Investigation of Radiation Damage of Insertion Devices at PETRA III due to Particle Losses using Tracking Results with SixTrack

PETRA III is a 3 generation synchrotron light source dedicated to users at 14 beamlines with 30 instruments since 2009. The horizontal beam emittance is 1 nmrad while a coupling of 1% amounts to a vertical emittance of 10 pmrad. Some undulators and wiggler devices have accumulated total radiation doses of about 100 kGy. Doses measured regularly by Thermo Luminescent Dosimeters (TLDs) are monitored, which lead to inspect the magnetic field of all insertion devices in the PETRA tunnel. We are investigating particle losses with tracking simulation using SixTrack to gain a certain understanding of the radiation damage of the insertion devices. The goal is to develop a strategy to protect the insertion devices from further radiation damage. INTRODUCTION PETRA III [1, 2] is a 3 generation synchrotron light source operating with electrons at beam energy of 6 GeV which is an upgrade of the previous machine PETRA II. The horizontal beam emittance of 1 nmrad is achieved using 20 damping wigglers each of 4 m length, while a coupling of 1% amounts to a vertical emittance of 10 pmrad. The machine is dedicated to users at 14 beamlines with 30 end-stations. Parts of PETRA III [3] have recently been rebuilt to accommodate 12 new beam lines including a super luminescence in near UV beamline providing bending magnet radiation. PETRA III operates with several filling modes, such as 40, 60, 240, 480 and 960 bunches with a beam current of 100 mA. The insertion devices (IDs) and other accelerator components are expected to experience extreme radiation in synchrotron light sources especially where higher beam energies, beam currents and smaller gaps are in place. It is worth to mention that, permanent magnets operating under conditions of high radiation are especially susceptible to demagnetization [4] caused by direct and scattered radiation induced by electrons, positrons, highenergy photons and neutrons. Serious demagnetization has been observed in some of the operating light sources such as ESRF, where insertion devices experienced field losses of as much as 8% [5] and at the APS [6]. Here we report a partial demagnetization profiles which is not linear along the device [7, 8] in some of the IDs in PETRA III caused by radiation, similar loss patterns are also clearly seen in tracking results. To protect the IDs additional collimators have been installed at PETRA III. OBSERVATION OF RADIATION DAMAGE OF INSERTION DEVICES Inspection of the magnetic structures and in-situ magnetic peak field measurements revealed a partial demagnetization of devices exhibiting performance losses. Some results of these measurements are summarized in Fig. 1 [7]. Devices located upstream in canted straight sections as PU02 and PU08 are damaged at the entrance end of the magnet structure while the downstream located device PU03 is damaged at the exit end (Fig. 1a). The measured decrease of the peak field is attributed to radiation damage and is most likely caused by particle losses. Figure 1: Recently measured longitudinal normalized peak field variation of (a) 2 m devices, (b) 5 m devices installed in PETRA III verses longitudinal position in mm. A similar situation is observed for the 5 m long devices (Fig. 1b). In sector 1, the upstream device PU01a is strongly damaged at the upstream end. The 5 m device PU10 also confirms the damage pattern observed at the 2 m devices installed in the canted straight sections. PU10 is installed in a standard (not canted) straight section. PU10 shows signs of demagnetization at the entrance and ___________________________________________ # gajendra.kumar.sahoo@desy.de Proceedings of IPAC2015, Richmond, VA, USA MOPWA041 5: Beam Dynamics and EM Fields D02 Nonlinear Dynamics Resonances, Tracking, Higher Order ISBN 978-3-95450-168-7 203 Co py rig ht © 20 15 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs the exit of the device. Moreover, a comparison of data taken in 2012 and 2013 shows that in spite of the decreasing total dose measured with TLDs the damage seems to continue unabatedly (Fig. 2) and have accumulated total radiation doses of about ~100 kGy in some undulator devices [9]. Radiation damage of IDs follows a general pattern that devices located at the entrance of a straight section are damaged at the upstream end while devices installed at the exit of a straight section show signs of demagnetization at the downstream end. This seems to indicate that particle losses occur in the vertical plane at locations where the beta functions become large while the physical aperture limits are still very small. Particle tracking studies are made to find a way to mitigate these events. Figure 2: Integrated radiation dose accumulated at every insertion device from the first day of its installation as measured by TLDs.