”Gamma-Ray Imager” - a mission idea for the next ESA call

1. ”Gamma-Ray Imager” - a mission idea for the next ESA call Niels Lund - for the GRI consortium

2. The GRI consortium The GRI consortium is a loosely organised group of people interested in gamma-ray astronomy. The intention is to propose a gamma-ray mission based on Laue focusing of gamma rays for the next ESA call for mission ideas. The current concept calls for a two-spacecraft mission with a lens and a detector spacecraft in formation flying. The cost envelope is for a medium size mission (one year science programme budget). The consortium chairman is Jürgen Knödlseder (Toulouse), other key members of the group are Peter von Ballmoos (Toulouse) and Filippo Frontera (Ferrara). The consortium also has organised itself with a number of subgroups dealing with the overall mission concept, the science case development, the Laue lens design, the detector design and a group elaborating the design of a multilayer telescope covering the energy range from 2 to 200 keV - this last group is chaired by Finn Cristensen (DNSC). GRI presentation | March 2, 2006 | page 2

3. A GAMMA RAY ASTROPHYSICS MISSION STUDY (450 – 530 keV & 800 – 920 keV) LENS SATELLITE ~ 86m A FORMATION FLYING MISSION WITH A LENS SAT. & A DETECTOR SAT. INTER SATELLITE DISTANCE ~ 86M DETECTOR SATELLITE MAX is one of the 4 formation flying astrophysics mission studied by CNES in 2005 The most advanced Laue lens study today: ”MAX” GRI presentation | March 2, 2006 | page 3

4. The Soyuz ST envelope: • The Soyuz launcher has been taken as a baseline for the study in order to provide some realistic constraints on the design. • Soyuz mass limit to the Lagrange point L2 or to a deep elliptical orbit (7 days): 2100 kg (Take 400 kg for the detector spacecraft and 1700 kg for the lens spacecraft) • The size constraints for the Soyuz ST-fairing: Maximum spacecraft diameter at launch: 3.8 m Maximum spacecraft height at launch: 9.5 m GRI presentation | March 2, 2006 | page 4

5. Laue-lens concept adapted to Soyuz at the time of the Bonifacio workshop – Sept. 2005 Copper crystals Focal length: 150 m, crystal mass: 416 kg Takes all available weight – no reserves for a multilayer telescope ! GRI presentation | March 2, 2006 | page 5

6. Developments prior to 1st GRI consortium meeting Ferrara, December 2005 • The desire to include a multilayer telescope in the payload made it essential to save weight on the Laue lens without sacrificing on its performance. • Therefore we took a second look at the relative merits of Copper, Silver and Gold crystals. All three have (fcc)-structure, high atomic density, and high quality crystals have already been grown of both copper and gold. GRI presentation | March 2, 2006 | page 6

7. Performance and weight of Au, Ag and Cu crystals All three have similar flux collection power as function of energy. But note the weights: Au: 246 kg Ag: 358 kg Cu: 401 kg The crystal thickness (below 511 keV) has been adjusted to keep the effective area constant GRI presentation | March 2, 2006 | page 7

8. Laue-lens performance including 2nd and 3rd order GRI presentation | March 2, 2006 | page 8

9. Combined Laue-lens and multilayer telescope The Laue-lens covers the energy band from 200 to 1000 keV. The multilayer telescope covers the energies below 200 keV. The Laue-lens has a central hole with a diameter of 1.8 m, the multilayer telescope (outside diam. 90 cm) fits easily here, and can be offset up to 45 cm to separate the two focal plane detectors. GRI presentation | March 2, 2006 | page 9

10. Effective area of combined Laue-lens and multilayer telescope It appears that a dual system offering more than 1000 cm2 eff. area between 0.5 and 600 keV and 600 cm2 at 1000 keV is feasible with Soyuz. (Dont worry that the Focal lengths dont match, this is only a first try!) Combined mass 440 kg GRI presentation | March 2, 2006 | page 10

11. Concerns expressed at the Ferrara meeting (Dec 2005) • Can we get crystals of sufficiently high quality? • Can we cut the crystals in thin slices without damaging the structure? • Can we mount and align thousands of crystals well enough. • Can the lens and detector design be improved? • Can we build rigid panels for the crystals? • How shall we deploy the panels and adjust to the correct angle? • What does the panel structure weigh? • What does the deployment mechanism weigh? GRI presentation | March 2, 2006 | page 11

12. Length 250 mm Diameter 80 mm Crystal fabrication meeting in Grenoble, February 2006 • Institut Laue-Langevin in Grenoble has for the last 20 years grown large copper crystals to be used for neutron monocromators. • They have demonstrated their capabilities to grow crystals suitable for a Laue lens for gamma astronomy. • But the crystals are very soft and easily ruined during later cutting and mounting! GRI presentation | March 2, 2006 | page 12

13. Can we avoid the lens deployment mechanism? • Since Grenoble meeting I have worked on a new lens design using only one, rigid panel. To achieve sufficient length of the panel it is placed vertically during launch, taking up the full length of the Soyuz fairing. • Software to calculate the available length of the crystal circle segments have been written. GRI presentation | March 2, 2006 | page 13

14. Further improvements to the lens performance • A constant collection area as function of energy has been set as a goal, eliminating the sharp jumps in collection area caused by the sudden appearence of higher order contributions. • Improved sensitivity at the higher energies can be obtained by using the (200) reflection in Au (or in Ag or Cu) as the basis and adding rings using the (111) reflection of the same crystal inside the innermost (200)-ring. • Additonal collection area at high energies is obtained by adding a secondary lens feeding the redundant focal point detector. GRI presentation | March 2, 2006 | page 14

15. Next step: The 2nd general GRI consortium meeting will take place on May 2-3 in Coimbra, Portugal. GRI presentation | March 2, 2006 | page 15