Equipartition design method of a quasi-periodic focusing-accelerating coupled system

Intense-beam proton linac sets a very severe requirement on the control of beam loss and emittance growth. Beam physics theory demonstrates that coupling of the strong space charge effect between different freedoms with different temperature will surely increase the beam emittance in the way of beam coherent instability. Therefore it is necessary to design an intense beam accelerator in accordance with the equipartition principle. However, this design is too tedious to reach full equipartition because the real proton linac is a quasi-periodic coupling system. Thus, the authors made a few modifications to TRACE3-D, which is a popular code in beam dynamics, and added the equipartition design function to it. When the modified TRACE3-D is used together with the PARMILA code, it is easy to realize equipartition. The author will introduce the modification to TRACE3-D code, and then illustrate its application to the design of a DTL linac section, which shows the importance of equipartition design in the intense beam linac