Design, construction, and testing of a radiofrequency electron photoinjector for the next generation linear collider

The design of a high bunch charge (8 nC), low emittance ({dollar}le{dollar}20 mm-mr) diofrequency electron photoinjector matched to the requirements of the TESLA Test Facility is presented. A 1.625-cell iris-coupled {dollar}pi{dollar}-mode structure with high average accelerating gradient is chosen for its high shunt impedance, simplicity, and ability to accommodate an externally mounted solenoid for simultaneous beam divergence control and emittance compensation. A novel split-solenoid focussing assembly is employed, allowing emittance compensated beam extraction over a wide range of gun gradients. Beam optics are optimized for an overall injector consisting of the electron gun followed by one linac capture section (providing acceleration to 18 MeV), and a dipole chicane for magnetic bunch compression to achieve a bunch length {dollar}sigmasb{lcub}z{rcub}{dollar} = 1 mm. Analytic and simulation work yielding a space charge emittance compensated gun design in a new high charge regime is detailed. Experimental measurements made on a prototype gun and injector at the Argonne Wakefield Accelerator Facility are detailed. Experimental results indicate a beam of 8 nC charge with bunch length {dollar}approx{dollar}1.1 mm has been produced at emittances of less than 60 {dollar}times{dollar} 60 {dollar}pi{dollar} mm-mr at an energy of 16 MeV with an energy spread of 240 keV. Experimental results, although in significant disagreement (by a factor of two) with initial simulations (which assume idealized laser properties), are in fair agreement with simulations carried out using the measured performance of the laser.