Thermal stress test of the depth-graded platinum/carbon reflectors

Yoshitomo Maeda,Takuya Miyazawa,Toshiki Sato,Hironori Matsumoto,Kazunori Ishibashi,Hideyuki Mori,Satoshi Sugita,Yoshiharu Namba,Yu Shionome,Michito Sakai,Takayuki Hayashi,Kou Ichihara,Hideaki Takahashi,Manabu Ishida,Yoshito Haba,Hiroaki Kan,Takuro Sato

doi:10.1117/1.jatis.1.3.034001

Abstract

The ASTRO-H hard x-ray telescope (HXT) is designed to reflect hard x-rays with energies up to 80 keV. It will make use of thin-foil, multinested conical optics with depth-graded platinum/carbon (Pt/C) multilayers. We report on thermal stress tests of the HXT reflectors. The reflectors were fabricated on a heat-formed aluminum substrate of thickness gauged at 200 μm of the alloy 5052. This was followed by an epoxy replication on Pt/C-sputtered smooth Pyrex cylindrical mandrels to acquire the x-ray reflective surface. For the thermal tests, the reflectors were maintained at three different temperatures: −5, 50, and 60°C, respectively, for a week. We found that the surface of the reflectors were significantly changed at temperatures of 60°C or higher. The change appears as wrinkles with a typical scale length of a few tens of microns. No changes on the surface were observed from the −5 and 50°C samples. There was also no change in the x-ray reflectivity for these two temperatures.

Highlights

The ASTRO-H1 hard x-ray telescope (HXT) has conical-foil mirrors with depth-graded multilayer reflecting surfaces that provide reflectivity over a 5 to 80 keV energy range.[2]
The effective area of the HXT is maximized for a long focal length of 12 m giving an effective area of ∼350 cm[2] at 30 keV for the two HXTs
In order to obtain high reflectivity up to 80 keV, the HXTs have a stack of multilayer reflectors with different sets of periodic length and number of layer pairs with a platinum/carbon (Pt/C) coating

Summary

Introduction

The ASTRO-H1 hard x-ray telescope (HXT) has conical-foil mirrors with depth-graded multilayer reflecting surfaces that provide reflectivity over a 5 to 80 keV energy range.[2]. In order to obtain high reflectivity up to 80 keV, the HXTs have a stack of multilayer reflectors with different sets of periodic length and number of layer pairs with a platinum/carbon (Pt/C) coating. The reflector has a bilayer structure with a ∼0.2-μm-thick depth-graded multilayer, a ∼20-μm-thick epoxy, and a 200-μmthick aluminum substrate. Wrinkle formation in such bilayers resulting from compressive stresses due to a heat load is a well-known problem (e.g., Ref. 3). The group ID of the sets of periodic length and number of layer pairs is six.[2] Details of the reflector production can be found in Ref. 2

Experiments

Measurements of the Surface “Waviness”

Roughness Measurements

Summary