|
abstract:
|
Laser driven RF photocathodes represent a recent advance in high-brightness electron beam sources. The authors investigate here a variation on these devices, that obtained by using a ribbon laser pulse to illuminate the cathode, yielding a flat beam (sigma_x >> sigma_y) which has asymmetric emittances at the cathode proportional to the beam size each transverse dimension. The flat-beam geometry mitigates space charge forces which lead to intensity dependent transverse and longitudinal emittance growth, thus limiting the beam brightness. The fundamental limit on achievable emittance and brightness is set by the transverse momentum distribution and peak current density of the photo-electrons (photon energy and cathode material dependent effects) and appears to allow, taking into account space charge and RF effects, normalized emittances epsilon_x <1x10(-4) m-rad and epsilon_y < 10(-6) m-rad, with Q = 5 nC and sigma_z = 1 mm. These source emittances are adequate for superconducting linear collider applications, and could preclude the use of a damping ring for the electrons in these schemes.
|