Johannes Gutenberg University Mainz > Faculty 08 > physics > Physics research > Institutes & research facilities > Institute of Nuclear Physics > MAMI accelerator & experiments
The most important tool for our research is the electron accelerator MAMI, which we have been operating and developing reliably since the 1980s. MAMI is structurally unique worldwide and provides us with high-precision electrons at moderate beam energies, which we can use to investigate the structure of atomic nuclei, their components and their interactions.
In particle accelerators, electrically charged particles, such as electrons, are accelerated using electric fields. The simplest principle is to use a high DC voltage to generate the electric field. However, the electric field generated in this way can only remain stable up to a few 100 kV of applied voltage, which limits the achievable electron energy to a few 100 keV.
To achieve higher electron energies of up to several hundred or thousand MeV, the electrons must pass through several accelerating electric fields sequentially. The fields are generated in special accelerator units using high-frequency microwave radiation, which allows the electrons to gain a few MeV of energy per meter. In a classic sequential linear setup (linear accelerator), however, a kilometer-long accelerator section would be necessary to achieve the electron energies required for our experiments (several hundred to a thousand MeV).
In the concept realized at MAMI (Mainz Microtron), the accelerated electrons are therefore deflected and returned by two magnets in such a way that an acceleration path is traversed several times. This allows the same energy gain to be realized in a much more compact design. As the paths of the electrons look like the race tracks of an ancient arena, this concept is referred to as a racetrack microtron (RTM).
At MAMI, we apply the concept of the racetrack microtron sequentially, whereby three microtrons of increasing size are run through one after the other until the MAMI B acceleration stage is reached. The last of these three microtrons reaches the mechanically limited size (each of the microtron’s two magnets is 5 m wide and weighs 450 t!) and is thus the largest microtron realized worldwide. MAMI B achieves electron energies of up to 855 MeV.
By switching on a further accelerator stage (MAMI C), the electron energy can be increased to around 1.5 GeV. In MAMI C, the concept of a harmonic double-sided microtron (HDSM) was implemented for the first time. In contrast to the racetrack microtron, four magnets are used for deflection and two acceleration paths are run through per circulation. This avoids the mechanical limitations that occur with MAMI B.
| MAMI B | MAMI C | |
| Final energy | 855.1 MeV | 1508 MeV |
| Circulations | 90 | 43 |
| Microwave frequency | 2.45 GHz | 2.45 / 4.90 GHz |
| Microwave power | 102 kW | 117 / 128 kW |
| Magnetic field (deflection magnets) | 1,28 T | 0,95 – 1,53 T |
| Mass (deflection magnets) | 2x 450 t | 4x 250 t |
| Area enclosed by the deflection magnets (L x W) | 21 m x 10 m | 30 m x 15 m |
| Length linear accelerator | 8,9 m | 8,6 / 10,1 m |
You can find the MAMI annual calendar with all planned beam times here
The MAMI accelerator and the experiments operated with it can be visited by school classes and other groups when the facility is switched off. This is possible on maintenance days, usually on Mondays.
A tour generally lasts around 2 hours. It begins with an introduction to the basics of the accelerator and the experiments in the Institute’s lecture hall. This is followed by a tour of the accelerator halls, the beamline and the experimental halls.
Please use our contact form to make an inquiry. Please also note our safety instructions.
Details
As space in the rooms is limited and there is sometimes a significant level of noise,
the group size during the tour is typically limited to 11 people. We divide larger groups into appropriate subgroups, which are then guided through the facility at the same time with different routing. Please understand that we are also limited in the number of possible subgroups due to the increased personnel requirements and the space available in the accelerator. Typically, the total group size should therefore not exceed 30.
All guided tours are planned on a case-by-case basis and can only be carried out by prior arrangement and confirmation. Guided tours for individuals are not possible. However, on request, interested individuals can take part in tours that have already been planned, provided that the group size still allows it.
Contact:
Contact form to request guided tours
Sabine Alebrand
E-mail
+49 6131 39-27830
Experiment A1 is used to carry out electron scattering experiments, for example to investigate the spatial structure of atomic nuclei or nuclear building blocks. For this purpose, the electron beam generated by MAMI is directed to the sample and both the electrons scattered by the sample (solids, cooled or liquefied gases) and any newly generated particles are detected using magnetic spectrometers. The spectrometers are mounted to move around a common center of rotation so that the scattered particles can be measured in different directions.
- Three high-resolution magnetic spectrometers
| Height | approx. 15 m |
| Weight | more than 200 t |
| Pulse resolution | better 0.01% |
| Accuracy of the runtime determination | 0.5 ns |
| Covered solid angle | up to ΔΩ=28 msr |
- A spectrometer for measuring very high pulses at short flight lengths (“KAOS spectrometer”)
- A short-orbit spectrometer (for the detection of pions at low energies)
- Large-area time-of-flight walls and heavily shielded, segmented scintillator detectors (for the detection of neutrons)
| Beam current | up to 100 µA |
| Luminosities | up to 10 MHz/μbarn |
| Polarization | unpolarized/polarized |
You can find more information about research at A1 on the A1 Collaboration website
In the A2 experiment, very high-energy photons are generated by means of bremsstrahlung. If a proton absorbs such a high-energy photon, new strongly interacting particles are generated as a result. The main aim of the experiments is to understand the interplay of forces in these processes in detail. Using a special system – the so-called tagger – the energy of the photons can be determined to within a few parts per thousand, enabling a highly precise interpretation of the experimental results. The central components of the detector system are the crystal ball and the TAPS detector, which make it possible to detect the resulting particles in almost the entire solid angle.
- Crystall-Ball: Calorimeter made of 672 NaI crystals
- TAPS forward detector: 352 BaFl crystals
- Multi-wire proportionality chambers
- Polarizable solid-state target (frozen spin target)
- Low-temperature targets (hydrogen 20K, deuterium 24K, 4helium 4K, 3helium 3K)
Generated photon beam:
| Photon energy | 180-1500 MeV |
| Energy resolution of various photons | 2-4 MeV |
| Beam current | up to 108 photons per second |
| Polarization | linear or circular |
You can find more information about research at A2 on the A2 Collaboration website
