10. Let $x \in \mathbf{R}$, the inequality $2 x^{2}-a \sqrt{x^{2}+1}+3 \geqslant 0$ always holds, then the maximum value of the real number $a$ is $\qquad$
Thus, $2 \sqrt{x^{2}+1}+\frac{1}{\sqrt{x^{2}+1}} \geqslant 3$,
so the maximum value of the real number $a$ is 3.