Images or other third-party material in this book are included in the book's Creative Commons license, unless otherwise indicated in a credit line for the material. This book provides an overview of the broad topic of safety in particle accelerators.
Summary It is not possible to write a book on Safety at Accelerators, or occupational safety in general, without a practical understanding of the technical language of the field.
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Accelerators for Pedestrians
Why Particle Accelerators?
In order to test theoretical models of particle physics, higher and higher energies than could be achieved by LEP were needed, a process that has so far culminated in the construction and operation of CERN's LHC at a central energy of mass 13-14 TeV . It allowed the discovery of the Higgs boson, the last missing element in the Standard Model of particle physics.
The Particle Accelerator Family
At the "Dees" outer radius, particles are extracted at their maximum energy by a septum magnet. Free-electron lasers (FELs) are a special type of synchrotron light source in which the undulating structure of the beam path emits coherent photons (i.e.
Particle Acceleration from Source to Target
Once the beam intensity has become too low to produce a satisfactory number of collisions or intensity of synchrotron light, the beam is deflected by switches into large absorbers, called beam dumps (section 2.6.3), where the energy is absorbed. If large deviations of the particle's path from its nominal trajectory are detected, an emergency beam dump is automatically activated to prevent damage to accelerator elements from a massive impact of the particle beam.
Normal Conducting Magnets
Here N is the number of turns of the electrical conductor, I is the electric current, lair is the gap width between the magnet poles and η is a coefficient of efficiency and usually close to unity. The shape factor A is related to the geometry of the magnet, in a dipole it roughly corresponds to the product of the length and width of the magnet pole.
The critical surface separates points in T-B-J space in which the magnet is superconducting from those where it is normally conducting. Right: Temperature margin at a given field and current density, i.e. how much T can increase before the magnet becomes normally conductive.
Safety Aspects of Magnets
The force in the magnetic moment of the switch in an inhomogeneous magnetic field with a gradient of 1 T/m is of the order of 500 N. Finally, the mechanical forces on ferromagnetic metal objects can be significant and can project them in the direction of the magnet.
Production of Low Temperatures
The cryogenic liquid produced in a refrigeration plant can be transported to the object to be cooled, where it absorbs some of the object's thermal energy. Safety aspects related to the construction of the compressors and refrigerators are taken into account by their manufacturer, who builds them according to industrial standards.
In the event that the thermal insulation of a cryostat fails, for example through a degradation of the insulation vacuum, thermal energy is transported from the environment to the cryogenic container by a combination of conduction and convection. Part of the cryogenic liquid evaporates, and by the ratio for an ideal gas pV = const., the pressure in the fixed-volume container increases.
Oxygen Deficiency Hazard from Cryogenic Fluids
Therefore, no accumulation of air or gas can occur, and the chamber outlet is (Q + R). A quick estimate shows that the thickness of the helium layer in a chamber of area A amounts to 5.6/A m for each kg of helium released.
- Principle of RF Acceleration
- Components of a RF Acceleration System
- Hazards from RF Systems
- Health Effects of Electromagnetic Fields (EMF)
- Protection against NIR
The field is at its maximum when the accelerated particle is in the center of the gap. The transit time factor, which can be influenced by the geometry of the accelerating structure.
Lasers at Accelerators
Application of Lasers at Accelerators
The sharply defined wavelength of a laser allows isotope-selective ionization of exotic atoms in radioisotope facilities, for example ISOLDE at CERN . Tunable lasers based on toxic dyes are mounted on an optical bench with frequency doubling crystals and other optical elements (Fig. 2.20).
Hazardous Effects of Lasers
The animal data are supported by clinical data from human exposure, either from volunteers, accidental cases or clinical patients. Chemical hazards from toxic and flammable dyes and solvents used in the operation of tunable wavelength tunable lasers.
Protection Against Laser Exposure
1 M Laser products that are safe, including long-term direct intrabeam viewing for the naked eye. 2 M Laser products that emit visible laser beams and are safe for short-term exposure to the naked (unprotected) eye only.
Cooling water or hydraulic fluids in a collimator may actuate slightly, although from experience, this is rarely a concern. However, devices for use in basic research may be exempt from the directive's descriptions and local prescriptions should be clarified with the licensing authorities (Fig. 2.24).
Stripping foils are very thin foils (in the range of micrometers) placed in a negatively charged beam to remove orbital electrons. They are used to remove heavy ions from all electrons or to remove two electrons from the H ion in an efficient injection process in a synchrotron.
Malecha et al., Experimental and numerical investigation of the emergency helium release in the LHC tunnel. Zhou et al., Radiation shielding study for the vertical test system for superconducting Rf cavities.
Beam Loss in Particle Accelerators
Next, the sources of ionizing radiation at accelerators are defined: beam loss is the cause of fast ionizing radiation. Material activated by the passage of particle cascades is a long-lived source of ionizing radiation.
- Electrons and Positrons
- Protons and Charged Heavy Particles
- Radiation Damage
- Activation of Matter
The cascade stops propagating when the average energy of the electrons has fallen below the critical energy Ec. When the energy of the projectile is high enough, new particles can form in nuclei.
Types of Ionising Radiation
Two main families of ionizing radiation can be distinguished: direct ionizing radiation, mediated by charged particles, and indirect ionizing radiation, mediated by neutral particles and photons. Due to this interaction mechanism, indirect ionizing radiation is exponentially attenuated in matter and has no finite range.
Sources of Ionising Radiation at Accelerators
The radionuclides produced are collected inside the targets or on the foil and they often present a risk of radioactive contamination. The relative advantage of radioactive pollution over chemical hazards is that ionizing radiation can be detected more easily than chemical pollution.
Radiation Dosimetry at Accelerators
Dose and Dose Equivalent
The paradigm of radiation protection is that the probability of radiation damage to a person is proportional to the effective dose E received, with no lower threshold. Effective dose limits, which limit the probability of stochastic effects occurring, are determined by comparison with the risk of disability or fatal accidents in other industries.
Practical Radiation Dosimetry at Accelerators
In this regime, the gain factor A ≈ 1010 and independent of the energy of the incoming particle. They consist of a proportional counter in which the pulse height, proportional to the energy of the recoil proton, is recorded.
Radiation Protection at Accelerators
Shielding Against Prompt Radiation
Here, H is the expected dose equivalent rate outside the shield of thickness d at the emission angle θ from the beam loss point or target. H0 is the energy-dependent emission of secondary particles from the target, conveniently expressed as a dose equivalent, and g(θ) is the angular dependence of the emission.
Protection Against Ionising Radiation from Activation
An example of the Monte-Carlo transfer calculation result for radiation protection is shown in Figure 2.16. Many nuclear facilities have learned that rigorous preparation for work in the radiation field benefits operational reliability and that the time and money spent on radiation dose reduction is repaid by increased intervention efficiency. .
Control of Radioactive Material
Schmidt, Proceedings of the CAS–CERN Accelerator School: Advanced Accelerator Physics, Trondheim, Norway, 18–29 August 2013, edited by W. Uznanski, Proceedings of the CAS–CERN Accelerator School: Power Converters, Baden, Switzerland, 7–14 May 2014, edited by R.
The resistance of the body depends on the applied voltage and environmental factors, especially humidity. When the body connects the electric current to earth, the magnitude of the electric current flowing through the body determines the extent of the damage (Table 4.1).
The magnet expert requests the electrical power group to separate the specific magnet from the power source. A member of the electrical power group will separate the connection supplying the indicated magnet from the power source.
- Machines at Particle Accelerators
- Machine Safety
- Transport at Particle Accelerators
- Safety of Transport and Handling
This is obviously in the interest of protecting the health and safety of workers and operators. These can come in the form of a machine in the broad definition of the EU, and then compliance with the European directive must be sought.
Pressure Vessels at Accelerators
They are used to contain the cooling medium of superconducting devices, and to contain cryogenic liquid particle detectors (Argon, Krypton and Xenon calorimeters). The components for conventional applications can be purchased from manufacturers who build the equipment according to legal prescription, for example according to the European directive and harmonized standards in the EU.
Pressure Vessel Safety
First, a solid ship construction that follows current engineering practice and described in national or international standards. These bursting valves or discs open at a certain predetermined pressure and eject the contents of the container in a controlled manner.
The European Directive on Pressure Vessels
In the regime where the pressure vessel operator cooperates with a notified body, the existence and operation of safety devices becomes an important part of the safety assessment. With regard to machines (see section 4.2.2), the construction of pressure vessels for proper use falls within the scope of the directive .
- The Fire Triangle
- Fire Hazards at Accelerators
- Tunnel Fires
- Fire Prevention
Under fuel-controlled conditions, the HRR of the fire increases until all the fuel is consumed. Controlling the characteristics and quantity of combustible materials is the second way to minimize the risk of fire.
To characterize noise at the workplace or in the environment, the sound pressure level (Lp) is measured. A simple method for obtaining a rough estimate of the instantaneous sound pressure level is described in Table 4.3.
Protection Measures Against Noise
Releases to the Environment
The World Health Organization recommends an environmental noise level of less than 35 dB at night to guarantee. At accelerator facilities, sources of environmental noise are cooling and ventilation systems (fans, fans), cryogenic systems (compressors), transformers and other electrical power equipment (transformer noise).
Reducing the Energetic Footprint
Directive 2014/35/EU of 26 February 2014 on the harmonization of the laws of the Member States relating to the making available on the market of electrical equipment designed for use within certain voltage limits, http://data.europa.eu/ eli /dir/2014/35/oj. On a larger scale, occupational activities can harm the environment and the public living in the vicinity of the plant.
The Occupational Safety Process
- Definition of Scope
- Hazard Register
- Application of Standard Best Practice
- Risk Assessment
- Definition and Implementation of Controls
The second step in the occupational safety process is the establishment of a hazard register. A fault tree (Fig. 5.1) places a system fault (a state in which the system no longer fulfills its purpose) at the top of the diagram.
Safety Organisation and Management
Employer- and Hierarchical Safety Responsibility
Reviews inscribe the safety process in the life cycle of the organization and are part of its Safety Management System. The safety policy should not be a dead document filed in an archive, but an expression of the living commitment of the organization to health and safety.
Administrative Safety Controls
These publications include, first, the organization's security policy and the principles of its security organization. Security policy and security regulations are only effective if they are known and accepted by employees at all levels of the hierarchy.
Accelerator Safety System
After longer service interruptions, for example after a shutdown, patrols of the accelerator area are organized. The patrol is formed by a minimum of two experienced members of the accelerator personnel with a good knowledge of the area.
Access Control System
Analogous to the prevention of personnel access, environmental protection considerations may enter the scope of the ASS, for example by preventing the release of harmful substances. Today, an ASS can be realized by transmitting the status of the elements through Ethernet or an equivalent data bus and the logic state can be evaluated by a programmable logic controller (PLC).
Functional Safety and Safety Integrity Levels
In the New EU Legislative Framework , formal requirements for declaration of conformity are effective. A summary of the directives in the New Legislative Framework with links to the original texts and further information can be found in .