Liquid-jet target positioning and stabilization system, and method for adjusting and stabilizing the position of a liquid-jet target
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SZEGEDI TUDOMANYEGYETEM
- Filing Date
- 2025-11-28
- Publication Date
- 2026-06-04
Smart Images
Figure HU2025050096_04062026_PF_FP_ABST
Abstract
Description
[0001] Liquid-jet target positioning and stabilization system, and method for adjusting and stabilizing the position of a liquid-jet target
[0002] The present invention relates to a positioning and stabilization system for a liquid-jet target.
[0003] The present invention further relates to a method for adjusting and stabilizing the position of a liquid-jet target.
[0004] Laser-driven particle acceleration is an innovative technology in which strong electromagnetic fields are generated by laser pulses in order to accelerate particles, for example electrons or ions. In this process, an important role is played by the target irradiated by the laser, which serves as a source of the particles. In the past decade, substantial research has been carried out in the field of laser ion acceleration, since this technology offers numerous potential applications, such as proton-based imaging, neutron generation and hadron therapy. Most of these applications require a high average particle flux, which can practically be achieved by irradiating the target at a high repetition rate. In high-power laser particle accelerators, thin plastic or metal foils have previously been used as solid targets. However, these solid targets are not suitable for sustained irradiation at high repetition rates, since the target is significantly damaged in the vicinity of the focal spot as a result of the laser-matter interaction, and therefore a new target has to be positioned and precisely aligned, which at high repetition frequencies is difficult or not feasible at all. In addition, debris originating from the interaction between the laser and the target may damage the surrounding optical elements and detectors. One of the major challenges of laser-driven particle acceleration is therefore to renew the target containing the particles to be accelerated in such a way that the target is in the same position from shot to shot.
[0005] In contrast to solid targets, freely flowing liquid-jet targets having a thickness in the micrometre range are more suitable for high-repetition-rate laser ion acceleration, since after the laser-matter interaction the damaged region is renewed in less than a millisecond, which enables continuous operation at repetition frequencies in the kilohertz range or even higher. In one possible method that allows the production of very thin liquid sheets ideal for laser ion acceleration, two liquid jets are generated by means of a pair of nozzles and the liquid jets are made to collide with each other at a certain angle. Under laminar flow conditions a leafshaped liquid sheet spontaneously forms. The essence of the process is that components of the momentum vectors of the colliding liquid jets that are directed against each other compensate one another, so that in a plane perpendicular to the plane defined by the liquid jets the liquid spreads radially outwards and then, under the effect of surface tension, gradually contracts to form a closed liquid sheet.
[0006] When a liquid-jet target is irradiated with a high-intensity laser required for particle acceleration (the peak power of which may exceed 1016W / cm2), the interaction has to take place in vacuum. There are two reasons for this: firstly, nonlinear optical phenomena occurring in the ambient gas during focusing of the laser beam would significantly degrade the beam quality. Secondly, the generated X- radiation and particles, in particular ions, would be completely absorbed at pressures above a few torr. The mechanical and pressure conditions prevailing in vacuum, as well as the assumed change in surface tension caused by cooling due to evaporation of the liquid, affect the physical properties of the liquid-jet target, such as the thickness of the liquid sheet and the stability of the target position.
[0007] The article by Fletcher et al. entitled “Development of an ultrathin liquid sheet target for laser ion acceleration at high repetition rates in the kilohertz range” discloses a solution in which a thin, planar liquid target is generated by colliding liquid jets emitted by two micro-nozzles arranged opposite each other. The stability of the target is characterised by means of a high-precision position-measuring system, and the stability is improved by varying the nozzle size and the pressure parameters. However, in this publication the position measurement serves exclusively for passive observation, and no automatic stabilisation is carried out on the basis of the measured data.
[0008] The publication by Poole et al. entitled “Liquid microjet targets for kHz repetition rate ultrafast lasers” likewise presents liquid jets generated by micronozzles. The geometry and stability of the target are investigated by CCD camera imaging with statistical analysis of several thousand images. The size, aspect ratio and positional stability of the target are determined from the image data; however, these data serve exclusively for characterisation and are not fed back into any automatic control.
[0009] Kim et aL, in the article entitled “Liquid sheet jet characterization with optical imaging”, analyse the properties of liquid-jet targets by means of optical imaging. In their system, a CCD camera and laser illumination are used to determine the tilt angle, thickness and position of the target. The tilt angle of the target can be modified by changing the liquid flow and the settings of the nozzles, but again only manual tuning is carried out, and no automatic, real-time stabilization is implemented.
[0010] Feister et aL, in the publication entitled “High-repetition-rate targets and optics for laser-plasma experiments at kHz repetition rate”, disclose an experimental arrangement in which a thin target that is continuously refreshed is generated from two colliding liquid jets. The position of the target is adjusted by a piezo actuator, and the target is monitored by in-situ optical diagnostics (shadowgraphy, interferometry). The publication presents the measurement and adjustment methods used in high-repetition-rate experiments, as well as the possibility of optimising the parameters during the experiment.
[0011] We have recognised that, for a given setting of the nozzle pair, the orientation of the surface of the target formed by the liquid jets is not constant in time; typically it rotates about its longitudinal (vertical) and transverse (horizontal) axes. Possible causes of this are nano-contaminants or nano-bubbles that inevitably enter the two nozzles, and stochastic variations in the fluid dynamics, some of which can be attributed to local vibrations.
[0012] We have further recognised that, in a vacuum environment, a further cause of the stochastic rotation of the liquid-jet target is the effective source of the liquid, namely its very rapid evaporation. In addition, during the laser interaction, if the laser pulse used for particle acceleration does not hit the sheet along the axis of rotation, it can exert an instantaneous torque, which likewise causes the target to rotate about its axis.
[0013] According to our recognition, since the direction of the accelerated particle beam emerging from a given point is approximately equal to the surface normal taken on the side of the surface opposite to the accelerating laser pulse, the actual position (tilt angle) of the liquid-jet target determines the direction of the ion beam. Therefore, for optimal and stable ion acceleration it is indispensable to adjust and stabilize the position of the target continuously.
[0014] We have recognised that, if the surface of the liquid-jet target is illuminated with a laser beam at an angle to the surface normal and the light reflected from the surface is captured in a detection plane, and then the position of the thus generated light spot in the detection plane is determined by means of a light-sensing detector, the rotation of the sheet about an arbitrary axis can be determined rapidly and with high accuracy, and on this basis the target can be rotated into the desired position. An advantage of the method is that the laser beam does not affect the optical elements used for particle acceleration, so the procedure can be used continuously during laser-driven particle acceleration. The speed of the correction is in practice limited only by the inertia of the elements that generate the liquid-jet target.
[0015] We have recognised that the direction of the surface normal of the liquid-jet target can be modified by changing the operating parameters of the nozzle pair that generates the target. According to our recognition, rotation of the target about a horizontal axis can be achieved by changing the relative pressure of the liquid jets emitted by the nozzles forming the nozzle pair, and / or by changing the common position of the nozzles. Rotation of the target about a vertical axis can be achieved by changing the relative position of the nozzles and / or by changing the common position of the nozzles.
[0016] We have further recognised that the actuator used to change the position of the nozzles is preferably of a type that is insensitive to electromagnetic interference and currents generated by particle acceleration, otherwise the actuator could be driven to move incorrectly by the electromagnetic interference and currents associated with particle acceleration. One preferred embodiment of an actuator that satisfies the above requirement is a closed-loop positioner. The object of the invention is to provide a positioning and stabilization system for a liquid-jet target and a method for adjusting and stabilizing the position of a liquid-jet target that are free from the disadvantages of solutions according to the prior art. A particular object of the invention is to provide a positioning and stabilization system and method for a liquid-jet target by means of which a liquid-jet target that continuously and stochastically rotates about its vertical and horizontal axes can be positioned successively, rapidly (with a repetition frequency comparable to that of the accelerator laser beam) and with high accuracy in the desired position.
[0017] The object is achieved, according to the invention, by a system for adjusting and stabilizing the position of a liquid-jet target, namely a liquid-jet target positioning and stabilization system which comprises a nozzle pair for generating a substantially planar moving liquid-jet target, an actuator suitable for changing operating parameters of the nozzle pair, a laser source suitable for oblique illumination of a surface of the liquid-jet target, a detection plane, imaging optics for imaging light of the laser source reflected from the surface of the liquid-jet target as a light spot onto the detection plane, a light-sensing detector for determining the position of the light spot in the detection plane, and a control unit in data communication with the lightsensing detector and suitable for controlling the actuator on the basis of a signal of the light-sensing detector.
[0018] The essence of the invention is that the laser beam illuminates the surface of the liquid-jet target obliquely, that is to say at an angle to the surface normal, and, after being reflected from the surface and passing through the imaging optics, forms in the detection plane a light spot produced by the laser beam. From the position of the light spot in the detection plane, the position (tilt of the surface plane) of the liquid-jet target can be determined unambiguously, and on this basis the target can be rotated back into the desired position.
[0019] The object is further achieved, according to the invention, by a method for adjusting and stabilizing the position of a liquid-jet target, the method comprising: generating, by means of a nozzle pair, a moving liquid-jet target having a reference position; illuminating a substantially planar surface of the liquid-jet target in the reference position with a laser beam at an angle to the surface normal; imaging light of the laser beam reflected from the surface of the liquid-jet target onto a detection plane so as to form a light spot on the detection plane; and determining, as the reference position, the position of the light spot in the detection plane by means of a light-sensing detector. Thereafter, the method comprises illuminating a surface of the liquid-jet target that has moved out of the reference position with the laser beam, imaging light of the laser beam reflected from the surface of the liquid-jet target onto the detection plane and determining, by means of the light-sensing detector, the position of the thus formed light spot in the detection plane, and returning the liquidjet target to the reference position by changing one or more operating parameters of the nozzle pair so as to move the light spot on the detection plane to the position corresponding to the reference position.
[0020] The essence of the invention is that there is an unambiguous relationship between the position of the light spot in the detection plane and the position (tilt about an arbitrary axis) of the liquid-jet target. In this way, by observing the position of the light spot in the detection plane, the position of the liquid-jet target is determined, and by changing one or more operating parameters of the nozzle pair the target is then moved such that the light spot assumes a desired position in the detection plane and, as a result, the target assumes the desired position.
[0021] Some preferred embodiments of the invention are defined in the dependent claims.
[0022] Further details of the invention are explained by way of exemplary embodiments with reference to the drawings. In the drawings,
[0023] Figure 1 a is a view showing main elements of one possible embodiment of a liquid-jet target positioning and stabilization system according to the invention;
[0024] Figure 1 b is a view showing main elements of another possible embodiment of a liquid-jet target positioning and stabilization system according to the invention.
[0025] Figure 1 a shows a view illustrating main elements of one exemplary embodiment of a liquid-jet target positioning and stabilization system 100 according to the invention. The system 100 comprises a nozzle pair 20 for generating a substantially planar moving liquid-jet target 10 and an actuator 30 configured to modify operating parameters of the nozzle pair 20. The nozzle pair 20 preferably has first and second nozzles 20a, 20b of identical design arranged at an angle to one another, which may for example be nozzles 20a, 20b made of quartz known per se. In one exemplary embodiment, at the inlets of the nozzles 20a, 20b the inner wall is parallel and then tapers towards the tips of the nozzles 20a, 20b, while the inner diameter decreases from approximately 0.5 mm to some tens of micrometres (not shown in the drawings). Through the nozzles 20a, 20b, a liquid forming the target 10 (for example water, ethylene glycol, etc.) is passed by a high-pressure liquid pump 40. The resulting parabolic flow profile has slower regions near the wall which detach in the conical inner channels preceding the tips of the nozzles 20a, 20b, and as a result first and second liquid jets 21 a, 21 b having laminar flow and a flat-topped flow profile are formed, as is known to the skilled person. The diameters of the liquid jets 21 a, 21 b essentially correspond to the diameters of the openings of the nozzles 20a, 20b. The liquid-jet target 10 is formed when the laminar-flow liquid jets 21 a, 21 b generated separately by the nozzles 20a, 20b collide with each other in a plane perpendicular to the plane of the nozzles 20a, 20b. It is noted that, in the context of the present description, the term liquid-jet target 10 is interpreted broadly and in a given case may denote not only a liquid sheet but also an ice ribbon, as is known to the skilled person. The target 10 according to the invention has a reference position in which the target 10, from among its possible positions, assumes a distinguished position. For example, in the case of a target 10 used for laser particle acceleration, the reference position is understood to mean the position of the target 10 that is most ideal for laser particle acceleration.
[0026] The system 100 according to the invention comprises an actuator 30 configured to change one or more operating parameters of the nozzle pair 20. In the context of the present invention, the operating parameters of the nozzle pair 20 are interpreted broadly and include all technical parameters relating to the setting of the nozzles 20a, 20b that have an influence on the position of the target 10, including the tilt of the surface of the target 10. The operating parameter of the nozzle pair 20 may preferably be, for example, the pressure of the first and second liquid jets 21 a, 21 b generated by the first and second nozzles 20a, 20b, the relative position of the nozzles 20a, 20b, including the distance and tilt angle of the nozzles 20a, 20b with respect to each other, and the common position of the nozzles 20a, 20b of the nozzle pair 20 relative to other elements of the system 100. It is noted that the actuator 30 is, as a matter of course, configured in accordance with one or more operating parameters of the nozzle pair 20 to be changed. In one exemplary embodiment, the actuator 30 comprises a positioning unit 31 configured to modify a common and / or relative position of the nozzles 20a, 20b of the nozzle pair 20. The positioning unit 31 may for example be a piezoelectric positioner known per se, by means of which the position of one of the nozzles 20a, 20b or of the nozzle pair 20 itself, as a rigid body, can be changed. Since the position of the target 10 is highly sensitive to the positions of the nozzles 20a, 20b, the displacement effected by the positioning unit 31 is preferably of the order of micrometres. In another exemplary embodiment, the actuator 30 comprises an electrically controllable valve 32 configured to change the pressure of at least one of the liquid jets 21 a, 21 b emitted by the nozzles 20a, 20b of the nozzle pair 20 and thus to change the relative flow velocity of the liquid jets 21 a, 21 b. It is also conceivable in an exemplary embodiment that the actuator 30 does not comprise a valve 32, but instead the liquid pump 40 is implemented as the actuator 30. In this case, the relative flow velocity of the liquid jets 21 a, 21 b is adjusted by means of the electrically controllable liquid pump 40 in such a way that either one or both of the pressures of the liquid jets 21 a, 21 b can be controlled.
[0027] The system 100 according to the invention comprises a laser source 50 for obliquely illuminating the surface of the liquid-jet target 10, a detection plane 60, and imaging optics 70 for imaging light of the laser source 50 reflected from the surface of the liquid-jet target 10 as a light spot 52 onto the detection plane 60. The laser source 50 may for example be a solid-state laser or a gas laser and may operate in continuous-wave or pulsed mode. In one exemplary embodiment, the laser source 50 is provided as a continuous-wave solid-state laser having a power of a few milliwatts. In another, preferred embodiment, the liquid-jet target 10 is a target 10 used for laser particle acceleration, and the laser source 50 is configured to generate an accelerating laser pulse used for particle acceleration. In this embodiment, the positioning unit 31 is conveniently provided as a closed-loop positioner which is insensitive to electromagnetic interference and currents generated by particle acceleration. By means of the laser source 50, an incident beam 51 b reaching the surface of the target 10 is generated, which leaves the surface of the target 10 in accordance with the law of reflection and propagates further as a reflected beam 51 a. The position of the laser source 50 within the system 100 is fixed, in other words, the target 10 is always illuminated from the same location and in the same direction, and the laser source 50 is arranged in such a way that, in the reference position, it illuminates the substantially planar surface of the target 10 obliquely, i.e. at an angle to the direction normal to the surface of the target 10.
[0028] In the embodiment shown in Figure 1 a, the detection plane 60 is formed as a screen fixed in position relative to the laser source 50. Between the target 10 and the detection plane 60, imaging optics 70 are arranged in the beam path of the reflected beam 51 a. The imaging optics 70 comprise optical elements known per se, such as one or more lenses, mirrors, further optical filters and deflecting elements, etc., and are arranged in such a way that they image the light of the laser source 50 reflected from the surface of the target 10, i.e. the reflected beam 51 a, onto the detection plane 60 in the form of a light spot 52. The diameter of the light spot 52 in the detection plane 60 is preferably adjustable by means of the imaging optics 70.
[0029] The system 100 according to the invention comprises a light-sensing detector 80 for recording the position of the light spot 52 in the detection plane 60, and a control unit 90 which is in data communication with the light-sensing detector 80 and is suitable for controlling the actuator 30 on the basis of a signal of the lightsensing detector 80. The light-sensing detector 80 may for example be a digital camera, a dual detector or a quadrant detector known per se. The light-sensing detector 80 records the position of the light spot 52 in the detection plane 60 by taking one or more digital images of the detection plane 60 and the light spot 52 thereon, which are transmitted to the control unit 90. It is noted that, in certain embodiments, the detection plane 60 is not provided as a separate screen but is formed as part of the light-sensing detector 80 itself (see Figure 1 b). In this embodiment, the imaging optics 70 image the reflected beam 51 a directly into the light-sensing detector 80, for example onto its CCD chip.
[0030] In the context of the present invention, the control unit 90 is understood to mean a collection of hardware and software components which are suitable for receiving, storing, processing and transmitting electronic data and for executing computer control programmes. The control unit 90 may be implemented for example as a personal computer, a laptop or another dedicated device such as a system-on- chip (SoC), a microcontroller, etc., as will be apparent to the skilled person. The control unit 90 is configured to control the light-sensing detector 80 and to process the digital images taken by the light-sensing detector 80. In the context of the present invention, processing of the images is understood to mean determining the position of the light spot 52, preferably its planar x and y coordinates in the detection plane 60. Control of the light-sensing detector 80 includes operating the lightsensing detector 80, such as setting the start times and durations of the exposures for taking the images. The control unit 90 is furthermore configured to control the actuator 30 on the basis of the signals received from and processed for the light- sensing detector 80.
[0031] The present invention further relates to a method for adjusting and stabilizing the position of a liquid-jet target 10. The method according to the invention is preferably implemented by means of the system 100. The method comprises: generating, by means of the nozzle pair 20, a moving liquid-jet target 10 having a reference position, and illuminating a substantially planar surface of the liquid-jet target 10 in the reference position, at an angle to the surface normal, with a laser beam generated by the laser source 50, that is to say with the incident beam 51 b, from an irradiation direction. In the context of the present description, the term irradiation direction is understood to mean the direction along the straight line which connects the laser source 50, fixed in position in the system 100, to the target 10, that is, the propagation direction of the incident beam 51 b, which remains unchanged during the method. In one exemplary embodiment, a continuous-wave laser source 50, for example a diode laser, is used and the surface of the liquid-jet target 10 is continuously illuminated with the laser beam. In another exemplary embodiment, a pulsed laser source 50 is used and the surface of the liquid-jet target 10 is intermittently illuminated with the laser beam. In these embodiments, the illumination frequency is preferably at least 10 Hz. In a particularly preferred embodiment, the liquid-jet target 10 is a target 10 used for laser particle acceleration and the laser source 50 is configured for laser-driven particle acceleration. In this embodiment, the laser beam, i.e. the incident beam 51 b, is generated by the same laser source 50 as the accelerating laser beam used for particle acceleration. This has the advantage that no separate laser source 50 is required for generating the light spot 52.
[0032] It is noted that, in the context of the present description, the movement of the target 10 primarily means stochastic rotation of the surface plane of the target 10 about an arbitrary axis and periodic motion caused by external effects such as external vibrations or, for example, accelerator laser pulses. The incident beam 51 b impinging on the surface of the target 10 propagates further as a reflected beam 51 a in accordance with the laws of reflection. The propagation direction of the reflected beam 51 a is determined by the instantaneous position (orientation of the surface plane) of the target 10. In the next step of the method, the light of the laser beam reflected from the surface of the liquid-jet target 10, that is, the reflected beam 51 a, is imaged onto the detection plane 60, thereby forming the light spot 52 on the detection plane 60. Thereafter, the position of the light spot 52 in the detection plane 60 corresponding to the reference position is determined. For this purpose, in a particularly preferred embodiment, one or more digital images are taken of the detection plane 60, together with the light spot 52 thereon, by means of the lightsensing detector 80, and these images are transmitted to the control unit 90. It is noted that, if the liquid-jet target 10 is a target 10 used for laser particle acceleration, the UV and X-ray radiation emerging from the plasma generated on the target 10 during particle acceleration may not only dazzle the light-sensing detector 80 but may also damage it. Therefore, in this embodiment, it is preferable that only light falling within the wavelength range of the reflected beam 51 a is allowed to enter the light-sensing detector 80 from the direction of the liquid-jet target 10. This can be achieved, for example, by using a band-pass filter that transmits only the wavelength of the reflected beam 51 a (not shown in the drawings). The band-pass filter can conveniently be integrated, for example, into the imaging optics 70. Another possible solution is to choose the exposure time of the light-sensing detector 80 such that it ends before the arrival of the accelerating laser pulse. The light-sensing detector 80 is preferably selected from the group consisting of a camera, a dual detector and a quadrant detector. By means of the control unit 90, the digital images originating from the light-sensing detector 80 are processed, as a result of which the position of the light spot 52 corresponding to the reference position, for example its planar x and y coordinates in the detection plane 60, is determined and stored in the control unit 90. For more accurate measurement, in a preferred embodiment the position of the light spot 52 in the detection plane 60 is determined as the centroid position of the light spot 52, but, of course, in a given case the position of another characteristic part of the light spot 52 (for example its lowermost point) can also be determined.
[0033] In a subsequent step a) of the method, step a) comprises illuminating the surface of the liquid-jet target 10 that has moved out of the reference position with the laser beam from the irradiation direction, imaging the light of the laser beam reflected from the surface of the liquid-jet target 10 onto the detection plane 60, and determining the position of the resulting light spot 52 in the detection plane 60. Since, during its motion, the surface plane of the target 10 is rotated relative to the reference position, the incident beam 51 b arriving from the same direction is correspondingly reflected in a direction different from that in the reference position, and therefore the light spot 52 is imaged onto a different region of the detection plane 60. Thus, in accordance with the displacement of the target 10, the light spot 52 also moves, for example its x and / or y coordinate changes.
[0034] Subsequently, in step b) of the method, step b) comprises returning the liquid-jet target 10 to the reference position by changing one or more operating parameters of the nozzle pair 20 so as to move the light spot 52 in the detection plane 60 to the position associated with the reference position. In one preferred embodiment, rotation of the target 10 about a horizontal axis is achieved by changing the relative pressure of the liquid jets 21 a, 21 b emitted by the nozzles 20a, 20b forming the nozzle pair 20 and / or by changing the common position of the nozzles 20a, 20b. Rotation of the target 10 about a vertical axis is carried out by changing the relative position of the nozzles 20a, 20b and / or by changing the common position of the nozzles 20a, 20b. In a particularly preferred embodiment, the method comprises repeatedly performing steps a) and b) in succession at a repetition frequency of at least 10 Hz, more preferably at least 100 Hz. In a particularly preferred embodiment, the liquid-jet target 10 is a target 10 used for laser particle acceleration, and step b) is carried out immediately before an accelerating laser pulse used for particle acceleration impinges on the liquid-jet target 10, preferably less than 25 ps before the accelerating laser pulse impinges on the liquid-jet target 10. In this way, it is possible for the system 100 to return the target 10 to the appropriate position immediately before the interaction between the accelerating laser pulse and the material, so that there is essentially no time for the target 10 to move. In one exemplary embodiment, the operating parameter of the nozzle pair 20 comprises changing, by means of the actuator 30, the pressure, preferably the relative pressure, of the liquid jets 21 a, 21 b emitted by the nozzles 20a, 20b. As explained above, the pressure of the liquid jets 21 a, 21 b can be controlled in several ways, for example by means of the valve 32 or the liquid pump 40, and an embodiment is also conceivable in which only the pressure of one of the liquid jets 21 a, 21 b is changed. In another exemplary embodiment, the operating parameter of the nozzle pair 20 comprises changing the relative position of the nozzles 20a, 20b. This may be done by displacing both nozzles 20a, 20b by means of the actuator 30 implemented as the positioning unit 31 , or by displacing only one of the nozzles 20a, 20b. In both cases, the relative position of the nozzles 20a, 20b is changed. In a third exemplary embodiment, the operating parameter of the nozzle pair 20 comprises changing the common position of the nozzles 20a, 20b, that is, moving the nozzles 20a, 20b together as a rigid body, for example tilting them by means of the actuator 30. In this case, the relative position of the nozzles 20a, 20b does not change. It is noted that, in a given case, several of the above-mentioned operating parameters can be changed simultaneously.
[0035] It is clear that other alternative solutions to those embodiments presented herein may also be conceived by the person skilled in the art, which nevertheless fall within the scope defined by the claims.
Claims
Claims1. A liquid-jet target (10) positioning and stabilization system (100), characterised in that the system (100) comprises a nozzle pair (20) for generating a substantially planar moving liquid-jet target (10), an actuator (30) configured to modify one or more operating parameters of the nozzle pair (20), a laser source (50) configured to illuminate a surface of the liquid-jet target (10) at an oblique angle, a detection plane (60), imaging optics (70) configured to image light of the laser source (50) reflected from the surface of the liquid-jet target (10) as a light spot (52) onto the detection plane (60), a light-sensing detector (80) configured to record a position of the light spot (52) in the detection plane (60), and a control unit (90) in data communication with the light-sensing detector (80) and configured to control the actuator (30) on the basis of a signal of the light-sensing detector (80).
2. The positioning and stabilization system (100) according to claim 1 , characterised in that the detection plane (60) is formed as part of the light-sensing detector (80).
3. The positioning and stabilization system (100) according to any one of claims 1 or 2, characterised in that the actuator (30) comprises a positioning unit (31 ) configured to modify a common and / or relative position of nozzles (20a, 20b) of the nozzle pair (20).
4. The positioning and stabilization system (100) according to claim 3, characterised in that the positioning unit (31 ) is provided as a closed-loop positioner.
5. The positioning and stabilization system (100) according to any one of claims 1-4, characterised in that the actuator (30) comprises a valve (32) that is electrically controllable and configured to modify a pressure of at least one of liquid jets (21 a, 21 b) emitted by nozzles (20a, 20b) of the nozzle pair (20).
6. The positioning and stabilization system (100) according to any one of claims 1-5, characterised in that the liquid-jet target (10) is a target (10) used forlaser particle acceleration, and the laser source (50) is configured to generate an accelerating laser beam used for particle acceleration.
7. The positioning and stabilization system (100) according to any one of claims 1-6, characterised in that the liquid-jet target (10) is an ice ribbon.
8. The positioning and stabilization system (100) according to any one of claims 1-7, characterised in that the light-sensing detector (80) is selected from the group consisting of a camera, a dual detector and a quadrant detector.
9. A method for adjusting and stabilizing the position of a liquid-jet target (10), characterised in that the method comprises: generating, by means of a nozzle pair (20), a moving liquid-jet target (10) having a reference position; illuminating a substantially planar surface of the liquid-jet target (10) in the reference position with a laser beam from an irradiation direction at an angle to a surface normal; imaging light of the laser beam reflected from the surface of the liquid-jet target (10) onto a detection plane (60) so as to form a light spot (52) on the detection plane (60); and determining, as the reference position, a position of the light spot (52) in the detection plane (60); and in that, in the course of the method: a) illuminating a surface of the liquid-jet target (10) that has moved out of the reference position with the laser beam from the irradiation direction, imaging light of the laser beam reflected from the surface of the liquid-jet target (10) onto the detection plane (60), and determining a position of the thus formed light spot (52) in the detection plane (60), and b) returning the liquid-jet target (10) to the reference position by modifying one or more operating parameters of the nozzle pair (20) so as to move the light spot (52), in the detection plane (60), to the position associated with the reference position.
10. The method according to claim 9, characterised in that the method comprises repeatedly performing steps a) and b) at a repetition frequency of at least10 Hz.1 1 . The method according to claim 9 or 10, characterised in that the method comprises using the liquid-jet target (10) as a target (10) for laser particle acceleration and carrying out step b) immediately before an accelerating laser pulse used for particle acceleration impinges on the liquid-jet target (10), preferably less than 25 ps before the accelerating laser pulse impinges on the liquid-jet target (10).
12. The method according to any one of claims 9-1 1 , characterised in that the method comprises using the liquid-jet target (10) as a target (10) for laser particle acceleration and generating both the laser beam and an accelerating laser pulse used for particle acceleration by the same laser source (50).
13. The method according to any one of claims 9-1 1 , characterised in that the method comprises continuously illuminating a surface of the liquid-jet target (10) with the laser beam.
14. The method according to any one of claims 9-12, characterised in that the method comprises intermittently illuminating a surface of the liquid-jet target (10) with the laser beam and setting an illumination frequency of at least 10 Hz.
15. The method according to any one of claims 9-14, characterised in that the method comprises rotating the liquid-jet target (10) about a horizontal axis by modifying, as an operating parameter of the nozzle pair (20), a relative pressure of liquid jets (21 a, 21 b) emitted by nozzles (20a, 20b).
16. The method according to any one of claims 9-15, characterised in that the method comprises rotating the liquid-jet target (10) about a vertical axis by modifying, as an operating parameter of the nozzle pair (20), a relative position of nozzles (20a, 20b).
17. The method according to any one of claims 9-16, characterised in that the method comprises rotating the liquid-jet target (10) about a horizontal and / orvertical axis by modifying, as an operating parameter of the nozzle pair (20), a common position of nozzles (20a, 20b).
18. The method according to any one of claims 9-17, characterised in that the method comprises determining, as the position of the light spot (52) in the detection plane (60), a centroid position of the light spot (52).