1. Preamps (PRE) and Sensors Rachel Hochman John Bonnell Space Sciences Laboratory University of California, Berkeley CDR September 30-October1, 2009 RBSP-EFW CDR 2009 9/30-10/1

2. Overview Motivations and Driving Requirements Sensors and Enclosures Resources: Mass, Power Schematics Frequency Response: modeling, bench testing, fully-assembled PWB Layout and Fabrication Parts Derating and Stress Analysis Radiation Effects Testing: TID and DDD ETU Thermal Qualification Test Plan and Flight Test Procedures Backup Slides RBSP-EFW CDR 2009 9/30-10/1

3. Motivation (In Words) The EFW Sensors, Preamp, BEB and EFW-EMFISIS interface represent the primary analog signal path for E-field measurements on RBSP. Measuring 0.1 mV/m DC E-fields required accuracies of 0.1% in the magnetosphere: –tens of mV of signal in the presence of tens to hundreds of mV/m of effective common-mode or systematic noise (photocurrents, SC charging), or tens of volts of common mode signal. The non-linear coupling (I-V curve) of EFW sensors to the external E-field can be optimized through current biasing (factor of 100 decrease in susceptibility to systematic error sources and density fluctuations). This current biasing of sensors drives volts to tens of volts floating potential differences between sensors and SC ground. High effective source impedance (plasma sheath, ten of MΩ), and low-noise and low-leakage current requirements (systematic error reduction again) drive use of low-voltage preamps in floating ground configuration. Deflection and collection of stray photoelectron currents prior to impingement upon sensor also reduces DC biases (WHIP/USHER and GUARD surfaces). RBSP-EFW CDR 2009 9/30-10/1

4. Board Requirements/Specs Driving Environmental Requirements –Radiation (TID and Deep Dielectric Discharge) –Temperature (sunlit to eclipse swings) Driving Measurement Requirements –0.3-mV/m accuracy at DC in the spin plane (EFW-49). –0.4-mV/m accuracy at DC on the spin axis (EFW-52). –400-mV/m signals in the kHz band (large-amplitude EM fluctuations). –400-kHz bandwidth with low noise floor (EMFISIS interface). Reference numbers from: RBSP_EFW_SYS_001H_Requirements.xls RBSP-EFW CDR 2009 9/30-10/1

5. EFW – Preamp RBSP-EFW CDR 2009 9/30-10/1

6. SPB Preamp Sensors and Enclosures SPB enclosure directly derived from THEMIS-EFI (20 units on- orbit 19 months); minor modifications to accommodate DDD-mitigation caps. fine wire usher surface guard surface SPB cable OP-15 and rad shield RBSP-EFW CDR 2009 9/30-10/1

7. AXB Preamp Sensors and Enclosures AXB enclosure is AXB sensor (spherical shell). Includes 7-mm Al equivalent 4π radiation shields around OP-15. Sphere Whip (Stub or Usher) Hinge (Guard) RBSP-EFW CDR 2009 9/30-10/1

8. The Preamps Themselves Each SPB PRE as shown weighs 3 g, with a 10-g Tantalum cover (13 g total). Each AXB PRE assembly masses 13 g. POWER Consumption: each preamp draws 3 mA of current per supply (+/-15V) within expected range of inputs/ operational environmental limits. RBSP-EFW CDR 2009 9/30-10/1

9. Schematic (SPB) RBSP-EFW CDR 2009 9/30-10/1

10. Schematic (AXB) RBSP-EFW CDR 2009 9/30-10/1

11. Sheath impedance is Rs || Cs, and connects to SPHERE. Output load is Cc || (Rc + RL), connected to Vout. EFW – Preamp Response Model RBSP-EFW CDR 2009 9/30-10/1

12. Faraday Box can be Grounded or Driven by Signal Generator. Measuring AC gain in both configurations allows for estimation of C stray and C i. EFW – Preamp Measuring Input Impedance RBSP-EFW CDR 2009 9/30-10/1 SPB PRE Stray Capacitance – Sphere and Fine Wire To Box Signal Gen

13. Bench Testing RBSP-EFW CDR 2009 9/30-10/1 Little difference in AC gain between Grounded and Driven configurations. Stray capacitance small. AC Gain ≈ Cs/(Cs+Ci) → Ci ≈ Cs*(1/Gv -1) ≈ 5 pF

14. ETU PRE and Cable Response RBSP-EFW CDR 2009 9/30-10/1 Sphere and partially-deployed Fine Wire in F-Box, with ETU SPB. Plasma Sim is 80-MΩ ║ 10-pF (worst case magnetospheric). Grounded AC Gain ≈ 0.7. Driven AC Gain ≈ 0.4. C i ≈ 7.5 pF, C stray ≈ 7.5 pF. Increasing plasma density: Moves knee to higher frequency (R s decreases). Moves AC gain closer to 1 (increases C s as Debye length approaches dimension of sensor).

15. ParameterDescriptionSPBAXB R s [Mohm]Sheath resistance50 C s [pF]Sheath capacitance144 Re [kohm]ESD protection – resistor100 Ce [pF]ESD protection – bypass capacitor 10 Ri [Tohm]Follower -- input resistance 1 Ci [pF]Follower – input capacitance 7.5 Ro [ohm]Output resistor100 Lc [m]Cable length487 dC/dL [pF/m]Cable cap/length100 dR/dL [ohm/m]Cable resistance/length1.5 RL [kohm]Load resistance100 EFW – Preamp Predicted Frequency Response Worst case Magnetospheric response, based on measured ETU input impedance (Aug 2009). RBSP-EFW CDR 2009 9/30-10/1

16. Layout (SPB) RBSP-EFW CDR 2009 9/30-10/1

17. Layout (AXB) RBSP-EFW CDR 2009 9/30-10/1

18. Board Fabrication The boards are made of Arlon 85NT, which is a polyimide resin on Thermount (non-woven aramid) to minimize differential CTE over broad temperature ranges experienced by the preamp PWBs: – -135 C to + 90 C; THEMIS-EFI experience. – -150 C to +70 C; RBSP-EFW CBE. Thermount is hygroscopic, therefore extra care must be exercised in handling and storing to avoid moisture absorption, and the boards must be baked out prior to mounting parts. Assembly instructions covering this already in-place. Coupons for both SPB and AXB PWBs are in-house, and will be sent out for testing in Q3 2009, according to schedule. RBSP-EFW CDR 2009 9/30-10/1

19. Derating All preamp components meet the voltage and stress derating guidelines set forth in EEE-INST-002.pdf Temperature range effects taken into consideration. Complete table with values in backup slides.

20. Radiation (TID) Testing As per an I-PDR RFA (REF#), a TID test of the flight lot and date code of OP-15 was performed. At 100-kRad(Si) TID, the only relevant parametric change was in VOS, which rose to as high as 32 mV, but was stable. EFW ConOps includes on-the-fly removal of differential offset voltage effects, so this magnitude of VOS (equiv. to up to.4 mV/m on 80-m antenna) can be tolerated, and still achieve measurement requirements. Test Report: ftp://apollo.ssl.berkeley.edu/pub/RBSP/1.2. Systems/3. Test/RBSP_EFW_TR_005_OP15TIDTest.doc RBSP-EFW CDR 2009 9/30-10/1

21. Deep Dielectric Discharge Mitigation The preamp enclosure does not provide 350-mil Al equivalent shielding for the preamp components, so evaluation of DDD susceptibility required. The OP-15 op amp was tested for susceptibility to damage by DDD using the test defined in the RBSP EMECP. Only pins found to be susceptible at the 1500-V test level were the COMP inputs. Mitigation capacitors were added between the COMP inputs and FGND, and were found to have no significant impact on frequency response. One N/C pin was also connected to FGND to implement the “no floating conductors allowed” requirement. Complete test report available on RBSP-EFW FTP site: ftp://apollo.ssl.berkeley.edu/pub/RBSP/1.2. Systems/3. Test/RBSP_EFW_PRE_TR_001A_OP15DDDTest.doc RBSP-EFW CDR 2009 9/30-10/1

22. ETU Thermal Qualification One survival cycle, two operational cycles. Survival cycle from -170 to +90 (powered off). Operational requirements are -160 to 80. With and additional 10 degrees at each extreme, the operational cycle tests were run at - 170 and +90 (powered on). Power cycle tests performed at extreme high and low limits. Cold limit is met in eclipse, and EFW not required to make measurements in eclipse, and so units must survive cold, but need not stay in spec. RBSP-EFW CDR 2009 9/30-10/1 Temperature profile for operational cycles

23. Load Preamp PWB Integrate Preamp PWB and Sphere to Cable Test Preamp PWB. Bench and Thermal. Test Preamp PWB. Bench and Thermal. Integrate Cable Assembly to SPB Chassis Stow Cable Adjust limits and setpoints Electrical Functional Test Functional Deploy/ Length Calibration Stow Cable Electrical Functional Test Vibration Test Electrical Functional Test Hot TVAC Deploy Stow Cable Cold TVAC Deploy Electrical Functional Test Deliver to Science Cal PER Test Flow (example of PRE→SPB)

24. Test Procedure for Flight THEMIS procedures used with slight modifications; for example: –preamp supply is now at +/- 15V rather than +/- 10V. –Large amplitude input tests in addition to lower amplitude frequency response. New documents: –RBSP_EFW_PRE_BenchTest_Proc.xls for board level checkout, –RBSP_EFW_PRE_TVAC_Proc.xls for thermal vacuum testing. RBSP-EFW CDR 2009 9/30-10/1

25. BACKUP SLIDES

26. Grounding the ground on the board is the floating ground from the LVPS and comes into the board on the shield pin. RBSP-EFW CDR 2009 9/30-10/1

27. Part TypePart NumbersRatingDerating Percentage (voltage, power) at 90C Expected V, Power CWRC1A, C1B50V40%, n/a (50% at 70C) 15 V CDRC2, C3, C4100V60%, n/a< 15 V RMR1, R2, R450V, 50mW46%, 35% (80%, 60% at 70C) R1 <15V,2mW R2 <1V,10mW R4 <1V, 1mW RMR3100V, 250mW46%, 35% (80%, 60% at 70C) 40 V,.02mW Derating and Stress (Ref. EEE-INST-002) RBSP-EFW CDR 2009 9/30-10/1

28. Parts List (AXB) ItemQtyReferenceValuePart Numbertypetolratingmfg 12C1B,C1ACWR06-0.1uFCWR06NH104KBBCWR0610%50VVishay 21C210pFCDR31BP100BKUSCDR3110%100VKMET 32C3,C41.0nFCDR31BX102BKUSCDR3110%100VKMET 41R1100kM55342E06B100ERRM07051%50VSOTA 51R2100M55342E06B100DRRM07051%50VSOTA 61R375MH1206CPX756JRM12065%100VSOTA 71R41kM55342E06B1E00RRM07051%50VSOTA 81U1OP15 AJ/883B TO-99 ADI 91Teflon Tubing8 x.15 inJ-3643 JT&T JT&T 101OpAmp Base ShieldUCB Custom PartRBSP-AXB-MEC-274 Davis MFG 111Gore Cable<2.5 inRCN8818 Gore 121PWBRBSP_EFW_PRE_002 RevB PWB Valley Circuits 131OpAmp Can ShieldUCB Custom PartRBSP-AXB-MEC-273 UCB 141ConnectorMCP12SSA22005-001 Omnetics 151Preamp PostUCB Custom PartRBSP-AXB-MEC-262 UCB 161Preamp Post NutUCB Custom PartRBSP-AXB-MEC-266 UCB 171Shield ClampUCB Custom PartRBSP-AXB-MEC-275 UCB 182Shield Clamp PostUCB Custom PartRBSP-AXB-MEC-276 UCB 194SHCS#0-80 x 3/16"from ME Stores 204Flat Washer#0from ME Stores RBSP-EFW CDR 2009 9/30-10/1

29. Parts List (SPB) ItemQtyReferenceValuePart Numbertypetolratingmfg 17Vout,Sheild,Bias,-V,+V, Usher, Guard0.025 Printed Circuit Pin3114-2-00-34-00-00-08-0PIN MILL_MAX 22C1B,C1ACWR06-0.1 uF, A_CaseCWR06NH104KBBCWR0610%50VVishay 31C210pFCDR31BP100BKUSCDR3110%100VKMET 42C3,C41.0nFCDR31BX102BKUSCDR3110%100VKMET 51R1100kM55342E06B100ERRM07051%50VSOTA 61R2100M55342E06B100DRRM07051%50VSOTA 71R375MH1206CPX756JRM12065%100VSOTA 81R41kM55342E06B1E00RRM07051%50VSOTA 91U1OP15 AJ/883B TO-99 ADI 101Teflon Tubing22 GA, Wall Thickness.010J-3643 JT&T JT&T 111Front ShieldUCB Custom PartRBSP-SPB-MEC-809 Davis MFG 121Can ShieldUCB Custom PartRBSP-SPB-MEC-810 Davis MFG 131SpringUCB Custom PartRBSP-SPB-MEC-812 Davis MFG 141PWBSPB PREAMP PWARBSP_EFW_PRE_001 RevAPWA Valley Circuits RBSP-EFW CDR 2009 9/30-10/1