The central research themes of the LPSC are to understand the structure of matter so one can answer the question “what is the universe made of?” We study the fundamental constituents of the universe and their interactions with complex experimental techniques, ranging from particle accelerators to space telescopes, we probe matter from a size of 10-18 meters (which is the scale of the quarks which make up protons and neutrons) up to 1026 meters (the size of the observable universe).
Besides fundamental physics studies, other, more applied, research branches are also being developed at the LPSC, such as the study of innovative nuclear power reactors or accelerator beams for cancer treatment. Recently plasma physics is also studied at the laboratory.
Most of the research themes of the LPSC are summarized in this document.
Evolution of the Universe
Since ancient times, mankind has asked questions about the form of the universe and its future. Today, the Big-Bang theory is supported by three observations; the expansion of the universe, deduced from the velocities of galaxies as a function of their distance, the abundance of certain atomic nuclei such as helium or lithium, created only minutes after the Big Bang and the presence of a cosmic background of photons at 3 K (-270°C). The latter was produced around 300,000 years after the Big Bang, when light and matter became separated. It still remains to be seen, on a larger scale, if space-time is flat or curved, if the expansion of the universe will continue eternally or not. We must also learn more about inflation, which started immediately after the Big Bang. The answers to these questions are becoming more and more precise, thanks to studies of small fluctuations of the cosmic-microwave background at 3 K, which favors a flat universe and not only further expansion, but indeed an accelerated one.
Composition of the Universe
Numerous astrophysical and cosmological measurements have allowed us so see how the different constituents of matter and energy of the universe are divided up, with high precision. We presently have available a rigorous and exhaustive classification of the contents of the cosmos; radiation (negligible), stars (0.5%), gas (5%), unusual non-atomic matter (25%), acceleration energy (70%). However, we do not know precisely the large majority of the physical components that make up 95% of the universe. To resolve this problem we must hypothesize the existence of new particles (for example “super-symmetric” particles) and a new mysterious unknown energy, which isn’t diluted when we expand its volume. This amazing face of the Universe makes us reflect about what it consists of and allows us to see a convergence between different scientific fields, as apparently unrelated in appearance, as cosmology and particle physics.
The Origin of Cosmic Rays
The Earth is permanently bombarded with around 2000 charged particles per second per square meter at the top of the atmosphere. The study of these rays lead to the discovery of several elementary particles at the beginning of the 20th century. The energy range covered by these particles is enormous, from several thousand electrons-volts (for particles in the solar wind) to about one hundred billion-billion electrons-volts (the kinetic energy of a speeding bullet concentrated on a particle smaller than an atom). Beyond the contribution from the solar wind, whose particles create the aurora borealis, the majority probably originate from supernova explosions in our galaxy. These ultra-high energy particles seemingly have an extra-galactic origin and remain rather mysterious. The study of these particles, and to search for their origin, is the aim of numerous experiments which vary from instruments aboard balloons or satellites, passing by large observatories on the Earth which cover thousands of square kilometers, for the detection of rare, ultra-high energy particles to finally underground observatories.
Unification of Fundamental Forces
We currently know of only four fundamental forces. The first, gravity, was discovered by Newton at the end of the 17th century. He managed to describe, in a unique theory, two seemingly different phenomena; the falling motion of terrestrial bodies and the motion of astral bodies. The second interaction discovered was electromagnetism resulting in the unification of electricity, magnetism and optics at the end of the 19th century. The third fundamental force is the weak interaction, which is responsible for radioactivity; the transformation of a neutron in to a proton in certain nuclear processes. Finally, the fourth fundamental force is the strong interaction, which acts as a cohesive force between protons and neutrons, allowing atomic nuclei to form.
Particle physics has already achieved a description of the elementary components of matter and the electromagnetic and weak interactions in a unified framework, called the “Standard Model”. The ambition of particle physicists is now to integrate the strong force in to this framework. This generalization leads to “Grand Unification Theories”, which will be tested by enormous particle accelerators or other installations such as ultra-cold neutron experiments.
Elementary Particles
One of the most important goals of high energy physics is the identification of the mechanism which gives their mass to the elementary particles that make up our universe. This mechanism is intimately linked to the symmetry laws, which govern our description of the world of particles and of the four known fundamental interactions.The currently most favoured model predicts that masses arise from the interaction between particles and a field, called the Higgs field. Some of the consequences of this model include the prediction of the existence of at least one new particle, the Higgs boson.
The creation processes of this boson are extremely rare and its experimental signature difficult to extricate. Searches for this particle have been ongoing for more than 10 years. Recently, the ATLAS and CMS experiment at the LHC, the CERN1 Large Hadron Collider, announced the discovery of a new boson whose first measured characteristics match those of the Standard Model Higgs boson.
Studies of the Strong Force
The strong force is responsible for the stability of the atomic nucleus. This force dominates the interaction between quarks, which are elementary constituents of matter, and possess remarkable properties described by quantum chromodynamics (QCD). It is of interest to note that the quarks stay confined to the interior of a proton and that the mass of the latter results not only from the mass of the constituents but mainly from their interactions.
Recent experimental and theoretical advances have allowed the internal structure of the proton or neutron to be better understood. Experiments at Jefferson Lab, which use probes sensitive to electric or weak charges, with energies adapted to the scale of the nucleon, have largely contributed to this progress.
Another important theme, in the understanding of the strong force, is the study of the quark-gluon plasma. Although quarks are confined to the interior of hadrons (protons and neutrons notably), QCD predicts the existence of a non-confined system for extremely high temperatures and densities. These conditions, which prevailed one microsecond after the big bang, can be reproduced in the laboratory, using collisions between ultra-relativistic heavy ions at certain accelerators, such as the LHC.
At a larger scale, the objective of nuclear physics is to understand the structure of the nucleus starting from basic nucleon-nucleon interactions. In order to improve our knowledge of these interactions, nuclei are currently studied at the extremes of existence; large neutron-to-proton ratios, extreme angular momentum, high proton numbers (super-heavy nuclei) or at high excitation energy (hot nuclear matter). Being able to correctly calculate nuclear forces is essential not only to test nuclear-model predications, different theories predict changes in the organization of the nucleons in the nuclei far from stability, but also for astrophysical-reactions responsible for the elemental abundances found on the Earth. These exotic nuclei are presently studied at several facilities, including the ILL2, GANIL3, CERN and GSI4.
What solutions for tomorrow’s nuclear power?
Since the end of the last century several problems have re-launched national research projects on nuclear reactors; the possibility to destroy some of the nuclear waste produced by reactors, their capacity to guarantee energy production over a long time scale, by optimizing the resources available, without sacrificing safety. The study of innovative nuclear reactors finds a resonance equally on a worldwide scale, as a possible solution to increased power demands, the necessity to combat global warming and the reduction in the fossil-fuel reserves.
For several years the CNRS5 in general and the LSPC in particular contribute to this research effort which concentrates on the use of thorium as a fissile fuel and the possibility to destroy long-lived nuclear waste products. This waste destruction can take place in dedicated reactors, such as sub-critical ones, driven by accelerators.
Nuclear Imagery and Radiotherapy
In the past, medicine has largely benefited from the fruits of subatomic physics research. The LPSC participates in this tradition in the nuclear medicine sector. The laboratory has contributed to several experimental efforts in the fields of hadron-therapy and tomography and today works on improving radiotherapy safety. Photon radiotherapy uses a technique which modulates the intensity and shape of an X-ray beam, in order to deliver the dose as precisely as possible, at the same time limiting the exposure of healthy tissue. To date, no standard control exists over the characteristics of the X-ray beam directed towards the patient. This is why a detector for measuring the shape of the irradiating beam, in real time, emanating from the accelerator is currently being developed. Naturally the development of such an apparatus requires close dialogue with the radiotherapy service of Grenoble hospital.
Plasma Physics
A new thematics on Plasmas, Matérial and Nanostructures physics is being developed since 2005 with the coming of a new group. With the existing LPSC Ion Source Service this has allowed to gather in a single place skills and know-how on the microwave plasmas, in particular those generated at the electronic cyclotronic resonance. Researches are being focused on the development of new generations of plasmas, which are able to provide improved performances (extended scales and uniformity), extended operation modes (pressure, volume), and a better control of the processes (engraving, surface deposit) involved.
Particle accelerators for multiple applications
Particle accelerators and their associated sources are used as probes for basic components of matter to increase our knowledge of fundamental physics. Beyond this objective, which remains the driving forces of their developments, particle accelerators and sources have nowadays numerous applications in the economical world. In order to take up the challenges of physics and its applications, techniques pushing the limits of the present knowledge must be developed, requiring specific Research and Development programs. The LPSC, has now created an Accelerators and Ion Sources pole to define and conduct such programs. The pole ensures the design, construction, and implementation of particle accelerators as well as innovating ion sources dedicated to monocharged and multicharged ion beams production. The pole is specialized in beam dynamics and radiofrequency acceleration techniques and it designs and realizes accelerator systems and sub-systems for various projects. Moreover, the pole operates a deuteron accelerator for the physics program of the laboratory.
Presently, LPSC contributes to the construction of SPIRAL26, a radioactive ion beam accelerator dedicated to nuclear physics at the GANIL and of machines forming the CERN accelerator complex. The pole develops the world’s most compact Electron Cyclotron Resonance ion sources permitting numerous treatments and analysis processes for materials. For studies on future nuclear energy production systems, LPSC developed an accelerator to drive an innovative nuclear reactor prototype. This accelerator provides a tunable neutron source for on-line characterization of the nuclear core. Some radio-resistant cancers can be cured by high energy ion beam (protons, carbon) irradiation. LPSC has worked on the design and implementation of such medical machines in Europe.
1. Organisation européenne pour la recherche nucléaire, Genève, Suisse
2. Institut Laue-Langevin, Grenoble
3. Grand accélérateur national d’ions lourds, Caen
4. Gesellschaft für Schwerionenforschung, Centre de recherche sur les ions lourds, Darmstat, Allemagne
5. Centre national de la recherche scientifique
6. Système de Production d’Ions RAdioactif en Ligne, Caen
