A pulsed power drilling tool and a method for breaking a mineral substrate

Abstract

A pulsed power drilling tool (100) configured for passing a pulsed electrical current through a mineral substrate (400) to break the mineral substrate (400), the drilling tool (100) comprising: a pulsed power generator (110) for generating high voltage current pulses, a drill head (120) comprising at least one electrode pair (200) comprising at least a first electrode (201) and a second electrode (202), the first electrode (201) comprising a first solid electrode portion (203) and the second electrode comprising a second solid electrode portion (204), the first and second solid electrode portions (203, 204) being electrically connectable to the pulsed power generator (110), and at least one ionization arrangement (130) configured for generating at least one ionized fluid volume (210, 210') extending at least from the first solid electrode portion (203) to a surface of the mineral substrate (400) and / or extending at least from the second solid electrode portion (204) to a surface of the mineral substrate (400), so as to allow a high voltage current pulse (150) to pass between the first solid electrode portion (203) and the second solid electrode portion (204) via the at least one ionized fluid volume (210, 210') and the mineral substrate (400), wherein the at least one ionization arrangement (130) comprises at least a first laser emitting device (131) configured to generate a first laser beam (135) and emit it in a direction toward the mineral substrate (400), the first laser beam (135) being configured to ionize a fluid present between the drill head (120) and the mineral substrate (400) to form a first ionized fluid volume (210) of the at least one ionized fluid volume.

Description

[0001] A PULSED POWER DRILLING TOOL AND A METHOD FOR BREAKING A MINERAL SUBSTRATE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a pulsed power drilling tool for breaking a mineral substrate and to a method for breaking a mineral substrate by passing a pulsed electrical current through the mineral substrate. The disclosed tool and method may for example be applied in rock drilling, concrete processing, mineral processing, and continuous mining.

[0004] BACKGROUND

[0005] In the field of rock drilling, a new technology has emerged during the recent years, referred to as electro pulse boring (EPB), plasma channel drilling, pulsed plasma drilling, etc. The technology relies on mechanical electrodes creating contact with a rock material, and the application of a high voltage between the electrodes. The discharge occurring, if successful, penetrates the rock material and breaks loose small pieces. In some applications, an insulating fluid is proposed to prevent direct discharge between the electrodes. For most applications however, water preferably be used for practical reasons, and in some cases even saline water. This makes it crucial to achieve a good contact between the electrodes and the rock material, since the discharge path through the water will otherwise become more attractive than the desired discharge path via the rock material.

[0006] A drill head usually comprises a plurality of electrode pairs. Since the rock surface is never ideally flat, one or more electrodes of the drill head are likely not to be in direct contact with the rock surface. Thus, some of the discharges are likely to occur directly between the electrodes, not penetrating the rock material. When the discharge does not penetrate the rock material, a loss of efficiency occurs. Ultimately, such a failed rock penetration will result in that no rock destruction is achieved.

[0007] WO23277751 discloses a pulsed power drilling tool in which one or both electrodes comprise at least one ionization arrangement for generating at least one ionized fluid volume. In this way, an electrical contact between the solid electrode portion and the rock surface is achieved.

[0008] The one or more electrodes may need to be positioned as close as possible to the rock surface to enable the good contact between them. However, if a distance between the electrodes and the rock surface is too short, it may result in ejected rock pieces or debris causing damage to the drilling head during the drilling process.

[0009] SUMMARY

[0010] A primary object of the present disclosure is to achieve an in at least some aspect improved drilling tool and method for pulsed power drilling. In particular, it is an object to achieve such a drilling tool and method which reduce a risk of unnecessary damage and / or wear on components of a drilling head, such that safe and efficient drilling operation is ensured.

[0011] According to a first aspect of the disclosure, at least the primary object is achieved by a pulsed power drilling tool according to claim 1 , hereinafter also referred to as a drilling tool. The drilling tool is configured for passing a pulsed electrical current through a mineral substrate to break the mineral substrate. It comprises a pulsed power generator for generating high voltage current pulses and a drill head comprising at least one electrode pair comprising at least a first electrode and a second electrode. The first electrode comprises a first solid electrode portion and the second electrode comprises a second solid electrode portion. The first and second solid electrode portions are electrically connectable to the pulsed power generator. The drilling tool further comprises at least one ionization arrangement configured for generating at least one ionized fluid volume extending at least from the first solid electrode portion to a surface of the mineral substrate and / or extending at least from the second solid electrode portion to a surface of the mineral substrate, so as to allow a high voltage current pulse to pass between the first solid electrode portion and the second solid electrode portion via the at least one ionized fluid volume and the mineral substrate. The at least one ionization arrangement comprises at least a first laser emitting device configured to generate a first laser beam and emit it in a direction toward the mineral substrate, the first laser beam being configured to ionize a fluid present between the drill head and the mineral substrate to form a first ionized fluid volume of the at least one ionized fluid volume. By providing an ionization arrangement comprising a laser emitting device, it is possible to create a region of high conductivity between the solid electrode portion and the mineral substrate. This is achieved through the high energy of the laser beam, which can effectively ionize a fluid present there. The resulting ionized fluid volume will have a substantially higher conductivity in comparison with non-ionized fluid surrounding it, which means that the high voltage current pulse will pass through the ionized fluid volume from the solid electrode portion to the mineral substrate. As such, no mechanical contact between the first solid electrode portion and the mineral substrate is needed. Moreover, by using the laser beam for the ionization, it is possible to create such an ionized fluid volume that may extend over a relatively long distance, typically up to a few centimeters, between the first solid electrode portion and the surface of the mineral substrate. In this way, a safe distance between the drilling head and the surface of the mineral substrate may be maintained. The risk of unnecessary damage and / or wear on components of the drilling head may therefore be reduced, while the efficiency of the drilling process may be improved.

[0012] Another advantage of the disclosure is that the ionized fluid volume(s) may easily be adapted to the dielectric properties of the mineral substrate by, e.g., adjusting a degree of ionization. The degree of the ionization may be adjusted by modifying various parameters of the laser beam. For instance, it may be possible to increase the degree of ionization by increasing an intensity of the laser beam, as more photons are delivered to the fluid, resulting in a higher probability of ionization. As another non-limiting example, the degree of ionization may be enhanced by emitting multiple lasers with different wavelengths and orientations. The degree of ionization may determine a certain conductivity of the ionized fluid, which may be exploited to reduce power reflectance at the surface of the mineral substrate. The possibilities for impedance matching are thus improved.

[0013] The term “ionized fluid” is herein to be understood as encompassing ionized gas and / or ionized liquid, as well as fluids containing electrically charged particles of solid matter, such as nanoparticles or microparticles.

[0014] Optionally, the at least one ionization arrangement further comprises at least a first waveguide configured to guide the first laser beam from the first laser emitting device to a first waveguide exit provided in the drill head. In this way, the laser beam may be guided to an appropriate position to ionize the fluid present between the drill head and the mineral substrate, such that the ionization may be performed in an effective and efficient manner. Optionally, the first waveguide exit is provided in or adjacent to the first solid electrode portion.

[0015] Optionally, the first waveguide exit is provided above a lower end of the first solid electrode portion. The lower end may herein be understood as being the closest end to the mineral substrate, i.e. , the drilling tool is used for drilling in a downward direction.

[0016] Optionally, the first waveguide comprises an optical fiber and / or a mirror tube. Generally, an optical fiber has a very small diameter, e.g., a few microns, which allows for a precise control of a laser beam’s direction. Furthermore, an optical fiber may have a very low attenuation, meaning that it can transmit the laser beam over a long distance without a significant loss of energy in the laser beam. As such, by using the optical fiber, the first laser beam may be guided to the appropriate position without a significant loss of energy such that the ionization may be performed in an effective and efficient manner. In a less preferred example, the mirror tube may be used to guide the laser beam.

[0017] Optionally, the at least one ionization arrangement further comprises at least a first multiplier, configured to modify a wavelength of the first laser beam as emitted from the laser emitting device such that a target wavelength for ionizing the fluid is achieved. The multiplier may, for instance, be a frequency multiplier. It may modify the wavelength of the first laser beam to the target wavelength through multiplying a frequency of the laser beam. The target wavelength may be within an appropriate range, which may match energy that is required to ionize the atoms or molecules in the fluid present between the drill head and the mineral substrate.

[0018] Optionally, the pulsed power drilling tool further comprises a fluid supply system for supplying a flushing fluid to a region between the drill head and the mineral substrate. The flushing fluid may be circulated through the drill head and the mineral substrate. As the flushing fluid passes through the drill head, it may cool the drill head and carry away any debris that is generated during a drilling process.

[0019] Optionally, the flushing fluid is water or air. Optionally, the first laser beam is configured to ionize the flushing fluid to form the first ionized fluid volume. In this way, it may eliminate a need of using a dedicated fluid source for providing the fluid to be ionized.

[0020] Optionally, the at least one ionization arrangement further comprises at least a first focusing device, arranged between the first laser emitting device and the mineral substrate, the first focusing device being configured to focus the first laser beam to a focus point formed between the first solid electrode portion and the surface of the mineral substrate. In this way, energy of the first laser beam may be concentrated at the focus point in an appropriate position. An effective and efficient ionization may therefore be achieved.

[0021] Optionally, the pulsed power drilling tool further comprises at least a first beam directing device configured to control an angle of the first laser beam emitted toward the mineral substrate such that a direction of extension of the first ionized fluid volume can be controlled. The first beam directing device may, by way of example, be provided at the solid electrode portion, and / or in connection with the waveguide exit. The direction of extension of the first ionized fluid volume may hereby be controlled to direct the laser beam toward a target spot on the mineral substrate, e.g., based on material type.

[0022] Optionally, the first laser beam has a wavelength within a range between 1 nm and 100000 nm (100 pm), more preferably between 5 nm and 10000 nm, and most preferably between 10 nm and 380 nm. The first laser emitting device may be configured to emit a laser beam at an appropriate wavelength, which may match energy that is required to ionize the atoms or molecules in the fluid present between the drill head and the mineral substrate. In some examples, the first multiplier, if applicable, may be configured to modify the wavelength of the first laser beam to a target wavelength within the appropriate range.

[0023] Optionally, the at least one ionization arrangement further comprises a second laser emitting device configured to generate a second laser beam and emit it toward the mineral substrate, the second laser beam being configured to ionize a fluid present between the drill head and the mineral substrate to form a second ionized fluid volume of the at least one ionized fluid volume.

[0024] The at least one ionization arrangement may hence comprise two ionization arrangements that may in some embodiments be similar, or identical, to one another. Hence, all embodiments described with respect to a first ionization arrangement comprising the first laser emitting device may apply to a second ionization arrangement comprising the second laser emitting device. The two ionization arrangements may in other embodiments have configurations that differ from one another.

[0025] Optionally, in other embodiments, the first laser emitting device is configured to generate a second laser beam and emit it toward the mineral substrate, the second laser beam being configured to ionize a fluid present between the drill head and the mineral substrate to form a second ionized fluid volume of the at least one ionized fluid volume. Hence, the same laser emitting device may be used to generate more than one laser beam.

[0026] Optionally, the first ionized fluid volume is configured to guide the high voltage current pulse between the first solid electrode portion and the mineral substrate, and the second ionized fluid volume is configured to guide the high voltage pulse between the second solid electrode portion and the mineral substrate. In this case, no mechanical contact between either one of the solid electrode portions and the mineral substrate is needed. A safe distance between both electrodes and the surface of the mineral substrate may be ensured. As a result, electrode wear can be further reduced, and the electrodes thereby become more robust and less expensive.

[0027] Optionally, the drilling tool comprises a positioning device for controlling a distance between at least the first solid electrode portion and the surface of the mineral substrate and / or between at least the second solid electrode portion and the surface of the mineral substrate. The positioning device may allow for precise control of the distance, such that an appropriate and safe distance is maintained throughout the drilling process.

[0028] According to a second aspect of the disclosure, at least the primary object is achieved by a method for breaking a mineral substrate according to claim 16. The method is performed by passing a pulsed electrical current through the mineral substrate by means of a pulsed power drilling tool. The pulsed power drilling tool comprises a pulsed power generator for generating high voltage current pulses and a drill head comprising at least one electrode pair comprising at least a first electrode and a second electrode. The first electrode comprises a first solid electrode portion and the second electrode comprises a second solid electrode portion. The first and second solid electrode portions are electrically connectable to the pulsed power generator. The drilling tool further comprises at least one ionization arrangement configured for generating at least one ionized fluid volume extending at least from the first solid electrode portion to a surface of the mineral substrate and / or extending at least from the second solid electrode portion to a surface of the mineral substrate, so as to allow a high voltage current pulse to pass between the first solid electrode portion and the second solid electrode portion via the at least one ionized fluid volume and the mineral substrate. The at least one ionization arrangement comprises at least a first laser emitting device configured to generate a first laser beam and emit it in a direction toward the mineral substrate, the first laser beam being configured to ionize a fluid present between the drill head and the mineral substrate to form a first ionized fluid volume of the at least one ionized fluid volume.

[0029] The method comprises positioning the drill head so that the solid electrode portions are at least in proximity of a surface of the mineral substrate, generating the at least one ionized fluid volume by the at least one laser beam emitted by the at least one laser emitting device, and generating and passing a high voltage current pulse from the first electrode to the second electrode via the at least one ionized fluid volume and the mineral substrate.

[0030] The pulsed power drilling tool may be embodied by any of the above-described embodiments of the first aspect. Thus, advantages and advantageous features of the method appear from the above description of the drilling tool.

[0031] Optionally, the method further comprises supplying a flushing fluid to a region between the at least one electrode pair and the mineral substrate at least prior to generating at least one ionized fluid volume by the at least one laser beam emitted by the at least one laser emitting device.

[0032] The present disclosure also relates to a drill rig comprising a pulsed power drilling tool according to the first aspect and use of a pulsed power drilling tool according to the first aspect for breaking of a mineral substrate, such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

[0033] Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] With reference to the appended drawings, below follows a more detailed description of embodiments of the disclosure cited as examples.

[0035] In the drawings:

[0036] Fig. 1 schematically illustrates a pulsed power drilling tool according to an embodiment of the disclosure,

[0037] Fig. 2 is a sectional view of an electrode pair for a drilling tool according to an embodiment of the disclosure,

[0038] Fig. 3 is a sectional view of an electrode pair for a drilling tool according to another embodiment of the disclosure,

[0039] Fig. 4 is a flow-chart illustrating steps of a method according to the disclosure, and

[0040] Fig. 5 is a drill rig comprising the drilling tool shown in fig. 1.

[0041] The drawings show diagrammatic, exemplifying embodiments of the present disclosure and are thus not necessarily drawn to scale. It shall be understood that the embodiments shown and described are exemplifying and that the disclosure is not limited to these embodiments. It shall also be noted that some details in the drawings may be exaggerated in order to better describe and illustrate the disclosure. Like reference characters refer to like elements throughout the description, unless expressed otherwise.

[0042] DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

[0043] Fig. 1 schematically illustrates a pulsed power drilling tool 100 configured for passing a pulsed electrical current through a mineral substrate 400 to break it. The drilling tool 100 has a pulsed power generator 110 for generating high voltage current pulses, and a drill head 120 extending in an axial direction of the drilling tool 100 between a front end 121 , configured to be positioned near or at a surface of the mineral substrate 400, and a rear end 122.

[0044] The pulsed power generator 110 comprises a pulse transformer 112 in the form of a bank of capacitors, connected to a power supply 113 via a charged 11. Electrodes 201 and 202 are selected and connected using switches (not shown). Using the switches, a short high voltage pulse is generated. The pulse is transferred to the electrodes 201 and 202. The pulsed power generator 110 is configured for generating pulses used for breaking the mineral substrate 400, such as nanosecond (ns) pulses to the electrodes 201 and 202.

[0045] A pair of a first electrode 201 and a second electrode 202 are arranged at the front end 121 of the drill head 120, protruding slightly therefrom. The second electrode 202 is, in the embodiment shown in Fig. 1 , identical to the first electrode 201. Thus, only the first electrode 201 will therefore be described in detail.

[0046] The first electrode 201 comprises a hollow first solid electrode portion 203 arranged at a front end of the electrode 201. The solid electrode portion 203 is herein shown to be screwmounted and thereby replaceable. It is made at least partially of electrically conductive material and may be either metallic or ceramic. At least a part must be heat resistant and capable to carry the plasma return current. By way of example, the solid electrode portion 203 may be made of tungsten, stainless steel, aluminum, copper, or zirconium oxide ceramics.

[0047] The pulsed power drilling tool 100 further comprises an ionization arrangement 130 comprising at least a first laser emitting device 131. The first laser emitting device 131 is configured to generate at least one laser beam and emit it in a direction toward the mineral substrate 400. The first laser emitting device 131 may comprise a semiconductor laser, a CO2 laser, a Nd:YAG laser, a fiber laser and / or a solid state laser. It may emit continuous or pulsed radiation. Purely by way of examples, the emitted laser beams may be pulsed lasers, continuous lasers, and / or CO2 lasers. The ionization arrangement 130 may further comprise a supporting device (not shown) to which the first laser emitting device 131 is attached. In some examples, a protective element (not shown) is provided to prevent any flushing fluid from entering the emitted laser beams. The protective element may, for instance, be a glass window, a lens and / or an optical fiber. In the illustrated embodiment shown in Fig. 1, the laser emitting device 131 is configured to generate two laser beams 135, 135’ and the ionization arrangement 130 further comprises a first waveguide 132 and a second waveguide 132’. The two waveguides 132 132’ are configured to guide a first laser beam 135 and a second laser beam 135’ from the first laser emitting device 131 to the first electrode 201 and the second electrode 202, respectively. The laser beams 135 135’ are configured to ionize a fluid present between the drill head and the mineral substrate to form a first ionized fluid volume 210 extending from the first solid electrode portion 203 to a surface of the mineral substrate 400 and / or a second ionized fluid volume 210’ extending from the second solid electrode portion 204 to a surface of the mineral substrate 400. The ionized fluid volumes 210, 210’ will have a substantially higher conductivity, allowing a high voltage current pulse to pass between the solid electrode portions 203, 204 via the respective ionized fluid volumes 210, 210’ and the mineral substrate 400. As such, no mechanical contact(s) between the solid electrode portion(s) 203, 204 and the mineral substrate 400 is / are needed, and a safe distance may therefore be ensured during the whole drilling process. In an alternative example, the second solid electrode portion 204 may be mechanically applied against the mineral substrate 400, which is illustrated in FIG.2. The ionization arrangement 130 for generating the ionized fluid volume 210 will be described in detail using this example along with FIG.2.

[0048] The ionized fluid volume 210, 210’ may easily be adapted to the dielectric properties of the mineral substrate by, e.g., adjusting a degree of ionization. The degree of the ionization may be adjusted by modifying various parameters of the laser beam. For instance, it may be possible to increase the degree of ionization by increasing an intensity of the laser beam, as more photons are delivered to the fluid, resulting in a higher probability of ionization. As another non-limiting example, the degree of ionization may be enhanced by emitting multiple lasers with different wavelengths and orientations. The degree of ionization may determine a certain conductivity of the ionized fluid, which may be exploited to reduce power reflectance at the surface of the mineral substrate. The possibilities for impedance matching are thus improved.

[0049] The pulsed power drilling tool 100 may further comprise a fluid supply system 140 for supplying a flushing fluid to a region between the drill head 120 and the mineral substrate 400. The flushing fluid may be used to cool the drill head 120 and carry away any debris that is generated during the drilling process. In this case, the laser beam(s) 135, 135’ is / are configured to ionize the flushing fluid to form the ionized fluid volume(s) 210, 210’. In some examples, the flushing fluid is water. In some other examples, air may be used as an alternative flushing fluid.

[0050] Fig. 2 shows an alternative electrode setup, in which the second solid electrode portion 204 is mechanically applied against the mineral substrate 400. As such, the ionization arrangement 130 varies from the embodiment in Fig. 1 and in this illustrated embodiment, only the first ionized fluid volume 210 is generated.

[0051] As mentioned above, the ionization arrangement 130 comprises a first waveguide 132 configured to guide the first laser beam 135 from the first laser emitting device 131 to the first electrode 201. More specifically, the first waveguide 132 may comprise an exit 136 provided in the first solid electrode portion 203, located above a lower end 205 of the first solid electrode portion 203. The lower end may for instance, and as illustrated herein, be the closest end to the surface of mineral substrate 400. In a preferred example, the first waveguide 132 comprises an optical fiber. In some other examples, the first waveguide 132 comprises a mirror tube.

[0052] The at least one ionization arrangement 130 may further comprise a multiplier 133, which is configured to modify a wavelength of the first laser beam 135 as emitted from the laser emitting device 131 , such that a target wavelength for ionizing the fluid is achieved. In some examples, the first laser beam 135 emitted by the first laser emitting device 131 has an appropriate wavelength A that is ideal for the ionization. Purely by way of example, the laser beam 135 may have a wavelength that is within a range between 1 nm and 100000 nm (100 pm), more preferably between 5 nm and 10000 nm, and most preferably between 10 nm and 380 nm. In this case, there is no need to modify the wavelength A of the first laser beam 135. In some other examples, the multiplier 133 may be configured to modify the wavelength to a target range within the preferred range. The preferred wavelength may depend on properties, e.g., dielectric properties, of the fluid present between the drill head 120 and the mineral substrate 400.

[0053] The ionization arrangement 130 may further a first focusing device 134, arranged between the first laser emitting device 131 and the mineral substrate 400. The first focusing device 134 is configured to focus the first laser beam 135 to a focus point formed between the first solid electrode portion 203 and the surface of the mineral substrate 400. In this way, energy of the first laser beam 135 may be concentrated at the focus point in an appropriate position, such that the ionization may be performed in an effective and efficient manner. In some examples, the first focusing device 134 may be a laser focusing lens.

[0054] The ionization arrangement 130 may further comprise a first beam directing device (not shown), configured to control an angle of the first laser beam 135 emitted toward the mineral substrate 400 such that a direction of extension of the first ionized fluid volume 210 can be controlled.

[0055] Fig. 3 shows yet an alternative ionization arrangement 130 for the electrode setup shown in Fig. 1. In this illustrated embodiment, the least one ionization arrangement 130 comprises two laser emitting device 131 , 13T, configured to emit a first laser beam 135 and a second laser beam 135’, respectively. Each laser emitting device 131 , 13T is provided with a power source 136, 136’. The ionization arrangement 130 further comprises a first waveguide and a second waveguide, not shown in detailed in Fig. 3, configured to guide the first laser beam 135 from the first laser emitting device 131 to the first electrode 201 and / or configured to guide the second laser beam 135’ to the second electrode 202, respectively. A first focusing device 134 and a second focusing device 134’ are provided to focus the first laser beam 135 and / or the second laser beam 135’ to a focus point formed between the first solid electrode portion 203 and the surface of the mineral substrate 400 and / or formed between the second electrode portion 204 and the surface of the mineral substrate 400. In this way, the laser beams 135, 135’ will ionize a fluid present between the drill head 120 and the mineral substrate 400, such that a first ionized fluid volume 210 and a second ionized fluid volume 210’ are formed. As such, no mechanical contact between either one of the solid electrode portions 203, 204 and the mineral substrate is needed. A safe distance between both electrodes 201 , 202 and the surface of the mineral substrate 400 may therefore be ensured during the drilling process.

[0056] The drilling tool 100 may comprise a positioning device (not shown) for controlling a distance X between at least the first solid electrode portion 203 and the surface of the mineral substrate 400 and / or the second solid electrode portion 204 and the surface of the mineral substrate 400. The positioning device may allow for a precise control of the distance X, such that an appropriate and safe distance, typically a few centimeters, is maintained throughout the drilling process. Turning back to Fig. 1 , the drilling tool 100 may further comprise an electronic control unit 160 for controlling operation of the drilling tool 100 in response to signals received from an external control unit 170, such as a control unit of a machine in which the drilling tool 100 is provided. The electronic control unit 160 may include a microprocessor, a microcontroller, a programmable digital signal processor or another programmable device. Thus, the control unit 160 comprises electronic circuits and connections (not shown) as well as processing circuitry (not shown) for communicating with different parts of the drilling tool 100 as well as with the external control unit 170. For example, the control unit 160 may be configured for communicating with various sensors, devices, systems and control units of the drilling tool 100. In the shown embodiment, the control unit 160 controls the charger 111 as well as the switches (not shown). Although not shown, the control unit 160 may also be used for controlling the at least one ionization arrangement 130 and / or the fluid supply system 140. Alternatively, several separate control units may be provided.

[0057] The electronic control unit 160 may comprise modules in either hardware or software, or partially in hardware or software, and communicate using known transmission buses such a CAN-bus and / or wireless communication capabilities. The processing circuitry may be a general-purpose processor or a specific processor. The control unit 160 may comprise a non-transitory memory for storing computer program code and data. Thus, the skilled person realizes that the electronic control unit 160 may be embodied by many different constructions.

[0058] A method for breaking a mineral substrate 400 by passing a pulsed electrical current through the mineral substrate 400 by means of the pulsed power drilling tool 100 described above is illustrated in Fig. 4. The method comprises the following actions:

[0059] S1 : Positioning the drill head 120 so that the solid electrode portions 203, 204 are at least in proximity of a surface of the mineral substrate 400. In some cases, one of the solid electrode portions 203, 204 is positioned such that it is in contact with the mineral substrate 400.

[0060] S2: Generating the at least one ionized fluid volume 210, 210’ by the at least one laser beam 135, 135’ emitted by the at least one laser emitting device 131 , 13T. If one of the solid electrode portions 203, 204 is in contact with the mineral substrate 400, it is sufficient to generate a single laser beam 135, while as two laser beams may be generated if none of the solid electrode portions is in contact with the mineral substrate.

[0061] S3: Generating and passing a high voltage current pulse 150 from the first electrode 201 to the second electrode 202 via the at least one ionized fluid volume 210, 210’ and the mineral substrate 400.

[0062] The method may also comprise an optional step S4 of supplying a flushing fluid to a region between the at least one electrode pair 200 and the mineral substrate 400, at least prior to generating at least one ionized fluid volume 210, 210’ by the at least one laser beam 135, 135’ emitted by the at least one laser emitting device 131 , 13T.

[0063] Fig. 5 illustrates schematically a drill rig 500 comprising a drilling tool 100, such as the drilling tool 100 shown in Fig. 1 , drilling a hole 401 in a mineral substrate 400 in the form of a rock. The rock drilling machine 500 comprises the alternating current (AC) power supply 113 for powering the pulsed power generator 110. A hydraulic, pneumatic, or electrically actuated arm 510 for at least vertical positioning of the drilling tool 100 is provided, such as in response to signals from one or more position sensors (not shown) or similar sensing the distance between the electrodes and the mineral substrate surface. The drill rig 500 further comprises ground engaging members 520 for moving the rock drilling machine 500 in a direction parallel with the rock 400.

[0064] It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1. A pulsed power drilling tool (100) configured for passing a pulsed electrical current through a mineral substrate (400) to break the mineral substrate (400), the drilling tool (100) comprising:- a pulsed power generator (110) for generating high voltage current pulses,- a drill head (120) comprising at least one electrode pair (200) comprising at least a first electrode (201) and a second electrode (202), the first electrode (201) comprising a first solid electrode portion (203) and the second electrode comprising a second solid electrode portion (204), the first and second solid electrode portions (203, 204) being electrically connectable to the pulsed power generator (110), and- at least one ionization arrangement (130) configured for generating at least one ionized fluid volume (210, 210’) extending at least from the first solid electrode portion (203) to a surface of the mineral substrate (400) and / or extending at least from the second solid electrode portion (204) to a surface of the mineral substrate (400), so as to allow a high voltage current pulse (150) to pass between the first solid electrode portion (203) and the second solid electrode portion (204) via the at least one ionized fluid volume (210, 210’) and the mineral substrate (400),- wherein the at least one ionization arrangement (130) comprises at least a first laser emitting device (131) configured to generate a first laser beam (135) and emit it in a direction toward the mineral substrate (400), the first laser beam (135) being configured to ionize a fluid present between the drill head (120) and the mineral substrate (400) to form a first ionized fluid volume (210) of the at least one ionized fluid volume.

2. The pulsed power drilling tool (100) according to claim 1 , wherein the at least one ionization arrangement (130) further comprises at least a first waveguide (132) configured to guide the first laser beam (135) from the first laser emitting device (131) to a first waveguide exit (136) provided in the drill head (120).

3. The pulsed power drilling tool (100) according to claim 2, wherein the first waveguide exit (136) is provided in or adjacent to the first solid electrode portion (203).

4. The pulsed power drilling tool (100) according to claim 2 or 3, wherein the first waveguide exit (136) is provided above a lower end (205) of the first solid electrode portion (203).

5. The pulsed power drilling tool (100) according to claims 2—4, wherein the first waveguide (132) comprises an optical fiber and / or a mirror tube.

6. The pulsed power drilling tool (100) according to claims 2-5, wherein the at least one ionization arrangement (130) further comprises at least a first multiplier (133), configured to modify a wavelength of the first laser beam as emitted from the laser emitting device such that a target wavelength for ionizing the fluid is achieved.

7. The pulse power drilling tool according to any one of the preceding claims, further comprising a fluid supply system (140) for supplying a flushing fluid to a region between the drill head (120) and the mineral substrate (400).

8. The pulse power drilling tool (100) according to claim 7, wherein the flushing fluid is water or air.

9. The pulsed power drilling tool (100) according to claim 7 or 8, wherein the first laser beam (135) is configured to ionize the flushing fluid to form the first ionized fluid volume (210).

10. The pulsed power drilling tool (100) according to any one of the preceding claims, wherein the at least one ionization arrangement (130) further comprises at least a first focusing device (134), arranged between the first laser emitting device (131) and the mineral substrate (400), the first focusing device being configured to focus the first laser beam (135) to a focus point formed between the first solid electrode portion (203) and the surface of the mineral substrate (400).

11. The pulsed power drilling tool (100) according to any one of the preceding claims, further comprising at least a first beam directing device configured to control an angle of the first laser beam (135) emitted toward the mineral substrate (400) such that a direction of extension of the first ionized fluid volume (210) can be controlled.

12. The pulsed power drilling tool (100) according to any one of the preceding claims, wherein the first laser beam (135) has a wavelength within a range between 1 nm and 100000 nm, more preferably between 5 nm and 10000 nm,, and most preferably between 10 nm and 380 nm.

13. The pulsed power drilling tool (100) according to any one of the preceding claims, wherein the at least one ionization arrangement (130) further comprises a second laser emitting device (131 ’) configured to generate a second laser beam (135’) and emit it toward the mineral substrate (400), the second laser beam (135’) being configured to ionize a fluid present between the drill head (120) and the mineral substrate (400) to form a second ionized fluid volume (210’) of the at least one ionized fluid volume.

14. The pulsed power drilling tool (100) according to claim 12, wherein the first ionized fluid volume (210) is configured to guide the high voltage current pulse (150) between the first solid electrode portion (203) and the mineral substrate (400) and wherein the second ionized fluid volume (210’) is configured to guide the high voltage pulse (150) between the second solid electrode portion (204) and the mineral substrate (400).

15. The pulsed power drilling tool (100) according to any one of the preceding claims, wherein the drilling tool (100) comprises a positioning device for controlling a distance between at least the first solid electrode portion (203) and the surface of the mineral substrate (400) and / or between at least the second solid electrode portion (204) and the surface of the mineral substrate (400).

16. A method for breaking a mineral substrate (400) by passing a pulsed electrical current through the mineral substrate (400) by means of a pulsed power drilling tool (100), wherein the pulsed power drilling tool (100) comprises:- a pulsed power generator (110) for generating high voltage current pulses,- a drill head (120) comprising at least one electrode pair (200) comprising at least a first electrode (201) and a second electrode (202), the first electrode (201) comprising a first solid electrode portion (203) and the second electrode comprising a second solid electrode portion (204), the first and second solid electrode portions (203, 204) being electrically connectable to the pulsed power generator (110), and- at least one ionization arrangement (130) configured for generating at least one ionized fluid volume (210, 210’) extending at least from the first solid electrode portion (203) to a surface of the mineral substrate (400) and / or extending at least from thesecond solid electrode portion (204) to a surface of the mineral substrate (400), so as to allow a high voltage current pulse (150) to pass between the first solid electrode portion (203) and the second solid electrode portion (204) via the at least one ionized fluid volume (210, 210’) and the mineral substrate (400),- wherein the at least one ionization arrangement (130) comprises at least a first laser emitting device (131) configured to generate a first laser beam (135) and emit it in a direction toward the mineral substrate (400), the first laser beam (135) being configured to ionize a fluid present between the drill head (120) and the mineral substrate (400) to form a first ionized fluid volume (210) of the at least one ionized fluid volume, the method comprising:- positioning (S1) the drill head (120) so that the solid electrode portions (203, 204) are at least in proximity of a surface of the mineral substrate (400),- generating (S2) the at least one ionized fluid volume (210, 210’) by the at least one laser beam (135, 135’) emitted by the at least one laser emitting device (131 , 131’),- generating and passing (S3) a high voltage current pulse (150) from the first electrode (201) to the second electrode (202) via the at least one ionized fluid volume (210, 210’) and the mineral substrate (400).

17. The method according to claim 16, further comprising:- supplying a flushing fluid to a region between the at least one electrode pair (200) and the mineral substrate (400) at least prior to generating (S2) at least one ionized fluid volume (210, 210’) by the at least one laser beam (135, 135’) emitted by the at least one laser emitting device (131 , 13T).

18. Use of a pulsed power drilling tool (100) according to claims 1-15 for breaking of a mineral substrate (400), such as in any one of rock drilling, concrete processing, mineral processing, and continuous mining.

19. A drill rig (500) comprising the pulsed power drilling tool (100) according to claims 1-15.

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