We report on the experimental generation of a train of subpicosecond electron bunches. The bunch train generation is accomplished using a beamline capable of exchanging the coordinates between the horizontal and longitudinal degrees of freedom. An initial beam consisting of a set of horizontally-separated beamlets is converted into a train of bunches temporally separated with tunable bunch duration and separation. The experiment reported in this Letter unambiguously demonstrates the conversion process and its versatility.
An experimental program to demonstrate a novel phase space manipulation in which the horizontal and longitudinal emittances of a particle beam are exchanged has been completed at the Fermilab A0 Photoinjector. A new beamline, consisting of a T M110 deflecting mode cavity flanked by two horizontally dispersive doglegs has been installed. We report on the first direct observation of transverse and longitudinal emittance exchange: {ε nx , ε n y , ε n z }={2.9 ± 0.1, 2.4 ± 0.1, 13.1 ± 1.3}⇒{11.3 ± 1.1, 2.9 ± 0.5, 3.1 ± 0.3} mm-mrad.
The possibility of using electron-beam phase-space manipulations to support a free-electron laser accelerator design optimization has motivated our research. An ongoing program demonstrating the exchange of transverse horizontal and longitudinal emittances at the Fermilab A0 photoinjector has benefited recently from the upgrade of several of the key diagnostics stations. Accurate measurements of these properties upstream and downstream of the exchanger beam line are needed. Improvements in the screen resolution term and reduced impact of the optical system's depth of focus by using YAG:Ce single crystals normal to the beam direction will be described. The requirement to measure small energy spreads (< 10 keV) in the spectrometer and the exchange process which resulted in bunch lengths less than 800 fs led to other diagnostics performance adjustments and upgrades as well. Application of these diagnostics in demonstrating the exchange of transverse (x) and longitudinal phase spaces is also reported.
One of the goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange (EEX) principle. Coherent synchrotron radiation in the emittance exchange line could limit the performance of the emittance exchanger at short bunch lengths. In this paper, we present experimental and simulation studies of the coherent synchrotron radiation (CSR) in the emittance exchange line at the A0 photoinjector. We report on time-resolved CSR studies using a skewquadrupole technique. We also demonstrate the advantages of running the EEX with an energy-chirped beam.
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