Flexible modes of operation

The TIARA array is designed to be operated with secondary radioactive beams from either fragmentation (using the LISE spectrometer at GANIL) or on-line separation and re-acceleration (SPIRAL at GANIL). The array is optimised for operation using the Exogam array of segmented clover germanium detectors for the gamma-ray measurement, but could also be deployed with alternative gamma-ray arrays. The access around the vessel and the signal processing electronics are sufficiently versatile. The principle modes of operation envisaged are:

• at the end of a GANIL beam line such as G2, surrounded with Exogam detectors in a gamma-cube or octagon geometry and coupled to the Exogam data acquisition system, for nucleon transfer or Coulomb excitation studies,
• at the end of a GANIL beam line such as D6, surrounded with either Exogam or other Ge or scintillator detectors in a gamma-cube or similar geometry and coupled to the GANIL data acquisition system using TIARA amplifiers for all detectors, for nucleon transfer studies,
• coupled in front of the VAMOS spectrometer, surrounded with Exogam detectors in a gamma-cube or octagon geometry and coupled to the Exogam data acquisition system, for nucleon transfer or fusion-evaporation studies,

and the forward-angle part of the array is able to be re-arranged and slid along rails in order to optimize for the different configurations. It would also be possible to introduce other zero-degree options, such as a beam-dumping device.

  

Figure 6: Close-up of the target chamber assembled in the beamline with the Exogam-style support stand around it and coupled to the VAMOS spectrometer. For clarity, only three detector cryostats are shown , and the detectors themselves are not shown. Also, the stand to support the Exogam detectors is shown only in outline. The two large quadrupoles of VAMOS are visible.

As indicated earlier, the VAMOS spectrometer offers many attractive possibilities for combined operation with TIARA, and hence the compatibility of the two devices was required in the initial design. The principle extra parameter imposed in the design was the tight space limitation between the target and VAMOS. The solution was to use a special flange that adapts the back of TIARA directly onto the entrance of the first quadrupole in VAMOS. The assembly of TIARA at the front of VAMOS, including the Exogam detectors, is shown in fig. 6. The first, C-shaped quadrupole can be seen to encroach extremely close to the target. In order to gain access to the TIARA detectors inside of the chamber, it is then necessary to be able to slide back the gamma-ray array and its support stand and then to slide back the opened vacuum chamber after removing a short section of beam line. The TIARA array will then be accessible, mounted from the back plate. The support stand and rails have been designed using actual VAMOS dimensions for the quadrupole and the pivot-point platform.