  We report the design of an angular array of electron Time-of-Flight (eToF)
spectrometers intended for non-invasive spectral, temporal, and polarization
characterization of single shots of high-repetition rate, quasi-continuous,
short-wavelength Free-Electron Lasers (FELs) such as the LCLS-II at SLAC. This
array also enables angle-resolved, high-resolution eToF spectroscopy to address
a variety of scientific questions of ultrafast and nonlinear light--matter
interaction at FELs. The presented device is specifically designed for the
Time-resolved atomic, Molecular and Optical science end station (TMO) at
LCLS-II. In its final version, it can comprise of up to 20 eToF spectrometers
aligned to collect electrons from the interaction point defined by the
intersection of the incoming FEL radiation and a gaseous target. There are 16
such spectrometers forming a circular equiangular array in the plane normal to
x-ray propagation and 4 spectrometers at 54.7$^\circ$ angle relative to the
principle linear x-ray polarization axis. The spectrometers are capable of
independent and minimally chromatic electrostatic lensing and retardation in
order to enable simultaneous angle-resolved photo-electron and Auger electron
spectroscopy with high energy resolution. They are designed to ensure energy
resolution of 0.25 eV across an energy window of up to 75 eV which can be
individually centered via the adjustable retardation to cover ranges of
electron kinetic energies relevant to soft x-ray methods, 0--2 keV. The full
spectrometer array will enable non-invasive and online spectral-polarimetry
measurements, polarization-sensitive attoclock spectroscopy for characterizing
the full time--energy structure of even SASE or seeded LCLS-II pulses, and also
supports emerging trends in molecular frame spectroscopy measurements.
