Ensinger, W.

Floch, E.

Lima, V.

Mustafin, E.

Seidl, T.

Trautmann, C.

GSI Repository

In-Situ High Voltage Tests on Pristine and Irradiated Polyimide * V. Lima1,2, #, T. Seidl1,2, E. Mustafin1, E. Floch1,C. Trautmann1,2, and W. Ensinger21GSI, Darmstadt, Germany; 2Technische Universität Darmstadt, GermanyConcerning radiation hardness, organic materials suchas polymeric insulators are identified as highly sensitivetowards ionizing radiation compared to inorganicmaterials [1]. Despite this fact, these materials are widelyused in accelerator components since they have favourable properties for application, often better thancomparable inorganic materials. Due to their superiormechanical and dielectric properties, even if irradiatedwith swift heavy ions [1], polyimides are commonly usedas insulator in beam-guiding magnets in ion beamfacilities such as the synchrotrons and storage rings of theplanned Facility for Antiproton and Ion Research (FAIR).FAIR will provide highest beam intensities, and beam losses will partly induce high secondary radiation fieldsduring the pulsed operation of the accelerator. Formerstudies of radiation induced modifications of electricalproperties of polyimide focused on ex-situ measurementsof (i) breakdown voltage [1] and (ii) electricalconductivity and dielectric constant [2].During accelerator operation, the insulators in themagnets are exposed to particle radiation and additionallyto electromagnetic fields. Because irradiation-induceddamage can initiate electrical breakdowns events [3], thisstudy tackles in-situ breakdown voltage tests during thedirect exposure of the material to ion beams. For thispurpose, a setup was built where non-irradiated and ionirradiated polyimide samples are mounted between twoelectrodes and a potential is applied between them.              Figure 1: Schematic presentation (left) and photograph(right) of experiment setup.50-μm thick KaptonTM-type polyimide foils with an areaof 50 × 50 mm2 were cut from commercial rolls. Sampleswere irradiated at the UNILAC (X0-beamline) with 11.1-MeV/u ruthenium ions and fluences up to 1012 cm-2(corresponding to a radiation dose of 8 MGy). For the in-situ breakdown voltage test, samples were mountedbetween two copper electrodes (see scheme Fig.1 left).These electrodes had a rounded-edge-geometry to avoidincreased electrical fields at the edges. The thickness ofthe electrodes was 2 mm, suitable for the irradiationexperiment due to the penetration depth of the ion beam(6 mm in copper, calculated with SRIM-2010 code). Theelectrode-sample configuration was attached to aglassfiber/composite sample holder having a thickness of1 mm. Breakdown measurements were conducted using ahigh voltage power supply (max. voltage: 7 kV) viacurrent measurements with a current clamp. Additionally, the dark current of the high voltage power supply wasmonitored with an oscilloscope.The in-situ-irradiation experiment was carried out at SIS 100 (Cave A). At first, a voltage of 500 V wasapplied to the electrodes. Subsequently, several spills of uranium ions (E= 500 MeV/u) were applied for. The fluxof the beam was about 2×108 cm-2s-1, while the size of thebeam spot was about 0.5 cm2. When no breakdownoccurred, the potential was increased in 500-V-steps andthe irradiation procedure was continued for eachpotential.For pristine non-irradiated samples no breakdown wasdetected after irradiation with about 20 spills (~ 4×109cm-2) up to the maximum potential of 7 kV. However,during a spill of ions, the dark current shortly increased.Samples pre-irradiated with Ru ions of fluences 5×1011cm-2, failed without or after a few U spills at electricalfields >1 kV.. This is ascribed to the dielectric strengthreduced by the Ru ion irradiation. Below 1 kV we did notobserve break down events of pre-irradiated samples.However, due to time constraints this stability was nottested over extended time periods.Samples pre-irradiated with 1012 Ru-ions cm-2 showedsurface flashovers at already low electrical fields ~1 kV.Due to ion-induced carbonization, the samples were blackindicating that the surface conductivity is already too highto be used as insulator.In summary, ion irradiated samples have in general alower dielectric strength, but there was no correlation observed between direct ion irradiation and in situbreakdown events [1] T. Seidl, A. Plotnikov, E. Mustafin, R. Lopez, D. Severin, E. Floch, C. Trautmann, A. Golubev, A.Smolyakov, D. Tommasini, and W. Ensinger, PolymerDegradation and Stability 97 (2012) 2396.[2] J.-P. Salvetat, J.-M. Costantini, F. Brisard, and L. Zuppiroli, Phys. Rev. B 55 (1997) 6238.[3] C. L. Wadhwa, “High Voltage Engineering”. NewAge International Publishers, New Delhi, 2007.* Work supported by BMBF project No. 06DA7027.# v.lima@gsi.deGSITemplate2007PNI-INHOUSE-EXP-35 GSI SCIENTIFIC REPORT 2012404

In-Situ High Voltage Tests on Pristine and Irradiated Polyimide

http://repository.gsi.de/record/52296/files/PNI-INHOUSE-EXP-35.pdf

In-Situ High Voltage Tests on Pristine and Irradiated Polyimide

Abstract

Similar works

Full text

Available Versions

GSI Repository