Simulations of ILC electron gun and bunching system Diagram of bunching system (from TESLA paper by Curtoni and Jablonka) -Electron gun generates electrons and accelerate them to 120keV -Bunching system shortens the bunch and further accelerates the electrons

Equipotential lines and current rays The electron gun Emittance at gun exit as function of laser radius z (mm) r (mm) Laser radius (mm)

Initial Particle Distribution -Random cylindrical angle added to get from radial line to disk -Particles started uniformly in time over 2ns in GPT -Emittance calculated using GPT agrees with Egun value y (m) x (m) y (m) z (m)

Axial solenoidal B-field Beam waist y (m) Axial magnetic field (T) z (m)

L-band buncher problem - buncher designed for  =1, but particles have  =0.58, so was unable to bunch and accelerate as needed - particles hit in first quarter wavelength, which either bunches and decelerates, or spreads and accelerates bunch - first cell of first buncher was spaced from the remaining four, and its phase varied independently to achieve required bunching Axial electric field (a.u.) z (m)

Histogram animation of e-bunch through bunchers

Length of bunch as it moves through bunching system Average z at given time (m) End to end bunch length (m)

Conclusions It was seen that reducing the laser radius from 10mm to 3.6mm gave an order of magnitude improvement in emittance at the end of the gun. The procedure developed to use the Egun output to specify the inital particle distribution in GPT allows for improved simulations of the bunch motion between the gun and the bunchers. Alterations to the first L-band buncher enabled the needed bunching and acceleration, but would require a high power phase shifter which is difficult to construct. Further work should go into developing a better bunching system, which is easier to implement, and into optimizing the solenoidal field.