| Caracteristics |
| crystals | 16 Germanium crystals (1 cm * 1cm * 1cm) in the innermost ring; [111] planes |
| lens diameter | 15 cm, the crystals are mounted on a radius of 6.2 cm from the lens center |
| motors | 16 piezo-driven srews (New Focus Model 8351)
resolution : 0.06 - 0.4 arcsec |
| sensors | 16 eddy current sensors (Kaman 2U)
resolution : 0.1 - 0.2 arcsec |
| elecronics | multiplexing of motors & sensors in a closed loop
PC interface / data acquisition of Ge detector |
| matrice de détection | 9 détecteurs Germanium HP, détecteurs coaxiaux, 1.5x1.5x4 cm |
| Performance |
The system stability has been tested by orienting all crystals alternately
between two energies of a Ba source, and verifying the count rate of the
focused line energy. Consecutive scans alternating between 303 and 356
keV were performed over a period of 10 days. Each scan was done by moving
all the crystals with the picomotors in increments of Da
at each scan step. The sensor values
for each crystal at each scan step were determined using the sensor
calibration. The scans were fitted with the sum of a Gaussian and a constant
background. The Figure below shows the total count rate as determined from
the fit as a function of time. Both
the peak count rate, as well as the width of the scans, remains stable
with time.
| stability | < 0.8 arcsec / jour |
| reproducibility | < 5 arcsec (3 times 14 rocking curves / during 9 days) |
a complete numerical simulation of the lens allows us to understand the measured performances of the lens
mise à jour : janvier 1999
questions et commentaires :Peter
von Ballmoos