EUV Imaging Spectrometer (EIS)The Extreme-Ultraviolet Imaging Spectrometer (EIS) is one of the three major scientificinstruments of the Solar-B. The EIS instrument was designed and is being developed by aninternational collaboration of the United Kingdom, the United States, and Japan. It utilizes
an off-axis parabolic primary and a toroidal diffraction grating in a normal incidence opticallayout with high-reflectance Mo/Si multilayer coatings. The multilayer coatings have highreflectance in two wavelength ranges, 170−210 Å and 250−290 Å, and these wavelength
ranges are simultaneously observed with two large back-illuminated CCDs. Many EUV
emission lines from the transition region, the corona, and flares are contained in thewavelength ranges and observers can select spectral windows up to 25 in the imaging area of
two CCDs. There is a slit/slot exchanger that contains two narrow slits (1″ & 2″ width) and
two wide slits (40″ & 250″ width) at the prime focus of the primary mirror, and two
dimensional EUV images are obtained with one of the narrow slits in a raster observation bya pivot rotation of the primary mirror in the east-west direction or with one of the wide slits ina slot observation of no primary-mirror motion, though the velocity information is convolvedin the latter case. The center of the field of view can be changed by ±800 arcsec in theeast-west direction by a translational motion of the primary and it enables to see ahigh-altitude region of the corona at the limb or to see the region near the limb when thenominal observing region of the Solar-B is located near the center of the sun.
Overview and instrumental performance of EIS are summarized in Tables 1 and 2.

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Table 1. EUV Imaging Spectrometer Overview
Telescope
Off-axis parabola

15 cm diameter;
half area:170−210Å, the other half: 250−290Å

Focal length

1934 mm

Off-axis distance

70 mm

Plate scale at slit

9.4 microns/arcsec

Multilayer coating

Mo/Si pairs

Slit & Slot1″, 2″, 40″, and 250″ width at primary focus

Fine mirror scan range±3 arcmin solar image motion
Max. FOV of raster (EW×NS): 360″×512″

Large FOV translation±800 arcsec shift of FOV center in East-West direction

SpectrometerGratingToroid
Holographic laminar, uniform line spacing

Wavelength range

Maximum coverage170−210Å, 250−290Å

Useful coverage180−204Å, 250−290Å

Dispersion

1.65 Å/mm or 0.0223 Å/CCD pixel

Pixel equivalent width

34.3km/s@195Å, 26.1km/s@256Å, and 23.6km/s @284Å

Plate scale at CCD

1.0 arcsec/CCD pixel

CCD camera

DeviceMarconi 42-20, MPP

Format (Spatial×Spectral)

1024×2048 pixels

Pixel size

13.5 µm

Readout

Window size

512×2048 max.

electronics

Num. of spectral windows

25 max.

CCD57

Table 2. EIS Instrumental Performance
Instrument Performance
Effective Area

0.5 cm2 peak @ ∼195Å for 170−210Å band
0.2 cm2 peak @ ∼270Å for 250−290Å band

Expected line intensity∼30 photons/s for Fe XII 195

Quiet Sun

∼6 ph/s for He II 256

from 1″ × 1″ area
Active Region∼9×102 ph/s for Fe XII 195∼4×101 ph/s for He II 256∼4×102 ph/s for Fe XV 284

M2-class Flare∼1×105 ph/s for Fe XXIV 192∼3×103 ph/s for He II 256∼2×104 ph/s for Fe XXIV 255∼1×103 ph/s for Fe XV 284

Accuracy of measurement

Doppler velocity: δv=1.0 km/s for ∼1×103 photons (Fe XV 284)
δv=1.0 km/s for ∼2×104 ph (Fe XXIV 255)
Line width: δw=1.0 km/s for ∼5×103 photons (Fe XV 284)
δw=10 km/s for ∼2×103 photons (Fe XXIV 255)

Data compression in MDP

Bit compression: 16-to-12 bit or 14-to-12 bit compression
Image compression: DPCM or 12bit-JPEG

Data rate∼1/8 of total telemetry; ∼40kbps after compression

Control of EIS observation

Observing sequence in EIS ICU58