Length of Single Helix Turn

$x = \cos \theta , \qquad y = \sin \theta, \qquad z = \theta, \qquad 0 \leq \theta \leq 2 \pi$

Consider a single helix turn, with parameters given above.

The arc length of this single turn can be expressed as $\sqrt{a} \pi$ . Determine the value of $a$ .