t = 0 : 0.1 : 6*pi;
x = sqrt (t) .* sin (2*t);
y = sqrt (t) .* cos (2*t);
z = 0.5 * t;
plot3 (x, y, z, 'k', 'linewidth', 1)
grid on
xlabel ('x')
ylabel ('y')
zlabel ('z')