Figure 2

Experimental results.
(a–d,e–h) are the betatron x-ray signals with nitrogen and helium gases, respectively, on IPs 1–4; (i,j) show the electron energy spectra with nitrogen and helium gases, which are shown in the same color scale (the charges denote electrons with energy greater than 100 MeV); (k,l) show the plasma channel images with nitrogen and helium gases, respectively.