LPW PreampSensor Overview MAVEN PFP PreCDR Peer Review

LPW Preamp/Sensor Overview MAVEN PFP Pre-CDR Peer Review May 10, 2011 Greg Delory, LPW Co-I gdelory@ssl. berkeley. edu

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 MAVEN PFP Pre-CDR Peer Review 2

LPW Sensor Design Whip – 50 x 0. 635 cm “Stub” “Guard” Preamp Enclosure • 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 MAVEN PFP Pre-CDR Peer Review 3

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

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

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 MAVEN PFP Pre-CDR Peer Review 6

Integrated Sensor Tests MAVEN PFP Pre-CDR Peer Review 7

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

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

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

Complete Signal Chain MAVEN PFP Pre-CDR Peer Review 11

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 here @ SSL MAVEN PFP Pre-CDR Peer Review 12

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

Backup Slides

LPW Preamp Circuit MAVEN PFP Pre-CDR Peer Review 15

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

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

EM Preamp Tests MAVEN PFP Pre-CDR Peer Review 18

Preamp Voltage Mode Results Resistive Coupling Capacitive Coupling Benchtop Preamp Tests 1 Meg/3. 3 p. F coupling MAVEN PFP Pre-CDR Peer Review Board Input Capacitance = 9 p. F 19

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

Whip Coating • Ti. N – Titanium Nitride – Required for chemical durability (atomic oxygen resistance) – Work function uniformity (ensures accurate Ne, Te measurements) • Has significant heritage – Cassini (IRF/Iowa 1997 - , Saturn), Astrid-2 (1998 - 1999, Earth’s ionosphere) – Cusp (NASA 35. 033 sounding rocket, GSFC 2002) – Rosetta (IRF 2004 - , comet) – Demeter (CNRS/ESTEC 2004 - , Earth’s ionosphere) – Swarm (IRF 2011 - , Earth’s ionosphere) MAVEN PFP Pre-CDR Peer Review 21

Whip Coating (2) • Previous Ti. N 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-6 Al-4 V, respectively (Scanning Electron Microscopy) A=fine grained Ti. N, B= Ti 2 N, C=Mixed phases, D=bulk material+nitrogen (increased hardness), E=Bulk material, F= βphase. MAVEN PFP Pre-CDR Peer Review 22