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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.

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The energy loss spectrum of 150 GeV muons has been measured with a prototype of the ATLAS hadron calorimeter in the H8 beam of the CERN SPS. The differential probability dP/d upsilon per radiation length of a fractional energy loss upsilon = Delta E(mu)E(upsilon) has been measured in the range upsilon = 0.01 divided by 0.95; it is compared with the theoretical predictions for energy losses due to bremsstrahlung and production of electron-positron pairs or of energetic knock-on electrons. The integrated probability integral(0.01)(0.95)(dP/d upsilon)d upsilon is (1.610 +/- 0.015(stat) +/- 0.105(syst)). 10(-3) in agreement with the theoretical predictions 1.556 . 10(-3) and 1.619 . 10(-3). Agreement with theory is also found in two intervals of upsilon where production of electron-positron pairs and knock-on electrons dominates. In the region of bremsstrahlung dominance (upsilon = 0.12 divided by 0.95) the measured integrated probability (1.160 +/- 0.040(stat) +/- 0.075(syst)). 10(-4) is in agreement with the theoretical value of 1.185 . 10(-4), obtained using the Petrukhin and Shestakov description of the bremsstrahlung process. The same result is about 3.6 standard deviations (defined as the quadratic sum of statistical and systematic errors) lower than the theoretical prediction of 1.472 . 10(-4) obtained using Tsai's description of bremsstrahlung