start to move faster and faster. They get so excited that they start jumping really high and bouncing off each other.
Now, let's say the cup doesn't have a lid on it. As the water gets really, really hot, some of the water particles start jumping and bouncing really, really high. They jump so high that they can't stay in the cup anymore. These water particles escape from the cup and turn into a gas called water vapor.
Water vapor is just water in gas form. That's why you see steam rising from hot water. The liquid water has changed into a gas because it got so hot.
This changing from a liquid to a gas is what we call the kappa mechanism. It happens when things get really hot, and the particles start moving really fast and jumping around like crazy. It's like a party inside the cup, and some of the particles get so excited that they turn into a gas and escape.