**2. Accelerator description**

In this section, we describe the fundamentals of a 5 MV Tandetron delivered by high-voltage engineering (HVE) for ion beam analysis (IBA) and ion beam modification of materials (IBMM) at operation in CMAM in the Universidad Autónoma de Madrid (Spain) [19]. In **Figure 1** it is possible to observe (a) plan view of the

*Ion Beam Techniques and Applications*

enough energy to move a third one and so on.

depending on the energy deposited [5].

by neutrons (PKA spectrum) will induce elastic reactions, which produce additional displacement damage (displacement cascades) because they eventually will produce large collision cascades, since the secondary atom impacted by the PKA has

Therefore, this PKA spectrum will be responsible to deposit the displacement damage in the material. On the other hand, if the neutron produced an inelastic reaction, an induced transmutation by neutron collision will be produced, generating light atoms as helium and hydrogen until hundreds of atomic parts per million (appm) in the whole life service of the reactor along with PKAs

Regarding helium atoms, one of the main issues in terms of structural material degradation is the nucleation and growth of He bubbles at grain boundaries which would produce a reduction of service lifetime. This degradation comes due to helium atoms produced by transmutation reaction of Fe; around 4 MeV of neutron energy may produce the following reaction generating alpha particles 56Fe (n.a) 53Cr [6]. It is well known that the combination between helium atoms and vacancies is very energetically favorable, so it will form eventually He bubbles. For that reason a deeper understanding of the effect of those bubbles in the evolution of microstructure and further degradation of mechanical properties are critical. However, several parameters have to be controlled and studied to determine properly the evolution of He bubbles during irradiation such as temperature, He

Candidate materials for being used as structural materials are reduced activation ferritic martensitic (RAFM) steels, since they show a high resistance to irradiation damage, higher thermal conductivity, good corrosion resistance, and good liquid metal compatibility than austenitic steels. Several studies have shown that grain boundaries or phase boundaries may also act as sinks for radiation-induced point

On the other hand, collision cascades known as accumulation of atoms displaced will form a complex form of Frenkel pair defects such as interstitial clusters which may turn into large dislocation loops or vacancy-type voids. Those irradiationinduced defects act as barriers to the dislocation movement, so they produce a

Neutron irradiation is not the most used technique to irradiate materials since the nuclear activation of the specimens makes necessary to have available hot cells to characterize the samples. On the other hand, nowadays there is no facility to emulate neutron fusion environment; for that reason ion beam irradiations are used to emulate neutron irradiation, of course, having into consideration the main differences such as shallow depth of irradiated material, elevated dose rate, and, clearly,

Current neutron sources with an energy spectrum typical of fusion reactions (14 MeV neutrons) are far from the fluence expected in a fusion reactor, and they are only useful for a few cases involving functional materials not exposed to high radiation doses [8, 9]. Therefore, a common approximation to test fusion materials consists of using ion irradiation to emulate the effects of neutron irradiation [10]. Ion irradiation can yield higher damage rates generating negligible activation levels in the irradiated samples at a reduced cost than other approximations to the problem like fission reactor irradiations. These elevated dose rates are very interesting to obtain samples submitted to an accelerated damage aging that would take several years to be achieved by fission irradiation. It is necessary to consider, however, that these accelerated tests may be driven by aging mechanisms very different from the real processes taking place under the low damage rate produced

production rate, displacement rate, and dose (accumulation of He).

defects and the cluster formed during irradiation [7].

significant hardening and hence a ductility reduction.

**16**

not transmutation.

by real fusion conditions.

### **Figure 1.**

*(a) Plan view of the tank and the lines of CMAM accelerator and (b) detail of the accelerator lines (courtesy of Jorge Álvarez Echenique, CMAM).*

mentioned accelerator and (b) all the lines which are nowadays working. This kind of facility is also of great interest to investigate fusion-induced material damages by creating a controlled environment to simulate these effects.

The Tandetron ion accelerator is a tandem type that counts with a Cockroft-Walton high-voltage generator system that will be presented briefly in the following paragraphs, describing sources for ion beam generation, beam acceleration, and two of the beamlines available used for experiments for nuclear fusion.

### **2.1 Ion beam production**

The first step for IBA or IBMM experiments is to generate the beam, i.e., to produce ions from neutral matter, extract them, and focus the beam. Since the selected ion and the current are a function of the experimental needs, the source constraints are of critical importance. CMAM facility is provided with two sources: a plasma source for gaseous substances and a sputtering source to obtain practically any element of the periodic table from a solid target.

**19**

*2.1.3 Injector system*

*Ion Beam Experiments to Emulate Nuclear Fusion Environment on Structural Materials…*

The range of current that can be obtained from the source varies from a few nA to tens of μA, depending on the source and the ion. As will be presented later, the tandem configuration requires the production of negative ions, which are more difficult to obtain than positive ones. It is much easier to rip off electrons from an atom than to add them on. It is not even possible to obtain negative ions from all elements, as is the case of nitrogen, so unstable that in practice cannot be produced [23].

This section addresses basic ideas of two specific kinds of ion sources, duoplas-

In this configuration, negative ions are effectively produced from a solid target which contains the desired beam material inside a cylindrical refrigerated copper cathode, the sputter target holder. A cesium reservoir is heated providing vapor to the main cavity of the source. The neutral flux of Cs has two functions: on the one hand, the cesium condensates over the target surface, and, on the other hand, a fraction of the Cs atoms in the gas becomes positively ionized by contact with a heated ionizer surface. The ionizer is kept at positive voltage with respect to the cathode so that positive Cs ions bombard the target producing the ejection of sputtered atoms that pass through the optimally cesiated surface with a low work function [20, 21]. By this surface effect method that involves cesium as a great electron donor, sputtered atoms from the target become negative (secondary negative ions). Those ions are repelled from the cathode to the extraction section of the source and focus into a negative beam. Beam currents of 2–40 μA are achieved, depending on the species. Elements with negative electronic affinity, such as nitrogen, can be

) and broken

extracted from the source in the form of a molecular beam (e.g. NH-

gen to uranium can be delivered, with the important exception of helium.

into its components at a later stage. Any element of the periodic table from hydro-

The duoplasmatron source permits two modes of operation, positive and negative ion beam extraction from a gas (typically H2 or He). Positive operation is required for helium atoms because being a noble gas is not possible to efficiently obtain negative helium ions directly from the source. After positive extraction, He+ ions pass through a charge-exchange cell filled with lithium vapor where the final negative beam emerges for further acceleration. Only about 1% of the He+ ions coming from the source turn negative, a fact that limits the maximum achievable current to a few μA versus tens of μA obtained when working in negative operation. The working principle of ion generation consists of a two-stage discharge where the gas is leaked into the source and the molecules are ionized. The first discharge is produced by means of thermo-ionic emission from a hot filament, between the filament (cathode) and the intermediate electrode (IE). A strong confining magnetic field guides the electrons through an aperture to the second discharge region between the intermediate electrode and the anode [22]. The magnetic field and the geometry of the IE are specially configured to enhance plasma density and high ionization degree. Finally, regarding the extraction direction, just comment that the

The ions in the beam exiting the source are shaped, focused, and led to the entrance of the accelerator, passing through a 90° analyzing magnet that bends the

*DOI: http://dx.doi.org/10.5772/intechopen.87054*

matron and negative sputtering source.

*2.1.1 Negative sputtering source (model HVE-860C)*

*2.1.2 Duoplasmatron source (model HVE-358)*

ions are axially extracted from the plasma.

### *Ion Beam Experiments to Emulate Nuclear Fusion Environment on Structural Materials… DOI: http://dx.doi.org/10.5772/intechopen.87054*

The range of current that can be obtained from the source varies from a few nA to tens of μA, depending on the source and the ion. As will be presented later, the tandem configuration requires the production of negative ions, which are more difficult to obtain than positive ones. It is much easier to rip off electrons from an atom than to add them on. It is not even possible to obtain negative ions from all elements, as is the case of nitrogen, so unstable that in practice cannot be produced [23].

This section addresses basic ideas of two specific kinds of ion sources, duoplasmatron and negative sputtering source.

### *2.1.1 Negative sputtering source (model HVE-860C)*

*Ion Beam Techniques and Applications*

mentioned accelerator and (b) all the lines which are nowadays working. This kind of facility is also of great interest to investigate fusion-induced material damages by

*(a) Plan view of the tank and the lines of CMAM accelerator and (b) detail of the accelerator lines (courtesy* 

The Tandetron ion accelerator is a tandem type that counts with a Cockroft-Walton high-voltage generator system that will be presented briefly in the following paragraphs, describing sources for ion beam generation, beam acceleration, and

The first step for IBA or IBMM experiments is to generate the beam, i.e., to produce ions from neutral matter, extract them, and focus the beam. Since the selected ion and the current are a function of the experimental needs, the source constraints are of critical importance. CMAM facility is provided with two sources: a plasma source for gaseous substances and a sputtering source to obtain practically

two of the beamlines available used for experiments for nuclear fusion.

creating a controlled environment to simulate these effects.

any element of the periodic table from a solid target.

**18**

**Figure 1.**

**2.1 Ion beam production**

*of Jorge Álvarez Echenique, CMAM).*

In this configuration, negative ions are effectively produced from a solid target which contains the desired beam material inside a cylindrical refrigerated copper cathode, the sputter target holder. A cesium reservoir is heated providing vapor to the main cavity of the source. The neutral flux of Cs has two functions: on the one hand, the cesium condensates over the target surface, and, on the other hand, a fraction of the Cs atoms in the gas becomes positively ionized by contact with a heated ionizer surface. The ionizer is kept at positive voltage with respect to the cathode so that positive Cs ions bombard the target producing the ejection of sputtered atoms that pass through the optimally cesiated surface with a low work function [20, 21]. By this surface effect method that involves cesium as a great electron donor, sputtered atoms from the target become negative (secondary negative ions). Those ions are repelled from the cathode to the extraction section of the source and focus into a negative beam. Beam currents of 2–40 μA are achieved, depending on the species. Elements with negative electronic affinity, such as nitrogen, can be extracted from the source in the form of a molecular beam (e.g. NH- ) and broken into its components at a later stage. Any element of the periodic table from hydrogen to uranium can be delivered, with the important exception of helium.

### *2.1.2 Duoplasmatron source (model HVE-358)*

The duoplasmatron source permits two modes of operation, positive and negative ion beam extraction from a gas (typically H2 or He). Positive operation is required for helium atoms because being a noble gas is not possible to efficiently obtain negative helium ions directly from the source. After positive extraction, He+ ions pass through a charge-exchange cell filled with lithium vapor where the final negative beam emerges for further acceleration. Only about 1% of the He+ ions coming from the source turn negative, a fact that limits the maximum achievable current to a few μA versus tens of μA obtained when working in negative operation.

The working principle of ion generation consists of a two-stage discharge where the gas is leaked into the source and the molecules are ionized. The first discharge is produced by means of thermo-ionic emission from a hot filament, between the filament (cathode) and the intermediate electrode (IE). A strong confining magnetic field guides the electrons through an aperture to the second discharge region between the intermediate electrode and the anode [22]. The magnetic field and the geometry of the IE are specially configured to enhance plasma density and high ionization degree. Finally, regarding the extraction direction, just comment that the ions are axially extracted from the plasma.

### *2.1.3 Injector system*

The ions in the beam exiting the source are shaped, focused, and led to the entrance of the accelerator, passing through a 90° analyzing magnet that bends the beam and selects the proper mass of the single negative-charged ions. Mass separation is done by tuning the magnetic induction so that only a given q/√m ratio is transmitted through the entrance and exit collimators. This is necessary because the beam exiting the source contains several species along with the desired one due to imperfect vacuum or impurities in the target. The electromagnet is water-cooled and capable of inflecting all ions in the periodic table, selecting them by momentum per unit charge, i.e., by magnetic rigidity [Eq. (1)] [23]:

$$\mathbf{Br} = \frac{\mathbf{P}}{\mathbf{q}} = \left(\frac{2\mathbf{m}\mathbf{E}}{\mathbf{q}^2}\right)^{1/2} \tag{1}$$

where B is the tunable magnetic induction, m the desired mass of the particle, E its energy, q its charge, and r the radius of curvature of its trajectory, which is determined by the entrance and exit of the magnet.

The guidance and focusing of the beam during its trajectory are achieved by electrostatic and magnetic devices called lenses for the analogy that can be drawn with the effect of thick optical lenses on light. Moreover, electrostatic or magnetic deflectors properly steer the beam into the optical axes of the lenses so that adjusting the lens will alter the focus but not the position of the beam.

### **2.2 Tandem accelerator system**

Following the injector system, the beam containing negative ions at a certain kinetic energy defined by the extraction voltages of the sources (tens of kV) goes through the next stage, the accelerator.

A tandem-type accelerator system consists of a two-step acceleration process. The high-voltage terminal electrode is enclosed in the center of a pressure vessel midway between the entrance and the exit of the acceleration tube, both at ground potential. Once injected into the low-energy part of the tube, the ions get attracted toward the positive terminal, increasing their energy in nVT electronvolts, where VT is the terminal voltage and n is the charge state, equal to 1. At this point, the beam passes through a region where N2 gas circulates, getting stripped off from one or more electrons, thus inverting their polarity and getting accelerated again to ground along the high-energy tube. The beam is composed now of a distribution of positive charge states n that vary from 1 to Z, Z being the atomic number of the atom. This second step leads to an energy gain of nVT electronvolts that depends on the specific charge state of each ion [24].

The extra energy obtained by inverting the polarity is the primary benefit of tandem-type accelerators over single-ended ones and the reason why negative ion sources are required. Additionally, this system allows the sources to be outside the tank, a fact that implies easier maintenance and simpler operation of the sources. On the contrary, the charge-exchange process results in a reduction of beam intensity, especially for heavy ions, being the transmission up to 50%. However, for IBA analysis and many material experiments, these currents are adequate.

The total kinetic energy achieved at the end of the accelerator tube is given in electronvolts [Eq. (2)]:

$$\mathbf{E} = \mathbf{E}\_{\text{ext}} + (\mathbf{1} + \mathbf{n})\,\mathbf{V}\_{\text{T}} \tag{2}$$

**21**

**Figure 2.**

*Ion Beam Experiments to Emulate Nuclear Fusion Environment on Structural Materials…*

The engineering challenge of electrostatic accelerators relies on how to produce high voltages, which main limitation is the breakdown due to insulation problems. As was previously described, the positive high-voltage terminal is located at the center of the tube. But in electrostatic accelerators, the high voltage is gradually distributed among multiple equipotential tubes with a slightly increased value, so that the ions feel a stepwise acceleration in the insulated gaps between each seg-

The accelerator at CMAM produces the terminal voltage by means of a Cockroft-

The hole voltage multiplier structure is placed around the evacuated acceleration tube in a coaxial configuration. High vacuum is required inside the tube to minimize unwanted secondary electron production by collisions of the ions with atoms of the residual gas. Furthermore, small magnets are placed to suppress these backstreaming electrons before they get accelerated generating hard X-rays. The electrodes are parallel fed with the increasing potential by resistive grading, and thus the voltage is smoothly distributed from terminal to ground. All the assembly is enclosed inside a pressurized tank filled with insulating sulfur hexafluoride gas (SF6) to prevent electrical breakdown, and every component is specifically designed to reduce local electric stress to avoid corona and

The advantage of C-W generator system relies on being entirely based on a solid-state circuit. The absence of moving parts, the high RF driving frequency (~38 kHz), a special RC filtering, and the feedback circuits that monitor the terminal voltage through a generating voltmeter (GMV) provide a remarkable terminal voltage stability and low terminal voltage ripple (less than 50 V at 5 MV). As a

*Simplified scheme of the Cockroft-Walton generator. The voltage across each stage of the cascade is equal to* 

result, a superior beam energy resolution is achieved.

*twice the peak input voltage in a half-wave rectifier.*

Walton (C-W) generator system, a design based on a cascade-type voltage multiplier circuit that was implemented for the first time in a DC accelerator in 1932 by J. D. Cockcroft and E. T. Walton [23] at the Cavendish Laboratory in England. It consists of a circuit feed by radio-frequency (RF) voltage power that supplies a higher DC voltage level. It is constituted by an assembly of repeated units of capacitors and rectifier diodes that double the voltage amplitude with each additional block. A final voltage of 2 nV is obtained, where n is the number of repeated blocks, 50 in the case of CMAM Tandetron [24], and Vo is the amplitude of the AC voltage. A simplified scheme of the multiplier circuit invented by Greinacher [25, 26] in 1921

*DOI: http://dx.doi.org/10.5772/intechopen.87054*

is shown in **Figure 2**.

sparking [22].

*2.2.1 High-voltage power generator: Cockroft-Walton*

ment. That keeps a reduced value of the local electric field.

where Eext is the extraction energy and VT is the positive terminal voltage, with a maximum nominal value of 5 MV.

Effective focusing of the beam waist at stripper canal is achieved by optically matching the injector part to the accelerator with a pre-acceleration electrode called Q-snout.

*Ion Beam Experiments to Emulate Nuclear Fusion Environment on Structural Materials… DOI: http://dx.doi.org/10.5772/intechopen.87054*

### *2.2.1 High-voltage power generator: Cockroft-Walton*

*Ion Beam Techniques and Applications*

beam and selects the proper mass of the single negative-charged ions. Mass separation is done by tuning the magnetic induction so that only a given q/√m ratio is transmitted through the entrance and exit collimators. This is necessary because the beam exiting the source contains several species along with the desired one due to imperfect vacuum or impurities in the target. The electromagnet is water-cooled and capable of inflecting all ions in the periodic table, selecting them by momen-

**<sup>q</sup>** <sup>=</sup> (

where B is the tunable magnetic induction, m the desired mass of the particle, E its energy, q its charge, and r the radius of curvature of its trajectory, which is

The guidance and focusing of the beam during its trajectory are achieved by electrostatic and magnetic devices called lenses for the analogy that can be drawn with the effect of thick optical lenses on light. Moreover, electrostatic or magnetic deflectors properly steer the beam into the optical axes of the lenses so that adjust-

Following the injector system, the beam containing negative ions at a certain kinetic energy defined by the extraction voltages of the sources (tens of kV) goes

A tandem-type accelerator system consists of a two-step acceleration process. The high-voltage terminal electrode is enclosed in the center of a pressure vessel midway between the entrance and the exit of the acceleration tube, both at ground potential. Once injected into the low-energy part of the tube, the ions get attracted toward the positive terminal, increasing their energy in nVT electronvolts, where VT is the terminal voltage and n is the charge state, equal to 1. At this point, the beam passes through a region where N2 gas circulates, getting stripped off from one or more electrons, thus inverting their polarity and getting accelerated again to ground along the high-energy tube. The beam is composed now of a distribution of positive charge states n that vary from 1 to Z, Z being the atomic number of the atom. This second step leads to an energy gain of nVT electronvolts that depends on the specific

The extra energy obtained by inverting the polarity is the primary benefit of tandem-type accelerators over single-ended ones and the reason why negative ion sources are required. Additionally, this system allows the sources to be outside the tank, a fact that implies easier maintenance and simpler operation of the sources. On the contrary, the charge-exchange process results in a reduction of beam intensity, especially for heavy ions, being the transmission up to 50%. However, for IBA

The total kinetic energy achieved at the end of the accelerator tube is given in

**E** = **E**ext + (**1** + **n**)**VT** (2)

where Eext is the extraction energy and VT is the positive terminal voltage, with a

Effective focusing of the beam waist at stripper canal is achieved by optically matching the injector part to the accelerator with a pre-acceleration electrode called Q-snout.

analysis and many material experiments, these currents are adequate.

\_\_\_\_ **2**mE **q<sup>2</sup>** ) **1** ⁄**2**

(1)

tum per unit charge, i.e., by magnetic rigidity [Eq. (1)] [23]:

ing the lens will alter the focus but not the position of the beam.

Br <sup>=</sup> **<sup>p</sup>**\_\_

**2.2 Tandem accelerator system**

charge state of each ion [24].

electronvolts [Eq. (2)]:

maximum nominal value of 5 MV.

through the next stage, the accelerator.

determined by the entrance and exit of the magnet.

**20**

The engineering challenge of electrostatic accelerators relies on how to produce high voltages, which main limitation is the breakdown due to insulation problems.

As was previously described, the positive high-voltage terminal is located at the center of the tube. But in electrostatic accelerators, the high voltage is gradually distributed among multiple equipotential tubes with a slightly increased value, so that the ions feel a stepwise acceleration in the insulated gaps between each segment. That keeps a reduced value of the local electric field.

The accelerator at CMAM produces the terminal voltage by means of a Cockroft-Walton (C-W) generator system, a design based on a cascade-type voltage multiplier circuit that was implemented for the first time in a DC accelerator in 1932 by J. D. Cockcroft and E. T. Walton [23] at the Cavendish Laboratory in England. It consists of a circuit feed by radio-frequency (RF) voltage power that supplies a higher DC voltage level. It is constituted by an assembly of repeated units of capacitors and rectifier diodes that double the voltage amplitude with each additional block. A final voltage of 2 nV is obtained, where n is the number of repeated blocks, 50 in the case of CMAM Tandetron [24], and Vo is the amplitude of the AC voltage. A simplified scheme of the multiplier circuit invented by Greinacher [25, 26] in 1921 is shown in **Figure 2**.

The hole voltage multiplier structure is placed around the evacuated acceleration tube in a coaxial configuration. High vacuum is required inside the tube to minimize unwanted secondary electron production by collisions of the ions with atoms of the residual gas. Furthermore, small magnets are placed to suppress these backstreaming electrons before they get accelerated generating hard X-rays. The electrodes are parallel fed with the increasing potential by resistive grading, and thus the voltage is smoothly distributed from terminal to ground. All the assembly is enclosed inside a pressurized tank filled with insulating sulfur hexafluoride gas (SF6) to prevent electrical breakdown, and every component is specifically designed to reduce local electric stress to avoid corona and sparking [22].

The advantage of C-W generator system relies on being entirely based on a solid-state circuit. The absence of moving parts, the high RF driving frequency (~38 kHz), a special RC filtering, and the feedback circuits that monitor the terminal voltage through a generating voltmeter (GMV) provide a remarkable terminal voltage stability and low terminal voltage ripple (less than 50 V at 5 MV). As a result, a superior beam energy resolution is achieved.

### **Figure 2.**

*Simplified scheme of the Cockroft-Walton generator. The voltage across each stage of the cascade is equal to twice the peak input voltage in a half-wave rectifier.*

### **2.3 Beamlines**

After acceleration, the beam is finally focused by an electrostatic quadrupole triplet lens. The first and third quadrupoles focus in the vertical direction (Y-axis) and defocus horizontally (X-axis), while the quadrupole in the middle makes the opposite.

A second magnet with seven exit ports at different angles steers the beam to direct it through an evacuated pipe to the selected experimental station. Since the beam is composed of a distribution of charge states n, the switching magnet has the additional important role of discriminating a certain charge state in order to establish well-defined beam energy.

CMAM counts with six operative beamlines devoted to different research fields: standard multipurpose beamline, internal μ-beam line, ERDA-ToF line, implantation beamline, external μ-beam line, and nuclear physics beamline.

The essential features of two of the routinely used beamlines for experiments for structural materials for nuclear fusion applications at CMAM accelerator are outlined below.

### *2.3.1 Multipurpose or standard beamline*

This line is attached to the 30° port of the switching magnet and is the one that was initially installed and tested by HVE. The experimental chamber is placed 3.5 meters away from the magnet, not needing additional focusing. A set of two slits separated 2 m from each other are used to control the size and divergence of the beam, and the current can be measured with a Faraday cup located immediately before reaching the chamber [27].

The standard line is mainly devoted to Rutherford backscattering spectrometry (RBS) and elastic recoil detection, but several ports are available to position additional setup. The entire structure is kept under high-vacuum conditions by means of a turbomolecular pump assisted by a rotary pump.

A fixed Si barrier particle detector is located at 170° with respect to the incident beam, while another movable detector can be positioned at any angle, counting with a carousel with different foils and slits that can be positioned in front of the movable detector. Also, an SDD detector for simultaneous particle-induced X-ray emission (PIXE) performance is implemented.

The sample holder is mounted on a three-axis goniometer and a vertical platform that permits to position the samples and to orient them with respect to the incident beam, so random and channeling experiments can be performed. The sample holder is electrically isolated; it can be biased at +180 V to suppress the effect of secondary electron emission, and the total dose or fluence can be monitored during irradiation by means of a current meter and integrator from HVE [28].

### *2.3.2 Implantation beamline*

The implantation CMAM beamline is at −20° with respect to the accelerator axis, 6 meters after a second switching magnet located at 0° line.

Ion beam modification of materials (IBMM) is the main research field carried out in this line, given that high electronic stopping powers and penetrations of several microns are achievable. Irradiation with ions from H to Pb at maximum terminal voltage can be performed selecting their more prolific charge state, i.e., irradiating with the highest current beam attainable. That allows heavy ion irradiations within the range of 2–50 MeV and currents up to a few μA, depending on the ion. The experimentation chamber is electrically isolated and designed for ultrahigh

**23**

**Figure 3.**

*Ion Beam Experiments to Emulate Nuclear Fusion Environment on Structural Materials…*

vacuum (UHV). Samples' temperature can be modified with a cryostat/furnace designed at CMAM within a range of −180–600°C and precisely controlled during irradiations with a system of thermocouples located at the sample holder and a

An important feature of this beamline is the capability of performing irradia-

of HVE is installed, which deflects the beam a maximum of 9 mm both in vertical and horizontal directions. The beam sweeper permits to scan the irradiation area at 2 and 31 kHz rates in X and Y directions, controlling the beam offset position and scan amplitude. In that way, homogeneous quasi-static beam areas are delivered, as

The irradiation fluence is calculated by measuring the beam current with a Faraday cup in the line and the irradiation area with the aid of a scintillator.

As it was described above, many applications of particle accelerators require varying the beam energy in an experimental beamline without changing accelerator settings. A multifoil (variable thickness) beam energy degrader provides a fast, reliable, and reproducible way of setting the beam energy, obtaining a uniform damage and implantation profile for both, heavy and light ions. The prototype installed at the implantation line of the CMAM has a disc with a diameter of 120 mm (**Figure 3**), which rotates at a thousand revolutions per minute to avoid foil melting under high-current beam irradiation [27]. On the outside the disc has nine aluminum foils of different thicknesses to achieve an energy sweep from maximum energy absorption (thicker foils) and minimum energy of ions to minimum energy absorption of the primary ion beam (thinner foils). The tenth window is free to let the ion beam pass without any energy mitigation. The aluminum foil thicknesses chosen for this prototype were 6–50 microns for H

*2.3.2.1 Beam energy degrader prototype for H, He, and Fe irradiation with a* 

on target. An electrostatic beam sweeper

*DOI: http://dx.doi.org/10.5772/intechopen.87054*

tions over large areas, up to 10 × 10 cm<sup>2</sup>

observed in several images below (**Figures 8, 9, 11**, and **13**).

and He ions and 0.8–4 microns for heavier ions like Fe.

*Umbrella shaped wheel of the beam energy degrader prototype.*

thermographic camera.

*broad profile*

*Ion Beam Experiments to Emulate Nuclear Fusion Environment on Structural Materials… DOI: http://dx.doi.org/10.5772/intechopen.87054*

vacuum (UHV). Samples' temperature can be modified with a cryostat/furnace designed at CMAM within a range of −180–600°C and precisely controlled during irradiations with a system of thermocouples located at the sample holder and a thermographic camera.

An important feature of this beamline is the capability of performing irradiations over large areas, up to 10 × 10 cm<sup>2</sup> on target. An electrostatic beam sweeper of HVE is installed, which deflects the beam a maximum of 9 mm both in vertical and horizontal directions. The beam sweeper permits to scan the irradiation area at 2 and 31 kHz rates in X and Y directions, controlling the beam offset position and scan amplitude. In that way, homogeneous quasi-static beam areas are delivered, as observed in several images below (**Figures 8, 9, 11**, and **13**).

The irradiation fluence is calculated by measuring the beam current with a Faraday cup in the line and the irradiation area with the aid of a scintillator.

### *2.3.2.1 Beam energy degrader prototype for H, He, and Fe irradiation with a broad profile*

As it was described above, many applications of particle accelerators require varying the beam energy in an experimental beamline without changing accelerator settings. A multifoil (variable thickness) beam energy degrader provides a fast, reliable, and reproducible way of setting the beam energy, obtaining a uniform damage and implantation profile for both, heavy and light ions. The prototype installed at the implantation line of the CMAM has a disc with a diameter of 120 mm (**Figure 3**), which rotates at a thousand revolutions per minute to avoid foil melting under high-current beam irradiation [27]. On the outside the disc has nine aluminum foils of different thicknesses to achieve an energy sweep from maximum energy absorption (thicker foils) and minimum energy of ions to minimum energy absorption of the primary ion beam (thinner foils). The tenth window is free to let the ion beam pass without any energy mitigation. The aluminum foil thicknesses chosen for this prototype were 6–50 microns for H and He ions and 0.8–4 microns for heavier ions like Fe.

**Figure 3.** *Umbrella shaped wheel of the beam energy degrader prototype.*

*Ion Beam Techniques and Applications*

establish well-defined beam energy.

*2.3.1 Multipurpose or standard beamline*

before reaching the chamber [27].

*2.3.2 Implantation beamline*

of a turbomolecular pump assisted by a rotary pump.

by means of a current meter and integrator from HVE [28].

axis, 6 meters after a second switching magnet located at 0° line.

emission (PIXE) performance is implemented.

After acceleration, the beam is finally focused by an electrostatic quadrupole triplet lens. The first and third quadrupoles focus in the vertical direction (Y-axis) and defocus horizontally (X-axis), while the quadrupole in the middle

A second magnet with seven exit ports at different angles steers the beam to direct it through an evacuated pipe to the selected experimental station. Since the beam is composed of a distribution of charge states n, the switching magnet has the additional important role of discriminating a certain charge state in order to

CMAM counts with six operative beamlines devoted to different research fields: standard multipurpose beamline, internal μ-beam line, ERDA-ToF line, implanta-

The essential features of two of the routinely used beamlines for experiments for structural materials for nuclear fusion applications at CMAM accelerator are

This line is attached to the 30° port of the switching magnet and is the one that was initially installed and tested by HVE. The experimental chamber is placed 3.5 meters away from the magnet, not needing additional focusing. A set of two slits separated 2 m from each other are used to control the size and divergence of the beam, and the current can be measured with a Faraday cup located immediately

The standard line is mainly devoted to Rutherford backscattering spectrometry (RBS) and elastic recoil detection, but several ports are available to position additional setup. The entire structure is kept under high-vacuum conditions by means

A fixed Si barrier particle detector is located at 170° with respect to the incident beam, while another movable detector can be positioned at any angle, counting with a carousel with different foils and slits that can be positioned in front of the movable detector. Also, an SDD detector for simultaneous particle-induced X-ray

The sample holder is mounted on a three-axis goniometer and a vertical platform that permits to position the samples and to orient them with respect to the incident beam, so random and channeling experiments can be performed. The sample holder is electrically isolated; it can be biased at +180 V to suppress the effect of secondary electron emission, and the total dose or fluence can be monitored during irradiation

The implantation CMAM beamline is at −20° with respect to the accelerator

Ion beam modification of materials (IBMM) is the main research field carried out in this line, given that high electronic stopping powers and penetrations of several microns are achievable. Irradiation with ions from H to Pb at maximum terminal voltage can be performed selecting their more prolific charge state, i.e., irradiating with the highest current beam attainable. That allows heavy ion irradiations within the range of 2–50 MeV and currents up to a few μA, depending on the ion. The experimentation chamber is electrically isolated and designed for ultrahigh

tion beamline, external μ-beam line, and nuclear physics beamline.

**2.3 Beamlines**

makes the opposite.

outlined below.

**22**
