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Thomas Otto - Safety for Particle Accelerators

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Nguyễn Gia Hào

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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.

Hazard

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.

Risk

Control

Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, so as long as you give appropriate credit to the original author(s) and source, you must provide a link to the Creative Commons license and indicate whether changes have been made. The images or other third-party material in this chapter are included in the chapter's Creative Commons license, unless otherwise indicated in a credit line for the material.

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 [3]. 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.

Fig. 2.1  Compact cyclotron IBA Cyclone® KIUBE for production of radiopharmaceuticals by  protons with kinetical energy up to E kin  = 18 MeV
Fig. 2.1 Compact cyclotron IBA Cyclone® KIUBE for production of radiopharmaceuticals by protons with kinetical energy up to E kin  = 18 MeV

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.

Magnets

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.

Fig. 2.4  Schematic cut  through a C-Type Dipole  magnet in direction of the  beam. l iron  and l air  are the  length of the magnetic flux  lines in the yoke and in the  air gap, respectively
Fig. 2.4 Schematic cut through a C-Type Dipole magnet in direction of the beam. l iron and l air are the length of the magnetic flux lines in the yoke and in the air gap, respectively

Superconducting Magnets

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.

Table  2.2 and Fig.  2.7 illustrate the LHC dipole magnet, the most powerful  accelerator magnet currently in operation
Table 2.2 and Fig.  2.7 illustrate the LHC dipole magnet, the most powerful accelerator magnet currently in operation

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.

Fig. 2.8  A dipole bending magnet with its equivalent circuit [10]. Instead of U, the author of the  figure uses V as symbol for voltage
Fig. 2.8 A dipole bending magnet with its equivalent circuit [10]. Instead of U, the author of the figure uses V as symbol for voltage

Cryogenics

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.

Cryogenic Fluids

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.

Figure 2.12 shows the schematic of a room into which a substance S is released with  a volume flow R (m 3  s − 1 ) and with a relative concentration C s,r  (Volume-% or m 3 m − 3 )
Figure 2.12 shows the schematic of a room into which a substance S is released with a volume flow R (m 3  s − 1 ) and with a relative concentration C s,r (Volume-% or m 3 m − 3 )

Radiofrequency Technologies

  • 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.

Figure  2.15 shows a block-diagram of an RF accelerating system. An amplifier  converts DC input voltage into RF (high-frequency AC) output power
Figure 2.15 shows a block-diagram of an RF accelerating system. An amplifier converts DC input voltage into RF (high-frequency AC) output power

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 [36]. Tunable lasers based on toxic dyes are mounted on an optical bench with frequency doubling crystals and other optical elements (Fig. 2.20).

Fig. 2.20  Optical bench in the ISOLDE RILIS laser laboratory. Operators must protect themselves  from direct and reflected laser beams with protection glasses
Fig. 2.20 Optical bench in the ISOLDE RILIS laser laboratory. Operators must protect themselves from direct and reflected laser beams with protection glasses

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.

Fig. 2.22  Maximum Permissible Exposure (MPE) limits expressed as radiant exposure [J cm −2 ]  versus wavelength for various exposure times (pulse durations)
Fig. 2.22 Maximum Permissible Exposure (MPE) limits expressed as radiant exposure [J cm −2 ] versus wavelength for various exposure times (pulse durations)

Beam-Intercepting Devices

Collimators

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).

Fig. 2.24  Collimator for extracted beamlines from the SPS at CERN. While not the latest design,  this photo shows the metal collimator blocks which, in this model, can be moved to restrict the  beam in two directions simultaneously
Fig. 2.24 Collimator for extracted beamlines from the SPS at CERN. While not the latest design, this photo shows the metal collimator blocks which, in this model, can be moved to restrict the beam in two directions simultaneously

Targets

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.

Beam Dumps

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.

Beam-Matter Interaction

  • Electrons and Positrons
  • Protons and Charged Heavy Particles
  • Neutrons
  • 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.

Fig. 3.1  Fractional energy loss per radiation length in lead for each of the interaction mechanisms  as a function of electron or positron energy
Fig. 3.1 Fractional energy loss per radiation length in lead for each of the interaction mechanisms as a function of electron or positron energy

Ionising Radiation

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.

Fig. 3.5  Schematic construction of a gas-filled detector for ionising radiation. (Adapted from  [20]
Fig. 3.5 Schematic construction of a gas-filled detector for ionising radiation. (Adapted from [20]

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.

Electrical Safety

Electrical Hazards

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).

Fig. 4.1  Warning sign  against electrical risk, after  [1]. (Image source: https://
Fig. 4.1 Warning sign against electrical risk, after [1]. (Image source: https://

Electrical Safety

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.

Fig. 4.2  Electrician equipped with PPE: Helmet, arc-flash resistant visor, insulating gloves, fire-  resistant jacket
Fig. 4.2 Electrician equipped with PPE: Helmet, arc-flash resistant visor, insulating gloves, fire- resistant jacket

Mechanical Safety

  • 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.

Fig. 4.3  Warning signs against hazards from machines: hand injury, entrainment, crushing, after  [1]
Fig. 4.3 Warning signs against hazards from machines: hand injury, entrainment, crushing, after [1]

Pressure Vessels

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 [40].

Fire Safety

  • 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.

Fig. 4.12  Sketches of smoke stratification during a tunnel fire. Top: low ventilation velocity  (0–0.5 m/s)
Fig. 4.12 Sketches of smoke stratification during a tunnel fire. Top: low ventilation velocity (0–0.5 m/s)

Occupational Noise

Noise Measurement

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.

Table 4.2 Selected  sound  pressure levels. From
Table 4.2 Selected sound pressure levels. From

Protection Measures Against Noise

Environmental Impact

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
  • Documentation
  • Review

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.

Table 5.1  Hazard domains for a hazard register, with examples. A detailed hazard list is given in  the Annex.
Table 5.1 Hazard domains for a hazard register, with examples. A detailed hazard list is given in the Annex.

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.

Beam Safety

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 [4], 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 [4].

Fig. 5.5  Fault tree for the  simple ASS in the example  for SIL determination. The  two safety systems,  electronic lock, and mobile  dump are independent and  can be represented as  parallel blocks feeding an  AND-gate: they must fail  both to lead to a
Fig. 5.5 Fault tree for the simple ASS in the example for SIL determination. The two safety systems, electronic lock, and mobile dump are independent and can be represented as parallel blocks feeding an AND-gate: they must fail both to lead to a

Hình ảnh

Fig. 2.1  Compact cyclotron IBA Cyclone® KIUBE for production of radiopharmaceuticals by  protons with kinetical energy up to E kin  = 18 MeV
Table  2.2 and Fig.  2.7 illustrate the LHC dipole magnet, the most powerful  accelerator magnet currently in operation
Fig. 2.7  LHC Dipole magnet. Left: cut through the magnet [17], Right: artist’s 3D view of an  opened dipole in the tunnel
Fig. 2.8  A dipole bending magnet with its equivalent circuit [10]. Instead of U, the author of the  figure uses V as symbol for voltage
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