Bradley Gabe picks up from the first video tutorial (XSI 7 ICE Video Tutorial: Building a Force from a Curve Video Tutorial) where he created a Curve Flow Force effect. By duplicating and modifying mostly existing nodes from this effect, combines three forces into a vortex force: Enjoy the XSI 7 Video Tutorial: Vortex Control with ICE.
1- Curve Flow Force: Generated from tangent to curve
2- Curve Attraction Force: Generated by subtracting point position vectors from cloud point to closest point on curve
3- Axial Force: Generated by taking the cross product of vectors from forces 1 and 2