January 12, 2009

1 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

January 12, 2009

Voyagers in the HeliosheathKauai, Hawaii.

The IBEX Hi Sensor: Detecting ENAs from the

Outer Heliosphere

Dan Reisenfeld & the IBEX Team

The IBEX Hi Sensor: Detecting ENAs from the

Outer Heliosphere

Dan Reisenfeld & the IBEX Team

2 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Outline

• How instrument subsystems work to provide energy-resolved all-sky ENA distribution━ Background Rejection

• Coincidence measurement technique

• Temporal resolution

• Predicted count rates

• Current status

3 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

ENAElectron, <0.6 keV

Ion, <10 keV Electron

RejectionElectrodes

Sunshade

Outer ESA plate

Inner ESA plate UltrathinConversion Foil

PhotoelectronSuppression Grid

Collimator

Detector Subsystem

Positively Ionized ENA

• Four major subsystems━ Entrance━ ENA-to-ion conversion━ Energy analysis━ Coincidence detector

• Entrance━ Rejects ions & electrons,

collimates neutrals

• ENA to ion conversion━ Converts neutrals to positive

ions

• Energy analysis━ Selects energy passband━ 0.3 – 6 keV

• Coincidence Detector━ Identifies ENA, rejects noise

IBEX-Hi Design: Large Single Pixel ENA ENA Camera

4 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Collimator Angular Response

• Simulation of single pixel response (measured response matches this)

5 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Calibration Results Match End-to-End Simulation

• ESA + foil throughput: Good agreement between IBEX-Hi electro-optic model and calibration results

6 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

IBEX-HI Detector Section / Background Monitor

CEM B

Ionized ENA

e-CEM C

CEM A

e-

e-

e-

e-

++

Background Monitor

Energetic Ion

7 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Instrument Response Functions

Incident ENA Energy [eV]1000 10000

Res

pons

e Fu

nctio

n, R

i(E)

10-4

10-3

10-2

10-1

Triple Coincidence ResponseDouble Coincidence Response

300

8 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Calibrated Geometric Factor

• Assuming an energy independent flux over the ESA passband:

Values of G from the response function, in cm2 sr eV/eV.

ESA Setting G (summed doubles) G (qualified triples)

1 0.00053 0.00013

2 0.0015 0.00037

3 0.0030 0.00073

4 0.0056 0.0014

5 0.0097 0.0025

6 0.016 0.0042

9 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Data Products: Double & Triple Coincidences

Short TOF Window = 7 ns

Long TOF window = 100 ns

Start(A,B,C)

time

• 13 coincidence types:Short Long Quality

1 a ABC Gold

2 b ABC Gold

3 ab ABC Gold

4 c ABC Poor*

5 ac ABC Poor*

6 a AB Silver

7 b AB Silver

8 ab AB Silver

9 a AC Silver

10 c AC Poor*

11 b BC Silver

12 c BC Silver

13 bc BC Silver

* Highly unlikely that a trigger in CEM C in the short window is a valid ENA event

10 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Event type probabilities: Triples

Triple Coincidence

Event SetCombination Event Probability

Qualified

aABC 0.63

bABC 0.14

abABC 0.21

Unqualified c in short window 0.02

Event-type ratios can be used to distinguish signal from backgrounds

11 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Noise & Background Rejection

• Ions: ━ energies within passband of ESA transmission rejected by positive

potential on collimator━ Correlation with background monitor

• Electrons: ━ rejected by negative potential on collimator entrance ring

• Photons (Vis, UV & X-ray): ━ Flux mitigated by 3 foils (conversion & detector section), ESA

serration and blackening, coincidence detection ━ correlation with background monitor

• Penetrating radiation:━ Triple coincidence, detectors not aligned ━ correlation with background monitor

12 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Penetrating Background Rates (Calibration)

Measurement Background rate

Singles

CEM A 89 mHz

CEM B 115 mHz

CEM C 69 mHz

Background Monitor 12 mHz

Double Coincidences

All AB 2.8 mHz

All BC 4.2 mHz

Qual(Not_C) AC 0.13 mHz

Triple CoincidencesAll ABC 1.04 mHz

Qual(Not_C) ABC 0.58 mHz

13 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Continuous Sampling of ENA Measurements vs. ecliptic latitude

7 days

14 days

1 month

6 months• Best statistics at high

latitudes

• Possibility of observing time variability in heliosheath/TS on time scales < 6 months?

14 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Time Resolution of ENA Measurements

ENA Energy [keV]

0.1 1.0 10.0

Day

s f

or H

ydro

gen

to T

rave

l 100

AU

10

100

1000

Time uncertainty within energy passbands (60- 120 days)

Tim

e [d

ays]

Travel time to 100 AU

Energy width of ESA passbands introduces uncertainty in ENA arrival time

15 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Aspera/MEX Flux and Other Models of ENA Flux at 1 AU

ENA flux predictions at a given energy range over ~5 decades!

16 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

Predicted IBEX Triple Coincidence Count Rates

Detection Limit

Increasing sensitivity with energy flattens steep flux distributions

17 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

IBEX HI Status

• Commissioning completing this week

• All systems operating nominally

• Detector gains as before launch

• Positive ENA detection:━ Heliospheric━ Magnetospheric

18 The IBEX-HI Sensor Voyagers in the Heliosheath Conference, January 12, 2009

IBEX-HI is performing fantastically… Wait for it!

Doubles (aAB)

Triples (aABC, bABC, abABC)