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Description
To meet the strict luminosity requirements of the baseline design of the International Linear Collider (ILC), its positron source must provide a sufficiently intense positron beam. In a first step, positrons are produced inside a conversion target, either by an electron beam in the electron-driven scheme or by synchrotron radiation in the undulator-driven scheme. The resulting positron beam then emerges from the target with large divergency and therefore requires, in a second step, collimation to make the beam available for the downstream acceleration, damping and finally for the collision experiments. This matching process is achieved using a strong magnetic focusing field generated by an optical matching device (OMD), situated directly downstream of the target. Conventionally, such an OMD is realized by some arrangement of electromagnetic coils. Recently, however, a plasma lens has been considered as an alternative.
A plasma lens consists of a discharge plasma confined within a tapered capillary and generates a longitudinally varying magnetic field. Although this technology remains experimentally unproven, initial particle tracking simulations with an idealized model of a plasma lens have shown some promise. These results are now scrutinized with simulations examining the magnetohydrodynamic behavior of the plasma. From these simulations a three-dimensional magnetic field is obtained, which is then tested for its effectiveness as an OMD in subsequent particle tracking simulations.
