Cryogenic ion catcher for high energetic ions
Contact person : Peter Dendooven ( email@example.com )
Many research fields make use of radioactive isotopes in the form of low energy beams or a cloud of ions or atoms in an electromagnetic trap. The newest and future “in-flight” facilities produce and select radioactive isotopes ideally at very high energies : from a few 100 MeV per nucleon for lighter elements up to 1 GeV per nucleon for the heaver elements. Techniques to transform high energy ions in low energy ions efficiently and fast (within 10 milliseconds) are thus essential. Due to the extreme high energies of the ions, traditional methods have problems both technically and conceptually.
In the framework of the future international 'Facility for Antiproton and Ion Research' (FAIR) in Darmstadt, Germany, we develop an ion catcher in which high energy ions are slowed down in cold helium gas (cooled down to 60 K) and subsequently guided efficiently and fast to an exit hole by using static and radiofrequent (RF) electric fields, thus transforming the high energy into a low-energy beam.
The cryogenic temperature ensures the necessary purity of the helium gas. Further challenges are put by the usage of high density helium, causing the usage of high electric fields and fine RF structures. This combination of parameters has never been tried before. Figure 1 shows the newly developed RF carpet which is used in the ion catcher with in the center the exit hole for the low energy ions.
Until the summer of 2010, the system is being build and tested at KVI with radioactive sources. After this date, the system will be moved to GSI, where it will be tested with a high energy ion beam in realistic circumstances.
In the framework of a BSc or MSc project, one can join the team during the assembly at KVI (ex. LabView-programming) and further perform tests on the system and analyze the results.
In-beam EXL demonstrator test
Contact person : Catherine Rigollet ( firstname.lastname@example.org )
The EXL (Exotic nuclei studied in light-ion induced reactions at the NESR storage ring) experiment at the upcoming FAIR facility in Darmstadt, Germany, aims at studying the structure of unstable exotic nuclei in light-ion scattering experiments at intermediate energies. The EXL detection system will be ideal for high resolution reaction studies at low momentum transfer, for example the study of giant resonance properties using inelastic light-ion scattering – such studies provide unique insights into the asymmetry energy in the nuclear equation of state and the properties of neutron stars. The design of the detector system considered is universal in the sense that it should allow the use of a large variety of nuclear reactions, addressing numerous physics questions. The detector system provides the capability of fully exclusive kinematical measurements, with target recoil detectors, fast ejectile forward detectors and an in-ring heavy-ion spectrometer.
Figure 2 : Recoil detector showing an inner sphere (coloured squares) with layers of Silicon detectors, surrounded by a calorimeter of CsI.
Because of the complexity of the target recoil detector (see figure 2), we have built a demonstrator, which represents a small part of the full system. We have tested one version of this demonstrator already, which included 2 thin and 2 thicker silicon detectors (inner sphere in figure 2).
With this upcoming experiment we aim at including the calorimeter part to the demonstrator. A stack of detectors, thin double sided silicon strip detectors, followed by Si(Li) detectors and two CsI crystals, encased in a vacuum chamber will be irradiated by a proton beam. The main goals of the experiment are to reconstruct the total energy of the incident particle, assess the energy resolution of the detectors and the general performance of the system.
The student will actively participating in the experiment at KVI and perform the analysis of the data.
Digital pulse shape discrimination : a future application for X-ray, electron and proton discrimination in the Si(Li) and/or CsI detectors of EXL
Contact person : Jarno Van de Walle (email@example.com)
Around 2018, the new Facility for Antiproton and Ion research (FAIR) will become operational at Darmstadt , Germany . This new facility is currently being developed and many European universities are performing research on new detection systems in order to equip the new facility with the most modern technologies.
At KVI, the hadron and nuclear physics group is investigating so-called “front-end” electronics, which is the part of the detection system that handles the signals from the detectors. Seen the high intensities that might be expected from the beams at FAIR, a first development was the implementation of a “pile-up” compensation algorithm that was tested and implemented on a Field Programmable Gate Array (FPGA). A possible next step is the implementation of a new pulse shape discrimination algorithm to discriminate between different charged particles in for example Si(Li) and/or CsI detectors. This will be relevant for the EXL detector which will be constructed on the “New Experimental Storage Ring” (NESR) at FAIR, a world unique detector concept without any precedent.
In the framework of a BSc or MSc project, first tests can be performed with CsI and Si(Li) detectors at KVI to identify changes in pulse shape from these detectors when they are irradiation with electrons, alpha particles or X-rays. In addition, from these results a new algorithm can be developed which discriminates automatically between these charged particles.
Quantum shape transition in short lived Srontium isotopes : analysis of a beta decay data set of 98,100,102Rb from CERN.
Contact person : Jarno Van de Walle (firstname.lastname@example.org)
Different theoretical models exist to describe the atomic nucleus. One approach is to see the nucleus as a liquid drop, which can vibrate or rotate, from which an excitation spectrum can be deduced. Around the nuclear chart it is observed that nuclei can suddenly undergo a “shape” transition. This can happen very abruptly by adding only two more neutrons to a nucleus, or gradually over a larger range of isotopes. The neutron-rich isotopes around Kr (Z=36) and Sr (Z=38) are such systems where an abrupt change of shape happens. The nature and the precise reason why this happens is so far pretty unclear. Much of this has to do with the limited experimental information which is available on these isotopes. This in turn is related to the fact that these isotopes happen to be very “exotic” : they do not appear on Earth and are very short lived (some milliseconds half life). Therefore, these isotopes have to be produced at facilities like the future FAIR facility or at CERN.
It is in the summer of 2009 at CERN that one of the most exotic Sr isotopes, 102Sr, has been observed in the laboratory for the second time in human history. Figure 4.1 (A) shows the spectrum that identified an excited state in 102Sr for the first time at CERN back in 1995. Figure 4.2 (B) shows the spectrum from 2009. Evidently, the statistics is much improved and by searching carefully new excited states might be found.
Figure 4 : (A) Spectrum observed in the beta decay of 102Rb (T1/2 = 37(3) ms) in 1995 (G. Lhersonneau et al., Z. Phys. A 351, 357-358 (1995)) (B) Spectrum observed at CERN in 2009. The much improved statistics might enable us to observe more excited states in the very exotic and short lived isotope 102Sr (T1/2 = 69(6) ms).
In the framework of a MSc project, this dataset can be analyzed thoroughly in order to extract unique spectroscopic information. Prerequisite for this is a creative, flexible mindset and a precise and accurate working spirit. Some knowledge of C++ might be an asset, though not a requirement.
“The Physics of Charm” - Projects for bachelor/master
Contact person : Myroslav Kavatsyuk (M.Kavatsyuk@rug.nl)
Quarks are the most elementary building elements of hadronic matter, such as protons and neutrons. The strong interaction between quarks is spectacular. At very short distance scales they behave as nearly free particles with small masses, whereas at larger distance scales, towards the size of a nucleon, the coupling increases drastically leading to effectively heavier objects. Hadrons which contain charm quarks are ideal objects to provide a better understanding of the mechanism behind the generation of the mass of hadrons and the confinement of quarks. The KVI is involved in various international experiments which aim to perform precision measurements of the properties of “charmed” objects. Of particular interest are spectroscopy measurements of Charmonium states, pairs of charm and anti-charm quarks. For this, we participate in a running electron-positron annihilation experiment, called BESIII, in Beijing, China, and work on plans for a future experiment at Darmstadt (Germany), PANDA, exploiting the annihilation of protons and antiprotons to study charmed objects.
Project 1: Efficiency determination of Charmonium decays
(bachelor or master)
For precision measurements of the decay properties of Charmonium states it is mandatory to determine very precisely the acceptance and efficiency of the BESIII detection system. In this project the combination of Monte Carlo simulations with a real-data analysis of well-known reaction channels will be used to provide an unambiguous determination of the detector efficiencies and acceptances.
Project 2: Particle identification using machine learning methods
The type of particles (electron, positron, pion, muon, kaon, proton, …) that are produced in electron-positron annihilations is determined by combining information of the various detection systems in BESIII. It turns out to be advantageous to explore machine learning techniques (multivariate data analysis methods) to efficiently and fast determine the particle type based on the information. Partly these techniques have been already applied for simulation studies of the PANDA experiment. For this project, we would like to extend these studies on real data taken with the BESIII setup.
Project 3: Response simulations for the PANDA EMC crystals
The electromagnetic calorimeter (EMC) of the PANDA detector is an essential device for the position and energy determination of photons, electrons, positrons, and other particles. The existing Monte Carlo simulation framework needs to be tuned to provide a realistic model of the response of the EMC crystals. For this, simulations need to be carried out including the fine details of the response to photons. The results are eventually confronted with prototype measurements.
The PANDA collaboration at the future FAIR synchrotron accelerator facility at Darmstadt, Germany, will make use of antiproton annihilations to investigate yet undiscovered charm-mesons, hybrid mesons (i.e. mesons with a strong glue component) and glueballs (i.e. pure gluon states). To discover such states it is important to build a detector with outstanding performance in terms of particle detection and event selection. This requires developing special electronics and new techniques of digital data treatment while the data are transferred to the computer systems. Our group is specialized in digital read-out electronics for the Electro-Magnetic Calorimeter (EMC) – one of the crucial sub-detectors of the PANDA experiment.
The projects discussed below are experimental projects and therefore involve laboratory and accelerator experiments with realistic prototypes of the PANDA-EMC, data analysis of the measured data, and the development of new software techniques of digital data treatment.
Project 4: Investigation of the high-rate performance of the PANDA EMC preamplifiers using a picosecond laser.
The PANDA experiment aims to detect very rare events. In order to limit the measurement time for such an ambitious physics goal, the interaction rate between protons and antiprotons must be increased to 20 million interactions per second. Consequently, each single detector element of the complex detector system will be exposed to a very high rate of particles. This project aims to find the rate limits for the PANDA EMC and will provide important design criteria for the stability and homogeneity of the proton target, which is crossed by the antiproton beam.
Project 5: Feature-extraction algorithm for the APFEL ASIC: Treatment of the dual-range amplifier data.
The PANDA EMC aims to register high-energy photons in a very broad range of energies, namely between a few MeV and 15 GeV. To accommodate such a large dynamic range, the specially developed preamplifiers deliver not just a single output pulse, but a two output pulses with different energy ranges, so that small signals will be recognizable in the high-gain output and large signals can be accommodated in the low-gain output. Moreover, each hit of a particle or a high-energy photon in the detector causes an output pulse of a certain length in time. Running an experiment at very high rates implies a high probability of two independent hits with a small separation in time. This causes a high probability of overlapping pulses in the detector – the so-called pile-up effect. In order to recover the energy and time information out of such events, a special treatment of the data is required. The pile-up event treatment algorithms are available for the single-range detector output. The aim of the project is to extend such algorithms to the dual-range detector output. This project involves measurements of pulses with various intensities and energies and the subsequent computer analysis.
Project 6: Investigation of a possible impact of the finite light collection time in a scintillating crystal on the time resolution of the PANDA-EMC
The PANDA EMC will be built of 17000 lead-tungstate (PbWO2 or simply PWO) scintillating crystal elements. The scintillation light produced by particles or high-energy photons will be measured by a photosensor attached to one side of the crystal. Particles with different energies will penetrate to different depths of the crystal. Therefore we expect slightly different light production profiles and light yields for particles with different energies. The project aims to investigate if such light-yield variations will have an impact on the time-resolution of the detector. This project involves measurements with radioactive sources and particles of an accelerator (e.g. the KVI cyclotron). The particles are aimed at different positions of the crystal and the results will be evaluated in a computer analysis.
Project 7: Investigation of the pulse-shape dependence for the PANDA EMC.
The PANDA EMC is designed to operate in such extreme conditions, when a high rate of particles hits the detector, and still it should be able to detect high-energy photons in large range of energies. The expected high performance of the EMC relies on the stable pulse shape of the detector output signals. The pulse shape should not depend on the type of the particle or the amount of energy that particles or photons deposit in the crystal. The goal of the project is to make a systematic study of the pulse-shape stability for the existing EMC prototypes. This project involves measurements with a laser light-source and with high-energy photons and particles from an accelerator (e.g. the synchrotron at Bonn or the KVI cyclotron). The measurements will be done with different extreme rates of particles and the results will be evaluated in a computer analysis.
There are usually opportunities for students to do an internship or thesis project at the HNP group. For more information please contact, Prof. Nasser Kalantar-Nayestanaki (group leader).
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