EP0137954B1 - Channel secondary electron multiplier - Google Patents

Channel secondary electron multiplier Download PDF

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Publication number
EP0137954B1
EP0137954B1 EP84109664A EP84109664A EP0137954B1 EP 0137954 B1 EP0137954 B1 EP 0137954B1 EP 84109664 A EP84109664 A EP 84109664A EP 84109664 A EP84109664 A EP 84109664A EP 0137954 B1 EP0137954 B1 EP 0137954B1
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EP
European Patent Office
Prior art keywords
channel
funnel
electron multiplier
multiplier
support member
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EP84109664A
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German (de)
French (fr)
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EP0137954A1 (en
Inventor
Hans Lauche
Wilhelm Barke
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Max Planck Gesellschaft zur Foerderung der Wissenschaften eV
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Max Planck Gesellschaft zur Foerderung der Wissenschaften eV
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H01J43/18—Electrode arrangements using essentially more than one dynode
    • H01J43/24—Dynodes having potential gradient along their surfaces
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
    • H01J9/125—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes of secondary emission electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/32—Secondary emission electrodes

Definitions

  • the present invention relates to a channel secondary electron multiplier having a carrier body which contains an elongated, tubular multiplier channel which has a main part and an adjoining, funnel-like widening initial section, and with a coating which is on the inner wall of the multiplier channel, including the initial section is arranged and the surface of which forms a secondary emission-resistant resistance layer.
  • Channel secondary electron multipliers are e.g. B. from US-A-4 305 744, GE-B-1 964 665, DE-A-1 902 293 and GB-A-1 440 037 and the Valvo data sheet X914AL, X914BL and have long been known for electron current amplification in Detectors for electrons, ions and photons are used.
  • the commercially available channel multipliers of the type of interest here which contain a single elongated, generally curved multiplier channel (in contrast to the so-called “channel plates", which contain a large number of closely adjacent, short and mostly straight multiplier channels) consist in general a curved tube made of lead glass.
  • the initial section of the multiplier channel formed by the glass tube, which adjoins the inlet opening, can be widened in a funnel-like manner to enlarge the capture cross section for the particles to be detected.
  • the surface of the multiplier channel formed by the glass tube consists of an electrically conductive layer with a high secondary emission coefficient, which has generally been formed by reducing the lead glass.
  • the known channel multipliers consisting of a glass tube are mechanically very sensitive, as a result of which their dimensions are also limited to relatively small values.
  • This disadvantage is avoided in the channel multiplier, which is known from the above-mentioned US-A-4 305 744, by using a mechanically resistant ceramic carrier body which forms the multiplier channel.
  • the inner wall of the channel is coated with a material which is capable of secondary emissions and which is different from the material of the carrier body and which is not formed from the latter by reduction or any other chemical reaction.
  • the coating can e.g. B. consist of lead glass, which is reduced on the surface.
  • the coating and the ceramic of the carrier body should have essentially the same coefficient of thermal expansion, with differences of up to 8% being regarded as permissible.
  • the collection capacity for primary particles obviously depends on the cross section of the inlet opening of the funnel-shaped initial section.
  • a relatively large inlet opening is imperative to achieve an acceptable signal-to-noise ratio.
  • the present invention achieves the object of further developing a channel multiplier of the type mentioned at the outset in such a way that stable operation is guaranteed and that it is also produced in larger dimensions without unduly impairing the electrical properties, in that the material of the carrier body has a coefficient of thermal expansion, which is at least 10% greater than the coefficient of thermal expansion of the material of the secondary emission resistive layer, and that this has been formed at a temperature which is above the maximum operating temperature of the electron multiplier.
  • the present invention is based on the knowledge that the electrical defects which occur when the dimensions of channel multipliers of the type mentioned above are increased, are mainly due to the fact that fine cracks form in the active, secondary-emissive layer, which result in electrical discontinuities and thereby interfere with the work of the multiplier.
  • This deficiency can, as stated above, be remedied by making the coefficient of expansion of the carrier material at least 10%, preferably 15%, most suitably at least 20 to 25% greater than the coefficient of expansion of the coating forming the secondary emission layer and making it z.
  • B. forms from a glaze coating at a temperature which is substantially above the maximum temperatures to be expected during operation, so that the coating is kept under a considerable compressive stress under all operating conditions. The occurrence of cracks and discontinuities is largely prevented by this compressive stress.
  • the channel multiplier 10 shown in FIG. 1 has a single elongate, tubular, curved channel, which is formed by a carrier body 12 made of metal, in particular stainless steel.
  • the carrier body 12 has a helical main part 12a which merges into a conically widening initial section or funnel 12b at the front and into a straight piece 12c at the rear.
  • the funnel 12b forms an inlet opening 12d, in which it is connected in a vacuum-tight manner to a fastening flange 14.
  • a metallic end piece 20, which is closed at one end, is melted in a vacuum-tight manner with its open end via a ceramic intermediate piece 18, insulated from the straight channel end 12c.
  • the inner surface of the metallic carrier body 12 including the funnel 12b delimiting the channel is essentially completely covered with a coherent layer 22 (FIG. 1a) made of a lead glass glaze.
  • the free surface of the glaze layer 22 is reduced in a conventional manner to form a resistance layer 22a with a high secondary emission coefficient.
  • the thin semiconducting secondary emission-capable layer 22a forms with the metal wall of the body 12 an electrical capacitor, the dielectric of which consists of the unreduced lead glass layer 22b. This capacitor can be used as an energy store for the electron avalanche current at the end of the multiplier channel. As a result, more secondary electrons can be released with each pulse than is possible with a conventional channel multiplier.
  • the flange 14 can serve as one connection to the semiconducting multiplier layer, while the other connection is formed by the end piece 20, which serves both as an anode and as a collector and in operation at a voltage of approx. +3.0 kV can be maintained with respect to the flange 14 lying on ground.
  • the inlet opening of the funnel 12b can easily have a diameter of more than 20 mm, z. B. 25 mm.
  • An advantage of the metal construction described with reference to FIG. 1 is the relatively good thermal conductivity of the carrier body, which also contributes to stability under high loads.
  • a creamy pulp made from finely ground glass powder in a liquid carrier material in particular isopropyl alcohol, is preferably used.
  • This paste is applied by pouring, brushing or spraying. In this way, the entire layer can be distributed on the desired surface at room temperature and checked visually before baking.
  • the carrier is then slowly heated until the glaze flows smoothly, for example to about 800 ° C., and then cooled again. So far, the glaze layer has been produced by pouring and pressing a liquid glass mass, which must have a much lower toughness and thus a much higher temperature (approx. 1000 ° C) than is necessary for the glass powder layer to run, which is the case with the known methods limits the number of carrier materials that can be used, requires a considerably higher outlay and is hardly applicable especially for large funnels.
  • the glaze material is preferably degassed. Burning in should therefore be carried out in a vacuum oven followed by smooth burning in an oxidizing atmosphere.
  • the lead glass glaze layer is then reduced in the usual way, e.g. B. by heating at 370 to 400 ° C for about six hours in hydrogen from 100 to 200 kPa to produce a uniform emission layer of about 10 nm in thickness.
  • the channel resistance can thus be calculated as a function of the channel cross section and the length and optimizable.
  • the effectiveness of the individual surface areas of the funnel surface depends on the extent to which the electrons knocked out of the layer are also sucked into the beginning of the main part 12a of the channel. Since the widening of the cross section of the funnel 12b causes a reduction in the resistance in the axial direction and thus a reduction in the field strength, the funnel is basically only fully effective on the inside at the transition to the channel 12a. The sensitivity drops quickly towards the front (entry-side) edge and you soon reach a point where increasing the funnel diameter is no longer profitable.
  • the resistance and emission layer in the funnel is made by a narrow spiral separation, i.e. H. a non-conductive space, divided into a spiral strip.
  • the width of the strip is preferably at least approximately equal to the inner circumference of the channel 12a. By varying the width of the strip, it is in your hand to create a guiding field towards the center of the funnel and thus collect all the electrons from all parts of the funnel.
  • the width of the z. B. separation produced by scratches 24 should be small against the width of the spiral strip 26.
  • the separation 24 can also be produced by appropriate shaping of the carrier body 12. 1, the inner surface of the carrier can be coated with an enamel before glazing in order to achieve a high dielectric strength with a large capacity. The melting point of this enamel intermediate layer must of course be between that of the support and that of the glaze and can replace the unreduced layer 22b.
  • the embodiment of the present channel multiplier shown in FIGS. 2 and 3 contains a carrier body 112 made of insulating ceramic.
  • the carrier body 112 has a substantially cylindrical outer wall and forms a multiplier channel with a funnel-shaped starting section ("funnel") 115 and a spiral-shaped channel part 117 (see also FIG. 3), the axial center line of which lies essentially in one plane.
  • the channel part 117 is through a spiral recess, for. B. increasing depth and substantially constant width, e.g. B. formed about 2 mm in the rear flat end face of the substantially cylindrical support body 112.
  • the depth and width of the channel can be varied.
  • the channel part 117 of the multiplier channel is closed by a ceramic plate 119.
  • the curvature of the multiplier channel is as uniform as possible and in order to achieve this during the transition from the funnel 115 into the channel part 117, the plate 119 can contain a corresponding recess 121 which forms part of the channel wall and thereby enables a transition with a uniform curvature from the funnel to the spiral .
  • the first piece of the channel part 117 adjoining the funnel is preferably somewhat narrower than the rest of the channel part 117.
  • the funnel 115 and the spiral channel part 117 are provided with a glaze which forms the secondary emission layer and can also be produced as was explained above with reference to FIG. 1.
  • the secondary emission layer ends at an anode terminal A, the z. B. can consist of a metallization.
  • a collector 120 At the end of the spiral-shaped recess forming the channel part 117 there is a collector 120, which can also consist of a metallization and is separated from the anode A by an uncoated, insulating piece 124 of the spiral-shaped channel part.
  • the metallization layers forming the anode A and the collector 120 are led outwards and with suitable connections, for. B. 123 connected.
  • the actual channel multiplier is welded into the flange 129 in a vacuum-tight manner by means of a cup-shaped intermediate piece 125 made of metal which is glass-bonded or soldered onto the support body 112 and the end plate 119.
  • An overlying housing 127 carries the electrical connections for a high-voltage input 131 and for a pulse output 133. Inside the housing, electrical components such. B. an amplifier for the output signal.
  • the vacuum-tight design according to FIG. 2 allows operation under vacuum conditions, while at the same time the connections 123 and 133 as well as the anode and high-voltage input 131 are freely accessible.
  • the emission layer in the funnel 115 is advantageously divided into a spiral-shaped strip 126 by a spiral-shaped narrow interruption 124, as was explained with reference to FIG. 1.
  • the width B of the strip is preferably approximately equal to 2 d, where d is the width of the main part of the multiplier channel (FIG. 3).
  • a voltage of +2400 to +3700 V with respect to a connection 135 at the inlet of the funnel 115 can be at the anode connection A, which voltage is preferably at ground potential and z. B. is electrically connected to the flange 129 via the intermediate piece 125.
  • the collector 120 should have a voltage of approx. +10 V. /. + 150 V compared to the anode.
  • the path resistance of the multiplier channel should generally be less than or equal to 10 8 ohms.
  • the channel multiplier according to FIG. 2 can be Modify in that the surface of the ceramic carrier body 112 forming the channel is first metallized and only then coated with the glaze, so that a capacitor is also available, as in the channel multiplier with a metallic carrier body according to FIG. 1.
  • the helical or spiral strip from which the secondary emissive layer consists in the funnel-shaped initial section is expediently essentially coaxial with the funnel axis.

Description

Die vorliegende Erfindung betrifft einen Kanal-Sekundärelektronenvervielfacher mit einem Trägerkörper, der einen langgestreckten, rohrförmigen Vervielfacherkanal enthält, welcher einen Hauptteil und einen sich an diesen anschließenden, sich trichterartig erweiternden Anfangsabschnitt aufweist, und mit einer Beschichtung, die auf der Innenwand des Vervielfacherkanals einschließlich des Anfangsabschnittes angeordnet ist und deren Oberfläche eine sekundäremissionsfähige Widerstandsschicht bildet.The present invention relates to a channel secondary electron multiplier having a carrier body which contains an elongated, tubular multiplier channel which has a main part and an adjoining, funnel-like widening initial section, and with a coating which is on the inner wall of the multiplier channel, including the initial section is arranged and the surface of which forms a secondary emission-resistant resistance layer.

Kanal-Sekundärelektronenvervielfacher (im folgenden kurz "Kanalvervielfacher") sind z. B. aus US-A-4 305 744, GE-B-1 964 665, DE-A-1 902 293 und GB-A-1 440 037 sowie dem Valvo-Datenblatt X914AL, X914BL bekannt und werden seit längerem zur Elektronenstromverstärkung in Detektoren für Elektronen, Ionen und Photonen verwendet. Die im Handel erhältlichen Kanalvervielfacher des hier hauptsächlich interessierenden Typs, die einen einzigen langgestreckten, im allgemeinen gekrümmten Vervielfacherkanal enthalten (im Gegensatz zu den sog. "Kanalplatten", die eine Vielzahl nahe benachbarter, kurzer und meist gerader Vervielfacherkanäle enthalten), bestehen im allgemeinen aus einem gekrümmten Rohr aus Bleiglas. Der sich an die Eintrittsöffnung anschließende Anfangsabschnitt des durch das Glasrohr gebildeten Vervielfacherkanales kann zur Vergrößerung des Einfangquerschnittes für die nachzuweisenden Teilchen trichterartig erweitert sein. Die Oberfläche des durch das Glasrohr gebildeten Vervielfacherkanales besteht aus einer elektrisch leitfähigen Schicht mit hohem Sekundäremissionskoeffizienten, die im allgemeinen durch Reduktion des Bleiglases gebildet worden ist.Channel secondary electron multipliers (hereinafter "channel multiplier") are e.g. B. from US-A-4 305 744, GE-B-1 964 665, DE-A-1 902 293 and GB-A-1 440 037 and the Valvo data sheet X914AL, X914BL and have long been known for electron current amplification in Detectors for electrons, ions and photons are used. The commercially available channel multipliers of the type of interest here, which contain a single elongated, generally curved multiplier channel (in contrast to the so-called "channel plates", which contain a large number of closely adjacent, short and mostly straight multiplier channels) consist in general a curved tube made of lead glass. The initial section of the multiplier channel formed by the glass tube, which adjoins the inlet opening, can be widened in a funnel-like manner to enlarge the capture cross section for the particles to be detected. The surface of the multiplier channel formed by the glass tube consists of an electrically conductive layer with a high secondary emission coefficient, which has generally been formed by reducing the lead glass.

Die aus einem Glasrohr bestehenden bekannten Kanalvervielfacher sind mechanisch sehr empfindlich, wodurch auch ihre Abmessungen auf verhältnismäßig kleine Werte beschränkt werden. Dieser Nachteil wird bei dem Kanalvervielfacher, der aus der oben bereits genannten US-A-4 305 744 bekannt ist, durch die Verwendung eines mechanisch widerstandsfähigen Trägerkörpers aus Keramik vermieden, der den Vervielfacherkanal bildet. Die Innenwand des Kanals ist mit einem sekundäremissionsfähigen Material beschichtet, das vom Material des Trägerkörpers verschieden ist und aus letzterem auch nicht durch Reduktion oder irgendeine andere chemische Umsetzung gebildet wird. Die Beschichtung kann z. B. aus Bleiglas bestehen, das an der Oberfläche reduziert ist. Die Beschichtung und die Keramik des Trägerkörpers sollen im wesentlichen den gleichen Wärmeausdehnungskoeffizienten haben, wobei Unterschiede bis zu 8 % als zulässig angesehen werden.The known channel multipliers consisting of a glass tube are mechanically very sensitive, as a result of which their dimensions are also limited to relatively small values. This disadvantage is avoided in the channel multiplier, which is known from the above-mentioned US-A-4 305 744, by using a mechanically resistant ceramic carrier body which forms the multiplier channel. The inner wall of the channel is coated with a material which is capable of secondary emissions and which is different from the material of the carrier body and which is not formed from the latter by reduction or any other chemical reaction. The coating can e.g. B. consist of lead glass, which is reduced on the surface. The coating and the ceramic of the carrier body should have essentially the same coefficient of thermal expansion, with differences of up to 8% being regarded as permissible.

Das Sammlungsvermögen für Primärteilchen hängt bei einem Kanalvervielfacher der hier interessierenden Art offensichtlich vom Querschnitt der Eintrittsöffnung des trichterförmigen Anfangsabschnittes ab. Für Anwendungen mit geringer Primärteilchenflußdichte ist eine relativ große Eintrittsöffnung zwingend notwendig, um ein annehmbares Verhältnis von Signal zu Rauschen zu erreichen.With a channel multiplier of the type of interest here, the collection capacity for primary particles obviously depends on the cross section of the inlet opening of the funnel-shaped initial section. For applications with a low primary particle flux density, a relatively large inlet opening is imperative to achieve an acceptable signal-to-noise ratio.

Durch die Verwendung eines Trägerkörpers aus einem mechanisch widerstandsfähigen Werkstoff, wie Keramik wird es zwar möglich, Kanalvervielfacher mit größeren Abmessungen, die mechanisch verhältnismäßig robust sind, herzustellen, dabei treten dann jedoch andere Probleme auf. Es hat sich nämlich gezeigt, daß bei Vergrößerung des Durchmessers des trichterförmigen Anfangsabschnittes des Vervielfacherkanals elektrische Instabilitäten auftreten und daß das Sammlungsvermögen für die nachzuweisenden Teilchen nicht im gleichen Maße die Abmessungen des Trichters zunimmt.The use of a carrier body made of a mechanically resistant material, such as ceramic, makes it possible to produce channel multipliers with larger dimensions that are mechanically relatively robust, but other problems then arise. It has been shown that when the diameter of the funnel-shaped initial section of the multiplier channel increases, electrical instabilities occur and that the collecting capacity for the particles to be detected does not increase the dimensions of the funnel to the same extent.

Die vorliegende Erfindung löst die Aufgabe, einen Kanalvervielfacher der eingangs genannten Art dahingehend weiterzubilden, daß ein stabiles Arbeiten gewährlistet ist und daß er ohne übermäßige Beeinträchtigung der elektrische Eigenschaften auch in größeren Abmessungen hergestellt werden dann, dadurch, daß der Werkstoff des Trägerkörpers einen Wärmeausdehnungskoeffizienten hat, der mindestens 10 % größer ist als des Wärmeausdehnungskoeffizient der Materials der sekundäremissionsfähigen Widerstandsschicht, und daß diese bei einer Temperatur gebildet worden ist, die über der maximalen Betriebstemperatur des Elektronen vervielfachers liegt.The present invention achieves the object of further developing a channel multiplier of the type mentioned at the outset in such a way that stable operation is guaranteed and that it is also produced in larger dimensions without unduly impairing the electrical properties, in that the material of the carrier body has a coefficient of thermal expansion, which is at least 10% greater than the coefficient of thermal expansion of the material of the secondary emission resistive layer, and that this has been formed at a temperature which is above the maximum operating temperature of the electron multiplier.

Die vorliegende Erfindung beruht auf der Erkenntnis, daß die elektrischen Mängel, die bei Vergrößerungen der Abmessungen von Kanalvervielfachern der obengenannten Art auftreten, hauptsächlich darauf zurückzuführen sind, daß sich in der aktiven, sekundäremissionsfähigen Schicht feine Risse bilden, die elektrische Unstetigkeiten zur Folge haben und dadurch das Arbeiten des Vervielfachers beeinträchtigen. Dieser Mängel kann, wie oben angegeben, dadurch beseitigt werden, daß man den Ausdehnungskoeffizienten des Trägermaterials mindestens 10 %, vorzugswiese 15 %, am zweckmäßigsten mindestens 20 bis 25 % größer als den Ausdehnungskoeffizienten der die sekundärmissionsfähige Schicht bildenden Beschichtung macht und diese z. B. aus einem Glasurüberzug bei einer Temperatur bildet, die wesentlich über den im Betrieb zu erwartenden maximalen Temperaturen liegt, so daß die Beschichtung unter allen Betriebsbedingungen unter einer erheblichen Druckspannung gehalten wird. Durch diese Druckspannung wird das Auftreten von Rissen und Unstetigkeiten weitestgehend verhindert.The present invention is based on the knowledge that the electrical defects which occur when the dimensions of channel multipliers of the type mentioned above are increased, are mainly due to the fact that fine cracks form in the active, secondary-emissive layer, which result in electrical discontinuities and thereby interfere with the work of the multiplier. This deficiency can, as stated above, be remedied by making the coefficient of expansion of the carrier material at least 10%, preferably 15%, most suitably at least 20 to 25% greater than the coefficient of expansion of the coating forming the secondary emission layer and making it z. B. forms from a glaze coating at a temperature which is substantially above the maximum temperatures to be expected during operation, so that the coating is kept under a considerable compressive stress under all operating conditions. The occurrence of cracks and discontinuities is largely prevented by this compressive stress.

Dadurch, daß man gemäß Anspruch 5 die sekundäremissionsfähige Schicht im Trichter durch eine spiralenförmige schmale Unterbrechung unterteilt, so daß sie im Trichter einen spiralenförmigigen Streifen bilden, ergibt sich eine Feldverteilung, die gewährleistet, daß alle aus der Trichteroberfläche herausgeschlagenen Elektronen in den Kanal gesaugt werden.The fact that according to claim 5, the secondary emission layer in the funnel divided by a spiral-shaped narrow interruption, so that they form a spiral-shaped strip in the funnel, there is a field distribution which ensures that all electrons knocked out of the funnel surface are sucked into the channel.

Im folgenden werden Ausführungsbeispiele der Erfindung unter Bezugnahme auf die Zeichnung näher erläutert.Exemplary embodiments of the invention are explained in more detail below with reference to the drawing.

Es zeigen:

  • Fig. 1 eine teilweise geschnittene Seitenansicht eines Kanalvervielfachers gemäß einer ersten Ausführungsform der Erfindung;
  • Fig. 1a eine Schnittansicht eines Teiles des Trägerkörpers des Kanalvervielfachers gemäß Fig. 1 in größerem Maßstab;
  • Fig. 2 einen Axialschnitt eines Kanalvervielfachers gemäß der zweiten Ausführungsform der Erfindung und
  • Fig. 3 eine Ansicht in einer Ebene lll-lll der Fig. 2.
Show it:
  • Figure 1 is a partially sectioned side view of a channel multiplier according to a first embodiment of the invention.
  • 1a shows a sectional view of a part of the carrier body of the channel multiplier according to FIG. 1 on a larger scale;
  • Fig. 2 is an axial section of a channel multiplier according to the second embodiment of the invention and
  • 3 is a view in a plane III-III of FIG. 2.

Der in Fig. 1 dargestellte Kanalvervielfacher 10 hat einen einzigen langgestreckten rohrförmigen, gebogenen Kanal, der durch einen Trägerkörper 12 aus Metall, insbesondere nichtrostendem Stahl, gebildet wird. Der Trägerkörper 12 hat einen wendelförmigen Hauptteil 12a, der vorne in einen sich konisch erweiternden Anfangsabschnitt oder Trichter 12b und hinten in ein gerades Stück 12c übergeht. Der Trichter 12b bildet eine Eintrittsöffnung 12d, bei der er mit einem Befestigungsflansch 14 vakuumdicht verbunden ist. Ein metallisches, an einem Ende geschlossenes Endstück 20 ist mit seinem offenen Ende über ein Keramik-Zwischenstück 18 isoliert an das gerade verlaufende Kanalende 12c vakuumdicht angeschmolzen.The channel multiplier 10 shown in FIG. 1 has a single elongate, tubular, curved channel, which is formed by a carrier body 12 made of metal, in particular stainless steel. The carrier body 12 has a helical main part 12a which merges into a conically widening initial section or funnel 12b at the front and into a straight piece 12c at the rear. The funnel 12b forms an inlet opening 12d, in which it is connected in a vacuum-tight manner to a fastening flange 14. A metallic end piece 20, which is closed at one end, is melted in a vacuum-tight manner with its open end via a ceramic intermediate piece 18, insulated from the straight channel end 12c.

Die den Kanal begrenzende Innenfläche des metallischen Trägerkörpers 12 einschließlich des Trichters 12b ist im wesentlichen vollständig mit einer zusammenhängenden Schicht 22 (Fig. 1a) aus einer Bleiglasglasur überzogen. Die freie Oberfläche der Glasurschicht 22 ist in üblicher Weise reduziert, um eine Widerstandsschicht 22a mit hohem Sekundäremissionskoeffizienten zu bilden. Bei der Fertigung ist darauf zu achten, daß eine dünne, zusammenhängende unreduzierte Bleiglasschicht 22b zwischen der reduzierten Schicht und dem Metall des Trägerkörpers verbleibt, um einen Kurzschluß zwischen der sekundäremissionsfähigen Schicht 22a und dem leitenden Trägerkörper 12 zu verhindern. Die dünne halbleitende sekundäremissionsfähige Schicht 22a bildet mit der Metallwand des Körpers 12 einen elektrischen Kondensator, dessen Dielektrikum aus der unreduzierten Bleiglasschicht 22b besteht. Dieser Kondensator kann als Energiespeicher für den Elektronen-Lawinenstrom im Ende des Vervielfacherkanals genutzt werden. Dadurch können bei jedem Impuls mehr Sekundärelektronen freigesetzt werden, als es bei einem konventionellen Kanalvervielfacher möglich ist.The inner surface of the metallic carrier body 12 including the funnel 12b delimiting the channel is essentially completely covered with a coherent layer 22 (FIG. 1a) made of a lead glass glaze. The free surface of the glaze layer 22 is reduced in a conventional manner to form a resistance layer 22a with a high secondary emission coefficient. During manufacturing, care must be taken that a thin, coherent, unreduced lead glass layer 22b remains between the reduced layer and the metal of the carrier body in order to prevent a short circuit between the secondary emission layer 22a and the conductive carrier body 12. The thin semiconducting secondary emission-capable layer 22a forms with the metal wall of the body 12 an electrical capacitor, the dielectric of which consists of the unreduced lead glass layer 22b. This capacitor can be used as an energy store for the electron avalanche current at the end of the multiplier channel. As a result, more secondary electrons can be released with each pulse than is possible with a conventional channel multiplier.

Bei dem Kanalvervielfacher gemäß Fig. 1 kann der Flansch 14 als der eine Anschluß an die halbleitende Vervielfacherschicht dienen, während der andere Anschluß durch das Endstück 20 gebildet wird, das sowohl als Anode als auch als Auffänger dient und im Betrieb auf einer Spannung von ca. +3,0 kV bezüglich des auf Masse liegenden Flansches 14 gehalten werden kann. Es ist jedoch auch möglich, den Anschluß am offenen Ende des Trichters 12b vom Flansch 14 elektrisch zu trennen, z. B. durch die Glasur oder eine Emaillierung, und zwischen den Flansch 14 und eine Anschlußelektrode an der Eintrittsöffnung des Trichters 12b eine Ziehspannung von 0 bis 200 V (Eingangsflansch negativ bei positiven Primärteilchen) zu legen, um das Einsammeln geladener Primärteilchen zu verbessern.1, the flange 14 can serve as one connection to the semiconducting multiplier layer, while the other connection is formed by the end piece 20, which serves both as an anode and as a collector and in operation at a voltage of approx. +3.0 kV can be maintained with respect to the flange 14 lying on ground. However, it is also possible to electrically separate the connection at the open end of the funnel 12b from the flange 14, e.g. B. by the glaze or enamelling, and between the flange 14 and a connecting electrode at the inlet opening of the funnel 12b a pulling voltage of 0 to 200 V (input flange negative for positive primary particles) to improve the collection of charged primary particles.

Die Eintrittsöffnung des Trichters 12b kann bei der beschriebenen Konstruktion ohne weiteres einen Durchmesser von mehr als 20 mm, z. B. 25 mm haben.The inlet opening of the funnel 12b can easily have a diameter of more than 20 mm, z. B. 25 mm.

Ein Vorteil der anhand von Fig. 1 beschriebenen Metallbauweise ist die relativ gute thermische Leitfähigkeit des Trägerkörpers, was bei hoher Belastung ebenfalls zur Stabilität beiträgt.An advantage of the metal construction described with reference to FIG. 1 is the relatively good thermal conductivity of the carrier body, which also contributes to stability under high loads.

Um den gewünschten großen Eingangstrichter und den daran anschließenden engen Kanal gleichmäßig und möglichst in einem Arbeitsgang mit der Glasur zu beschichten, wird vorzugsweise ein cremiger Brei aus feingemahlenem Glaspulver in einem flüssigen Trägermaterial, insbesondere Isopropylalkohol verwendet. Dieser Brei wird durch Eingießen, Streichen oder Spritzen aufgebracht. Die gesamte Schicht kann auf diese Weise bereits bei Zimmertemperatur auf der gewünschten Oberfläche verteilt und noch vor dem Einbrennen visuell kontrolliert werden. Der Träger wird nun langsam so weit erhitzt, bis die Glasur glatt verfließt, also beispielsweise auf etwa 800°C, und anschließend wieder abgekühlt. Bisher hat man die Glasurschicht durch Eingießen und Hindurchpressen einer flüssigen Glasmasse hergestellt, die dabei eine weit geringere Zähigkeit und damit eine wesentlich höhere Temperatur (ca. 1000°C) haben muß als es für das Verlaufen der Glaspulverschicht erforderlich ist, was bei den bekannten Verfahren die Anzahl der verwendbaren Trägermaterialien begrenzt, einen wesentlich höheren Aufwand erfordert und speziell für große Trichter kaum anwendbar ist.In order to coat the glaze with the desired large inlet funnel and the subsequent narrow channel evenly and if possible in one work step, a creamy pulp made from finely ground glass powder in a liquid carrier material, in particular isopropyl alcohol, is preferably used. This paste is applied by pouring, brushing or spraying. In this way, the entire layer can be distributed on the desired surface at room temperature and checked visually before baking. The carrier is then slowly heated until the glaze flows smoothly, for example to about 800 ° C., and then cooled again. So far, the glaze layer has been produced by pouring and pressing a liquid glass mass, which must have a much lower toughness and thus a much higher temperature (approx. 1000 ° C) than is necessary for the glass powder layer to run, which is the case with the known methods limits the number of carrier materials that can be used, requires a considerably higher outlay and is hardly applicable especially for large funnels.

Vor dem Verschmelzen wird das Glasurmaterial vorzugsweise entgast. Das Einbrennen sollte daher im Vakuumofen erfolgen mit anschließendem Glattbrennen in oxidierender Atmosphäre. Die Bleiglas-Glasurschicht wird dann in üblicher Weise reduziert, z. B. durch Erhitzen auf 370 bis 400° C für etwa sechs Stunden in Wasserstoff von 100 bis 200 kPa, um eine gleichmäßige Emissionsschicht von ca. 10 nm Dicke zu erzeugen. Damit wird der Kanalwiderstand als Funktion des Kanalquerschnitts und der Länge berechenbar und optimierbar.Before the melting, the glaze material is preferably degassed. Burning in should therefore be carried out in a vacuum oven followed by smooth burning in an oxidizing atmosphere. The lead glass glaze layer is then reduced in the usual way, e.g. B. by heating at 370 to 400 ° C for about six hours in hydrogen from 100 to 200 kPa to produce a uniform emission layer of about 10 nm in thickness. The channel resistance can thus be calculated as a function of the channel cross section and the length and optimizable.

Bei den bekannten Kanalvervielfachern mit trichterartig erweitertem Eintritt hängt die Wirksamkeit der einzelnen Flächenbereiche der Trichteroberfläche davon ab, in welchem Maße die aus der Schicht herausgeschlagenen Elektronen auch in den Anfang des Hauptteiles 12a des Kanals hineingesaugt werden. Da die Erweiterung des Querschnitts des Trichters 12b eine Verringerung des Widerstandes in Axialrichtung bewirkt und damit eine Verkleinerung der Feldstärke, ist der Trichter im Grunde genommen nur innen beim Übergang zum Kanal 12a voll wirksam. Zum vorderen (eintrittsseitigen) Rand hin fällt die Empfindlichkeit schnell ab und man erreicht bald einen Punkt, bei dem eine Vergrößerung des Trichterdurchmessers keinen Gewinn mehr bringt. Gemäß der Erfindung wird die Widerstands- und Emissionsschicht im Trichter durch eine schmale spiralige Trennung, d. h. einen nichtleitenden Zwischenraum, in einen spiralenförmigen Streifen unterteilt. Die Breite des Streifens ist vorzugsweise wenigstens annhähernd gleich dem inneren Umfang des Kanals 12a. Durch Variation der Breite des Streifens hat man es in der Hand, ein Führungsfeld in Richtung zur Trichtermitte zu erzeugen und damit alle Elektronen von allen Teilen des Trichters einzusammeln. Die Breite der z. B. durch Ritzen erzeugten Trennung 24 soll klein gegen die Breite des spiralenförmigen Streifens 26 sein. Die Trennung 24 kann auch durch entsprechenden Formgebung des Trägerkörpers 12 erzeugt werden. Bei dem Kanalvervielfacher gemäß Fig. 1 kann man dem die innere Oberfläche des Trägers vor dem Glasieren mit einer Emaille beschichten, um eine hohe elektrische Durchschlagsfestigkeit bei gleichzeitig großer Kapazität zu erreichen. Der Schmelzpunkt dieser Emaille-Zwischenschicht muß selbstverständlich zwischen dem des Trägers und dem der Glasur liegen und kann die unreduzierte Schicht 22b ersetzen.In the known channel multipliers with funnel-like entry, the effectiveness of the individual surface areas of the funnel surface depends on the extent to which the electrons knocked out of the layer are also sucked into the beginning of the main part 12a of the channel. Since the widening of the cross section of the funnel 12b causes a reduction in the resistance in the axial direction and thus a reduction in the field strength, the funnel is basically only fully effective on the inside at the transition to the channel 12a. The sensitivity drops quickly towards the front (entry-side) edge and you soon reach a point where increasing the funnel diameter is no longer profitable. According to the invention, the resistance and emission layer in the funnel is made by a narrow spiral separation, i.e. H. a non-conductive space, divided into a spiral strip. The width of the strip is preferably at least approximately equal to the inner circumference of the channel 12a. By varying the width of the strip, it is in your hand to create a guiding field towards the center of the funnel and thus collect all the electrons from all parts of the funnel. The width of the z. B. separation produced by scratches 24 should be small against the width of the spiral strip 26. The separation 24 can also be produced by appropriate shaping of the carrier body 12. 1, the inner surface of the carrier can be coated with an enamel before glazing in order to achieve a high dielectric strength with a large capacity. The melting point of this enamel intermediate layer must of course be between that of the support and that of the glaze and can replace the unreduced layer 22b.

Die in den Fig. 2 und 3 dargestellte Ausführungsform des vorliegenden Kanalvervielfachers enthält einen Trägerkörper 112 aus Isolierkeramik. Der Trägerkörper 112 hat eine im wesentlichen zylindrische Außenwand und bildet einen Vervielfacherkanal mit einem trichterförmigen Anfangsabschnitt ("Trichter") 115 und einem spiralenförmigen Kanalteil 117 (siehe auch Fig. 3), dessen axiale Mittellinie im wesentlichen in einer Ebene liegt. Der Kanalteil 117 wird durch eine spiralenförmige Ausnehmung, z. B. zunehmender Tiefe und im wesentlichen konstanter Breite, z. B. etwa 2 mm in der hinteren ebenen Stirnfläche des im wesentlichen zylindrischen Trägerkörpers 112 gebildet. Um eine gewünschte Feldstärkeverteilung im Kanal zu erreichen, können Tiefe und Breite des Kanals variiert werden. Der Kanalteil 117 des Vervielfacherkanals wird durch eine Keramikplatte 119 geschlossen. Die Krümmung des Vervielfacherkanals ist möglichst gleichmäßig und um dies beim Übergang vom Trichter 115 in den Kanalteil 117 zu erreichen, kann die Platte 119 eine entsprechende Vertiefung 121 enthalten, die einen Teil der Kanalwand bildet und dadurch einen Übergang mit gleichmäßiger Krümmung vom Trichter zur Spirale ermöglicht. Das sich an den Trichter anschließende erste Stück des Kanalteiles 117 ist vorzugsweise etwas enger als der Rest des Kanalteiles 117.The embodiment of the present channel multiplier shown in FIGS. 2 and 3 contains a carrier body 112 made of insulating ceramic. The carrier body 112 has a substantially cylindrical outer wall and forms a multiplier channel with a funnel-shaped starting section ("funnel") 115 and a spiral-shaped channel part 117 (see also FIG. 3), the axial center line of which lies essentially in one plane. The channel part 117 is through a spiral recess, for. B. increasing depth and substantially constant width, e.g. B. formed about 2 mm in the rear flat end face of the substantially cylindrical support body 112. In order to achieve a desired field strength distribution in the channel, the depth and width of the channel can be varied. The channel part 117 of the multiplier channel is closed by a ceramic plate 119. The curvature of the multiplier channel is as uniform as possible and in order to achieve this during the transition from the funnel 115 into the channel part 117, the plate 119 can contain a corresponding recess 121 which forms part of the channel wall and thereby enables a transition with a uniform curvature from the funnel to the spiral . The first piece of the channel part 117 adjoining the funnel is preferably somewhat narrower than the rest of the channel part 117.

Der Trichter 115 und der spiralenförmige Kanalteil 117 sind mit einer Glasur versehen, die die sekundäremissionsfähige Schicht bildet und ebenso hergestellt werden kann, wie es oben unter Bezugnahme auf Fig. 1 erläutert worden war. Die Sekundäremissions schicht endet an einem Anodenanschluß A, der z. B. aus einer Metallisierung bestehen kann. Am Ende der den Kanalteil 117 bildenden spiralenförmigen Ausnehmung befindet sich ein Auffänger 120, der ebenfalls aus einer Metallisierung bestehen kann und von der Anode A durch ein unbeschichtetes, isolierendes Stück 124 des spiralenförmigen Kanalteils getrennt ist.The funnel 115 and the spiral channel part 117 are provided with a glaze which forms the secondary emission layer and can also be produced as was explained above with reference to FIG. 1. The secondary emission layer ends at an anode terminal A, the z. B. can consist of a metallization. At the end of the spiral-shaped recess forming the channel part 117 there is a collector 120, which can also consist of a metallization and is separated from the anode A by an uncoated, insulating piece 124 of the spiral-shaped channel part.

Die die Anode A und den Auffänger 120 bildenden Metallisierungs schichten sind nach außen herausgeführt und mit geeigneten Anschlüssen, z. B. 123, verbunden.The metallization layers forming the anode A and the collector 120 are led outwards and with suitable connections, for. B. 123 connected.

Der eigentliche Kanalvervielfacher ist durch ein am Trägerkörper 112 und der Abschlußplatte 119 angeglastes oder angelötetes becherförmiges Zwischenstück 125 aus Metall in den Flansch 129 vakuumdicht eingeschweißt. Ein darüber fassendes Gehäuse 127 trägt die elektrischen Anschlüsse für einen Hochspannungs-Eingang 131 sowie für einen Impulsausgang 133. Im Inneren des Gehäuses können elektrische Bauelemente, z. B. ein Verstärker für das Ausgangssignal untergebracht werden.The actual channel multiplier is welded into the flange 129 in a vacuum-tight manner by means of a cup-shaped intermediate piece 125 made of metal which is glass-bonded or soldered onto the support body 112 and the end plate 119. An overlying housing 127 carries the electrical connections for a high-voltage input 131 and for a pulse output 133. Inside the housing, electrical components such. B. an amplifier for the output signal.

Die vakuumdichte Ausführung gemäß Fig. 2 erlaubt den Betrieb unter Vakuumbedingungen, während gleichzeitig die Anschlüsse 123 bzw. 133 sowie Anode bzw. Hochspannungseingang 131 frei zugänglich sind.The vacuum-tight design according to FIG. 2 allows operation under vacuum conditions, while at the same time the connections 123 and 133 as well as the anode and high-voltage input 131 are freely accessible.

Die Emissionsschicht im Trichter 115 ist vorteilhafterweise durch eine spiralenförmige schmale Unterbrechung 124 in einen spiralenförmigen Streifen 126 unterteilt, wie es anhand von Fig. 1 erläutert worden war. Die Breite B des Streifens ist vorzugsweise etwa gleich 2 d, wobei d die Breite des Hauptteiles des Vervielfacherkanals bildet (Fig. 3). Im Betrieb kann an dem Anodenanschluß A eine Spannung von +2400 bis +3700 V bezüglich eines Anschlusses 135 am Eintritt des Trichters 115 liegen, welcher vorzugsweise auf Massepotential liegt und z. B. über das Zwischenstück 125 mit dem Flansch 129 elektrisch verbunden ist. Der Auffänger 120 sollte eine Spannung von ca. +10 V./. + 150 V gegenüber der Anode aufweisen.The emission layer in the funnel 115 is advantageously divided into a spiral-shaped strip 126 by a spiral-shaped narrow interruption 124, as was explained with reference to FIG. 1. The width B of the strip is preferably approximately equal to 2 d, where d is the width of the main part of the multiplier channel (FIG. 3). In operation, a voltage of +2400 to +3700 V with respect to a connection 135 at the inlet of the funnel 115 can be at the anode connection A, which voltage is preferably at ground potential and z. B. is electrically connected to the flange 129 via the intermediate piece 125. The collector 120 should have a voltage of approx. +10 V. /. + 150 V compared to the anode.

Der Bahnwiderstand des Vervielfacherkanals sollte im allgemeinen kleiner oder gleich 108 Ohm betragen.The path resistance of the multiplier channel should generally be less than or equal to 10 8 ohms.

Der Kanalvervielfacher gemäß Fig. 2 läßt sich dadurch abwandeln, daß die den Kanal bildende Oberfläche des keramischen Trägerkörpers 112 zuerst metallisiert und dann erst mit der Glasur überzogen wird, so daß man ebenfalls einen Kondensator zur Verfügung hat, wie bei dem Kanalvervielfacher mit metallischem Trägerkörper gemäß Fig. 1.The channel multiplier according to FIG. 2 can be Modify in that the surface of the ceramic carrier body 112 forming the channel is first metallized and only then coated with the glaze, so that a capacitor is also available, as in the channel multiplier with a metallic carrier body according to FIG. 1.

Der wendel- bzw. spiralförmige Streifen, aus dem die sekundäremissionsfähige Schicht im trichterförmigen Anfangsabschnitt besteht, ist zweckmäßigerweise im wesentlichen koaxial mit der Trichterachse.The helical or spiral strip from which the secondary emissive layer consists in the funnel-shaped initial section is expediently essentially coaxial with the funnel axis.

Claims (10)

1. A channel type secondary electron multiplier having a support member (12, 112) including an elongate tubular multiplier channel having a main part merging into an initial part (12b, 115) widening funnel-like towards an entry aperture, the multiplier having a coating (22) which is disposed on the channel surface including the initial part and whose surface forms a resistive layer (22a) capable of secondary emission, characterized in that the material of the support member (12, 112) has a coefficient of heat expansion at least 10 percent greater than that of the material of said resistive layer, and the same has been formed at a temperature above the maximum working temperature of the electron multiplier.
2. An electron multiplier according to claim 1, characterized in that the coefficient of heat expansion of the material of the support member is at least 15 percent greater than that of the material of the resistive layer.
3. An electron multiplier according to claim 1, characterized in that the coefficient of heat expansion of the material of the support member is at least 20 - 25 percent greater that that of the material of the resistive layer.
4. An electron multiplier according to any of claims 1 to 4, characterized in that the resistive layer (22a) forms a helical strip (26) in the funnel-like windening initial part (12b).
5. An electron multiplier according to claim 4, characterized in that the width of the strip (26) is of the same order of magnitude as the circumference of the main part (12a) of the multiplier channel.
6. An electron multiplier according to any of the previous claims, characterized in that the entry aperture of the multiplier channel is connected in vacuum-tight manner to a connection flange (14, 129).
7. An electron multiplier according to any of claims 1 to 6, characterized in that the support member (12) is made of metal and an electrically insulating layer (22b) is disposed between the resistive layer (22a) and the support member (12).
8. An electron multiplier according to any of claims 1 to 6, characterized in that the support member (112) is made of ceramic, is formed with a recess which widens funnel-fashion towards an entry aperture and which is operative as an initial part (115) of a multiplier channel, and has a surface with an open spiral channel part (117) whose radially inwards disposed start communicates with the funnel shaped initial part, and the spiral channel is closed by an insulating plate (119) (Figs. 2 and 3).
9. An electron multiplier according to claim 8, characterized in that at the transition in the channel from the funnel-shaped initial part (115) to the spiral channel part (117) the plate (19) is formed with a trough-like recess (121) forming a curved wall part of the multiplier channel.
10. An electron multiplier according to claim 8 or 9, characterized in that the spiral channel start communicating with the funnel- shaped initial part (115) is narrower than the remainder of the spiral channel (117).
EP84109664A 1983-08-18 1984-08-14 Channel secondary electron multiplier Expired EP0137954B1 (en)

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DE19833329885 DE3329885A1 (en) 1983-08-18 1983-08-18 CHANNEL SECOND ELECTRONISM multiplier
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US4652788A (en) 1987-03-24
EP0137954A1 (en) 1985-04-24

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