ANL, Lemont, Illinois, USA
In order to maximise the injection efficiency from the booster synchrotron into the proposed Advanced Photon Source Upgrade storage ring, beam-based optimisation of the booster electron optical lattice is anticipated. In the present work, we present non-destructive beam size and emittance measurements using the booster synchrotron light monitor and destructive quadrupole scan emittance measurements in the booster to storage ring transport line. Destructive measurements are performed with a 0.1 mm thickness Cerium-doped Yttrium Aluminium Garnet screen. In order to characterise performance, both the beam energy at extraction (5, 6 and 7 GeV) and the bunch charge are varied.
Fermilab, Batavia, Illinois, USA
The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of a photocathode rf gun beam injecting two TESLA-type single cavities (CC1 and CC2) in series prior to the cryomodule. Beam propagation off axis in these cavities can result in both long-range and short-range transverse wakefields which can lead to emittance dilution within the macropulses and micropulses, respectively. Two configurations of a Hamamatsu C5680 streak camera viewing a downstream OTR screen were utilized to track centroid shifts during the macropulse (framing mode) for the long-range case and during the micropulse for the short-range case (~10-micron spatial resolution and 2-ps temporal resolution). Steering off axis before CC1, resulted in a 100-kHz bunch centroid oscillation within the macropulse that was detected by the downstream rf BPMs and the streak camera*. At 500 pC/b, 50b, and 4-mrad off-axis vertical steering into CC2, we observed an ~ 100-micron head-tail centroid shift in the streak camera image y(t) profiles which we attributed to a short-range wakefield effect. Additional results for kick-angle compensations and model results will be presented.
*A.H. Lumpkin et al., Phys. Rev. Accel. and Beams 21,064401 (2018).
Fermilab, Batavia, Illinois, USA
Private Address, Silver Spring, USA
The need for single-shot diagnostics of the periodic longitudinal density modulation of relativistic electrons at the resonant wavelength (microbunching) in a free-electron laser (FEL) or at broadband visible wavelengths as in a laser-driven plasma accelerator (LPA) has been reaffirmed. In the self-amplified spontaneous emission (SASE) FEL case, statistical fluctuations in the microbunching occur in the startup-from-noise process. In the LPA, the plasma itself is chaotic and varies shot to shot. Fortunately, we have shown that coherent optical transition radiation (COTR) techniques, can assess beam size, divergence, spectral evolution, and z-dependent gain (100, 000) of microbunched electrons in a past SASE FEL experiment at 530 nm*. Recently, the application to LPAs has been demonstrated with single-shot near-field (NF) and far-field (FF) COTR imaging done at the exit of an LPA for the first time**. In this case few-micron beam sizes and extensive fringes due to sub-mrad divergences were measured based on point-spread-function effects and an analytical model for COTR interferometry, respectively. A proposed diagnostics application at 266 nm to pre-bunched beams is also described.
*A.H. Lumpkin et al., Phys. Rev. Lett. 88, No.23, 234801 (2002).
**A.H. Lumpkin, M. LaBerge, D.W. Rule, et al., Proceedings of AAC18, (IEEE), 2019.