Our beam-beam parameter study using beam-beam simulations and PWFA
(particle-driven plasma acceleration) beam parameters indicates that at 3 TeV,
for examined electron beam lengths 2 μm≤σz​≤10 μm, the total luminosity, as well as the sharpness of the
luminosity spectrum for a γγ collider are independent of the beam
length of the electron beams used to scatter the photons, given that the
hourglass effect is avoided. The total luminosity can consequently be maximised
by minimising the horizontal and vertical beta functions βx,y∗​ at the
interaction point.
Furthermore, we performed background studies in GUINEA-PIG where we
considered the smallest currently achievable βx,y∗​ combined with PWFA
beam parameters. Simulations results show that our proposed parameter set for a
3 TeV PWFA γγ collider is able to deliver a total luminosity
significantly higher than a γγ collider based on CLIC parameters,
but gives rise to more background particles