For the tracking of light charged particles, i.e. protons, behind the R3B dipole magnet two identical drift chambers (DHC) are foreseen. Each DCH covers an active area of 100×80 cm², thus providing a large enough acceptance behind the magnet to detect decay protons (matched to the geometrical acceptance given by the gap of the dipole magnet of ±80 mrad). The geometry and the operational parameters are optimized to detect minimum ionizing particles with an efficiency of larger than 95% and a spatial resolution of better than 0.2 mm (σ). The tracking through the dipole field provides a relative momentum resolution Δp/p~3×10^-3 for the protons according to Monte-Carlo simulations (including detector resolution and the straggling in the detectors at a beam energy of 500 MeV/nucleon). Each DCH comprises 2 planes (x and y) placed in one housing with in total 250 read-out channels. The chambers will be operated with the gas mixture [Ar:C2H6] = [50:50] at 1 atm. In order to resolve many-particle ambiguities the two chambers will be inclined with respect to each other by ±10 deg. relative to x,y. 

Responsible: TU Darmstadt and TU Munich

In most cases experiments using exotic beams have to include a twofold setup for identifying particles and their kinematic properties before and after the secondary reaction target. For the large variety of different experiments proposed for the R3B setup, various tracking-detector systems with different demands are required. 

In most cases experiments using exotic beams have to include a twofold setup for identifying particles and their kinematic properties before and after the secondary reaction target. The incoming beam will be tracked (starting from the dispersive focus at the Super-FRS) in order to determine beam momentum, angle and position of incidence on the target, and, similarly, for the spectrometer after the target. The velocity of the incoming beam as well as of the fragments has to be determined with a resolution of Δβ/β<10^-3 in order to achieve unique isotope identification after the target also for heavy beams. Using 40 m distance between the dispersive focus at the Super-FRS and the reaction target the requirements for time-of-flight (TOF) detectors are quite moderate (σ(t) < 100 ps) in this case. Also moderate position resolution of Δx=3 mm would be sufficient. The detectors should be able to cope with rates of 10⁷ to 10⁸ s^-1 heavy ions at the dispersive focus of the Super-FRS. For the large-acceptance mode, large-area detectors are placed behind the R3B dipole magnet. For detection of light charged particles drift chambers with a size of about 1.2×0.8 m² including dedicated front-end electronics are presently being considered, see section on proton tracking. For heavy ions, a position detector with the size of 30×20 cm² is needed. For fission and spallation studies, even larger detectors are needed. Those are described in the section 'Large-area ToF wall'.

In view of the high momentum resolution mode (Δp/p < 10^-4  (σ)) needed for several experiments, the situation is quite different. The position resolution of all tracking devices has to be better than Δx < 0.5 mm. Especially the vertex and angle reconstruction at the secondary target will need much better resolution of Δx ~ 0.1 mm. The angular scattering and momentum spread introduced by the tracking detectors in the target region have to be small compared to this numbers while the detectors inside the Super-FRS and after the spectrometer could use a more massive layout. Also the expected γ-background limits the material budget of the detectors in the target area. For the R3B project being a multi-purpose setup for very different branches of experiments the development of position sensitive time-of-flight detectors with good resolution for tracking of exotic heavy ions using minimized mass density in order to suppress parasitic reactions and multiple scattering efficiently is thus mandatory. Four different types of detectors are being or have been developed for tracking of heavy ions according to the demands of the different experiments:

• Diamond detectors will be used for tracking through the Super-FRS up to the R3B target. Responsible: TU Münich

• Si-strip detectors will be used for coincident detection of fragments and protons after the target as well as behind the large-acceptance magnet, where an array of Si-strip will be installed. Responsible: CCLRC Daresbury

• A large-area scintillating fiber detector is foreseen for the second position measurement few meters behind the magnet. Responsible: TU Darmstadt, GSI

• Next-generation time-of-flight wall TOFD is designed for high-precission time-of-flight and nuclear-charge measurements of nuclei up to Pb region at coutning rates up to 1 MHz. Responsible: GSI

• For experiments at lower energies and for lighter ions (e.g. measurements of (γ,n) cross sections at very low relative energy of astrophysics relevance) low-mass channel-plate detectors (with less resolution) are foreseen. Responsible: FZD Rossendorf

The main requirements of such a detector are to cover the full acceptance of the charged particles and ions produced in relativistic heavy-ion collisions while providing a time-of-flight resolution such that isotopes around the mass 200 can be isotopically resolved. Taking projectile fission at energies around 600 A MeV as the reaction mechanism covering the larger angular range, the detector should accept all particles and ions emitted within 50 mrad. Then, this detector should have an area of 1 m² at 10 m from the target and 1.5 m² at 15 m. In addition, the mass resolution we need to identify in mass all fission residues is 3x10^-3, then the required time resolution is σ(ToF) = 19 ps for a flight path of 10 m and σ(ToF) = 28 ps for 15 m flight path. Another physic cases like spallation or multi-fragmentation require the identification of heavy residues at energies around 700 A MeV. Here, the mass resolution we need is of the order of 2.5x10^-3 and the corresponding time resolution is σ(ToF) = 9 ps for a flight path of 10 m and σ(ToF) = 16 ps for 15 m flight path. Two technologies are considered for large-area high-resolution time-of-flight detectors:

• Organic scintillators coupled to fast photomultipliers
Responsible: CEA Bruyeres le Chatele
• Resistive plate chambers (RPCs)
Responsible: USC Santiago de Compostela

The detector for light (target-like) particles is a substantial part of the R3B setup. It allows registration of recoils in coincidence with the heavy fragments, neutrons and the γ-rays. This set-up gives thus a unique possibility to study elastic, inelastic and quasi-free scattering, knockout and breakup reactions. The recoil particle detector provides precise tracking, vertex determination as well as energy and multiplicity measurement with high efficiency and acceptance. The latter two parameters are very important when dealing with radioactive beams. According to previous experience, for the case of (in)elastic scattering, the angular resolution (in centre-of-mass and laboratory system) should be around a few mrad and the resolution in excitation energy, E*, better than 1 MeV.

Responsible: STFC UK

The calorimeter will be used for the study of most of the physical cases presented in the R3B Technical Proposal, though the requirements differ significantly from one experiment to the other. In some cases it is the γ−ray sum energy that is required, while in others the detector has to be able to provide γ-ray multiplicities and individual γ−ray energies for spectroscopic purposes. A key requirement of the detector is that it also has to act as the calorimeter for the target recoil. Hence the detector has to stop and measure the total energy of high-energy light charged particles, e.g. protons up to 300 MeV, with good energy resolution. The main properties of this device, high efficiency and good angular resolution, are imposed by the very particular kinematics of energetic γ-rays emitted by sources moving with relativistic velocities and by the typically low intensities of the secondary beams involved. The main requirements are listed below:

• Total absorption efficiency: 80% (up to E_γ=15 MeV Lab system).
• γ sum energy: σ(E_sum)/<E_sum> < 10%.
• γ multiplicity: σ(N_γ)/<N_γ> < 10%
• γ energy resolution: ΔE/E = 3-5 %.
• LCP energy resolution: ΔE_p/E_p < 3%.

Responsible: USC Santiago de Compostela

Spin-isospin giant resonances can be strongly excited in (p,n) reaction using inverse kinematics. One can use at the same time thick targets, without disturbing the energy spectrum of the recoiled neutrons, which has an importance in experiments with rare isotope beams. For such type of studies, a low-energy neutron detector around secondary target is needed. The energy of the neutrons will be measured with resolution better than 10 % and the scattering angle in laboratory frame with better than 1° angular resolution. We require also high efficiency for the spectrometer. The best candidate for such a setup is a time-of-flight (TOF) ball consisting of plastic scintillators.

Responsible: Debrecen and Uni Frankfurt

The tracking of heavy ion trajectories through the magnetic field of the large-acceptance dipole provides a Bρ measurement with a precision of ΔBρ/Bρ~10^-3 (sigma), as discussed above. In conjunction with energy-loss and time-of-flight measurements fragments are uniquely identified also in case of heavy nuclei. On the contrary, for a precise measurement of the momentum of recoiling fragments produced in reactions an additional momentum analysis is required. In case of high beam energies and medium-heavy to heavy nuclei a precision of the momentum measurement Δp/p in the order of 10^-4 (sigma) is needed.

The proposed solution is based on a spectrometer placed behind the large-acceptance dipole. The spectrometer will be placed at an angle of 18º, which is the maximum bending angle of the dipole (5 Tm field integral) for a beam with magnetic rigidity of 15 Tm, and will be operated as a zero-degree spectrometer. The focus at the R3B target is an achromatic focus with a beam spot size of around 2×2 cm², as in the usual operation mode. The momentum resolution will be obtained by tracking the particles through the spectrometer. The position at the focal plane will thus not be directly related to the momentum transfer in the reaction but rather reflect the momentum spread of the incoming beam. The spectrometer will have an acceptance of ±2.5% in momentum and ±40(±20) mrad in the (non)dispersive direction, respectively. The maximum rigidity of the Super-FRS amounts to 20 Tm in order to allow separation of fully stripped ions also for heavy nuclei. Considering energy-loss in two degraders at the pre-separator and at the mid-focal plane of the main separator, the maximum rigidity of the spectrometer will be limited to15 Tm.

The spectrometer will be installed in the Phase II of the R3B project, i.e. the R3B experiment would run during the first two years without the spectrometer.

Information for staff and guests

If you are planning to come to GSI and work at the R³B experimental setup, the following information will be important for you; it is strongly recommended to use Internet Explorer/Edge and/or Mozilla Firefox, with Chrome some of the registration forms below do not function properly:

• Registration at GSI - if you register for the first time, please fill in Haik Simon as the local contact person.
• GSI Welcome Office - if you need an invitation, questions about insurance, funding oportunities...
• User service of GSI (guest house)
• Entrance requirements for caves during beam operation
• Online safety training - important: for Cave C, you need the radiation safety AND the general safety AND the Cave C safety training not older than 12 months. In case you have problems with Cave C safety training access, please contact Haik Simon. Please note, when you log in for the first time, you need to type in the local contact person. Please fill in Haik Simon. This is mandatory, otherwise Haik Simon can not asign the needed instructions to the user.
• Internet is available via wifi with an eduroam account or by a guest account (link to application form).

If you have any further questions concerning the webpage of our group, please contact Aleksandra Kelic-Heil.