Magnetic-compression heating may invert the velocity distribution of alpha particles and lead to the possibility of exciting velocity space instabilities. A sufficient stability condition is derived for these modes in compression-heated tokamaks. A high-field high-density compression scenario like Zephyr satisfies this stability condition, while a medium-field high-temperature compression scheme like TFTR or a rather fast and strong compression scheme like T-14 has some chance t o excite velocity-space thermonuclear instabilities.
Magnetic-surface compression heating in helical systems