A Neutral Atom Imager NUADU for the Chinese Double Star-Polar mission

10th Space Physics Conference Shanghai, China 1 October 17 - 21, 2003

Space Technology Ireland, Ltd.

A Neutral Atom Imager

NUADU

for the Chinese Double Star-Polar mission

Susan McKenna-Lawlor1, Jan Balaz1, Stas Barabash2, Klas Johnsson2, Lu Li3, Chao Shen3, Jiankui Shi3, Qingang Zong3, Karel Kudela4, Suiyan Fu5, Edmond C. Roelof 6 and Pontus C:son Brandt6 1. Space Technology Ireland, National University of Ireland

Maynooth, Co. Kildare, Ireland 2. Swedish Institute of Space Physics, Kiruna, Sweden 3. Center for Space Science and Applied Research of the

Chinese Academy of Sciences, Beijing, China 4. Institute of Experimental Physics, Kosice, Slovakia 5. School of Earth and Space Sciences, Peking University,

Beijing, China 6. Applied Physics Laboratory, Johns Hopkins University,

Maryland, USA



The Equatorial Spacecraft (DSP-1) Launch: December, 2003 Orbit: Elliptical (550 x 67,000 km)

Inclination 28.5 degrees

The Polar Spacecraft (DSP-2) Launch: June, 2004 Orbit: Elliptical (700 x 38,000 km)

Inclination 90 degrees



The NUADU instrument



ENAs are produced in the Earth's atmosphere via a charge-exchange mechanism between singly charged energetic ions and the cold neutral atoms of the exosphere. The neutrals thereby produced leave the interaction region with essentially the same energy and velocity as the incident ions and they are unaffected by ambient electric and magnetic fields. They can thus be used to image, and remotely diagnose, plasma populations in the neutral gas in which they were created i.e. imaging the neutral atom distribution provides a means to make the magnetospheric plasma visible. The energy distribution of the ENAs depend on the ion energy distributions and on the cross sections of the relevant charge exchange interactions.



In the case of energetic neutral hydrogen and oxygen (the products of H+ and O+ charge exchange), the energy distributions span a range between a few eV and several hundred keV. Remote sensing of ENAs involves making line-of-sight integrated observations of the source populations. The polar orbit of DSP-2 is particularly favorable for neutral atom imaging of the Earth's Ring Current and of the near-Earth magnetotail. ENA images provide important morphological information on features of the Ring Current (e.g. global asymmetry, energy-dependent particle drifts and the locations of initiating plasma injections). By suitably composing ENA images in ENA movies it is then possible to study the instantaneous responses of the Ring Current to changes in interplanetary conditions and to monitor the process of Ring Current decay.





The main Scientific Objectives of the NUADU experiment are: • To define the morphology of the Ring Current

under different magnetospheric conditions and to characterize the inner magnetosphere

• To study particle energization processes in the

inner magnetosphere and to image plasma convection and sub-storm evolution

• To monitor the Ring Current to define space

weather conditions • To monitor the global ENA Index





Layer 1 of the detection system

(the fields of view of the detectors are shown in blue, a HV deflector plate in red and insulators in yellow)

DETECTOR 1

APERTURE 1FOV 1

HV DEFLECTOR PLATE

HV INSULATOR(PEEK)

FOV 5

FOV

9

FOV 13

ANGULARMEASURE

NORTH

SOUTH

ECLIPTIC.PLANE



The Sensor Head is equipped with a four-layer high voltage deflection system that sweeps energetic charged particles away from the detectors up to a cutoff energy of 300 keV. The 16 Passivated Ion Implanted Silicon (PIPS) detectors are individually characterized by a custom designed rectangular active area of 14,2 × 10 mm and are mounted at four different heights. The detectors have equal fields of view (11.5° × 2.5° fwhm) regularly distributed over an 180° angle in the elevation plane. An important feature of the NUADU instrument is its very large geometric factor (0.014 cm2sr per 11.5° × 2.5° pixel). Since a mechanical collimator is used, the pixel size does not depend on particle energy and mass. Also, because of the deposition on each detector of a metalization layer (200 nm of Al), the sensor head is completely blind to UV radiation.



+Z

-Z

TO NORTHECLIPTICAL

POLE

TO SOUTHECLIPTICAL

POLE

EQUATORIAL PLANE

S/C

SP

IN A

XIS

8°

15°

5°

5.6° 11.25° 11.25°

SINGLE DETECTORFOV DEFINITION

POINTING DIRECTIONSOF THE DETECTORS

14.2

DETECTOR14.2 x 10

INPUTAPERTURE46 x 10

10

46 10

DET4

DET3DET2

DET1

DET5

DET6

DET7

DET8

DET9

DET10

DET11

DET12

DET13

DET14DET15DET16

228

DEF

LEC

TOR

PLA

TE

+50

00V

DEF

LEC

TOR

PLA

TE

-50

00V



A high voltage (HV) converter provides symmetrical, bipolar voltages in the range 0 to ±5000 V for the deflector plates. The output voltage is controlled by the NUADU Data Processing Unit (DPU) with 8 bit resolution. Moreover, the preset voltage can be switched on-off by HV optocouplers. This ‘HV-Toggle Mode’ allows the contribution of charged particles to the registered events to be evaluated. The events recorded by the detectors are discriminated to four energy levels and counted in separate channels by registration electronics. The spacecraft spin (15 rpm) allows the azimuthal plane to be divided into 128 equal sectors through counting the pulses of the Spin Segment Clock which are supplied to NUADU by the Spacecraft Service System.



The full 4π solid angle is divided into 16 × 128 = 2048 pixels and, given the spacecraft spin period (4s), the integration time for one pixel is 4s / 128 = 31.25 ms, NUADU can record a complete 4π image on the completion of each spacecraft spin. Data acquisition software is synchronized by means of the Sun Reference Pulse and Spin Segment Clock. A data frame is produced by integrating N complete images (i.e. N complete spacecraft spins where N = 1, 2, 3, …, 32) and this frame is then sent to the spacecraft telemetry system. The number of spins to be integrated is determined by telecommand.



CSA

1

CSA

2

CSA

16

PA1

PA2

PA16

TH1

TH1

TH1

TH2

TH2

TH2

TH3

TH3

TH3

TH4

TH4

TH4

CO

UN

TER

8bi

t

CO

UN

TER

8bi

t

CO

UN

TER

8bi

t

CO

UN

TER

8bi

t

CO

UNT

ER 8

bit

CO

UNT

ER 8

bit

CO

UN

TER

8bi

tD

ATA

&C

ON

TRO

L

CO

UNT

ER 8

bit

CO

UNT

ER 8

bit

CO

UNTE

R 8

bit

CO

UN

TER

8bi

t

CO

UN

TER

8bi

t

MAX

475

MAX

475

MAX

475

16 x

MAX

908

16 x

A22

54

x M

AX47

5

64 x

SN

J54H

C590

A225

A225

A225

PIPS

-PD

PIPS

-PD

PIPS

-PD

= 2.

50V

/ MeV

= 2.

50V

/ MeV

= 2.

50V

/ MeV

~ 24

0mV

/ MeV

~ 24

0mV

/ MeV

~ 24

0mV

/ MeV

HK1

80C

85R

H

HK2

HKn

DPUAD

C

STG

CO

NTR

OL

ON

/O

FFR

EFM

ON

AUX

DC

/DC

HV

DC

/DC

DC

DC

NUAD

U -

FUN

CTI

ON

AL B

LOC

K D

IAG

RAM

SEN

SOR

HEA

DEL

ECTR

ON

IC B

OX + 5V

+12V

+24V

-12V

HV

+50

00V

HV

-500

0V

HV

+ 5

000V

HV

- 50

00V

-12V

(M

ESH)

BIAS

HV

SAFE

TY P

LUG

BIAS

BIAS

BIAS

DET

1

DET

2

DET

16

D

C /

DC

(550

kH

z, n

on-s

ync.

)C

OM

MO

NM

OD

E EM

I

MAI

N

RED

UN

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TC/T

M

MIL

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SYN

CH

RO

SRP

(MAI

N+R

EDU

N )

SYN

CH

RO

SSC

(MAI

N+R

EDUN

)

TEST

RS2

32 (d

ownl

oad,

deb

ug, m

onit)

+28V

mai

n+2

8V re

dund

ant

retu

rn m

ain

S/C

pow

ered

The

rmis

tors

HEA

TER

retu

rn re

dund

ant

INST

RU

MEN

T BO

X

4 x

LUG

MEP

CO

MM

AND

&

DAT

A

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emot

e Te

rmin

al

I/F

2 x

NTC

SYN

C.

I/F

(MAI

N+R

EDU

N)

EXTR

A G

RO

UN

DIN

G W

IRE

MEP



Each of the 16 detectors has its own analog signal conditioning electronics. The conditioning electronics is located inside the sensor head and consist of charge sensitive preamplifiers and pulse amplifiers. The (electrical) conversion gain of each electronic channel is set to 5mV/keV. As was already noted, the analog pulse signal is discriminated to four energy levels between approximately 20 and 300 keV. The pulses on the outputs of the discriminator stack are counted using 8-bit counters under the direct control of the DPU. The DPU also supports data processing and formatting as well as data transmission to the spacecraft Onboard Data Handling System via a MIL-STD-1553B interface. The physical calibration of NUADU will take place at the accelerator of the Mahne Siegbahn Laboratory in Stockholm, where an ENA beam is available.



One of the challenges of ENA imaging is to obtain quantitative information about pitch angle distributions (PADs) in the Ring Current. From a single vantage point it is impossible to obtain unambiguous information about the PADs. The best local time coverage of the Ring Current is obtained by an imager at a polar position. An imager located at a lower latitude provides an estimate of large scale PADs. In 2005 the apogee of the IMAGE spacecraft will approach 90° magnetic latitude. Perigee passages of IMAGE will provide, using its onboard HENA instrument, ENA measurements of high spatial and temporal resolution.



By appropriately combining NUADU information with HENA measurements made during this kind of DSP/2-IMAGE conjunction, a detailed understanding of the interaction between the Ring Current and the Earth's upper atmosphere can be derived

Y

Z

Double Star-Polar

IMAGE Jan2005

IMAGE Jan2004



The TWINS mission consists of two spacecraft with one ENA imager on each. These spacecraft will fly in two opposing Molnyia orbits, each with 63.4° inclination and a 7,2 RE apogee. The TWINS spacecraft each carry an ENA instrument and thus can provide an additional pair of vantage points for imaging. It is expected that DSP-2 will overlap with part of ESA's CLUSTER mission - which consists of four spacecraft flying in different regions of geospace.



The correlation of NUADU data with RAPID/CLUSTER measurements can, for example, support continuous monitoring of the evolution of dynamical processes in the magnetosphere (storms and sub-storms). Such observations can significantly support studies to detect the location of and resolve the spatial extent of plasma injections into the active magnetosphere.

(area reserved for DSP + Cluster constellation)



CONCLUSION A sophisticated Energetic NeUtral Atom Detector Unit (NUADU) operating in the range approximately 25 - 300 keV has been designed for the Chinese Double Star Polar Mission. This instrument has the capability to record full 4π ENA distributions through employing 16 PIPS detectors and exploiting spacecraft rotation. The data obtained will provide insights into the dynamics of the Ring Current responsible for stimulating disturbed magnetospheric conditions underlying many aspects of space weather. Multi-point ENA sampling obtained through combining with NUADU data contemporaneous measurements made aboard the CLUSTER, IMAGE and TWINS spacecraft provide the potential for, hitherto unprecedented, integrated studies of global, dynamic, magnetospheric processes.

Documents

A Neutral Atom Imager NUADU for the Chinese Double Star-Polar mission