Beam optics simulations of achromatic section of Delhi Light Source

The Delhi Light Source is an upcoming user facility for coherent THz radiation and electron beam. Electron beam of energy upto 8 MeV generated from a RF photo-cathode gun will be used for coherent THz generation from a planer undulator. The beam after passing through the undulator field will be separated from the THz and THz line by a $60^{o}$ achromatic section and delivered to electron experimental area. Simulation studies has been performed to achieve achromatic condition and acceptable beam size at the electron experimental area for the case of electron transmission through non-trivial undulator field. However for the case of open gap undulator (no THz generation), the study shows that the same design gives a limited control on the overall beam size at the electron experimental area. To overcome this the extended quadrupole correction (EQC) coils of the undulator can be used as a suitable focussing element to achieve required beam size control in addition to the achromatic condition. The paper presents the simulation studies of the achromatic section for both with and without(open gap) undulator field.