1. RFI Characterisation of Karoo Array Telescope Structure P. Gideon Wiid (PhD) Howard C. Reader Riana H. Geschke Stellenbosch University December 2008

2. Where do I fit in? RFI - Radio Frequency Interference Extremely low RFI needed Earth-bound RFI, e.g. direct and indirect lightning strikes Scale model measurements Computational modelling Fig 1: Lightning strike

3. What am I doing and how? Correctly define and minimise RFI on KAT structure: Lightning policies – RAO sites RFI measurements – XDM @ HartRAO CEM Modelling and Measurement – KAT scale models MoM w.r.t. lightning, shielding Result analysis for RFI minimisation Fig 2: ADM design (June 2008)

4. What have I done? 1 Site Visits to: –Astron, LOFAR & Westerbork in Netherlands –Jodrell Bank & Manchester University in UK –Shielding of enclosures Measurements at HartRAO on XDM –Importance of loops Fig 3: Westerbork and HartRAO Observatories

5. What have I done? 2 2 nd Model - 1/40 th scale as per XDM Focus: structure, conduit and soil CADFEKO and CST verified by measurement Memory and license limitations Eskom load shedding CHPC runtimes 4 days, 1 day Towards ADM for KAT-7 Specific concerns re RFI on ADM Fig 4: XDM model with saltwater

6. What have I done? 3 3 rd 1/20 th Scale model – Willem Esterhuyse June 2008 ADM KAT-7, simplified Measurement – anechoic chamber Geometry replicated in CADFEKO CHPC runtimes / unknowns CADFEKO verified by measurement MoM investigations: lightning, shielding Fig 5: ADM Scale Model

7. What have I done? 4 Fig 6: Excitations on ADM model with LDC Indirect lightning strike – EM plane wave Direct lightning strike – current injection Consider LDC, shielding Electric field strengths Current densities Runtimes / file-sizes CHPC and SU HPC

8. What have I done? 5 EM Plane Wave Current density Magnetic flux cutting closed conducting loop Top & bottom struts “hot” Other positions Edges “hot” Shadowing Bearings Fig 7: Current densities on dish struts

9. What have I done? 6 Current injection Current distribution struts Injection source loop influences levels Shielding – top closed Raised structure: “hot” Cables entering: “hot” Partial shields for cost Feedback to SKA Fig 8: Electric field around and inside structure

10. Where am I going? Project plan: 2009 –CADFEKO Investigations: Lightning protection over bearings Pedestal shielding, earthing interfaces –Result analysis: cost-effective RFI solutions –Feedback to SKA offices, influencing design

11. Confucius says Confidence built for CADFEKO usage E-fields, Current density Shielding, earthing interfaces LDC layout and design LDC over bearings Cost-effective solutions

12. Conclusions Confidence built for CADFEKO usage E-fields, Current density Shielding, earthing interfaces LDC layout and design LDC over bearings Cost-effective solutions

13. Whether you believe you can do a thing or not, you are right. - Henry Ford Acknowledgements -SA SKA for bursary and travel grants -Eskom TESP for bursary grants -CST for use of Microwave Studio -EMSS for CADFEKO license and usage -Mel van Rooyen at EMSS for CADFEKO support -Willem Esterhuyse for enormous mechanical insights in scale model -Prof. DB Davidson, Danie Ludick and Evan Lezar for help in setting up simulations and CADFEKO on CHPC and SU HPC -CHPC and SU HPC for usage of facility Are we done yet?