Don't look at the wavefront of the first 100m, the pod there is gone anyways in case of a bomb. Turbulence on the phase of what comes after the near vacuum. T

Don't look at the wavefront of the first 100m, the pod there is gone anyways in case of a bomb. Turbulence on the phase of what comes after the near vacuum. The plug essentially plugs itself from resticted airflow. If you want to be extra safe you could even add small tesla valve style fins around the border of the tube, to increase turbulence.