The Damping wigglers (DW) will be used in the storage ring of PETRA IV to reduce the transverse phase space of the electron beam by damping the emittance and increasing the brilliance of the light. As the electron emittance decreases, the intensity of higher harmonics in the emitted undulator spectrum increases. In a DW, the beam emittance is reduced because the electrons loose transverse momentum inside the DW. The electron energy is thereby compensated by the RF cavities resulting in overall emittance reduction. The radiation emitted by the DW is absorbed without effecting the beamline elements. DWs have been successfully used in PETRA III to achieve a record emittance of around 1.4 nm rad. For PETRA IV, a 20 pm beam emittance is aimed for. Permanent magnet based DWs will be installed at PETRA IV. The wigglers will have an approximate period length of λU = 74 mm with 22mm gap and a peak magnetic field amplitude of B = 0.85 T. Most of the wigglers will have a fixed gap and will reduce the emittance from the baseline value of 43 pm down to 20 pm. The undulators for the beamlines will also contribute to a visible extent to the beam damping. However, as undulator gaps are moved by the experiments in an arbitrary way, the emittance of the storage ring would not be constant over time. In order to mitigate this effect, some of the DWs are considered to be gap-variable so that they could compensate the insertion devices-induced emittance changes over time. Undulator-like standard mechanics and support structures will be employed for the gap variable DWs.
Contact: S.Yamin, M. Tischer
Publications and further literature:
Batrakov A.M., Vagin P.V., Vobly P.D. et al. Permanent magnet wigglers for reducing the emittance of the Petra III synchrotron radiation source. J. Surf. Investig. 5, 1038–1044 (2011). https://doi.org/10.1134/S1027451011110048
R. Bartolini et al., “Status of PETRA IV Machine Project”, in Proc. IPAC2022, Bangkok, Thailand, doi:10.18429/JACoW-IPAC2022-TUPOMS02 .
