LPW Preamp/Sensor Overview Greg Delory, LPW Co-I MAVEN PFP Pre-CDR Peer Review May 10, 2011

2 MAVEN PFP Pre-CDR Peer Review Overview LPW sensor consists of: –Preamp: analog circuitry for current and voltage measurements –Whip: antenna used by the preamp LPW preamp design based on: –FAST (relays, switching from voltage to current mode) –THEMIS (similar/identical op-amps, temperature requirements) LPW preamp is: –Similar to THEMIS for temperature requirements –Less than THEMIS for radiation requirements –Lower in complexity than FAST preamp

3 MAVEN PFP Pre-CDR Peer Review LPW Sensor Design Whip – an antenna, a conductor through which voltage and current in the plasma are measured –Needs to be of sufficient size for high coupling capacitance and current collection area –Requires coating for chemical/structural durability and surface uniformity (Titanium Nitride) Stub, Guard – each biased at a controlled voltage depending on measurement mode –Mitigates photoelectron effects in voltage mode, end effects in current mode Preamp enclosure – houses preamplifier electronics at the base of the whip antenna. –High impedance interface to the plasma / buffer for driving boom cable Whip – 50 x cm“Stub”“Guard” Preamp Enclosure

4 MAVEN PFP Pre-CDR Peer Review LPW Sensor EM (1)

5 MAVEN PFP Pre-CDR Peer Review LPW Sensor EM (2)

6 MAVEN PFP Pre-CDR Peer Review Preamp – Since PDR No major changes Decisions made for critical active/unique parts (see next slides) Added Whip guard to reduce input capacitance of final sensor assembly Comprehensive measurement and test program

7 MAVEN PFP Pre-CDR Peer Review Integrated Sensor Tests

8 MAVEN PFP Pre-CDR Peer Review Sensor Tests: Voltage Mode 2m cal chamber 1 Meg/chamber capacitive coupling Resistive Coupling Capacitive Coupling Input Capacitance = 13 pF

9 MAVEN PFP Pre-CDR Peer Review Assembled EM Unit EM Whip, preamp, boom, harness in RBSP-derived cal chamber. Test stimulus delivered through coupler block

10 MAVEN PFP Pre-CDR Peer Review Assembled EM Unit DFB/BEB External power supplies MISG

11 MAVEN PFP Pre-CDR Peer Review Complete Signal Chain

12 MAVEN PFP Pre-CDR Peer Review Current Status Summary Few changes from PDR EM Sensor, boom fabrication and assembly complete LPW Whips fabricated, and currently out for coating Tests of integrated preamp/sensor assembly yielded no surprises First tests with complete EM system conducted –No major anomalies, but more analysis needs to be done Electronics boards back at LASP – will continue testing boom/sensor combination SSL

13 MAVEN PFP Pre-CDR Peer Review Work Remaining for CDR/FM Build Relay Life Test –Happening now Preamp Qualification Model (QM) –Flight-quality board, low CTE Arlon 85NT construction –Used to verify temperature predicts (~-170 to +80 C) Integrated EM system test: –Understand details of instrument response –Perform complete calibration

Backup Slides

15 MAVEN PFP Pre-CDR Peer Review LPW Preamp Circuit

16 MAVEN PFP Pre-CDR Peer Review Parts Selection (1) Voltage mode op-amp: –Candidates at PDR were OP-16A, OP-15A –Chose OP-16A due to superior frequency response –Similarity with OP-15A = confidence it will pass qualification –OP-15A remains a valid, swap-in backup Current mode op-amp: –Candidates at PDR were AD-549 and OP-15A –Chose OP-15A satisfies measurement requirements – chosen due to reliability history –AD-549 has superior sensitivity, but less heritage Teledyne 422DD Latching Relay –Same as PDR. Heritage from FAST –Undergoing life tests now (several million cycles)

17 MAVEN PFP Pre-CDR Peer Review Parts Selection (2) DT-471 Temperature sensor –Same as PDR –Tested in benchtop environment 50M surface mount chip resistor –Special order from SOTA –Same basic specification/design as 75M resistor used in RBSP Remaining components are standard passives

18 MAVEN PFP Pre-CDR Peer Review EM Preamp Tests

19 MAVEN PFP Pre-CDR Peer Review Preamp Voltage Mode Results Benchtop Preamp Tests 1 Meg/3.3 pF coupling Resistive Coupling Capacitive Coupling Board Input Capacitance = 9 pF

20 MAVEN PFP Pre-CDR Peer Review Current Mode Tests 1. Pick point on simulated V-I curve 2. Corresponding point on impedance curve Verified sensitivity from ~nA to 200 uA levels Instability noted at high coupling impedances Verified and mitigated through stability analysis (22 pF lead cap) Simulate voltage, current, and coupling impedance encountered in different measurement regimes.

21 MAVEN PFP Pre-CDR Peer Review Whip Coating TiN – Titanium Nitride –Required for chemical durability (atomic oxygen resistance) –Work function uniformity (ensures accurate Ne, Te measurements) Has significant heritage –Cassini (IRF/Iowa , Saturn), Astrid-2 ( , Earth’s ionosphere) –Cusp (NASA sounding rocket, GSFC 2002) –Rosetta (IRF , comet) –Demeter (CNRS/ESTEC , Earth’s ionosphere) –Swarm (IRF , Earth’s ionosphere)

22 MAVEN PFP Pre-CDR Peer Review Whip Coating (2) Previous TiN applications have been tested for uniformity and durability (Wahlström, 1992; Steigies, 2005) (SEM, electrical tests, others…) Result after Nitriding illustrated by cross section of structure after Nitriding of titanium and Ti-6Al-4V, respectively (Scanning Electron Microscopy) A=fine grained TiN, B= Ti2N, C=Mixed phases, D=bulk material+nitrogen (increased hardness), E=Bulk material, F= β- phase.