Production of the Hard X-ray Mirror of the ASTRO-H satellite

1. The ASTRO-H satellite

Hironori Matsumoto (Nagoya University) & HXT team

Total Length 14m

Mass 2.7 ton

Mission Life > 3 years

Launch Vehicle JAXA HII-A rocket

Orbit Altitude 550 km

ASTRO-H carries four X-ray instruments which realize X-ray observations of the universe in the very wide energy range from 0.3 to 600 keV.

2. The Hard X-ray Telescope (HXT)ASTRO-H carries two Hard X-ray Telescopes (HXTs). Two Hard X-ray Imagers (HXIs) are placed at the foci of the HXTs, and this combination makes it possible to take pictures of the high-energy universe with high-energy X-rays from 5 to 80keV. Also it is possible to obtain X-ray spectra with good energy resolution.

ASTRO-H is an international X-ray observatory which will be launched in FY2015. More than 160 scientists from Japan, USA, Europe, and Canada participate this project, and the Japanese team takes the lead.

The HXT mirrors employ tightly-nested, conically-approximated thin-foil Wolter-I optics (a schematic view is shown in the right figure).

X-ray source

http://www.x-ray-optics.com/

Image point

The HXT comprises foils 450 mm in diameter and 200 mm in length, with a focal length of 12 m. To obtain a large effective area, 213 aluminum foils 0.2 mm in thickness are tightly nested confocally.

12m

The HXT utilizes two principles for reflecting X-rays: the total reflection for low-energy X-rays (E<10keV) and the Bragg reflection for high-energy X-rays (E>10keV). The mirror surfaces are coated with Pt/C depth-graded multilayers for the Bragg reflection. A cross section of the HXT mirror surface (left). The layer thickness (d) gradually changes to reflect X-rays of various energies. In the case of HXT, the thickness ranges from 24 to 136Å. The right panel shows reflectivity curves for a single layer (black; d=100Å), a multilayer (red; d=40Å, N=30, Γ=0.4), and a depth-graded multilayer (blue; d=26-50Å, N=78, Γ=0.4), where N is the number of layers, and Γ is a fraction of Pt.

3. Mirror ProductionBelow is a summary of the mirror production of the HXT.

Thermal Forming (Preparing mirror foils)

Al sheet (t0.2mm) roller

Stack on mandrel

Al Sheet

Heat forming (200 , 12hrs)℃Mirror foil

Sputtering (multilayer deposition)

Pt CGlass Mandrel

Replica

rotate

Put Al sheet

epoxy

Al sheet with epoxy

Glass mandrel with multilayer

4. HXT properties

30keV

before after

We have three sputtering machine. Inside of the machine, a multilayer is deposited onto the surface of a glass mandrel. It takes 4 to 12 hours to complete one multilayer.

Epoxy is sprayed to the Al sheet. The glass mandrel deposited the multilayer is pressed against the Al sheet inside a vacuum chamber. Finally the Al sheet is peeled off from the mandrel.

One of the two HXTs (HXT-1) was completed in the last year. The characteristics of the HXT1 were measured using the synchrotron facility, SPring-8. The image of a point source at E=30keV is shown in the left panel. The encircled energy function is shown in the middle, and the half power diameter is 1.92 arcmin at E=30keV. The effective area is shown in the right, and it is larger than the required values.