There is a meditation by HP Mageson about vibrating SHAMMASH into certain chakras for the Kundalini to rise but I couldn't find it, so if anyone knows a link to it or can copy and paste it here, I'll really appreciate it.
You don't raise the serpent with any particular mantra. Shammash is the Sumerian word for the Sun and is a powerful solar mantra. You use it to empower your solar plexus chakra and other purposes solar mantras are used for.