Demonstration of a High-Field Short-Period Superconducting Helical Undulator Suitable for Future TeV-Scale Linear Collider Positron Sources

The first demonstration of a full-scale working undulator module suitable for future TeV-scale positron-electron linear collider positron sources is presented. Generating sufficient positrons is an important challenge for these colliders, and using polarized $e^{+}$ would enhance the machine’s capabilities. In an undulator-based source polarized positrons are generated in a metallic target via pair production initiated by circularly polarized photons produced in a helical undulator. We show how the undulator design is developed by considering impedance effects on the electron beam, modeling and constructing short prototypes before the successful fabrication, and testing of a final module.

Figure 1

(Left) Example 3D model showing the field in the winding blocks (red) with an iron former (green). (Right) 3D modeling results of $W_b$ vs ${\lambda }_u$ (points) and a line of best fit to the data.

Figure 2

Photographs of four of the short undulator prototypes (left), 4 m long cryomodule, containing two 1.74 m long undulators, being tested (right).

Figure 3

Training curves (a) and K per period (b) for M1 (black lines) and M2 (gray lines). Number of photons per electron per 10 keV bandwidth (c) and CP rates (d) for measured fields (black lines) and ideal fields (gray lines).