Figure 6.

RMS radius ${\sigma }_x$ evolves during propagation at various longitudinal compression strengths, while the solid black line is 0, the red dashed line is $1.45\times {10}^6$ V/m, the blue dot is $1.45\times {10}^5$ V/m, the green dashed line is $1.45\times {10}^4$ V/m and the purple double-dotted line is $1.45\times {10}^7$ V/m.