The user wants me to write a concise summary of a long transcript of a video. I should use my own words and highlight the main points and details. I should also use markdown elements to format the summary.
Here are the key facts extracted from the text:
1. A Korean nuclear fusion reactor achieved 100 million°C for 30 seconds.
2. The experiment demonstrated that nuclear fusion is moving from a physics problem to an engineering one.
3. The core temperature of the Sun is approximately 15 million Kelvin.
4. The Korean experiment's temperature was nearly seven times hotter than the Sun's core.
5. The Korea Superconducting Tokamak Advanced Research (KSTAR) facility conducted the experiment.
6. A net energy gain was achieved in the experiment.
Please note that these are simplified statements and the full context can provide more detailed information.