1. Stave Core Electrical Considerations Ned Spencer (UCSC), Sergio Diez (DESY), David Lynn (BNL) Local Support Assembly, AUW Nov 3 2014 1

2. 2 Electrical Isolators. 2.275 mm OD Ti pipe internal to stave — 2.5 mm OD pipe external Drawings by Peter Sutcliffe→ https://twiki.cern.ch/twiki/bin/viewauth/Atlas/UKThermoMECHDocs Note both isolators are identical; there are no capillaries (0.8 mm OD) into the stave

3. 3 Dual purpose Kapton cable proposal Kapton Cable Proposal From Mike Dawson Two conductor cable 2. NTC 1.Electrical insulates isolator’s nipples But only need to isolate this nipple

4. 4 Motivation Just before the September ITK meeting Mike wanted comments on his cable proposal as well as suggestions on how to ground the pipe to the foam This led to discussions at the ITK about stave grounding and the electrical isolators This talk is the beginning of the considerations of the stave core grounding scheme Plan is for Ned, Dave, and maybe a few others to generate and short stave core grounding requirements document There is some opposing considerations between wanting to “RF ground everything” (Ned) and keeping the stave core easy to build (Dave) We expect these electrical grounding considerations will be very useful for the petals as well

5. 5 Stave Lumped Element Model Preliminary model for discussion of necessary connections (e.g. transverse facing resistances not yet included) Boldface lines shows ground connections we think we need (via discussion with Ned) A. Ti pipe, foam, and facings to EOS. One location for each element only B. DC connection (e.g. pins) between adjacent foam pieces A B

6. 6 Stave Lumped Element Model at 2.5 MHz In blue are shown capacitive and inductive impedances at 2.5 MHz, estimate peak of ABC130 bandwidth. See backup slides for bandwidth estimate. Note at 2.5 MHz  = 120 m >> 1.3m stave length; lumped element model holds

7. 7 Inputs for Stave Lumped Element Model Resistance of K9 Allcomp foam =.15  : Assumes  foam ≈ 4.3 x 10 -3   cm Measured at UCSC Half length foam dimensions 15 cm x 5.2 mm x 10 mm Don’t yet know AC characteristics (Ned to study) Longitudinal resistance of facing = 0.6  :  face ≈ 4.3 x 10 -3   cm Calculated for two layers of 45 gsm K13C2U fiber assuming electrical resistivity quoted in K13C2U data sheet of  K13C2U ≈ 1.9 x 10 -4   cm. Should be measured. Resistor dimension 15 cm long, 10 cm wide, 40  m thick. Don’t yet know AC characterstics (Ned to study) Resistance of Ti Pipe = 0.1  : Assume  Ti = 5 x 10 -5   cm Source: http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTU020http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTU020 Resistor dimension, 15 cm long, 2.275 mm OD, 100  m wall Ned measured 4.3 x 10 -5   cm Capacitance of foam to facing ~ 2.5 nF 30 cm long sections, 50  m hysol/BN thickness, 10 mm wide foam dielectric constants of hysol and BN are 4 and 4.5 respectively. Assume 4.2 as average.

8. 8 Things to Consider for Stave Lumped Element Model Capacitance of foam to pipe ~ 1 nF 30 cm long sections, 100  m hysol/BN thickness, 10 mm wide foam dielectric constants of hysol and BN are 4 and 4.5 respectively. Assume 4.2 as average. Inductance of 1 mm pin connecting foam pieces < 1 nH Complete guess for now. Should be small but need to consider what is the current loop. Model to be used to understand couplings and grounding

9. 9 Pipe grounding Our specially ordered pipe has a thinner than normal oxide on surface; it is electrically conductive One option is to braze litz wire between nipple/pipe joint, but we haven’t found a small litz wire yet to try. Also, litz wire looses effectiveness > 3 MHz. Maybe make a square metal collar (see figure) that allows a low inductance kapton/copper ground plane to be glue into seem. Collar is Ag-epoxy connected to pipe. Bonus is that NTC (thermistor) has a flat surface on which to mount.

10. 10 Foam grounding One possible idea In any case grounding the foam should not be difficult

11. 11 Simultaneous Foam Pipe Grounding + NTC for Interlocks Later make out of Titanium for CTE match with pipe? Update. To avoid Ag-epoxy, Ned suggests maybe plating part of Ti pipe and then soldering a metal tab to it (replaces collar). Is this possible?

12. 12 Carbon fiber facing grounding Resistance between layers of 0/90/0 layup now being investigated Capacitance between layers should be measured as well For now LBNL will investigate embedding of metal strip in EOS region during co-cure Possible suggestion where metal runs through slits in pre-preg to contact all three layers

13. 13 Foam to Foam Connection Want to ground all foam pieces So connect adjacent foam blocks with pins or some other mechanism Ned suggests Kapton tubes with a sputtered nickel rather than pins to give larger surface contact area. Use epoxy to keep contacts airtight. Note: pipe not shown

14. Additional Connections? Do we need to ground honeycomb? Do we need to ground C-channels? In both cases Ned suggests we should, but this may be difficult. We will study this Also, do both the inlet and outlet side of pipe need grounding (rather than just one or the other?)

15. 15 Next Steps Continue to measure/characterize each element in terms of RF behavior Better understand where/which DC connections are needed Design best/simplest connection methods Write up a short electrical requirements documents (Ned, Dave, others?) Determine if there is a good way to make useful measurements on an actual stave to verify expected RF behavior

16. 16 Backup Slides

17. 17 RF Frequencies of Interest Assumption is most sensitive electrical element is the high gain input of the ABC readout chip Have been unable to obtain frequency response of ABC chip from designers So use a published ABC shaping function and make an LTspice model with a similar response function Then generate a Bode plot from that LTspice model to obtain the frequency response

18. Circuit to Mimic ABC Impulse Response 1 fC impulse response shown Used a ABC130 paper to approximate the impulse response Unlike ABC130 this circuit inverts; easier to implement with standard LT Opamp models 1 fC impulse response 18

19. Circuit to Mimic ABC Impulse Response : Frequency Response 19 Bode plot

20. Circuit to Mimic ABC Impulse Response : Frequency Response on Linear Scale 20 30 MHz100kHz 2.5 MHz

21. 21 Related Note: Detector with Two Hybrid LTspice model Hybrid ABC Sub-circuit of previous slides Available if anyone wants it; email D. Lynn