that's not actually a power-up, and you don't just drive through it.
it recharges your shields (your health). but it takes a few seconds to do it, you can't just drive thru like you're at a McDonalds. so in other words, if you're on like red or red/orange health, hop inside that energy field in the main Mining building and stay in there a few seconds until you see your life health regenerate back to green or blue (blue if you have the Advanced Shields powerup).
i guess thats all i have to say, but whats up with those of you using Double Missiles codes for Gold medals? on the first level no less! dam! i beat this whole game without any codes and that includes all Platinums, of course i had some help but gave lots of help also (only on the Plat medals). but you should at least be able to get all Golds by yourself without cheating. the Golds are waay easier than the Golds in Rogue Squadron (for n64 anyway. i heard the PC version of Rogue is easier, i only played the 1-level demo so it's hard to say).