HIGH REPETITION RATE SAMPLE DELIVERY SYSTEM FOR SUPERCONDUCTING-RF AND MULTI-BUNCH X-RAY FREE ELECTRON LASER

This topic seeks the development of a high-speed sample delivery system for experiments to be performed at high-pulse-power, MHz-repetition-rate XFELs, like LCLS-II and LCLS-II-HE, and at XFELs having multi-pulse capabilities within one RF cycle with a nanosecond scale separation. When focused, high-intensity X-ray pulse trains with up to MHz or sub-GHz frequency can damage a sample in a single shot, requiring the sample material to be replaced with a new fresh sample on the time scales of a microsecond and down to a nanosecond, in time for the next shot. For some applications, like serial femtosecond crystallography, the sample may be renewed as a dilute solution in a high-speed liquid jet. However, other experiments such as a population inversion X-ray laser oscillator or regenerative amplifier, being developed to generate transform limited and fully coherent pulses, require a high sample concentration or a solid sample. Unfortunately, the velocity of the liquid jet is reduced by viscosity at higher concentration, making it difficult to reach the high speed required for high-frequency X-ray pulse repetition rates. For this class of experiments, an alternative to liquid jets capable of delivering samples at high speed, above 200 m/s, is required. A possible solution to this problem is to use a high-angular-velocity rotating disk, within which samples can be embedded, or made from the solid material to be used in the experiment. Today small electric motors are easily obtained commercially with high angular velocities in the range 50,000 to 100,000 RPM. Using a 5 cm-radius disk and an angular velocity of 60,000 RPM the tangential velocity on the disk border is 300 m/s. Such a system can be useful for many experiments to be done in the future at high-repetition rate XFELs. In addition to the speed, the system is also required to satisfy safety and durability criteria, while having the flexibility to be used for different types of experiments. Two options are to be considered: one in which the angular velocity is synchronized to the FEL pulses' repetition rate, and one in which it is not. The first case is needed for experiments such as femtosecond serial crystallography, the second for experiments using multi-pulse XFEL operation at near-GHz repetition rate. Grant applications are sought in the following subtopics: a. Development of High-Variable Speed Rotating Disks with Vibration Control and Long Lifetime In this subtopic applications are sought to develop a high-angular-speed rotating disk for sample delivery to a high-repetition-rate XFEL. The required tangential speed of the target must be in the 300 m/s range while the target remains well within the Rayleigh length of the FEL pulse. The system lifetime must exceed one day of operation at full speed and must operate in a Helium atmosphere with dimensions smaller than 30x15x15 cm in order to be placed at the focal point of the X-ray pulses for the nano- to micrometer focus beamlines available at LCLS/LCLS-II. The system must be also easily interchangeable during experimental runs. The disk angular velocity must be controllable, and in the case of use at MHz frequencies with a superconducting FEL, it must be possible to synchronize the angular velocity with the linac frequency. A full system demonstration is expected to be performed by the end of the contract. Questions - Contact: Eliane Lessner, Eliane.Lessner@science.doe.gov b. Other In addition to the specific subtopic listed above, the Department invites grant applications in other areas that fall within the scope of the topic description above.