I cut the mandelbulb set at y>0 (on y=0 is the Mandelbrot set) and use the following formula in iteration (found here on fractalforums).
The non trigonometric variant of the sin power 2 mandelbulb:
double r_xy=Math.Sqrt(xx+yy);
double a = 1;
if(r_xy!=0.0)
a= 1 - zz *( r_xy);
y=2 *x*y*a+bj;
x = (xx - yy) * a+br;
z = 2 * z * r_xy+bi;
xx = x * x; yy = y * y; zz = z * z;
// Bailout:
r = Math.Sqrt(xx + yy + zz);
http://www.youtube.com/v/tvz0zUpHySU&rel=1&fs=1&hd=1