MONITOR OF SOLAR EUV/XUV IRRADIATION PHOKA

MONITOR OF SOLAR EUV/XUV IRRADIATION

PHOKA

A. Kochemasov

Astrophysics institute atMoscow engineering-physics institute

Instrument Phoka. Satellite «CORONAS-PHOTON»

Instrument Phoka

Instrument Phoka is being designed at Astrophysics Institute at MEPhI. Phoka will operate onboard Russian space observatory “CORONAS-PHOTON”.

Phoka is the photometer of solar EUV/XUV irradiation with temporal resolution up to 0,1s.

During entering the Earth shadow and leaving it instrument will measure solar irradiation passed throw the Earth atmosphere (make occultation measurements).

Scientific data received with Phoka instrument will be used for:

• studying of development of solar flares and variation of solar irradiation.

•Studying of the Earth upper atmosphere layers


Solar spectrum

Typical solar spectrum


PHOKA channels

Channel No.

Filtercoating

Filterthickness, nm

Bandpass, nm Comment

Primary channels

1 None - <1100 Optic channel

2 Ti/Pd 200/100 1- 11 Deposited filter

3 Cr/Al 100/200 27- 37 Deposited filter

4 2 external filters 116- 125 Ly-α channel

Calibration (redundant) channels

5 Ti/Pd 200/100 1- 11 Deposited filter

6 Cr/Al 100/200 27- 37 Deposited filter

7 2 external filters 116- 125 Ly-α channel


Signal at Ti/Pd channel

Useful signal at Ti/Pd channel calculated for solar spectrum on 23.02.2004: 210 pA

Useful signal purity for range 0,1-10nm: 99,8%


Signal at Al/Cr channel

Useful signal at Al/Cr channel calculated for solar spectrum on 23.02.2004 : 340 pA

Useful signal purity: for range 0,1-7nm 68,5%for range 27-35nm 29%


Signal at Ly-α channel

collimator

interference filters

photodiode

Ly-α channel (measuring solar irradiation at wavelength 121,6 nm):Bare photodiode AXUV + 2 filters Acton 122-XN-.5D

Useful signal 110-190 pASignal purity ~80%


AXUV photodiodes

Silicon photodiodes IRD AXUV are used in PHOKA. AXUV have one hundred percent internal carrier collection efficiency in EUV/XUV region. Some of photodiodes have directly deposited metal filters Ti/Pd and Cr/Al).Such photodiodes were successfully used in many European and American space instruments.


Phoka calibration

•Photodiodes will be absolutely calibrated at VNIIOFI (Russia) and PTB (Germany).

•Expected absolute calibration accuracy <10%


PHOKA block-diagram


Block of detectors Phoka-DM

Phoka-DM onboard“CORONAS-PHOTON”with closed cover


Block of detectors Phoka-DM


- Visible light- EUV/XUV

photodiodedeposited filtersilica filter 1. Measuring without filter. EUV/XUV + Visible light

photocurrent = I tot

2. Measuring with silica filter. Visible light photocurrent = I vl

3. EUV/XUV photocurrent: I uv = Itot - I vl

For measuring visible light background signal Phoka has fused silica filters.

Visible light background

Transmittance of fused silica KS-4V.Sample 10мм thick, rejections are included.

1.

2.


Fused silica filters are placed in filter wheel.

Different wheel positions corresponds to different Phoka operation regimes.

Silica filter wheel

Enter mask

Closed aperture

Silica filter

Open aperture

Stepper motor

Optocoupler

Photodiodesplate

Collimators

Visible light channel collimator


Phoka operation regimes

Filter wheelposition

Primarychannelsstatus

Redundantchannelsstatus

Phokaoperation regimes

AOpen Closed Regular

measurements

B

Withsilica filter

Withsilica filter

Visible lightbackground measuring

COpen Open In-flight calibration

DClosed Closed Measuring of

dark currents


Conclusion

At present Phoka has successfully passed almost all preflight tests. Flight model is under making now.

Phoka Web-page:http://iaf.mephi.ru/coronas-photon_phoka_e.htm

Documents

MONITOR OF SOLAR EUV/XUV IRRADIATION PHOKA