Hydrogen, the simplest element in the universe, has unique properties and a surprisingly complex phase diagram . Because of applications in fusion research, planetary science, proton sources and fundamental physics, we have developed a novel cryogenic jet capability . At cryogenic temperatures of 17 K, hydrogen is liquid and can be formed into a rapidly expanding jet. We are taking advantage of these properties and have developed jets of different shapes. Examples of these jets are shown in the figure. On the left, we show a cylindrical jet with a diameter of 5 μm. In addition, we have successfully demonstrated jet diameters of 2 μm and 10 μm. The middle figure shows a flat jet that we are slowly rotating to illustrate the shape. The jet is 30 μm wide and about 1 μm thick. Finally, the right hand side figure shows a droplet jet with 6 μm diameter. These jets emanate from the nozzle at a speed of approximately 100 m/s and are thus well-suited for experiments at high repetition rates now available at many laser facilities including LCLS free electron x-ray laser. These jets have been successfully fielded in experiments that have characterized the structure of hydrogen  and for proton acceleration . Recent experiments have already demonstrated energies with tens of MeV protons at high repetition rates.
This work is supported through DOE Fusion Energy Science, FWP 100182. Patent pending for Stanford University to 'H Flat Jets for Proton Therapy', inventor Siegfried Glenzer, Sebastian Goede and Jongjin Kim.