HK1124392B - Exposed conductor system and method for sensing an electron beam - Google Patents

Description

System and method for detecting exposed conductor of electron beam

Background

Electron beams are used in a variety of different applications including, but not limited to, irradiation of packaging materials for sterilization purposes. For example, packaging materials, such as cartons that contain liquids for mass consumption, are sterilized using plasma beam irradiation. To provide immediate control of the electron beam intensity, and to monitor uniformity variations, electronic sensors are used for dose exposure measurements. The signal from the sensor is analyzed and fed back into the electron beam control system as a feedback control signal. In the sterilization of packaging material, such sensor feedback may be used to ensure a sufficient sterilization level. Different sterilization levels may be selected depending on how long shelf life is desired and whether the dispensing and storage of the packages is done at refrigerated or ambient temperatures.

One type of existing sensor that measures electron beam intensity based on a direct measurement method uses a conductor placed inside a vacuum chamber. The vacuum chamber is used to provide isolation from the ambient environment. Because vacuum-based sensors can be relatively large, they are positioned outside the direct electron beam path to avoid obscuring the target object. This shielding may for example hinder a correct irradiation of the packaging material (and thus a correct sterilization). Thus, the sensors rely on secondary information from the periphery of the electron beam, or information from the secondary irradiation, to provide measurements.

In operation, electrons from an electron beam having sufficient energy will penetrate a window, such as the titanium (Ti) window of the vacuum, and be absorbed by the conductor. The absorbed electrons establish a current in the conductor. The magnitude of the current is a measure of the number of electrons penetrating the window of the vacuum chamber. This current provides a measure of the electron beam intensity at the sensor location.

One known electron beam sensor, having a vacuum chamber with a protective coating and electrodes representing signal lines inside the chamber, is described in published U.S. patent application No. us 2004/0119024. The chamber walls serve to maintain a vacuum volume around the electrode. The vacuum chamber has a window precisely aligned with the electrode to detect the electron beam intensity. The sensor is configured to be disposed opposite the electron beam generator relative to a moving article being irradiated for detecting the secondary irradiation.

A similar ion beam sensor is described in patent application WO 2004/061890. In one embodiment of the sensor, the vacuum chamber is removed and the electrode is provided with an insulating layer or film. The insulating layer is provided to avoid effects from electrostatic fields and plasma electrons generated by the electron beam, thereby substantially avoiding effects on the electrode output.

U.S. Pat. No.6,657,212 describes an electron beam irradiation processing apparatus in which an insulating film is provided on a conductor member (e.g., a stainless steel conductor member) of a current detection unit disposed outside a window of an electron beam tube. The current measuring unit includes a current meter that measures a current. This patent describes the advantages of a ceramic coated detector.

Disclosure of Invention

A detector for detecting the intensity of an electron beam generated along a path is disclosed. An exemplary detector includes an exposed conductor coupled to a support configured to position the conductor within an electron beam path; a second conductor isolated from the exposed conductor, the second conductor connected to a voltage potential and partially surrounding the exposed conductor to form a plasma sheath, the plasma sheath having a window through which the exposed conductor is exposed to the electron beam, the window being disposed at least in a direction of the electron beam.

An apparatus for detecting the intensity of an electron beam generated along a path is disclosed. The exemplary apparatus includes means for conducting an electric current established by electrons of the electron beam; and means for shielding the conducting means from the plasma, the shielding means having a window arranged to directly expose at least a portion of the conducting means to the path of the electron beam.

A detector for detecting the intensity of an electron beam generated along a path is disclosed. An exemplary detector includes an exposed conductor coupled to a support configured to position the conductor within an electron beam path; and a second conductor isolated from the exposed conductor and configured to affect the induction of secondary electrons on the exposed conductor by substantially limiting the exposure of the exposed conductor to at least the direction of the electron beam path.

A method for irradiating a target area with an electron beam emitted along a path is disclosed. An exemplary method is disclosed that includes emitting an electron beam through an electron exit window and along a path; detecting the electron beam exiting from the electron exit window, the detecting being performed using an exposed conductor and a second conductor isolated from the exposed conductor, the second conductor partially surrounding the exposed conductor to form a plasma shield having a window, the window being arranged at least in the direction of the electron beam path; and holding the moving target material at a desired measurement location relative to the exposed conductor.

Drawings

Other features and embodiments will become apparent to those skilled in the art upon review of the following detailed description of the embodiments in conjunction with the drawings, in which like reference numerals are used to designate like elements, and in which:

FIG. 1 illustrates an exemplary system for irradiating a target area with an electron beam according to one exemplary embodiment;

FIGS. 2 and 3A-3B illustrate exemplary embodiments of a multi-detector configuration;

fig. 4A-4K and fig. 5 show alternative embodiments of electron beam detectors.

Detailed Description

Fig. 1 illustrates an apparatus, shown as an exemplary system 100, for irradiating a target area within an electron beam emitted along the path. The system 100 may include a device, such as a detector 104, for detecting the intensity of the electron beam generated along the path. The detector 104 may include means, such as an exposed conductor 105, for conducting the current created by the electrons of the electron beam. In an exemplary embodiment, the exposed conductor 105 is coupled to a support 112, the support 112 configured to position the conductor within the path of the electron beam 106.

The detector 104 may also include means, such as a second conductor 107, for shielding the conducting means from the plasma, the shielding means having a window arranged to expose the conducting means to the electron beam path. The second conductor 107 may be isolated from the exposed conductor 105 and may be configured to partially surround the exposed conductor to form a plasma shield. The plasma sheath may comprise, for example, a window through which at least a portion of the exposed conductor is directly exposed to the electron beam, the window being disposed at least in the direction of the electron beam path.

In an exemplary embodiment, the second conductor 107 is connected to a voltage potential, such as a ground potential of the detector (e.g., a ground potential of the exemplary system 100), or a voltage potential sufficient to affect a rate of extraction of electrons from plasma in a vicinity of the detector.

As referenced herein, the rate may be determined empirically by adjusting the voltage applied to the second conductor until the desired level of consistency and accuracy of the electron beam intensity measurements over a specified period of time is achieved. The electron beam intensity is monitored during the specified time period, for example, by connecting the second conductor to a test potential, and by simultaneously using a second independent detector (similar to the configuration of the detector in fig. 1 or other suitable configuration, with its outer layer at ground potential). The second detector can be periodically disposed in the electron beam path over the specified time period to measure the electron beam intensity during a setup phase. When periodically inserted into the electron beam path, the second detector can be used to obtain a measurement that is compared to the measurement obtained using the detector of fig. 1 (which is continuously held within the electron beam path). Between two measurements, the second detector may be removed from the electron beam path and any plasma build-up (plasma build dup) may be released. The voltage potential on the FIG. 1 detector can be adjusted cyclically through different setup phases until the voltage potential applied to the second conductor is identified, which provides the desired consistency and accuracy of the FIG. 1 detector measurements. In an exemplary embodiment, a voltage potential on the order of 0 to 10 volts may be applied to the second conductor.

In the embodiment in fig. 1, the second conductor 107 is arranged below the conductor 105, so that the "window" is formed by the exposed portion of the conductor 105 that does not directly face the second conductor 107. Another exemplary embodiment of this window will be discussed below with respect to fig. 4. The second conductor 107 is isolated from the exposed conductor and is arranged to influence the induction (infiluence) of secondary electrons on the exposed conductor by substantially limiting the exposure of the exposed conductor to at least the direction of the electron beam path.

The exemplary detector 104 may be used in conjunction with other portions of the system 100 of fig. 1. In FIG. 1, the system 100 includes means for emitting electrons, such as an electron beam generator 102, for emitting an electron beam 106 along a path. Means such as a support 114 is provided for supporting the target material within the target region 108. The detector 104 is operable to detect an intensity of an electron beam 106 generated by the electron beam generator along a path, the electron beam 106 irradiating a target area 108.

An electron beam generator 102 for emitting an electron beam 106 along a path includes a vacuum chamber 110. A support 112 is provided to hold the electron beam detector at a position along the path between the vacuum chamber and the target area. The detector 104 is isolated from the support 112 by an insulator 109. The electron beam detector 104 may be formed with exposed conductors disposed at locations along the path between the vacuum chamber 110 and the target area 108 to detect and instantaneously measure the intensity of the electron beam 106 present within the vacuum chamber.

A support 114 provided for supporting the target material in the vicinity of the target area 108 may be associated with a packaging material fixing device 116, for example. In an exemplary embodiment, the support 114 for the target material may be a web of packaging material (web) transport roll or any other suitable apparatus. The support 114 may be used to hold the target material within the target area at a desired measurement location relative to the exposed conductor of the electron beam detector 104.

For example, the desired measurement location may be a location a fixed distance from the exposed conductive member. Alternatively, the position may be a controllable, repeatable variable distance from the exposed conductor. Thus, the desired measurement location may be one of a number of situations when the target material is moved into and near the vicinity of the electron beam 106.

The support 112 for the electron beam detector 104 may be configured to position the detector between the electron beam generator 102 and the target area 108 within a direct path of an electron beam to be generated by the electron beam generator. As referred to herein, the phrase "in-direct-path" refers to a location between the electron beam output of the electron beam exit window and the target area, such that all electrons along a desired width of the electron beam 106 are detected, rather than just electrons within a restricted area. Electrons from the electron beam in the parallel path affect any target disposed within the target region 108.

As shown in the exemplary fig. 1 embodiment, the electron beam generator 102 includes a high voltage power supply 118 suitable for providing sufficient voltage to drive the electron beam generator for the desired application. The electron beam generator also includes a filament power supply 120, referenced to the high voltage of the high voltage power supply 118, having a suitable output voltage for the electron emitting filaments 122 of the electron beam generator. In addition, the high voltage power supply includes a gate control 119.

The filament 122 may be placed within a reflector within the vacuum chamber 110. In an exemplary embodiment, the vacuum chamber 110 may be hermetically sealed. In operation, electrons (e) from the filament 122^-) Is emitted along the path of the electron beam, for example along the path of the electron beam 106 in a direction towards the target area 108.

In the exemplary FIG. 1 embodiment, the detector 104 is shown as being separate from the electron beam generator 102. The electron beam 106 generated by the filament 122 may pass through an electron exit window 124 of the electron beam generator.

Electrons reaching the electron beam detector 104 may be detected and measured. For example, a current meter 126 may be provided to measure the current in the exposed conductor of the electron beam detector 104 as a measure of the intensity of the electron beam. The output from the galvanometer may be provided to a controller 128, which controller 128 may serve as a means for adjusting the intensity of the electron beam in response to the output of the electron beam detector. For example, the electron beam intensity may be adjusted to a set value using negative feedback from the controller 128. In exemplary embodiments, the emitted electron beam can have an energy of, for example, less than 100keV or less or greater as desired (e.g., 60 to 80 keV).

The current meter 126 may be any suitable device for directly or indirectly measuring the intensity of the electron beam. For example, the current meter may be a voltmeter in combination with a resistor, or an ammeter, or any other suitable device.

The exemplary electron beam detector 104 includes an exposed conductor that may be formed, for example, as a bare wire probe. In an exemplary embodiment, the exposed conductor of the detector 104 may be a copper or stainless steel wire, or any other suitable conductor. To protect the wire from the environment, the wire may be coated with a conductive coating. For example, the outer conductive coating may be an inert conductive material, such as gold or diamond.

When a conductor is introduced into the electron beam, electrons can be captured, which can be recorded as a current representing an instantaneous measurement of the electron beam intensity. The conductor member may be configured to be of relatively small size to fit into any geometry.

When electrons emitted from the filament 122 in fig. 1 move toward the target area, the electrons collide with air molecules along the path. The emitted electrons may have sufficient energy to ionize the gas along the path, thereby generating a plasma comprising ions and electrons. Plasma electrons are secondary electrons, or thermal electrons, which have a lower energy than electrons from the electron beam. The plasma electrons have an irregular distribution of vector velocities and the length of the travel distance is only a small fraction of the mean free path of the electron beam.

In an exemplary embodiment, the detector may be formed as a dose mapping unit. For example, FIG. 2 shows an exemplary embodiment in which two-dimensional electron beam intensity measurements may be provided. At this point, the exemplary detector array is formed as a grid to measure the electron beam intensity at each of a plurality of locations in two dimensions of the electron beam path cross section (i.e., in a plane transverse to the electron beam path).

In the detector 300 of fig. 2, the array of detectors 302 may be provided in a grid structure, which may be connected to an electron beam exit window 306. Thus, the detector 300 may be considered a detector mesh, or a dose matching unit. Information from the conductors (e.g., signal amplitudes, signal differences/ratios, conductor locations, etc.) may be used to generate an emission intensity profile by the processor 304. In addition, the mesh structure may function to protect the exit window 306.

Additionally, in the exemplary embodiment of fig. 2, the detectors 302 may be disposed at an angle to each other, and/or to the desired direction of transport of the target material within the target area, and in a plane transverse to the electron beam path. This configuration may minimize the obstruction of target material passing under the mesh.

For example, when an object (e.g., packaging material) moves from the lower portion of the schematic in FIG. 2 to the top of the schematic, all portions of the packaging material will be equally irradiated by the electron beam as the packaging material passes by. The angled detector will detect the electron beam at a plurality of locations across its two-dimensional cross-section, thereby providing an accurate profile of the electron beam without affecting the sterilization process. However, it should be understood that in an exemplary embodiment (not shown), the angle may also be 0 or 90 degrees, i.e. the detector may be arranged at a perpendicular angle to the electron exit window.

Fig. 3A and 3B show exemplary embodiments in which the exit windows 308 and 310 are formed as structures with honeycomb supports, respectively. The exit window may be formed using a foil supported on the honeycomb support. The holes of the honeycomb structure allow the electron beam to move from the vacuum chamber toward the detector 104a in fig. 3A. In fig. 3B, a plurality of detectors 104B, 104c, 104d, and 104e are provided in a symmetrical arrangement. Of course, any number of such detectors may be used. The detector in these embodiments may also serve as window protection.

Fig. 4A-4K illustrate yet further embodiments of exemplary detectors. These detectors may be used in accordance with an exemplary embodiment as detector 104 of fig. 1.

In fig. 4A, the detector is shown to include an exposed conductor 404 for detecting the instantaneous intensity of electrons in the electron beam. The second conductor 402 of the detector 104 is formed as an outer layer that is isolated from the exposed conductor 404 by an insulating layer 406. The second conductor 402 may be connected to a voltage potential, such as ground potential or any other desired potential, in the manner discussed with respect to the second conductor 107 in the embodiment of fig. 1.

The second conductor 402, and the insulating layer 406, only partially surround the conductor 404, thereby exposing the conductor 404 via the window 408 at a desired shielding/exposure angle. In the exemplary embodiment described herein, the exposure angle is an angle representing the portion of the conductor 404 that is directly exposed to the electron beam 106 (e.g., the electron beam emitted via the electron beam window 124).

In fig. 4A, the exposed portion of the conductor 404 is approximately 60 degrees, so that the shielding/exposure angle is 300 degrees. Of course any suitable shielding/exposure angle may be used, including but not limited to angles of 180 degrees or less or more.

In the embodiment of fig. 4A, the plasma does not substantially affect the conductor and the measurement of the electron beam intensity when the target material is disposed at a fixed distance from the conductor. The plasma is substantially attracted to the target material and is not captured by the conductor 404.

Fig. 4A-4K illustrate embodiments of detectors that may be used, for example, in situations where the distance between the detector and the target material varies. These detectors are also used for distances that are e.g. fixed or vary in a controlled manner.

Fig. 4B shows an alternative embodiment that includes an exposed conductor 404 and a second conductor 402 held at a voltage potential such as ground. The second conductor is formed with a U-shaped cross-section and, as shown, with a shielding/exposure angle of 180 degrees. The second conductor 402 is provided such that changes in the amount of plasma electrons proximate to the exposed conductor 404 can be replaced by the second conductor 402.

The second conductor 402 may be used to minimize the effect of the plasma on the current measurement and form a shield for the conductor 404 to prevent the conductor 404 from being substantially affected by the surrounding plasma electrons. The plasma electrons are instead attracted to the grounded conductor 402. In the embodiment shown in fig. 4B, the air between the conductor 404 and the grounded conductor 402 serves as an insulator. Alternative configurations using cylindrical conductors 404 will be apparent to those skilled in the art. For example, a square, rather than cylindrical, conductor may be formed.

In fig. 4C, the ground conductor 402 is formed to have a more square configuration with a shield/exposure angle of 180 degrees.

Similar to fig. 4A, fig. 4D-4J include an insulating material as an insulator between the exposed conductor 404 and the grounded conductor 402. Fig. 4D-4J show another configuration of the detector 104, wherein the shield/exposure angle is 180 degrees for illustrative purposes.

In fig. 4D, a more square cross-section is used for the exposed conductor 404 and the grounded conductor 402, and an insulating material 406 is provided between the two conductors.

The detector shown in fig. 4E includes an exposed conductor 404 having a rectangular cross-section and a second conductor formed as a grounded substrate 402 with an insulating element 406 between the two conductors.

Fig. 4F shows a similar structure, where the substrate 402 is formed to match the shape of the insulating layer 406 and exposed insulating member 404.

In fig. 4G, the configuration of fig. 4F is used with the cylindrical exposed conductor 402. In figure 4G, it is noted that the second conductor 402 surrounds the upper surface of the insulating layer 406 facing the electron beam generator.

In fig. 4H, a cylindrical exposed conductor and a grounded conductor are used, wherein the second conductor 402 has a window 408 formed as an opening in a direction facing the electron beam generator.

In fig. 4I, another embodiment is shown, in which the detector is formed as a layered structure with a U-shaped cross-section, comprising an exposed conductor 404 and a second conductor 402 with an insulating layer 406 in between.

In fig. 4J, an embodiment somewhat similar to that of fig. 1 is shown, wherein the insulating layer 406 has a U-shaped cross-section. The second conductor 402 is divided into two portions, with each respective portion being provided on an end of one of the U-shaped brackets. The exposed conductor 404 is provided on the inside of the U-shaped insulating layer and is isolated from the second conductor 402.

Thus, in these configurations, at least a portion of the conductor 404 is directly exposed to the electron beam from the electron beam generator. Of course, one skilled in the art will appreciate that other configurations, shapes, and material selections for the exposed conductor, the second conductor, and the insulating layer may be used. For example, the exposed conductor may be formed as a conductive surface of a substrate. Also, the second conductor may be formed as a conductive surface of the substrate. The substrate on which the two conductors are formed may be an insulating layer or an insulating element.

Fig. 4K shows another embodiment in which the exposed conductor 404 is included in an insulator formed as an insulating layer 406, which is of an H-shaped configuration. The second conductor 402 is provided within a portion of the H-shaped insulating element 406 such that it is isolated from the exposed conductor 404 and is not directly exposed to the electron beam 106 emitted from, for example, the electron exit window 104. The conductors 402, 404 may be formed as bare wires.

Each of the exposed conductor 404 and the second conductor 402 may be connected to a measurement device, such as current meters 412 and 414, respectively, which produce an output A₁And A₂. The outputs of the current meters 412 and 414 may be provided to the controller 128 of fig. 1. The electron beam intensity can be determined as a measure A₁-A₂Wherein A is₁Is a measure proportional to the current of the electrons and plasma, and A₂Is simply a measure of the plasma. These measurements can also be used to determine electron beam intensity.

In fig. 5, an embodiment somewhat similar to that of fig. 4A is shown. Exposed conductors 504 are provided, which are preferably made of metal, such as aluminum. The conductor 504 is partially covered by an insulating layer 506, which is made of an oxide, such as aluminum oxide (Al)₂O₃). The insulating layer is optionally made of another insulating material, such as a polymer. The second conductor 502 is formed on the outside of the insulating layer 506. The second conductor 502 is preferably made of gold (Au). The second conductor 502 and the insulating layer 506 only partially surround the conductor 504 within the target area, exposing the conductor 504 via the window 508. However, the window 508 does not extend along the entire length of the detector, but only within the target area (i.e., within the electron beam path). At the detector end, the aluminum wire is exposed to serve as a connector for the detector. The detector according to this embodiment may be processed to cover the aluminum wire with a thick layer of aluminum oxide using, for example, an anodization process. The gold layer is deposited using, for example, a plasma vapor deposition technique. The window 508 is then ground to expose the wire 504.

The embodiment depicted in fig. 5 optionally includes an insulating layer 506 made of a ceramic tube, such as alumina (Al)₂O₃) A tube. The exposed conductor 504 may be a stainless steel wire and may have a thin gold coating. The diameter of the wire is preferably slightly smaller than the internal diameter of the tube, so that detection is performedThe wire may be pushed into the tube during machining. Thus, the detector will not easily thermally expand. The tube is coated with a second conductor in the form of a layer 502 of gold on the outer surface of the tube. The window 508 is then ground to expose the wire 504. The window may have any shape, such as rectangular, oval, etc.

It will be readily understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

Claims (29)

1. A detector (104; 300) for detecting an intensity of an electron beam (106) generated along a path, comprising:

an exposed conductor (105; 404) connected to a support (112), the support (112) being configured to dispose the conductor within a path of an electron beam (106); and

a second conductor (107; 402) isolated from the exposed conductor (105; 404), the second conductor (107; 402) being connected to a voltage potential and partially surrounding the exposed conductor (105; 404) to form a plasma shield, the plasma shield having a window through which the exposed conductor (105; 404) is exposed to an electron beam (106), the window being arranged at least in the direction of the electron beam path.

2. The detector according to claim 1, wherein the second conductor (107; 402) is connected to a ground potential of the detector (104).

3. The detector of claim 1, wherein the second conductor (107; 402) is connected to a voltage potential sufficient to affect a rate of extraction of electrons from a plasma in a vicinity of the detector (104).

4. The detector of claim 1, comprising:

a current meter (126) for sensing a current in the exposed conductor (105) as a measure of electron beam intensity.

5. The detector according to claim 1, wherein the exposed conductor (105) is formed with an outer conductive coating.

6. The detector of claim 5, wherein the outer conductive coating is an inert conductive material.

7. The detector of claim 1, comprising:

the array of exposed conductors for detecting an intensity of the electron beam (106) at each of a plurality of locations within the path.

8. The detector of claim 7, wherein the exposed conductors of the array are disposed at an angle relative to a desired direction of transport of the target material within the target area (108) and lie in a plane transverse to the path.

9. The detector of claim 7, comprising:

means for comparing the detected current levels as a measure of electron beam intensity in at least two different exposed conductors.

10. The detector of claim 1, wherein the exposed conductor is formed as a conductive surface of a substrate.

11. The detector of claim 10, comprising:

the array of exposed conductors, each exposed conductor formed on a substrate to detect the electron beam intensity at each of a plurality of locations.

12. A detector according to claim 11, wherein the exposed conductor is disposed at an angle relative to the intended direction of transport of the target material in the target area (108) and lies in a plane transverse to the path.

13. The detector of claim 2, comprising:

an insulating element (406) connected to the second conductor (402).

14. The detector (104) of claim 1 in combination with a system (100) for irradiating a target area (108) with an electron beam (106) emitted along a path, the system comprising:

an electron beam generator (102) for emitting the electron beam (106) along a path, wherein the electron beam generator (102) comprises an electron exit window (124), the detector (104) being arranged at a position along the path between the electron beam generator (102) and the target area (108) for detecting and measuring the intensity of the electron beam (106) exiting the electron exit window (124).

15. The detector according to claim 14, wherein the detector (104; 300) is applied outside the electron exit window (124).

16. The detector of claim 14, comprising:

an electron beam controller (128) for adjusting the intensity of the electron beam (106) in response to the output of the detector (104, 300).

17. The detector according to claim 14, wherein the electron beam (106) is emitted at an energy of less than 100 keV.

18. The detector of claim 14, comprising a support (114) for supporting a target material in a target area vicinity for holding the target material in the target area (108), the support (114) for supporting the target material in the target area vicinity comprising:

at least one packaging material web transfer roll.

19. The detector of claim 1, comprising:

an insulator (406) formed in an H-shaped configuration, wherein the exposed conductor (404) and the second conductor (402) are isolated from each other by the insulator (406).

20. A system in combination with the detector of claim 19, comprising:

a first sensor connected to the exposed conductor (404);

a second sensor connected to the second conductor (402); and

a processor for combining the outputs of the first and second sensors for use as a measure of electron beam intensity.

21. A detector for detecting the intensity of an electron beam generated along a path, comprising:

an exposed conductor (404) connected to a support (112), the support (112) configured to dispose the conductor (404) within a path of an electron beam (106); and

a second conductor (402) isolated from the exposed conductor (404), the second conductor (402) being connected to a voltage potential and arranged to influence the induction of secondary electrons on the exposed conductor (404) by defining the exposure of the exposed conductor (404) to at least the direction of the path of the electron beam (106).

22. A detector according to claim 21, wherein the secondary electron induction on the exposed conductor (404) is obtained by limiting the exposure angle of said exposed conductor to be exposed at least in the path direction of the electron beam (106).

23. The detector of claim 21, comprising:

a current meter (126) for detecting a current in the exposed conductor (404, 105) as a measure of the intensity of the electron beam.

24. The detector of claim 21, comprising:

the array of exposed conductors to detect the electron beam (106) intensity at each of a plurality of locations within the path.

25. The detector of claim 21, wherein the exposed conductor is formed as a conductive surface of a substrate.

26. A detector according to claim 21, wherein the detector (104) is applied on the outside of the electron exit window (124).

27. Method for irradiating a target area (108) with an electron beam (106) emitted along a path, comprising:

emitting an electron beam (106) through an electron exit window (124) and along a path;

detecting the electron beam (106) exiting the electron exit window (124), the detecting being performed using the exposed conductor (105; 404); and

a second conductor (107; 402) isolated from the exposed conductor (105; 404), the second conductor (107; 402) being connected to a voltage potential and partially surrounding the exposed conductor (105; 404) to form a plasma shield having a window (408) arranged at least in the direction of the electron beam path; and

the moving target material is maintained at a desired measurement position relative to the exposed conductor (105; 404).

28. The method according to claim 27, wherein the exposed conductor (105; 404) is arranged between the electron exit window (124) and the target material.

29. The method of claim 27, comprising:

the current from the exposed conductor (105; 404) is measured as a measure of the intensity of the electron beam.