Resistive type particle detection device and particle detection method

A resistive type particle detection device includes a cathode, an amplification micro-gate, and an anode composed of a flat insulator including resistive tracks arranged on a face of the flat insulator facing the amplification micro-gate and reading tracks arranged on the opposite face of the flat insulator, the reading tracks being connected to a reading system. In a non-limiting embodiment, the resistive type particle detection device further includes a conductive track positioned between two resistive tracks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to French Patent Application No. 1555754, filed Jun. 23, 2015, the entire content of which is incorporated herein by reference in its entirety.

FIELD

The present invention relates to a resistive type particle detection device, such as a detector of gaseous particles known as “micromegas detector” (for “MICRO MEsh GAseous Structure”). The invention also relates to a particle detection method implementing a resistive type particle detection device in accordance with that of the invention.

BACKGROUND

Micromegas detectors are known comprising a gas enclosure that is filled with a suitable gaseous mixture, such a detector enabling the amplification of electrons by an avalanche process.

As illustrated inFIG. 1, a first category of micromegas detector1relates to conventional micromegas detectors comprising notably a cathode2, an amplification micro-gate3and an anode4provided with reading tracks5connected to a reading device6. The cathode2, the amplification micro-gate3and the anode are arranged in a gas enclosure7. The cathode2diverts the electrons to the reading tracks5, whereas the amplification micro-gate3makes it possible to amplify the signal so that it is read. In order to amplify the signal passing through the amplification micro-gate3, an electric voltage of approximately 500 V is applied to the amplification micro-gate3.

During the implementation of such a micromegas detector1, the electric voltage is increased progressively on the amplification micro-gate3until 500 V are obtained. Above this value of 500 V, sparks appear between the amplification micro-gate3and the reading tracks5making the micromegas detector1momentarily inoperative. Normally, the sparks develop where impurities are situated, in other words between the reading tracks5and the amplification micro-gate3. Then, the plasma of the spark vaporises the impurity and the voltage may continue to be increased up to the value of 500 V.

Moreover, sparks may also be produced when the micromegas detector1is operational. These sparks generally appear when the flux of particles becomes too intense. The micromegas detector1then undergoes breakdowns making the voltage drop and discharging the amplification micro-gate3. During the time taken to re-establish the electric voltage of the amplification micro-gate3, around 1 ms, the micromegas detector1is inoperative.

The development of breakdowns in the micromegas detector1is often a limiting factor in extreme conditions of use, notably in very high particle fluxes generating therein drops in gain as well as a possible degradation of the micromegas detector1in the long term.

In order to reduce the amplitude and the impact of breakdowns, a second category of micromegas detector20has been developed, namely so-called resistive micromegas detectors. As illustrated inFIG. 2, this type of resistive micromegas detector20, moreover comprises resistive tracks21connected to the common ground M21and positioned facing reading tracks5. The reading tracks5and the resistive tracks21are moreover separated by an insulating layer22. The presence of these resistive tracks21makes it possible to avoid the formation of the breakdown, and to evacuate the charges to the common ground M21. Hence, resistive micromegas detectors20are particularly sensitive to impurities. In fact, not being able to break down, it is no longer possible to eliminate the impurities during the powering up of the amplification micro-gate3. If an impurity is present or is introduced into the resistive micromegas detector20, an important leakage current makes the whole of the resistive micromegas detector20difficult to use. Also, resistive micromegas detectors20have to be assembled in a clean room so as to reduce the risk of introducing dust. The use of a clean room for the assembly of resistive micromegas detectors20in order to leave the minimum of dust on the reading tracks5significantly increases the manufacturing costs without however guaranteeing 100% cleanliness reliability.

Moreover, despite assembly in a clean room, resistive micromegas detectors remain not very reliable for usage outside of the laboratory. In fact, it is possible that a dust of around 50 μm is introduced via the introduction of gas into the gas enclosure. To overcome this problem, numerous pressurised water washings are regularly carried out.

SUMMARY

An aspect of the invention aims to resolve the aforementioned problems of the prior art. More particularly, a problem that an aspect of the invention proposes resolving is to provide a micromegas detector of which the manufacturing conditions are reasonable, while assuring optimum operating reliability.

To this end, an aspect of the invention pertains to a resistive type particle detection device including:a cathode,an amplification micro-gate, andan anode composed of a flat insulator comprising resistive tracks arranged on a face of the flat insulator facing the amplification micro-gate and reading tracks arranged on the opposite face of the flat insulator, the reading tracks being connected to a reading system.

Moreover, the resistive type particle detection device comprises at least one conductive track positioned between two resistive tracks.

Thanks to the conductive track positioned between two resistive tracks, the particle detection device is self-cleaning. At start-up but also during its life, if dusts are generated and/or introduced, the conductive track is connected up to the ground in order to generate electric fields and to induce a spark which eliminates the impurities.

Since the impurities may be implemented during the start-up of the device, it is not necessary to assembly the device in a clean room and the manufacturing cost is thereby reduced. Moreover, since the impurities may be eliminated in operation, the reliability of the particle detection device is improved.

Apart from the main characteristics that have been mentioned in the preceding paragraph, the resistive type particle detection device according to the invention may have one or more of the additional characteristics below, considered individually or according to any technically possible combinations thereof.

In a non-limiting embodiment, the resistive type particle detection device comprises at least one conductive track out of ten resistive tracks.

In a non-limiting embodiment, the resistive type particle detection device comprises an alternation of conductive tracks and resistive tracks.

In a non-limiting embodiment, the maximum distance separating a conductive track from a neighbouring resistive track is equal to half of the step separating two resistive tracks situated on either side of the conductive track less half of the width of said conductive track.

In a non-limiting embodiment, the electric connections of the resistive tracks and/or conductive tracks are situated outside of a sealed enclosure comprising the cathode, the amplification micro-gate, and the anode.

In a non-limiting embodiment, the resistive tracks and the conductive track are physically independent of each other.

In a non-limiting embodiment, the resistive type particle detection device comprises at least one electric contact, the electric contact being connected at a first end to a first resistive track and at a second end to a second resistive track, the conductive track positioned between the two resistive tracks being sectioned at the level of the at least one electric contact, two sections of the conductive track being connected together via a connection track arranged in the flat insulator.

Another aspect of the invention pertains to a method for detecting particles implementing a resistive type particle detection device according to the invention.

In a non-limiting embodiment, the method for detecting particles comprises, in particle detection mode, the following steps:Application of a first determined electric voltage to the cathode,Application of a second determined electric voltage to the amplification micro-gate,Establishment of an electric connection between the reading tracks and the reading system,Establishment of an electric connection between the resistive tracks and a ground, andEstablishment of a floating connection to the conductive track.

In a non-limiting implementation, the method for detecting particles comprises, in impurities cleaning mode, the following steps:Application of a first determined electric voltage to the cathode,Application of a second determined electric voltage or a voltage ramp to the amplification micro-gate,Establishment of an electric connection between the reading tracks and the reading system or a floating connection of the reading tracks,Establishment of an electric connection between the resistive tracks and a ground, andEstablishment of an electric connection between the conductive track and a ground.

In a non-limiting implementation, the method for detecting particles comprising, in amplification optimisation mode, the following steps:Application of a first determined electric voltage to the cathode,Application of a second determined electric voltage or a voltage ramp to the amplification micro-gate,Establishment of an electric connection between the reading tracks and the reading system,Establishment of an electric connection between the resistive tracks and a ground, andApplication of a third determined electric voltage to the conductive track, the third determined electric voltage being negative.

For reasons of clarity, only elements useful for the understanding of the invention have been represented, and have been done so without respect for scale and in a schematic manner. Moreover, similar elements situated in the different figures bear identical references.

DETAILED DESCRIPTION

FIGS. 1 and 2have already been described previously with reference to the prior art.

FIG. 3illustrates a resistive type particle detection device30in accordance with that of the invention. The resistive type particle detection device30comprises:a cathode31,an amplification micro-gate32, andan anode33, this anode33comprising a flat insulator34(forming a substrate) comprising resistive tracks35arranged on a face of the flat insulator34and facing the amplification micro-gate32. The anode33also comprises reading tracks36arranged on the opposite face of the flat insulator34, the reading tracks36being connected to a reading system37.

The resistive type particle detection device30further comprises, in the example illustrated, several conductive tracks38, each conductive track38being positioned between two resistive tracks35. This alternation of resistive tracks35and conductive tracks38on the active surface of the particle detection device30situated under the amplification micro-gate32is illustrated inFIG. 4.

It should be noted that the resistive tracks35may be connected to a same voltage supply of the resistive tracks A35(or to the ground M35) and the conductive tracks38may also be connected to a same voltage supply of the conductive tracks A38(or to the ground M38). In this non-limiting implementation, the electric connections made between the resistive tracks35and the voltage supply of the resistive tracks A35(or to the ground M35) are formed outside of a sealed enclosure39comprising the cathode31, the amplification micro-gate32, and the anode33. Similarly, the electric connections made between the conductive tracks38and the voltage supply of the conductive tracks A38(or to the ground M38) are made outside of the sealed enclosure39comprising the cathode31, the amplification micro-gate32, and the anode33. The fact that the electric connections are positioned outside of the gas tight frame formed by the sealed enclosure39makes it possible to electrically disconnect one or more resistive35and/or conductive38tracks without opening, and thus polluting, the resistive type particle detection device30.

In order to avoid perturbing the operation of the particle detection device30, it is beneficial that the two types of tracks, namely the resistive tracks35and the conductive tracks38, do not have contact with each other. The conductive tracks38and the resistive tracks35are thus physically independent of each other (infinite Ohmic contact). In other words, the conductive tracks and the resistive tracks do not touch physically.

The conductive tracks38may be formed by screen printing of polymer paste filled with conductor, for example copper oxide.

In a non-limiting implementation, the conductive tracks38are made of copper on the flat insulator34, which flat insulator34may be made of Kapton®.

In a non-limiting implementation, the resistive tracks35are formed by the screen printing application of carbon filled polymer paste. To avoid any contact between the conductive tracks38and the resistive tracks35, the screen printing spares the conductive tracks38. If the positioning precision of the printing screen is not sufficient to avoid contact between the conductive tracks38and the resistive tracks35, then a protective mask, for example formed by a UV polymerisable film, is used. This protective mask in fact makes it possible to protect the tracks formed first, for example the conductive tracks38, and to enable the deposition of the second, in this non-limiting example, the resistive tracks35.

The example illustrated inFIGS. 3 and 4is in no way limiting. It is understood that the resistive type particle detection device30according to the invention may comprise a different number of conductive tracks38, for example only one conductive track38out of ten resistive tracks35.

In a beneficial example illustrated inFIG. 4, the maximum distance d separating a conductive track38and a neighbouring resistive track35is equal to half of the step p separating two resistive tracks35situated on either side of the conductive track38less half of the width L of the conductive track38situated between the two resistive tracks35. Thus, for a step p of 500 μm between two resistive tracks35and a conductive track38having a width L of 80 μm, the maximum distance d between the conductive track38and the neighbouring resistive track35is d: (500/2)-(80/2)=210 μm. It follows that in this implementation the maximum distance between an impurity and a conductive track38will not exceed 210 μm. This distance is sufficiently low so that the electric field generated by the conductive track38can vaporise the dust.

In a non-limiting example illustrated inFIG. 5, the particle detection device30comprises electric contacts40(also known as ladders). Each of the electric contacts40is connected at a first end to a first resistive track35and at a second end to a second resistive track35. In this embodiment, the conductive track38(only one is represented for reasons of clarity) positioned between a first resistive track35and a second resistive track35is sectioned at the level of the electric contacts40connecting the first resistive track35and the second resistive track35in order not to touch the electric contacts40. In this case, the conductive tracks38are constituted of segments connected together by the use of internal connection tracks positioned in the flat insulator.FIG. 6is a view along the section A-A ofFIG. 5and represents a connection track41arranged in the flat insulator34.

Generally speaking, the electric contacts40make it possible to increase the flow of charges and to avoid the electric voltage charging of the resistive tracks35.

An aspect of the invention also relates to a method for detecting particles implementing a resistive type particle detection device30according to the invention.

FIG. 7represents a method100for detecting particles operating in particle detection mode and implementing a resistive type particle detection device30according to an embodiment of the invention.

In this non-limiting implementation, the method100for detecting particles comprises a step101of application of a first determined electric voltage HV1to the cathode31.

It also comprises a step102of application of a second determined electric voltage HV2to the amplification micro-gate32.

The method100further comprises a step103of establishing an electric connection between the reading tracks36and the reading system37.

In addition, the method100implements a step104of establishing an electric connection between the resistive tracks35and a ground M35.

In this particle detection mode, the method100further comprises a step105of establishing a floating connection to the conductive track38, in other words no electric voltage is applied and no connection to the ground M38is established.

In such an implementation, the electric field present between the amplification micro-gate32and the resistive tracks35connected to the ground M35directs the charges of the electron avalanche linked to the detection to the resistive tracks35. If the conductive tracks38charge over time under the effect of collection of electrons due to the electron avalanche, and do so despite the absence of electric voltage, then the collection of electrons will be reduced because the charging will be negative. A reduction in the efficiency of the detector ensues therefrom.

If this reduction becomes bothersome, then the method100implements a step106(represented in dotted line inFIG. 7) of establishing a connexion to the ground M38of the conductive tracks38. Furthermore such a step may also be programmed and thus become systematic at predetermined time intervals.

FIG. 8represents a method100for detecting particles operating in impurities cleaning mode and implementing a resistive type particle detection device30according to an embodiment of the invention.

In this non-limiting implementation, the method100for detecting particles comprises a step101of application of a first determined electric voltage HV1to the cathode31.

It also comprises a step107of application of a second determined electric voltage HV2or a voltage ramp (not illustrated) to the amplification micro-gate32.

The method further comprises a step108of establishing an electric connection between the reading tracks36and the reading system37or a floating connection (illustrated in dotted line inFIG. 8) of the reading tracks36.

It also comprises a step104of establishing an electric connection between the resistive tracks35and the ground M35.

In addition, the method100comprises a step106of establishing an electric connection between the conductive track38and the ground M38.

In such an implementation, this layout makes it possible to generate electric fields in the enclosure39and to induce a spark at the places where the impurities are located and thus to eliminate them.

FIG. 9represents a method100for detecting particles operating in amplification optimisation mode and implementing a resistive type particle detection device30according to an embodiment of the invention.

In this non-limiting implementation, the method100for detecting particles comprises a step101of application of a first determined electric voltage HV1to the cathode31.

The method100further comprises a step107of application of a second determined electric voltage HV2or a voltage ramp (not illustrated) to the amplification micro-gate32.

It also comprises a step103of establishing an electric connection between the reading tracks36and the reading system37.

The method100further comprises a step of establishing104an electric connection between the resistive tracks35and the ground M35.

In addition, the method100comprises a step109of application of a third determined electric voltage HV3to the conductive track38, the third determined electric voltage HV3being negative. Then, in the same way as with the floating conductive tracks38, the electric field between the amplification micro-gate32and the resistive tracks35connected to the ground M35directs the charges of the electron avalanche linked to the detection to the resistive tracks35. The fact that the conductive tracks38are connected to a negative electric voltage generates an electric field that focuses the collection of charges of the electron avalanche to the resistive tracks35. For example, the third determined negative electric voltage HV3is 100V. Moreover, it is desirable that the difference in electric voltage between the amplification micro-gate32and the conductive tracks38, for example 400 V in absolute value, is lower than that between the resistive tracks35and the amplification micro-gate32, for example 500 V in absolute value. In addition, this difference in electric voltage should be sufficiently low so as not to drive sparks between the amplification micro-gate32and the conductive tracks38. The focusing effect induced by an electric voltage on the conductive tracks38, focusing which pushes back the charges of the electron avalanche, then generates a gain of the resistive type particle detection device30.