A chemical microreactor with a high aspect ratio. In one embodiment the chemical microreactor has a chemical microreactor section with channels having a height and with spacings having a width. There is a high aspect ratio of the height to the width. The high aspect ratio in one embodiment is more than substantially 5:1. The high aspect ratio in another embodiment is more than substantially 10:1. The high aspect ratio another embodiment is more than substantially 15:1. The high aspect ratio in one embodiment is substantially 20:1.
 The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.