WO2012138792A1 - Dispositif de surveillance de la position d'un faisceau de type réseau annulaire à résolution sous-micronique et procédé paramétrique pour optimiser les photodétecteurs - Google Patents

Dispositif de surveillance de la position d'un faisceau de type réseau annulaire à résolution sous-micronique et procédé paramétrique pour optimiser les photodétecteurs Download PDF

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Publication number
WO2012138792A1
WO2012138792A1 PCT/US2012/032215 US2012032215W WO2012138792A1 WO 2012138792 A1 WO2012138792 A1 WO 2012138792A1 US 2012032215 W US2012032215 W US 2012032215W WO 2012138792 A1 WO2012138792 A1 WO 2012138792A1
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Prior art keywords
array
photodetector
bpm
annular
working distance
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Phil Sung-Yong YOON
David Peter Siddons
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Brookhaven Science Associates LLC
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Brookhaven Science Associates LLC
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
    • G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
    • G21K1/043—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers changing time structure of beams by mechanical means, e.g. choppers, spinning filter wheels

Definitions

  • the present invention relates to the design and manufacture of a device for aligning beamline components and/or for real-time monitoring of a series of the beamline optics elements and or the determination or monitoring of the x-ray beam position within the beamline. More particularly, the present invention relates to the design and manufacture of an annular-array type beam-position monitor that meets the stringent requirements for beam stability by significantly reducing the displacement- and angular-errors in the beam trajectory measurement.
  • Synchrotron radiation is an example of such a structural tool. Synchrotron radiation is produced by accelerating charged particles (e.g. electron or proton) in particle accelerators and the synchrotron facilities are capable of generating radiation from visible, ultraviolet, and into the X-ray frequency portions of the spectrum. Compared to conventional light sources, synchrotron radiation is characterized by the properties of extremely high intensity and a high level of collimation at the sample target (i.e. high brilliance) which enables many experimental applications of light-matter interactions that would otherwise not be feasible.
  • charged particles e.g. electron or proton
  • BPMs are: (1) fluorescent screens (Winick H., World
  • BPM beam position monitor
  • annular array-type beam position monitor and a method of optimization of said beam position monitor that avoids the shortcomings of the prior art including inadequate spatial resolution and stability, the presence of small number of displacement- and angular- errors in a radiation source that can degrade the end-station experiments, and a nondestructive intensity perturbation downstream of its position suitable for continuous use
  • a method for positioning and optimizing a detector array and a fluorescent target in the annular-array type beam position monitor system by (1) detennining an optimal working distance between the detector array and a secondary radiation target, (2) determining a radial displacement of the detector array from the center of the beam-through aperture on the annular photodetector array, (3) determining the optimal curvature of the array segments, (4) determining the optimal surface area of each photodetector segment, and (5) determining the widths and the radial displacement/position of the guard rings.
  • This method can similarly be applied to BPM systems employing beams of electromagnetic radiation of frequencies other than X-rays, such as visible, and/or ultraviolet frequencies.
  • This method can likewise be applied to BPM systems employing a target that emits secondary radiation in response to the incident radiation beam, i.e. a target that absorbs radiation of the incident beam frequency and re- emits incoherent, inelastically scattered, unpolarized, isotropic secondary radiation, such as fluorescence, luminescence, electrons or radiation emitted due to other secondary radiation mechanisms.
  • a target that emits secondary radiation in response to the incident radiation beam i.e. a target that absorbs radiation of the incident beam frequency and re- emits incoherent, inelastically scattered, unpolarized, isotropic secondary radiation, such as fluorescence, luminescence, electrons or radiation emitted due to other secondary radiation mechanisms.
  • the detector array may be composed of metallic elements.
  • the model depends on the optimization of the total solid angle given by a parametric equation (1 1) exploring nine system dependent parameters
  • These system dependent parameters include (1) radial positions and azimuthal angles ( p + , p ⁇ , ⁇ + , ⁇ ⁇ ) of each photodetector segment in the annular/polar array about the beam centroid, (2) a bi-Gaussian distribution ( ⁇ ⁇ and a y are rms transverse beam sizes) of the beam centered around the beam centroid, although other multivariate non-Gaussian probability models of beam approximation are also envisioned and are available in the art, and (3) the coordinates ( p * , ⁇ * ) of a flux of secondary radiation, e.g. fluorescence, at an axial working distance (z*) from the plane of the annular array of the photodetectors.
  • a flux of secondary radiation e.g. fluorescence
  • a new solid angle i.e. , a solid angle projected onto the flat sensor plane
  • the first-order derivatives ( dQ. ring l dz * ) with respect to axial distance (z) may be calculated to find a local maximum.
  • an optimum working distance of the target from the annular/polar array may be determined by finding a zero-crossing.
  • the point-source model may be used for the working-distance in the range of a few millimeters.
  • the coordinates of a radiation source can be simplified with five parameters using the parametric equation ( 12):
  • a method for determining the off-axis displacement of the inner radius of the detector, and the separation between the outer edge of the beam incident upon the target and the detector inner radius based on the calculated maximum spatial sensitivity.
  • the method embodies a step of calculating difference-over-sum ( ⁇ / ⁇ ) as sweeping across the photodetector array along any transverse direction, as shown in Eqn. (15) where the solid angle ⁇ is a function of a radial position and azimuthal angle ( p + , p ⁇ , ⁇ + , ⁇ ⁇ ) of each photodetector segment (j) in the annular/polar array about the beam centroid.
  • the method further embodies the steps of calculating an absolute value of the slope in a difference-over-sum ( ⁇ / ⁇ ) which provides for a maximum spatial sensitivity in the transverse plane along the longitudinal axis of the beam.
  • ⁇ / ⁇ difference-over-sum
  • the highest value of the slope in a difference-over-sum ( ⁇ / ⁇ ) calculation provides for a maximum spatial sensitivity in the transverse plane along the longitudinal axis of the beam and the optimal axial displacement (radial position, p ) of the sensor segment in an annular sensor array along the transverse plane may be determined.
  • the radius of a beam-through aperture in one embodiment is made large enough to accommodate the entire beam profile, e.g. a Gaussian distribution. Hence, the outer edge of an incident beam may not be intercepted by the aperture rim.
  • a method for optimizing the surface area of an annular detector array.
  • the method embodies the step of calculating a surface area of the sensor segment in the annular photodetector array and the radial dimensions of the array by solving equation (13).
  • the method further embodies the step of optimizing the segment surface area and the radial dimensions of the annular photodetector array based on the capacitance matching. Optimizing the capacitance of each segment is achieved by adjusting radial positions (p. and p + ) according to equation (13). The azimuthal angle (Q s ) is constrained by the total number of sensor array segments.
  • a method for optimizing the curvature of the surface of an annular detector array in a BPM in order to maximize photodetector light collection efficiency.
  • the method includes the steps of calculating the total solid angle and the optimal working distance.
  • the calculated total solid angle describes the curved surface of a portion of a sphere having a radius equal to the optimal working distance and centered at the beam target intercept.
  • the sphere of optimum radius defines the optimal curvature of the photodetector array. Therefore, no projection factor, or a projection factor essentially equal to unity, is used to modify the curved surface described by the sphere of optimum radius because the photodetectors are designed to be aligned or coincide with the curved surface.
  • a method for finding a beam centroid based on fitting data points representing photon counts registered at each of the photodetector segments is provided.
  • the segment-by-segment display of photon counts is fitted with a sinusoidal function.
  • the amplitude of the sinusoidal function is a radial offset and its phase is a polar angle, which then can be converted to Cartesian coordinates of the beam centroid.
  • the beam position monitor comprises a plurality of sensor segments that are sensitive to electromagnetic radiation and which are positioned in an annular array.
  • This embodiment may also include a radiation target separated from the array of sensors by a working distance.
  • the radiation beam centroid e.g. the centroid of a synchrotron X-ray beam
  • the beam is intercepted by the target, preferably having a transmission rate of more than 90%.
  • the remaining radiation is absorbed and re-emitted by the target.
  • absorption of an incident photon causes an electron in the target material to be elevated to a higher shell and then fall back down, a photon of energy equal to the difference of the two shells is emitted.
  • the backscattered photons can illuminate the annular array of photodetectors isotropically. Subsequently, an electronic readout circuit counts photons from each of a plurality of segments, which record the varying intensities due to motions of the beam on the target surface.
  • FIG. 1 illustrates a fluorescent screen based beam position monitor disclosed in Alkire, R. W. et al, 1997.
  • FIG. 2A illustrates an exemplary schematic of a beamline layout including a photon shutter, Beryllium (Be) windows, slits, double crystal monochromator (DCM), and a monochromatic fluorescent X-ray beam position monitor
  • FIG. 2B illustrates a conceptual schematic diagram showing a ring-array photodetectors and a fluorescent thin film as in FIG. 2A and the backward-scattering mode of operations of the ring array in relationship to the working distance.
  • FIG. 2C illustrates an AutoCAD drawing of a ring array of 32-segmented photodetectors, e.g., Si PI -j unction photodiodes, with the upper and lower radial positions of 4.1088 mm and 2.5625 mm, respectively.
  • 32-segmented photodetectors e.g., Si PI -j unction photodiodes
  • FIG. 2D illustrates a single photodetector segment of the ring array shown in
  • FIG. 2A is a diagrammatic representation of FIG. 2A.
  • FIG. 3 illustrates a diagram of a solid angle that a differential surface area
  • FIG. 4 illustrates a plot of a projection factor versus a working distance for the ring array with 32 photodetector segments and the upper and lower radial positions of 4.1088 mm and 2.5628 mm, respectively.
  • FIG. 5 illustrates an exemplary plot of a five-point Gaussian beam profile.
  • FIG. 6A illustrates a profile of total solid angles versus a working distance for an exemplary annular-array BPM.
  • the upper trace indicates the projected total solid angle ( ⁇ ⁇ , ⁇ ) and the lower trace indicates the non-projected total solid angle (O tot ).
  • FIG. 6B illustrates a plot of the fist order derivatives with respect to axial distance (z) of the profiles shown in FIG. 6A to determine the optimum working distances from the gradient of the total solid angle.
  • FIG. 7A illustrates a solid angle variations as a function of working distance for different beam sizes on linear-linear scale.
  • the traces correspond to transverse beam sizes of 2 mm, 1 mm, 0.5 mm, 100 ⁇ , 10 ⁇ , 1 ⁇ , and 0.5 ⁇ , respectively.
  • FIG. 7B illustrates a solid angle variations as a function of working distance for different beam sizes of FIG. 7A on linear-log scale.
  • FIG. 8 illustrates a plot of a projected solid angle seen by a point-source beam and a Gaussian beam for the ring array of FIG. 2C.
  • FIG. 9 is a block diagram illustrating the optimization algorithm.
  • FIG. 10 illustrates a plot of peak projected total solid angles versus lower radial position of sensor segment.
  • the peak solid angle of the photodetector sensor of FIG. 2C is denoted as Prototype I. The closer the radial position of a sensor segment is brought to a beam axis, the higher the peak solid angle is.
  • FIG. 11 illustrates a schematic of the beam position monitor with a virtual sphere where the optimal working distance is the radius of the virtual sphere.
  • FIG. 12 illustrates a schematic of a cross-sectional view of the Si-PIN junction photodiode and the target film.
  • FIG. 13A illustrates a design schematics of a photodetector sensor with 32- segmented Si PIN-junction photodiodes with surface area of each segment set at about 1.0 mm 2 and the upper and lower radial positions of 4.109 mm and 2.563 mm respectively.
  • FIG. 13B illustrates a design schematics of a photodetector sensor with 64- segmented Si PIN-junction photodiodes with surface area of each segment set at about 0.44 mm 2 and the upper and lower radial positions of 4.109 mm and 2.563 mm respectively.
  • FIG. 14A illustrates an exemplary annular array of multi-segmented photodetectors implemented on the electronic readout circuit with a single ASIC chip wire- bonded to the photodetector array.
  • FIG. 14B illustrates an exemplary annular array of multi-segmented photodetectors implemented on the electronic readout circuit with a double-ASIC chip wire- bonded to the photodetector array.
  • FIG. 15 illustrates an I-V characteristic curve.
  • FIG. 16 illustrates a C-V characteristic curve
  • FIG. 17 illustrates plots of simulated ⁇ ,, ⁇ -absorption edge profiles for Co, Cr,
  • FIG. 18 illustrates a plot of the fist order derivatives with respect to axial distance (z) of the total solid angles for a system shown in FIG. 13B.
  • FIG. 19 illustrates a plot of difference-over-sum against transverse position for the photodetector sensor in comparison to that of quadrant X-ray BPM design.
  • FIG. 20 illustrates the method of finding a beam centroid by fitting the intensities using a sinusoidal fit function (exemplary sinusoidal plot of the intensity representing photon counts is shown).
  • FIG. 21 illustrates a sinusoidal plot of the intensity representing photon counts of 2,000 per second (A), 20,000 per second (B), or 200,000 per second (C) registered at each of the photodetector segments as a function of segment location on the annular array.
  • the beam position monitor comprises a plurality of electromagnetic radiation sensitive detector segments positioned in an annular array and a radiation target, separated from each other by a working distance.
  • the detector segments may be sensitive to various forms of electromagnetic radiation, specifically including radiation generated by a synchrotron source such as visible, ultraviolet, and X-ray radiation in preferred embodiments.
  • the target of the beam position monitor may absorb frequencies of the incident radiation beam and re-emit secondary radiation, e.g. fluorescence, luminescence, or electrons, in response to intercepting the beam of radiation.
  • the BPM may serve as a diagnostic device for aligning beamline components and for real-time monitoring of a series of the instantaneous beam positions.
  • the secondary radiation is electron radiation
  • the detector array may be composed of metallic elements.
  • FIG. 2A An exemplary beamline layout, including a BPM and optical components is provided in FIG. 2A.
  • the beam can be intercepted by a target, having a transmission rate sufficient to allow the majority of radiation to pass through.
  • the sufficient transmission rate is greater than 80%, with the transmission rate of greater than 90% being more preferred.
  • the remaining radiation is absorbed and re-emitted by the target. When absorption of an incident photon causes an electron in the target film to be elevated to a higher atomic shell, this creates vacancies in the outer electron shells of the target material atoms.
  • a novel method(s) is (are) provided for designing and optimizing a beam position monitor with an annular array configuration, e.g., a fluorescent-type X-ray beam-position monitor (XBPM), based on full parameterization of a peak solid angle projection at the detector.
  • a novel beam-position monitor is provided that utilizes an annular array of PIN-junction photodiodes.
  • annular, polygonal, rhombic oval or similar geometric shape configurations of photodetectors may be applied depending on the requirements of the overall system, the beamline layout, and/or the requirement of the end user.
  • a method for finding a beam centroid based on fitting data points representing photon counts registered at each photodetector segment with a sinusoidal function is provided.
  • an optimum working distance (z* 0 pt) for transverse beam sizes ( ⁇ ⁇ ) of interest can be determined and, thereby set the limits on transverse beam sizes for the specific dimensions ( ⁇ detector) of the sensor in use.
  • FIG. 3 depicts a solid angle ( ⁇ ) that an infinitesimal surface area (d ⁇ ) on a photodetector segment subtends at a source of fluorescence radiation.
  • ⁇ an infinitesimal surface area
  • a line-of-sight vector ( r ) points to a differential surface area (d ⁇ ) from a target source (P ), such as a source of fluorescent radiation.
  • P target source
  • the angle of ⁇ results from a unit vector ( h ) normal to a planar detector ring and the line-of-sight vector ( F ).
  • Pd(x,y,z) denotes the Cartesian coordinates of a photodetector, e.g., a Si ⁇ - junction photodiode, surface-area element (d ⁇ ), and P * (x * ,y * ,z * ) denotes the coordinates of a source of target radiation.
  • a sphere centered at this target source (P*) may be drawn.
  • the solid angle may be defined as a surface area (physical area), normalized by the square of the radius ( f 2 ).
  • an appropriate choice for the ring geometry of the photodetector array and a target may be the cylindrical coordinate system.
  • a line- of-sight vector ( ? ) pointing to a surface element from a target source is defined.
  • the line- of-sight vector ( r ) can be defined in terms of p, which denotes the radial coordinate component either in the cylindrical coordinates or in the polar coordinates ( 1 ): where ⁇ - ⁇ , ⁇ - ⁇ , and Az ⁇ -z .
  • the differential solid angle ( dQ ri ) in the cylindrical coordinates can be defined as (2):
  • n-parameter solid angle ⁇ ⁇ /3 ⁇ 4 n for applying to the ring geometry is derived in Eqn. (3): pdpdQ z pdp (3)
  • the parameter Ip defined in Eqn. (3), can be calculated according to Eqn. (4):
  • a fully parameterized solid angle ⁇ ,.,., for a generalized point source beam may be defined as follows (6): ( ⁇ ', ⁇ ', ⁇ '; ⁇ ⁇ -, ⁇ ⁇ ' )
  • the projection factor scales substantially down as the function of the working distance below a certain threshold, e.g., ⁇ 5.0 mm, whereas at substantially long working distances, the projection factor is close to unity.
  • the profile of a Gaussian beam may be selected from 95%- and 68%-confidence levels and defined (8).
  • An ideal Gaussian distribution is symmetric around a beam centroid with no skewness. Hence, the selected five points are sufficient to represent an entire Gaussian distribution, as shown in FIG. 5.
  • the Gaussian distribution is not ideal and more than five points, e.g., 6, 7, 8 . . . 100, may be required to represent the entire Gaussian distribution.
  • other multivariate non- Gaussian probability models of beam approximation may be used to define the distribution of the beam centered around the beam centroid.
  • Gaussian profile the sum may be averaged over the number of points (Nj), and then multiply it by the number of pads/segments (N pa d)- Accordingly, a total solid angle ( ⁇ ⁇ tol G ) subtended by the secondary, e.g., fluorescent, radiation of Gaussian profile with a certain beam size ( ⁇ ⁇ or a y ) is obtained (10): where and G denote the point index and Gaussian, respectively.
  • G denote the point index and Gaussian, respectively.
  • the coordinates of a fluorescent-source can be simplified with five parameters, i.e., Ap ⁇ p* L and ⁇ ⁇ *. Hence, the following parametric equation is obtained:
  • a method for optimizing the surface area of an annular detector array in a beam position monitor of interest, e.g., XBPM.
  • the method embodies the steps of calculating a surface area of the sensor segment in the annular photodetector array and the radial dimensions of the array by solving equation ( 15)
  • p T and p " represent the upper and lower radial positions of each photodetector segment.
  • the segment surface area and the radial dimensions of the annular photodetector array may be optimized based on the calculated optimal working distance and the total solid angle of each segment.
  • the surface area of each segment may be reduced without sacrificing the sensitivity of the beam position monitor by varying the upper and lower radial positions of each photodetector segment, which in turn will affect the projection factor and the resulting total projected solid angle.
  • the parameterized analytical model of the beam position monitor used to calculate the solid angle may also be used to explore the correlation between the solid angle and the radial positions of the photodetector segments where the optimal working distance is held constant.
  • the predicted gains of peak solid angle over at each lower radial position is indicated in FIG. 10.
  • calibration of the photodetector array response versus beam position may be determined by using a technique referred to as the difference over the sum.
  • a calibration of the beam in one particular direction e.g., 0°
  • a calibration of the beam in one particular direction may be computed by subtracting the photodetector signal in the segment in this location from the photodetector signal in the counterpart segment on the opposite side of the annular array, e.g., 180°, then dividing by their sum.
  • 16 separate directions may be monitored simultaneously.
  • 32 separate directions may be monitored simultaneously.
  • the difference-over-sum calculation describes the sensitivity of photon counts detected at two counterpart photodetector segments symmetric around the reflection axis (y, or x axis) while an X-ray beam is stepping across a transverse direction (either x, or y).
  • the difference in photon counts detected at two segments are more distinct and pronounced, while the total sum ( ⁇ Q) of the photon counts registered at all of photodetector segments, e.g., 32, 64, etc., is preserved and used as a normalization factor. Since the difference/sum is a normalized signal, it is inherently independent of beam intensity and photon energy. In addition, because the entire beam is used in the measurement, the true center-of-mass is measured.
  • the slope of difference-over-sum curve may be used as an indirect measure of position sensitivity of the photodetector. As shown in FIG. 15, as a beam approaches to each end, the sensitivity curve converges to an upper- and a lower-bound value. In other words, according to this method the photodetectors should be positioned within the linear regions of the slope to achieve the highest spatial sensitivity.
  • a method for optimizing the curvature of the surface of an annular detector array in a BPM in order to maximize photodetector light collection efficiency.
  • the method includes the steps of calculating the total solid angle and the optimal working distance.
  • the calculated total solid angle describes the curved surface of a portion of a sphere having a radius equal to the optimal working distance and centered at the beam target intercept.
  • the sphere of optimum radius defines the optimal curvature of the photodetector array as shown in FIG. 11. Therefore, because the projection factor is essentially equal to unity, it can be ignored and not used to modify the curved surface described by the sphere of optimum radius because the photodetectors are designed to be aligned or closely coincide with the curved surface.
  • a detector array of any curvature between the disclosed planar annular detector array and an annular detector array of optimal curvature will improve photodetector light collection efficiency over the planar configuration. Even a detector array with a surface curvature defined by a sphere having a radius less than the working distance of the sphere of optimum radius by not more than 5 percent could theoretically give improved photodetector collection efficiency over the planar configuration.
  • each detector segment can be aligned to coincide with a plane tangent to the surface of the sphere of optimum radius to approximate a spherical detector surface.
  • each detector segment can be aligned to be parallel to a plane tangent to the surface of the sphere of optimum radius, where the center of the detector segment dips below the tangent point of the surface of the sphere of optimum radius by some distance with the edges of each detector segment lying some distance above the surface.
  • the detector segments of the array may comprise isometric polygons, e.g. an array of isosceles triangles, an array of isometric rhombuses, an array of interspersed isometric pentagons and hexagons, or any other array configuration of isometric polygons forming an approximate spherical surface.
  • the detector segments may have essentially the same shape as those depicted in FIG. 2D, but rather than comprising a planar detector the outer radius of the detector array may be tilted towards the target, such that the surface of the detector segments coincide with respective planes tangent to the spherical surface defined by the total solid angle.
  • Each tangent point representing the intersection of the surface of a detector segment with the spherical surface defined by the total solid angle would lie on a circle.
  • the tangent points would represent the intersection of the spherical surface of the total solid angle with the center of each respective detector segment.
  • the beam position monitor may comprise a plurality of radiation sensitive segments positioned in an annular array and a radiation target separated from the plurality of radiation sensitive segments by a working distance.
  • the radiation sensitive photodetector segments may be specifically tuned to be responsive to particular frequencies emitted from the target materials when it intercepts the beam of, for example, synchrotron radiation.
  • This assembly may serve as a diagnostic device for aligning beamline components and for real-time monitoring of the instantaneous photon beam position.
  • FIG. 12 depicts a schematic of an exemplary photodetector array, e.g. an annular array of photodiodes, in relation to the target film, e.g. a target film that re-emits secondary radiation upon intercepting the incident radiation beam.
  • the optimal spectral sensitivity of the photodetector array can be tuned to visible, ultraviolet, or X-ray frequencies.
  • the target film can provide fluorescent back- scattering from 4 to 8 keV to the photodetector array when illuminated by an incident X-ray beam.
  • the photodetector array may comprise any number of PIN diodes such as 32 (see FIG. 13A) or 64 (see FIG.
  • PIN diodes e.g., Si-PIN-junction diodes
  • annular conformation e.g., "doughnut"
  • other permutations of PIN diodes in an annular array are also envisioned, and the number depends on the desired efficiency and available resources.
  • the number of photodiode segments may be constrained by an integer multiple of the number of channels on the circuitry directly connected to the annular photodetector array.
  • HERMES4 ASIC chips have 32 available channels (see FIG. 14A).
  • the photodetector ring may be designed and fabricated to have a multiple of 32 as the number of segments, e.g., 32, 64, 96, etc.
  • the photodetectors can be precisely and contiguously positioned to form an unbroken ring structure and each of the photodetector segments can be wire-bonded to each of the ASIC channels on the readout circuit as shown, for example, in FIG. 14A.
  • each segment is about 0.192 radian wide ( ⁇ 1 1 °) as shown in FIG. 13 A.
  • each segment is 0.096 radian wide ( ⁇ 5.5°) as shown in FIG. 13B.
  • all the segments have the same size regardless of their position within the annular array.
  • each photodetector segment may vary depending on the specific model chosen.
  • the photodetector array may incorporate the photodetector segments of two or more width profiles.
  • the photodetector array may also incoiporate multiple concentric rings of annular photodetector arrays, wherein the inner radius of one ring is greater than the outer radius of another ring.
  • the multiple concentric rings of annular photodetector arrays may have the same number of photodetector segments or the different rings may have different numbers of photodetector segments.
  • the multiple concentric rings of photodetector segments may be angled so as to be aligned or to coincide with the curved surface of the peak solid angle as closely as possible.
  • the photodetector array is curved as shown in FIG. 11.
  • a virtual sphere of a radius of the optimum distance that may range from 2 mm to 10 mm is drawn from the target. It is envisioned that the photon-detection efficiency should be enhanced if the annular-array photodetector segments are embedded on the curved surface whose curvature radius closely matches the radius of the optimum sphere.
  • the radius of the virtual sphere is about 3 mm and the photodetector segments lie on the curvature of the sphere.
  • the area size of photodetector segment in the beam position monitor depends on the number of segments in the array and the upper and lower radial positions, which in turn depend on the rms size of the beam.
  • the lower radial position may range from about 1 mm to about 3 mm, whereas the upper radial position may range from about 3.5 mm to about 6 mm.
  • the lower radial position may range from about 2 mm to about 3 mm, whereas the upper radial position may range from about 4 mm to about 5 mm. More preferably, the lower radial position is about 2.5 mm and the upper radial position is about 4.1 mm.
  • the surface area of the photodetector segment is set to a value to match the capacitance of the readout electronics.
  • the surface area of each segment may range from about 0.2 mm 2 to about 2.0 mm 2 with a range of about 0.3 mm 2 to 0.6 mm 2 being preferred for a 64-segment array and a range of about 0.9 mm 2 to about 1.2 mm 2 being more preferred for a 32-segment array.
  • the number of segments within the annular array is 32 and each photodetector segment has a surface area that measures approximately 1 mm 2 .
  • the number of photodetector segments within the annular array is 64 and each photodetector segment has a surface area that measures approximately 0.44 mm 2 . Table 1 provides a summary of these exemplary embodiments.
  • leakage current measured from one segment is linear against the increasing reverse bias voltage on a log-log scale. Up to the operational bias voltage of 100 (V), the leakage current is measured to be held below 100 pA with a bias voltage of 150 V applied at room temperature. As FIG. 16 shows, the depletion region is created at around 200 (V) from the C-V characteristic.
  • the guard rings encircling the ring array of photodetector segments can isolate each of the detector segments from the inactive region.
  • a multiple guard-ring structure is introduced to the design of the photo-detector sensors. In so doing, the structure of multiple guard rings helps to control the potential gradient.
  • the photodetector array may further comprise a plurality of concentric guard rings around ( 1 ) the inner periphery of the polar photodetector array formation, (2) the outer periphery of the polar photodetector array formation, or (3) the inner and the outer periphery of the polar photodetector array formation.
  • the number of inner and/or outer guard rings will depend on the electric leakage of the photodetector array and may range from 1 to 5 guard rings per each periphery, with 3 being preferred. It should be noted that the number of guard rings depends on how to control the potential gradient.
  • the total width of the inner and outer guard rings, summed together, should be comparable to the total thickness of the depletion depth of the photodetectors at full bias.
  • the target may be positioned downstream of the photodetector array.
  • the target can be a metal film free-standing or coated onto any thin suitable material transparent to the incident radiation, including ceramics such as silicon nitride (S13N4) which is transparent to X-ray radiation.
  • ceramics such as silicon nitride (S13N4) which is transparent to X-ray radiation.
  • the position of the metal film is approximated based on the method provided above for the optimization of the working distance.
  • the choice of material for the target film is crucial for optimizing signal according to the beam energy available at each beamline.
  • Three primary criteria must be considered when selecting the film.
  • the first criteria are yield, i.e., the amount of radiation re-emitted per unit of incident radiation intensity.
  • yield is the amount of radiation re-emitted per unit of incident radiation that is absorbed. In the case of fluorescence as the type of secondary radiation, the yield increases with atomic number.
  • the energy of the re-emitted secondary radiation should occur in a region where the spectral sensitivity on the photodetector, e.g. PIN photodiode, is relatively high.
  • the film material must be chemically stable, able to tolerate high doses of radiation and be easily manufactured into a film of uniform thickness without voids. Because it is desirable to preserve the transmission rate of the radiation beam, e.g. synchrotron X-ray radiation beam, at or greater than 90%, the film has thickness of preferably 50 to 1000 nm for beam kinetic energies ranging from 200 eV to 100 keV, with 100 nm to 500 nm comprising a more
  • Some materials which meet these requirements are Cr , Fe , Mn , Ti ⁇ , or Co 27 , or alloys thereof.
  • the emission energies of these materials are low ranging between 4.5 and 7.5 keV as shown in Table 2 (also see FIG. 17) with absorption rate range between 2 and 14 % and fluorescence yield of 0.214 to 0.406.
  • a ⁇ 500 nm- thick film of Ti ⁇ , Cr , MrT 3 , and Fe ⁇ for the beam energy of 8 keV may be used.
  • the thickness desired depends on the beam photon energy employed.
  • a method for finding a beam centroid is provided based on fitting data representing photon counts registered at each of the photodetector segments. As illustrated in FIG. 20, the method relies on the fact that the maximum beam intensity ⁇ I ma ) is acquired when a beam centroid is positioned on the photodetector annular array axis at the working distance (z*).
  • the working distance (z*) also can be referred to as the shortest radial distance possible (Ro).
  • the beam intensities of the diametrically opposing segments ( If and if 01 ) inversely correlate with its corresponding radial distances ⁇ Rf and R- "' ), i.e., the distance between the center of the segment and the contact point between the beam and the target, it is possible to deduce the radial distance ( R i ) of any segment in the annular array by solving Eqn. (18), [0093]
  • the polar coordinates of the beam on the target plane which is defined as a distance (p) of the beam centroid at the target from the annular array segment and a polar angle (or azimuth; ⁇ ) of each segment.
  • this approach can utilize an EGS4-based Monte Carlo photon-transport package to estimate inelastic and elastic scattering arising from ambient scattering.
  • EGS4-based Monte Carlo photon-transport package to estimate inelastic and elastic scattering arising from ambient scattering.
  • implementation both geometric parameters of the BPM system and beamline parameters allows estimating both inelastic and inelastic scattering events that comprise background events at a given energy and beamline condition.
  • the numerical calculations show that background events are not significant and cannot be of concern.
  • a beam position monitor was designed with annular array of 32 PIN-junction photodiodes with the lower radial position (p " ) of 2.5625 mm and the upper position (p + ) of 4.1088 mm of each photodiode segment from the center of the array.
  • the transverse beam size ( ⁇ _ ⁇ _) was 0.5 mm.
  • a projection factor was calculated as a function of working distance z* as illustrated in FIG. 4.
  • Eqn. (11) the influence of beam sizes on the solid-angle calculation was investigated and the projected total solid angle ( ⁇ , ⁇ .
  • the optimal working distance that would provide the highest spatial sensitivity is at about 3.0 mm.
  • FIG. 7 illustrated a plot of the profiles for solid angles versus working distance as a function of beam sizes. Moving from top to bottom, each of the traces on the plot corresponds to transverse beam sizes ( ⁇ ), 2 mm, 1 mm, 0.5 mm, 100 ⁇ , 10 ⁇ , 1 ⁇ , and 0.5 ⁇ , respectively - rms beam sizes over four orders of magnitude were explored in calculations. As shown in the plots on both linear scale (FIG. 7A) and log scale (FIG. 7B), the solid-angle profiles are essentially identical for the beam sizes below 10 ⁇ . Accordingly, in this exemplary embodiment, the performance of the beam position monitor can be expected to be optimized for the rms beam sizes below 10 ⁇ where optimum working distance is about 7 mm.
  • the calculations may be simplified if the beam's transverse dimensions are sufficiently smaller than the working distance of interest.
  • the working distance is about 3.0 mm for a Gaussian beam, whereas the transverse beam size ( ⁇ ) employed was 0.5 mm.
  • ⁇ transverse beam size
  • the solid-angle profiles of a point-source beam and a Gaussian beam are compared.
  • the projected solid angle with a Gaussian beam which is considered an actual case, peaks at around 3.0 mm.
  • the point-source beam also peaks at around 3.0 mm.
  • FIG. 13B depicts the ring array of 64 photodetector segments that were designed and fabricated at in-house facilities. Boron ions are implanted on the front side of the wafer through 1 kA oxide, forming a p-n junction. Phosphorous ions are implanted on the back side to make an ohmic contact with the front side. All 64 segments, configured as a polar array, were positioned between an inner ring radius of 2562.5 ⁇ and an outer ring radius of 4108.8 ⁇ . The active surface area of each segment is about 0.44 (mm 2 ), and each photodiode is 470- ⁇ thick. Table 4 provides a summary of the fabricated ring array.
  • the photodiodes are operated with reverse bias voltage of about 100 volt.
  • An X-ray beam that impinges on a target results in partial absorption and re-emission of secondary radiation, which scatters backward to illuminates the backside of the photodetector array isotropically.
  • the photodetector was devised for both back-side and front-side illumination.
  • Simulations have been conducted to determine the optimal working distance of the fabricated beam position monitor with 64 segments. As illustrated in FIG. 18, based on the parameterization method provided above, it was determined that the optimal distance is about 3 mm.
  • an application-specific integrated circuit e.g., an application-specific integrated circuit
  • HERMES4 may be designed for photon-counting application.
  • a HERMES4 utilizing CMOS technology provides 32 channels, a charge pre-amplifier, a high-order charge shaper, discriminators, an array of five 10-bit global DACs, and counters per channel as illustrated in FIG. 14A.
  • a double-ASIC may be used as illustrated in FIG. 14B.
  • the HERMES4 may be designed to read out input signals generated by the Si-photodiode sensor.
  • the measured electronic resolution is about 15 rms e " at a peaking time of 4 ⁇
  • the gain settings available on HERMES4 are 750 mV/fC and 1,500 mV/fC.
  • the settable peaking times are 0.5, 1, 2, and 4 ⁇ 5 ⁇ Stray capacitance may be reduced by direct Al-wire wedge-bonding between the 32 channels and sensor pads.
  • the present invention can also be configured to operate with other application specific integrated chips (ASIC), field programmable gate arrays (FPGA), complex programmable logic devices (CPLD), and similar circuits and chips.
  • ASIC application specific integrated chips
  • FPGA field programmable gate arrays
  • CPLD complex programmable logic devices
  • the BPM may be housed in a vacuum chamber, where the pressure of 10 "6 torr and below is preferably maintained.
  • circular windows transparent at the frequencies of the beam, may be mounted to allow for unobstructed transmission of the incident beam through the beam position monitor housed within the vacuum chamber.
  • Beryllium windows may be used.
  • the BPM may be manufactured to operate at low temperature, e.g., below -40°C.
  • a Peltier-cooling module coupled to a thermo-sensor, may be attached to the Cu-support frame on the rear side of the ring photodetectors and the cooling water may flow through the Cu support to extract heat deposited on the heat sink.

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Abstract

La présente invention concerne la conception et la fabrication de dispositifs servant à aligner les composants d'une ligne de faisceau et/ou à surveiller en temps réel un faisceau de rayons X et/ou une série des éléments optiques de la ligne de faisceau. Plus particulièrement, la présente invention concerne un nouveau dispositif de surveillance de la position d'un faisceau de type réseau annulaire, un procédé analytique pour concevoir et optimiser le dispositif de surveillance de la position d'un faisceau dans les trois dimensions et un nouveau procédé direct servant à trouver un centroïde du faisceau pour obtenir une sensibilité de la position du faisceau inférieure au micron, un alignement très précis et un fonctionnement du système sans génération de bruit.
PCT/US2012/032215 2011-04-04 2012-04-04 Dispositif de surveillance de la position d'un faisceau de type réseau annulaire à résolution sous-micronique et procédé paramétrique pour optimiser les photodétecteurs Ceased WO2012138792A1 (fr)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101742187B1 (ko) 2015-12-28 2017-05-31 한국원자력의학원 비선형 효과 최소화를 위한 슈박스 형태의 빔 위치 모니터
CN110248460A (zh) * 2019-05-24 2019-09-17 北京大学 一种探测激光驱动质子束流横向位置的方法及装置
CN111982278A (zh) * 2020-08-04 2020-11-24 中国科学院高能物理研究所 一种利用同步辐射偏振性探测束流位置的探测器及方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5387795A (en) * 1993-07-26 1995-02-07 The University Of Chicago Photon beam position monitor
US5717214A (en) * 1995-04-07 1998-02-10 Rikagaku Kenkyusho X-ray beam position monitor and its position measurement method
US20100219350A1 (en) * 2006-03-02 2010-09-02 Koji Kobashi Beam Detector and Beam Monitor Using The Same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5387795A (en) * 1993-07-26 1995-02-07 The University Of Chicago Photon beam position monitor
US5717214A (en) * 1995-04-07 1998-02-10 Rikagaku Kenkyusho X-ray beam position monitor and its position measurement method
US20100219350A1 (en) * 2006-03-02 2010-09-02 Koji Kobashi Beam Detector and Beam Monitor Using The Same

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101742187B1 (ko) 2015-12-28 2017-05-31 한국원자력의학원 비선형 효과 최소화를 위한 슈박스 형태의 빔 위치 모니터
CN110248460A (zh) * 2019-05-24 2019-09-17 北京大学 一种探测激光驱动质子束流横向位置的方法及装置
CN110248460B (zh) * 2019-05-24 2020-07-28 北京大学 一种探测激光驱动质子束流横向位置的方法及装置
CN111982278A (zh) * 2020-08-04 2020-11-24 中国科学院高能物理研究所 一种利用同步辐射偏振性探测束流位置的探测器及方法
CN111982278B (zh) * 2020-08-04 2021-07-13 中国科学院高能物理研究所 一种利用同步辐射偏振性探测束流位置的探测器及方法

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