EP0037051B1 - Linear accelerator for charged particles - Google Patents

Linear accelerator for charged particles Download PDF

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Publication number
EP0037051B1
EP0037051B1 EP81102176A EP81102176A EP0037051B1 EP 0037051 B1 EP0037051 B1 EP 0037051B1 EP 81102176 A EP81102176 A EP 81102176A EP 81102176 A EP81102176 A EP 81102176A EP 0037051 B1 EP0037051 B1 EP 0037051B1
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Prior art keywords
accelerator
accelerator tube
charged particles
magnetic coils
tube
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EP81102176A
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German (de)
French (fr)
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EP0037051A1 (en
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Volker Adolf Stieber
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Siemens AG
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Siemens AG
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H9/00—Linear accelerators

Definitions

  • the invention relates to a linear accelerator for charged particles intended for therapy, with an evacuated accelerator tube with walls made of non-ferromagnetic material, with a device for accelerating the charged particles in the forward direction, the particles forming radiation pulses with a predeterminable pulse frequency, and with a vacuum-tight tube final exit window for the accelerated particles.
  • Accelerators for charged particles are mainly used in medical radiation therapy, but less frequently for purposes of radiation screening and sterilization of all kinds of samples. They create a tightly focused beam of accelerated charged particles.
  • electron accelerators mostly linear accelerators, more rarely circular accelerators (betatrons), are also used to generate X-rays with a target exposed to the electron beam. This mostly very hard X-ray radiation is mostly used for medical radiation therapy, but occasionally also for the sterilization of samples of all kinds.
  • the charged particles are accelerated inside an evacuated accelerator tube.
  • the charged particles or the X-rays of the target exposed to the particle beam must pass through an exit window that seals the accelerator tube in a vacuum-tight manner.
  • the exit window generally consists of a thin metal foil.
  • the beam of charged particles has energy of around 4 MeV in common electron accelerators.
  • the exit window is heated at the point of impact of the particle beam. Some of the secondary electrons are directed backwards, i. H. inside the accelerator tube, made of the material of the radiation exit window.
  • Linear accelerators of the type mentioned at the outset, which are intended for therapy, are available on the market.
  • An accelerator for charged particles, in particular for electrons, with an evacuated accelerator tube, a device for accelerating the charged particles in the forward direction and with an exit window for the particles is known from US Pat. No. 3,222,558.
  • the end piece of the accelerator tube widens and the exit window is elongated.
  • magnetic deflection coils at the beginning of the widening end piece in order to scan the beam at high frequency over the (narrow) window width and at low frequency over the (larger) window height. This leads to a more uniform beam distribution on the product to be irradiated and to an increase in the area that is covered by the beam.
  • this is not a therapy device, it must be noted that nothing is said in this document about the exact construction of the magnetic deflection unit.
  • DE-A-2 040 158 describes a method for increasing the output power of an electron accelerator, by means of which the risk of window overheating is reduced.
  • the direction of the electron beam is controlled by four electromagnetic scanning coils, which are arranged at 90 ° to one another outside the acceleration container.
  • the electron beam is deflected on the exit window on a closed rectangular path. This requires a relatively complex control device.
  • CH-A-363 272 discloses an electron accelerator in which an electron beam deflected by a main deflection system passes through an acceleration tube. The heating is distributed over the entire exit window by additionally subjecting the electron beam to a transverse deflection perpendicular to the main deflection. It is assumed that electromagnetic windings cannot be used. Instead, the transverse deflection system has two conductors connected in series and through which current flows in the opposite direction, which are fitted inside the tube on opposite sides and parallel to the axis thereof. Such a solution requires expensive bushings for the two conductors if vacuum problems are not to arise.
  • the invention is based, to build a linear accelerator of the type mentioned smaller, lighter and safer and at the same time the radiation protection and the task improve driving safety.
  • this object is achieved according to the invention in that an electromagnetic device known per se for repeated deflection of the beam of charged particles is arranged in the vicinity of the exit window, in that the device comprises three magnetic coils, that the three magnetic coils against one another by 120 ° are arranged around the beam of charged particles around the outer circumference of the walls of the accelerator tube, which walls are made of non-ferromagnetic material, the axes of the three magnet coils intersecting at a common point lying on the axis of symmetry of the accelerator tube, and the three magnet coils on are connected to a three-phase network, the frequency of which is lower than the aforementioned pulse frequency of the radiation pulses, as a result of which the device generates an alternating magnetic field which circularly deflects the point of incidence of the beam of the charged particles on the exit window.
  • This electromagnetic device has the advantage that the thermal secondary electrons emitted at the exit window are also deflected. However, due to their lower energy, they are deflected far more than the accelerated primary electrons. The consequence of this is that the secondary electrons emitted by the exit window are deflected onto the wall of the accelerator tube surrounding the exit window, while the accelerated primary electrons experience only a very slight deflection at the same time. The secondary electrons striking the wall of the accelerator tube can no longer be accelerated backwards and can no longer trigger X-ray quanta at the end of the accelerator tube opposite the exit window. The radiation protection measures in this area can therefore be largely reduced.
  • the impact area of the accelerated electrons on the exit window increases on average over time, so that the local thermal load is reduced.
  • the yield of secondary electrons is reduced and, as a side effect, the maximum thermally permissible beam power is increased.
  • the device deflects the beam of charged particles in a circular manner, this has the consequence that the deflecting field is always non-zero and that secondary electrons generated at the exit window cannot be accelerated backwards at any time interval.
  • the area of impact of the particle beam on the window is increased with the least possible deflection force.
  • the changing magnetic field can be generated differently than a deflecting electric field outside the accelerator tube and can be brought into effect inside the accelerator tube without bushings or other internals inside the accelerator tube.
  • a particularly expedient construction results if the electromagnetic device according to a development of the invention is arranged at that end of the accelerator tube which faces the exit window.
  • This has the advantage that it is located in the immediate vicinity of the point of origin of the secondary electrons and that it detects the secondary electrons before it passes through the first cavity resonator of the accelerator tube, i.e. H. with the least possible energy, distracts from the wall of the accelerator tube.
  • the deflecting forces can be kept particularly small, and the deflection of the beam of accelerated particles - the primary radiation - is kept small.
  • FIG. 1 and 2 show a highly schematic representation of a linear accelerator 1 as used for medical purposes.
  • Its accelerator tube 2 carries a particle source 4 at one end and a radiation exit window 8 at its other end.
  • electrons are emitted from the particle source 4 into the interior of the acceleration tube 2. These electrons are accelerated by the electric fields generated inside the accelerator tube.
  • the accelerator tube consists of a series of mutually coupled cavity resonators 5, to which an electromagnetic wave, whether as a standing wave or as a traveling wave, is coupled in a manner not shown here.
  • the accelerator tube 2 of a linear accelerator is essentially rotationally symmetrical and has a straight axis of symmetry 6. It is evacuated.
  • Such an accelerator tube is known, for example, under the type designation "Los Alamos".
  • a pulsed electron beam therefore strikes the exit window 8.
  • the exit window consists of a thin metal foil that seals the accelerator tube in a vacuum-tight manner.
  • the metal foil in particle accelerators should be as thin as possible in order to weaken the particle beam as little as possible.
  • the electron beam striking the beam exit window has a diameter of approx. 0.5 mm. 3 and 4, the point of incidence of the undeflected electron beam on the exit window is designated by 10.
  • the accelerated electrons leave the exit window 8 as an electron beam 12.
  • the electrons have an energy of 4 MeV.
  • This emerging electron beam 12 can also strike a target 13 that is brought into its path if necessary, in order to generate X-ray pulses. Either the emerging electron beam 12 or the X-rays emitted by the target are used in radiation therapy.
  • a magnetic deflection device 14, 16, 18 for repeated deflection of the beam on the accelerator tube is arranged in a plane immediately in front of the beam exit window 8.
  • the wall of the accelerator tube consists of non-ferromagnetic material, preferably of copper.
  • the effect of such a deflection device is that it deflects the secondary electrons emerging from the exit window into the interior of the accelerator tube 2 against the wall of the accelerator tube.
  • it increases the impact area 10 of the accelerated electrons on the exit window averaged over time and thus reduces its local thermal load.
  • FIGS. 3 and 4 the impact surface 10a of the particle beam on the exit window 8, which is enlarged by periodic deflection over time, is shown in an enlarged representation.
  • the magnetic deflection device has three magnetic coils 14, 16, 18. In order for these to bring their variable magnetic field as close as possible to the impact surface of the electrons on the exit window, these magnetic coils are on the outside of the accelerator tube
  • the radiation direction is arranged somewhat in front of the radiation exit window 3.
  • the three magnetic coils are arranged offset by 120 ° relative to one another about the axis of symmetry 6 of the accelerator tube 2 and thus at the same time also about the electron beam accelerated along the axis of symmetry.
  • the three axes of symmetry 24, 26, 28 of the magnetic coils 14, 16, 18 are aligned perpendicular to the direction of the electron beam. They meet at a common point on the axis of symmetry of the accelerator tube.
  • the solenoids 14, 16, 18 are connected to AC voltage. Three-phase current is best suited as an AC voltage source. As shown in Fig. 5, the solenoids can be connected to the poles U, V and W of the three-phase source. When the current is switched on, each of the three coils generates a magnetic field that has a force component directed at right angles to the axis of symmetry of the accelerator tube.
  • the magnetic field of the magnetic coil 14 is drawn out in FIG. 2 and designated 25. 2 shows that the magnetic coils 14, 16 and 18 of the exemplary embodiment are adapted to the circular circumference of the accelerator tube 2. In this way, a better transition of the magnetic field is achieved than with straight coils. Solenoid coils without a core have proven their worth.
  • the three magnetic coils can be arranged at different distances from the accelerator tube 2 if, for example, other components are attached to the accelerator tube at one point.
  • the uniform rotating field can be achieved by applying the one coil further away to a higher voltage via a matching transformer.
  • a matching transformer 30 in a delta connection is shown in FIG. 6. It serves to adjust the magnet coil current with different numbers of turns or different turn diameters so that the magnetic field is the same size in the interior of the accelerator tube despite different coil dimensions and / or coil spacing. Even if one coil has to be kept smaller than the other coil, for example for reasons of space, this can be compensated for by a corresponding adjustment of the current through this coil.
  • the transformer 30 is connected on one side to the connections U, V, W of a three-phase supply and on the other side to the magnet coil or coils. The easiest way to do this is to use three-phase current from the public grid.
  • the point of impact 15 on the circuit 10a rotates about 50 or 60 times per second. Five to six electron pulses will strike the radiation exit window during a single revolution. As a result, the thermal energy generated when the electrons impact the radiation exit window is distributed over a much larger cross section. For example, the original impact area can be increased from 0.5 mm 2 to 2 mm 2 . As a result, the local heating and thus the emission of secondary electrons itself is reduced. As a side effect, the risk of the radiation exit window blowing through is also reduced.
  • the primary electrons are accelerated to energies of around 4 MeV and are deflected only very slightly by the circular magnetic field, the secondary electrons have lower, so-called thermal energy. They would be accelerated without the coils 14, 16, 18 along the axis of symmetry of the accelerator tube in the opposite direction to the electron source 4 and would generate high-energy X-rays when they hit the wall there or the particle source 4 used in the wall. This, in turn, would require a complex, heavy and space-consuming shield. This undesired backward directed hard X-ray radiation is designated by 44 in FIG. 1. However, the magnetic fields of the switched-on magnetic coils 14, 16, 18 deflect these slow-moving thermal electrons from their original direction at the exit window and let them hit the inner walls of the accelerator tube. In this way, the effort can be used for radiation lenabtubun g significantly reduced.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Particle Accelerators (AREA)
  • Radiation-Therapy Devices (AREA)

Description

Die Erfindung bezieht sich auf einen für die Therapie bestimmten Linearbeschleuniger für geladene Teilchen mit einer evakuierten Beschleunigerröhre mit Wänden aus nichtferromagnetischem Material, mit einer Einrichtung zur Beschleunigung der geladenen Teilchen in Vorwärtsrichtung, wobei die Teilchen Strahlungspulse mit vorgebbarer Pulsfrequenz bilden, und mit einem die Beschleunigerröhre vakuumdicht abschließenden Austrittsfenster für die beschleunigten Teilchen.The invention relates to a linear accelerator for charged particles intended for therapy, with an evacuated accelerator tube with walls made of non-ferromagnetic material, with a device for accelerating the charged particles in the forward direction, the particles forming radiation pulses with a predeterminable pulse frequency, and with a vacuum-tight tube final exit window for the accelerated particles.

Beschleuniger für geladene Teilchen, vorwiegend Elektronen-, gelegentlich auch Protonenbeschleuniger, werden hauptsächlich in der medizinischen Strahlentherapie, seltener dagegen für Zwecke der Strahlendurchleuchtung und Sterilisation von Proben aller Art, benützt. Sie erzeugen einen eng gebündelten Strahl beschleunigter geladener Teilchen. Elektronenbeschleuniger, meist Linearbeschleuniger, seltener Kreisbeschleuniger (Betatrons), werden jedoch auch dazu verwendet, um Röntgenstrahlung mit einem dem Elektronenstrahl ausgesetzten Target zu erzeugen. Diese meist sehr harte Röntgenstrahlung wird wiederum meist zur medizinischen Strahlentherapie, gelegentlich aber auch zur Sterilisation von Proben aller Art verwendet.Accelerators for charged particles, predominantly electron accelerators, sometimes also proton accelerators, are mainly used in medical radiation therapy, but less frequently for purposes of radiation screening and sterilization of all kinds of samples. They create a tightly focused beam of accelerated charged particles. However, electron accelerators, mostly linear accelerators, more rarely circular accelerators (betatrons), are also used to generate X-rays with a target exposed to the electron beam. This mostly very hard X-ray radiation is mostly used for medical radiation therapy, but occasionally also for the sterilization of samples of all kinds.

Die Beschleunigung der geladenen Teilchen erfolgt im Inneren einer evakuierten Beschleunigerröhre. Zur Applikation müssen die geladenen Teilchen oder aber die Röntgenstrahlung des dem Teilchenstrahl ausgesetzten Targets muß durch ein die Beschleunigerröhre vakuumdicht abschließendes Austrittsfenster nach außen gelangen. Das Austrittsfenster besteht im allgemeinen aus einer dünnen Metallfolie. Der Strahl geladener Teilchen besitzt bei gängigen Elektronenbeschleunigern Energie von etwa 4 MeV. Beim Auftreffen des Teilchenstrahls auf der Metallfolie werden Sekundärelektronen aus der Metallfolie herausgeschlagen. Außerdem wird das Austrittsfenster an der Auftreffstelle des Teilchenstrahls erwärmt. Ein Teil der Sekundärelektronen tritt nach rückwärts gerichtet, d. h. ins Innere der Beschleunigerröhre hinein, aus dem Material des Strahlenaustrittsfensters aus. Diese Sekundärelektronen werden im elektrischen Feld der Beschleunigerröhre nach rückwärts beschleunigt und treffen mit der vollen Beschleunigungsenergie auf das dem Austrittsfenster gegenüberliegende Ende der Beschleunigungsröhre auf. Dort erzeugen sie wiederum Sekundärelektronen und vor allem harte Röntgenstrahlung. Zur Abschirmung derselben ist eine starke und schwere Strahlenschutzkleidung auch dieses Endes der Beschleunigungsröhre erforderlich. Schließlich besteht bei hoher Strahlleistung auch die Gefahr des Überhitzens des Austrittsfensters am Auftreffpunkt des Teilchenstrahls. Dies führt zu einer Steigerung der Erzeugungsrate der Sekundärelektronen und ist in Extremfällen auch mit der Gefahr des Durchschmelzens des Austrittsfensters mit der Folge der Zerstörung der Beschleunigerröhre verbunden.The charged particles are accelerated inside an evacuated accelerator tube. For application, the charged particles or the X-rays of the target exposed to the particle beam must pass through an exit window that seals the accelerator tube in a vacuum-tight manner. The exit window generally consists of a thin metal foil. The beam of charged particles has energy of around 4 MeV in common electron accelerators. When the particle beam hits the metal foil, secondary electrons are knocked out of the metal foil. In addition, the exit window is heated at the point of impact of the particle beam. Some of the secondary electrons are directed backwards, i. H. inside the accelerator tube, made of the material of the radiation exit window. These secondary electrons are accelerated backwards in the electrical field of the accelerator tube and hit the end of the accelerator tube opposite the exit window with the full acceleration energy. There they in turn generate secondary electrons and above all hard X-rays. To shield them, strong and heavy radiation protective clothing is also required at this end of the acceleration tube. Finally, with a high beam power, there is also the risk of the exit window overheating at the point of impact of the particle beam. This leads to an increase in the generation rate of the secondary electrons and in extreme cases is also associated with the risk of the exit window melting through, with the result that the accelerator tube is destroyed.

Für die Therapie bestimmte Linearbeschleuniger der eingangs genannten Art sind auf dem Markt erhältlich.Linear accelerators of the type mentioned at the outset, which are intended for therapy, are available on the market.

Ein Beschleuniger für geladene Teilchen, insbesondere für Elektronen, mit einer evakuierten Beschleunigerröhre, einer Einrichtung zur Beschleunigung der geladenen Teilchen in Vorwärtsrichtung und mit einem Austrittsfenster für die Teilchen ist aus der US-A-3 222 558 bekannt. Das Endstück der Beschleunigerröhre verbreitert sich, und das Austrittsfenster ist langgestreckt ausgebildet. In dieser Literaturstelle ist angegeben, daß es gebräuchlich sei, beim Anfang des sich verbreiternden Endstücks magnetische Ablenkspulen anzuordnen, um den Strahl mit hoher Frequenz über die (schmale) Fensterbreite und mit niedriger Frequenz über die (größere) Fensterhöhe zu rastern. Dies führt zu einer gleichmäßigeren Strahlverteilung auf dem zu bestrahlenden Produkt und zu einer Vergrößerung der Fläche, die vom Strahl bestrichen wird. Abgesehen davon, daß es sich hierbei nicht um ein Therapiegerät handelt, muß festgehalten werden, daß in dieser Druckschrift über die genaue Konstruktion der magnetischen Ablenkeinheit nichts ausgesagt ist.An accelerator for charged particles, in particular for electrons, with an evacuated accelerator tube, a device for accelerating the charged particles in the forward direction and with an exit window for the particles is known from US Pat. No. 3,222,558. The end piece of the accelerator tube widens and the exit window is elongated. In this reference it is stated that it is customary to arrange magnetic deflection coils at the beginning of the widening end piece in order to scan the beam at high frequency over the (narrow) window width and at low frequency over the (larger) window height. This leads to a more uniform beam distribution on the product to be irradiated and to an increase in the area that is covered by the beam. Apart from the fact that this is not a therapy device, it must be noted that nothing is said in this document about the exact construction of the magnetic deflection unit.

In der DE-A-2 040 158 ist ein Verfahren zur Vergrößerung der Abgabeleistung eines Elektronenbeschleunigers beschrieben, durch welches das Risiko einer Fensterüberhitzung verringert wird. Hierbei erfolgt die Steuerung der Richtung des Elektronenstrahls durch vier elektromagnetische Abtastspulen, die um 90° gegeneinander versetzt außerhalb des Beschleunigungsbehälters angeordnet sind. Der Elektronenstrahl wird auf dem Austrittsfenster auf einer geschlossenen rechteckförmigen Bahn abgelenkt. Dies erfordert eine verhältnismäßig aufwendige Steuerungseinrichtung.DE-A-2 040 158 describes a method for increasing the output power of an electron accelerator, by means of which the risk of window overheating is reduced. The direction of the electron beam is controlled by four electromagnetic scanning coils, which are arranged at 90 ° to one another outside the acceleration container. The electron beam is deflected on the exit window on a closed rectangular path. This requires a relatively complex control device.

Aus der CH-A-363 272 schließlich ist ein Elektronenbeschleuniger bekannt, bei dem ein durch ein Hauptablenksystem abgelenkter Elektronenstrahl eine Beschleunigungsröhre durchläuft. Die Erwärmung wird hier auf das ganze Austrittsfenster verteilt, indem man dem Elektronenstrahl zusätzlich einer Querablenkung senkrecht zur Hauptablenkung unterwirft. Dabei wird davon ausgegangen, daß elektromagnetische Wicklungen nicht anwendbar sind. Statt dessen weist das Querablenksystem zwei in Serie geschaltete, in entgegengesetzter Richtung stromdurchflossene Leiter auf, die im Innern der Röhre an gegenüberliegenden Seiten und parallel zur Achse derselben angebracht sind. Eine solche Lösung erfordert kostspielige Durchführungen für die beiden Leiter, wenn sich keine Vakuumprobleme einstellen sollen.Finally, CH-A-363 272 discloses an electron accelerator in which an electron beam deflected by a main deflection system passes through an acceleration tube. The heating is distributed over the entire exit window by additionally subjecting the electron beam to a transverse deflection perpendicular to the main deflection. It is assumed that electromagnetic windings cannot be used. Instead, the transverse deflection system has two conductors connected in series and through which current flows in the opposite direction, which are fitted inside the tube on opposite sides and parallel to the axis thereof. Such a solution requires expensive bushings for the two conductors if vacuum problems are not to arise.

Der Erfindung liegt die Aufgabe zugrunde, einen Linearbeschleuniger der eingangs genannten Art kleiner, leichter und sicherer zu bauen und zugleich den Strahlenschutz sowie die Betriebssicherheit zu verbessern.The invention is based, to build a linear accelerator of the type mentioned smaller, lighter and safer and at the same time the radiation protection and the task improve driving safety.

Bei einem Linearbeschleuniger der eingangs genannten Art wird diese Aufgabe erfindungsgemäß dadurch gelöst, daß in der Nähe des Austrittsfensters eine an sich bekannte elektromagnetische Vorrichtung zur wiederholten Ablenkung des Strahls geladener Teilchen angeordnet ist, daß die Vorrichtung drei Magnetspulen umfaßt, daß die drei Magnetspulen gegeneinander um 120° versetzt um den Strahl geladener Teilchen herum am äußeren Umfang der aus nicht-ferromagnetischem Material bestehenden Wände der Beschleunigerröhre angeordnet sind, wobei sich die Achsen der drei Magnetspulen in einem gemeinsamen, auf der Symmetrieachse der Beschleunigerröhre gelegenen Punkt schneiden, und daß die drei Magnetspulen an einem Drehstromnetz angeschlossen sind, dessen Frequenz niedriger ist als die erwähnte Pulsfrequenz der Strahlungspulse, wodurch die Vorrichtung ein wechselndes Magnetfeld erzeugt, daß den Auftreffpunkt des Strahls der geladenen Teilchen auf dem Austrittsfenster kreisförmig ablenkt.In the case of a linear accelerator of the type mentioned at the outset, this object is achieved according to the invention in that an electromagnetic device known per se for repeated deflection of the beam of charged particles is arranged in the vicinity of the exit window, in that the device comprises three magnetic coils, that the three magnetic coils against one another by 120 ° are arranged around the beam of charged particles around the outer circumference of the walls of the accelerator tube, which walls are made of non-ferromagnetic material, the axes of the three magnet coils intersecting at a common point lying on the axis of symmetry of the accelerator tube, and the three magnet coils on are connected to a three-phase network, the frequency of which is lower than the aforementioned pulse frequency of the radiation pulses, as a result of which the device generates an alternating magnetic field which circularly deflects the point of incidence of the beam of the charged particles on the exit window.

Diese elektromagnetische Vorrichtung hat den Vorteil, daß auch die am Austrittsfenster emittierten thermischen Sekundärelektronen abgelenkt werden. Sie werden jedoch in Folge ihrer geringeren Energie ungleich stärker abgelenkt als die beschleunigten Primärelektronen. Dies hat zur Folge, daß die vom Austrittsfenster emittierten Sekundärelektronen auf die das Austrittsfenster umgebende Wandung der Beschleunigerröhre abgelenkt werden, während die beschleunigten Primärelektronen gleichzeitig eine nur ganz geringe Ablenkung erfahren. Die auf die Wandung der Beschleunigerröhre auftreffenden Sekundärelektronen können nun nicht mehr nach rückwärts beschleunigt werden und keine Röntgenquanten mehr an dem dem Austrittsfenster gegenüberliegenden Ende der Beschleunigerröhre auslösen. Daher können die Strahlenschutzmaßnahmen in diesem Bereich weitgehend vermindert werden. Außerdem vergrößert sich so im zeitlichen Mittel die Auftrefffläche der beschleunigten Elektronen auf dem Austrittsfenster, so daß die lokale thermische Belastung vermindert wird. Dadurch wird sowohl die Ausbeute an Sekundärelektronen vermindert und als Nebeneffekt auch die maximale thermisch zulässige Strahlleistung erhöht.This electromagnetic device has the advantage that the thermal secondary electrons emitted at the exit window are also deflected. However, due to their lower energy, they are deflected far more than the accelerated primary electrons. The consequence of this is that the secondary electrons emitted by the exit window are deflected onto the wall of the accelerator tube surrounding the exit window, while the accelerated primary electrons experience only a very slight deflection at the same time. The secondary electrons striking the wall of the accelerator tube can no longer be accelerated backwards and can no longer trigger X-ray quanta at the end of the accelerator tube opposite the exit window. The radiation protection measures in this area can therefore be largely reduced. In addition, the impact area of the accelerated electrons on the exit window increases on average over time, so that the local thermal load is reduced. As a result, the yield of secondary electrons is reduced and, as a side effect, the maximum thermally permissible beam power is increased.

Da die Vorrichtung den Strahl geladener Teilchen kreisförmig ablenkt, hat dies zur Folge, daß das ablenkende Feld stets ungleich Null ist und daß am Austrittsfenster erzeugte Sekundärelektronen zu keinem Zeitintervall nach rückwärts beschleunigt werden können. Außerdem wird so die Auftrefffläche des Teilchenstrahls auf dem Fenster bei geringstmöglicher Ablenkkraft vergrößert. Das wechselnde Magnetfeld läßt sich anders als ein ablenkendes elektrisches Feld außerhalb der Beschleunigerröhre erzeugen und ohne Durchführungen oder sonstige Einbauten im Innern der Beschleunigerröhre im Inneren der Beschleunigerröhre zu Wirkung bringen.Since the device deflects the beam of charged particles in a circular manner, this has the consequence that the deflecting field is always non-zero and that secondary electrons generated at the exit window cannot be accelerated backwards at any time interval. In addition, the area of impact of the particle beam on the window is increased with the least possible deflection force. The changing magnetic field can be generated differently than a deflecting electric field outside the accelerator tube and can be brought into effect inside the accelerator tube without bushings or other internals inside the accelerator tube.

Eine besonders zweckmäßige Konstruktion ergibt sich, wenn die elektromagnetische Vorrichtung nach einer Weiterbildung der Erfindung an demjenigen Ende der Beschleunigerröhre angeordnet ist, das dem Austrittsfenster zugewandt ist. Dies hat den Vorteil, daß sie sich in unmittelbarer Nähe des Entstehungsortes der Sekundärelektronen befindet und daß sie die Sekundärelektronen noch vor dem Durchlaufen des ersten Hohlraumresonators der Beschleunigerröhre, d. h. mit der geringstmöglichen Energie, an die Wand der Beschleunigerröhre ablenkt. Hierdurch können die ablenkenden Kräfte besonders klein gehalten werden, und es wird die Ablenkung des Strahls beschleunigter Teilchen - der Primärstrahlung also - klein gehalten.A particularly expedient construction results if the electromagnetic device according to a development of the invention is arranged at that end of the accelerator tube which faces the exit window. This has the advantage that it is located in the immediate vicinity of the point of origin of the secondary electrons and that it detects the secondary electrons before it passes through the first cavity resonator of the accelerator tube, i.e. H. with the least possible energy, distracts from the wall of the accelerator tube. As a result, the deflecting forces can be kept particularly small, and the deflection of the beam of accelerated particles - the primary radiation - is kept small.

Weitere Einzelheiten der Erfindung werden anhand eines in den Figuren dargestellten Ausführungsbeispiels erläutert. Es zeigt

  • Fig. 1 eine schematische Darstellung einer Beschleunigerröhre,
  • Fig. einen Schnitt längs der Linie 11-11 der Fig.1,
  • Fig. 3 eine Aufsicht auf den Auftreffpunkt des Strahls geladener Teilchen auf das Austrittsfenster bei ausgeschalteten und eingeschalteten Magnetspulen,
  • Fig. 4 eine Aufsicht auf den Auftreffpunkt des Strahls geladener Teilchen auf das Austrittsfenster bei einer einzigen eingeschalteten Magnetspule,
  • Fig. eine Schaltanordnung für die Magnetspulen der Fig. 2 und
  • Fig. 6 eine Schaltanordnung zur Änderung der an den drei Spulen der Fig. 2 anliegenden Spannung.
Further details of the invention are explained with reference to an embodiment shown in the figures. It shows
  • 1 is a schematic representation of an accelerator tube,
  • 1 shows a section along the line 11-11 of FIG. 1,
  • 3 is a plan view of the point of impact of the beam of charged particles on the exit window with the solenoids switched off and on,
  • 4 is a plan view of the point of impact of the beam of charged particles on the exit window with a single magnet coil switched on,
  • Fig. A switching arrangement for the magnetic coils of Fig. 2 and
  • Fig. 6 shows a switching arrangement for changing the voltage applied to the three coils of Fig. 2.

Die Fig. 1 und 2 zeigen in stark schematisierter Darstellung einen Linearbeschleuniger 1, wie er für medizinische Zwecke verwendet wird. Seine Beschleunigerröhre 2 trägt an ihrem einen Ende eine Teilchenquelle 4 und an ihrem anderen Ende ein Strahlenaustrittsfenster 8. Von der Teilchenquelle 4 werden im Falle des vorliegenden Ausführungsbeispiels Elektronen ins Innere der Beschleunigungsröhre 2 emittiert. Diese Elektronen werden durch die im Innern der Beschleunigerröhre erzeugten elektrischen Felder beschleunigt. Zu diesem Zweck besteht die Beschleunigerröhre aus einer Reihe von aneinandergekuppelten Hohlraumresonatoren 5, an die, in hier nicht weiter dargestellter Weise, eine elektromagnetische Welle, sei es als stehende oder als Wanderwelle, angekuppelt wird. Die Beschleunigerröhre 2 eines Linearbeschleunigers ist im wesentlichen rotationssymmetrisch und besitzt eine gerade Symmetrieachse 6. Sie ist evakuiert. Eine solche Beschleunigerröhre ist beispielsweise unter der Typenbezeichnung »Los Alamos« bekannt.1 and 2 show a highly schematic representation of a linear accelerator 1 as used for medical purposes. Its accelerator tube 2 carries a particle source 4 at one end and a radiation exit window 8 at its other end. In the case of the present exemplary embodiment, electrons are emitted from the particle source 4 into the interior of the acceleration tube 2. These electrons are accelerated by the electric fields generated inside the accelerator tube. For this purpose, the accelerator tube consists of a series of mutually coupled cavity resonators 5, to which an electromagnetic wave, whether as a standing wave or as a traveling wave, is coupled in a manner not shown here. The accelerator tube 2 of a linear accelerator is essentially rotationally symmetrical and has a straight axis of symmetry 6. It is evacuated. Such an accelerator tube is known, for example, under the type designation "Los Alamos".

Die durch die Teilchenquelle 4, einer Glühkathode mit nachgeschalteter Vorbeschleunigungsstrecke (nicht dargestellt), in die Beschleunigerröhre 2 eingeschossenen Elektronen werden längs der Symmetrieachse 6 der Beschleunigerröhre 2 im Takt der angekuppelten Hochfrequenz beschleunigt. Auf das Austrittsfenster 8 trifft daher ein gepulster Elektronenstrahl auf. Das Austrittsfenster besteht aus einer dünnen Metallfolie, die die Beschleunigerröhre vakuumdicht abschließt. Die Metallfolie soll bei Teilchenbeschleunigern möglichst dünn sein, um den Teilchenstrahl so wenig wie möglich zu schwächen. Der auf das Strahlenaustrittsfenster auftreffende Elektronenstrahl hat einen Durchmesser von ca. 0,5 mm. In den Fig. 3 und 4 ist der Auftreffpunkt des nicht abgelenkten Elektronenstrahls auf das Austrittsfenster mit 10 bezeichnet.The electrons injected into the accelerator tube 2 by the particle source 4, a hot cathode with a downstream pre-acceleration path (not shown), along the axis of symmetry 6 of the loading accelerator tube 2 accelerated in time with the coupled high frequency. A pulsed electron beam therefore strikes the exit window 8. The exit window consists of a thin metal foil that seals the accelerator tube in a vacuum-tight manner. The metal foil in particle accelerators should be as thin as possible in order to weaken the particle beam as little as possible. The electron beam striking the beam exit window has a diameter of approx. 0.5 mm. 3 and 4, the point of incidence of the undeflected electron beam on the exit window is designated by 10.

Die beschleunigten Elektronen verlassen das Austrittsfenster 8 als Elektronenstrahl 12. Die Elektronen haben im Ausführungsbeispiel eine Energie von 4 MeV. Dieser austretende Elektronenstrahl 12 kann auch auf ein im Bedarfsfall in seinen Weg gebrachtes Target 13 auftreffen, um Röntgenstrahlenimpulse zu erzeugen. In der Strahlentherapie werden entweder der austretende Elektronenstrahl 12 oder die vom Target emittierten Röntgenstrahlen eingesetzt.The accelerated electrons leave the exit window 8 as an electron beam 12. In the exemplary embodiment, the electrons have an energy of 4 MeV. This emerging electron beam 12 can also strike a target 13 that is brought into its path if necessary, in order to generate X-ray pulses. Either the emerging electron beam 12 or the X-rays emitted by the target are used in radiation therapy.

Wie die Fig. 1 und 2 zeigen, ist eine magnetische Ablenkvorrichtung 14, 16, 18 zur wiederholten Ablenkung des Strahls an der Beschleunigerröhre in einer Ebene unmittelbar vor dem Strahlenaustrittsfenster 8 angeordnet. Die Wandung der Beschleunigerröhre besteht im Ausführungsbeispiel aus nicht ferromagnetischem Material, vorzugsweise aus Kupfer. Die Wirkung einer solchen Ablenkvorrichtung besteht darin, daß sie die vom Austrittsfenster aus ins Innere der Beschleunigerröhre 2 austretenden Sekundärelektronen gegen die Wandung der Beschleunigerröhre ablenkt. Außerdem vergrößert sie über die Zeit gemittelt die Auftrefffläche 10 der beschleunigten Elektronen auf das Austrittsfenster und vermindert so dessen örtliche thermische Belastung. In den Fig. 3 und 4 ist in vergrößerter Darstellung die durch periodische Ablenkung im Zeitmittel vergrößerte Auftrefffläche 10a des Teilchenstrahls auf dem Austrittsfenster 8 eingezeichnet.1 and 2 show, a magnetic deflection device 14, 16, 18 for repeated deflection of the beam on the accelerator tube is arranged in a plane immediately in front of the beam exit window 8. In the exemplary embodiment, the wall of the accelerator tube consists of non-ferromagnetic material, preferably of copper. The effect of such a deflection device is that it deflects the secondary electrons emerging from the exit window into the interior of the accelerator tube 2 against the wall of the accelerator tube. In addition, it increases the impact area 10 of the accelerated electrons on the exit window averaged over time and thus reduces its local thermal load. In FIGS. 3 and 4, the impact surface 10a of the particle beam on the exit window 8, which is enlarged by periodic deflection over time, is shown in an enlarged representation.

Im Ausführungsbeispiel der Fig. 1 und 2 besitzt die magnetische Ablenkvorrichtung drei Magnetspulen 14, 16, 18. Damit diese ihr veränderliches Magnetfeld so nah wie möglich an der Auftrefffläche der Elektronen auf das Austrittsfenster zur Wirkung bringen, sind diese Magnetspulen an der Außenseite der Beschleunigerröhre in Strahlenrichtung etwas vor dem Strahlenaustrittsfenster 3 angeordnet. Die drei Magnetspulen sind um 120° gegeneinander um die Symmetrieachse 6 der Beschleunigerröhre 2 und damit zugleich auch um den längs der Symmetrieachse beschleunigten Elektronenstrahl versetzt angeordnet. Die drei Symmetrieachsen 24, 26, 28 der Magnetspulen 14,16,18 sind senkrecht zur Richtung des Elektronenstrahls ausgerichtet. Sie treffen sich in einem gemeinsamen Punkt auf der Symmetrieachse der Beschleunigerröhre.In the exemplary embodiment of FIGS. 1 and 2, the magnetic deflection device has three magnetic coils 14, 16, 18. In order for these to bring their variable magnetic field as close as possible to the impact surface of the electrons on the exit window, these magnetic coils are on the outside of the accelerator tube The radiation direction is arranged somewhat in front of the radiation exit window 3. The three magnetic coils are arranged offset by 120 ° relative to one another about the axis of symmetry 6 of the accelerator tube 2 and thus at the same time also about the electron beam accelerated along the axis of symmetry. The three axes of symmetry 24, 26, 28 of the magnetic coils 14, 16, 18 are aligned perpendicular to the direction of the electron beam. They meet at a common point on the axis of symmetry of the accelerator tube.

Die Magnetspulen 14, 16, 18 sind an Wechselspannung angeschlossen. Als Wechselspannungsquelle eignet sich am besten Drehstrom. So wie das in der Fig. 5 gezeigt ist, können die Magnetspulen an den Polen U, V und W der Drehstromquelle angeschlossen werden. Bei eingeschaltetem Strom erzeugt jede der drei Spulen ein Magnetfeld, das eine rechtwinklig zur Symmetrieachse der Beschleunigerröhre gerichtete Kraftkomponente besitzt. Das magnetische Feld der Magnetspule 14 ist in der Fig. 2 herausgezeichnet und mit 25 bezeichnet. Die Fig. 2 läßt erkennen, daß die Magnetspulen 14, 16 und 18 des Ausführungsbeispiels, an den kreisförmigen Umfang der Beschleunigerröhre 2 angepaßt sind. Auf diese Weise wird ein besserer Übergang des magnetischen Feldes als mit geraden Spulen erreicht. Magnetspulen ohne Kern haben sich gut bewährt.The solenoids 14, 16, 18 are connected to AC voltage. Three-phase current is best suited as an AC voltage source. As shown in Fig. 5, the solenoids can be connected to the poles U, V and W of the three-phase source. When the current is switched on, each of the three coils generates a magnetic field that has a force component directed at right angles to the axis of symmetry of the accelerator tube. The magnetic field of the magnetic coil 14 is drawn out in FIG. 2 and designated 25. 2 shows that the magnetic coils 14, 16 and 18 of the exemplary embodiment are adapted to the circular circumference of the accelerator tube 2. In this way, a better transition of the magnetic field is achieved than with straight coils. Solenoid coils without a core have proven their worth.

Mit Hilfe der drei Magnetspulen 14, 16 und 18 wird ein Drehfeld erzeugt. Unter der Voraussetzung, daß die drei Spulen dieselbe Dimension haben und vom selben Drehstrom durchflossen werden, wird der Elektronenstrahl kreisförmig um den Auftreffpunkt der Symmetrieachse 6 auf dem Strahlenaustrittsfenster 8 herum verschoben. Dies wird in der Fig. 3 gezeigt. Dort ist in vergrößerter Darstellung sowohl die Auftrefffläche 10 des Elektronenstrahls bei abgeschalteten Magnetspulen als auch die Auftrefffläche 10a des kreisförmig abgelenkten Elektronenstrahls auf dem Austrittsfenster bei eingeschalteten Magnetspulen dargestellt. Wird nur eine der drei Magnetspulen 14, 16, 18 eingeschaltet, so wird nur eine lineare Verschiebung des Auftreffpunkts des Elektronenstrahls auf dem Austrittsfenster erreicht, so wie das in Fig. 4 gezeigt wird.With the help of the three magnetic coils 14, 16 and 18, a rotating field is generated. Provided that the three coils have the same dimension and the same three-phase current flows through them, the electron beam is shifted in a circle around the point of impact of the axis of symmetry 6 on the beam exit window 8. This is shown in Figure 3. There, in an enlarged representation, both the impact surface 10 of the electron beam when the magnet coils are switched off and the impact surface 10a of the circularly deflected electron beam on the exit window when the magnet coils are switched on are shown. If only one of the three magnetic coils 14, 16, 18 is switched on, only a linear displacement of the point of impact of the electron beam on the exit window is achieved, as is shown in FIG. 4.

Es ist auch möglich, daß die drei Magnetspulen in unterschiedlichem Abstand von der Beschleunigerröhre 2 anzuordnen sind, wenn beispielsweise an einer Stelle andere Bauelemente an der Beschleunigerröhre befestigt sind. In solch einem Fall kann das gleichmäßige Drehfeld dadurch erreicht werden, daß die eine, weiter entfernte Spule über einen Anpassungstransformator an eine höhere Spannung gelegt wird. Ein solcher Anpassungstransformator 30 in Dreieckschaltung ist in der Fig. 6 dargestellt. Er dient dazu um den Magnetspulenstrom bei unterschiedlichen Windungszahlen oder unterschiedlichem Windungsdurchmesser so einzustellen, daß das magnetische Feld trotz unterschiedlicher Spulenabmessungen und/oder Spulenabstand im Innern der Beschleunigerröhre gleich groß ist. Auch wenn die eine Spule zum Beispiel aus Platzgründen kleiner gehalten werden muß als die andere Spule, dann kann dies durch eine entsprechende Einstellung des Stromes durch diese Spule ausgeglichen werden. Der Transformator 30 ist auf einer Seite an die Anschlüsse U, V, W einer Drehstromversorgung und auf der anderen Seite an der oder die Magnetspulen angeschlossen. Am einfachsten ist es, hierzu den Drehstrom aus dem öffentlichen Netz zu verwenden.It is also possible for the three magnetic coils to be arranged at different distances from the accelerator tube 2 if, for example, other components are attached to the accelerator tube at one point. In such a case, the uniform rotating field can be achieved by applying the one coil further away to a higher voltage via a matching transformer. Such a matching transformer 30 in a delta connection is shown in FIG. 6. It serves to adjust the magnet coil current with different numbers of turns or different turn diameters so that the magnetic field is the same size in the interior of the accelerator tube despite different coil dimensions and / or coil spacing. Even if one coil has to be kept smaller than the other coil, for example for reasons of space, this can be compensated for by a corresponding adjustment of the current through this coil. The transformer 30 is connected on one side to the connections U, V, W of a three-phase supply and on the other side to the magnet coil or coils. The easiest way to do this is to use three-phase current from the public grid.

Wenn die Elektronen mit einer Pulsfrequenz von 300 Impulsen pro Sekunde beschleunigt werden und die Netzfrequenz des Drehstromes 50 oder 60 Hz beträgt, so dreht sich der Auftreffpunkt 15 auf dem Kreis 10a etwa 50 oder 60mal pro Sekunde. Dabei werden während einer einzigen Umdrehung fünf bis sechs Elektronenimpulse auf das Strahlenaustrittsfenster auftreffen. Das führt dazu, daß die thermische Energie, die beim Aufprallen der Elektronen auf das Strahlenaustrittsfenster erzeugt wird, sich auf einem wesentlich größeren Querschnitt verteilt. So läßt sich beispielsweise die ursprüngliche Auftrefffläche von 0,5 mm2 auf 2 mm2 vergrößern. Das hat zur Folge, daß auch die örtliche Aufheizung und damit die Emission von Sekundärelektronen selbst vermindert wird. Als Nebeneffekt wird außerdem die Gefahr eines Durchbrennens des Strahlenaustrittsfensters verringert.If the electrons with a pulse frequency are accelerated by 300 pulses per second and the mains frequency of the three-phase current is 50 or 60 Hz, the point of impact 15 on the circuit 10a rotates about 50 or 60 times per second. Five to six electron pulses will strike the radiation exit window during a single revolution. As a result, the thermal energy generated when the electrons impact the radiation exit window is distributed over a much larger cross section. For example, the original impact area can be increased from 0.5 mm 2 to 2 mm 2 . As a result, the local heating and thus the emission of secondary electrons itself is reduced. As a side effect, the risk of the radiation exit window blowing through is also reduced.

Während die Primärelektronen auf Energien von etwa 4 MeV beschleunigt werden und nur sehr geringfügig durch das kreisförmige Magnetfeld abgelenkt werden, haben die Sekundärelektronen niedrigere, sog. thermische Energie. Sie würden ohne die Spulen 14, 16, 18 längs der Symmetrieachse der Beschleunigerröhre in entgegengesetzter Richtung auf die Elektronenquelle 4 zu beschleunigt werden und dort beim Auftreffen auf die dortige Wandung, bzw. in der Wandung eingesetzten Teilchenquelle 4, energiereiche Röntgenstrahlen erzeugen. Dies würde ihrerseits wiederum eine aufwendige, schwere und platzbeanspruchende Abschirmung erforderlich machen. Diese unerwünschte nach Rückwärts gerichtete harte Röntgenstrahlung ist in der Fig. 1 mit 44 bezeichnet. Die Magnetfelder der eingeschalteten Magnetspulen 14,16,18 lenken aber diese am Austrittsfenster noch langsamen thermischen Elektronen aus ihrer ursprünglichen Richtung ab und lassen sie gegen die inneren Wände der Beschleunigerröhre stoßen. Auf diese Weise kann der Aufwand für die Strah- lenabschirmung deutlich vermindert werden.While the primary electrons are accelerated to energies of around 4 MeV and are deflected only very slightly by the circular magnetic field, the secondary electrons have lower, so-called thermal energy. They would be accelerated without the coils 14, 16, 18 along the axis of symmetry of the accelerator tube in the opposite direction to the electron source 4 and would generate high-energy X-rays when they hit the wall there or the particle source 4 used in the wall. This, in turn, would require a complex, heavy and space-consuming shield. This undesired backward directed hard X-ray radiation is designated by 44 in FIG. 1. However, the magnetic fields of the switched-on magnetic coils 14, 16, 18 deflect these slow-moving thermal electrons from their original direction at the exit window and let them hit the inner walls of the accelerator tube. In this way, the effort can be used for radiation lenabschirmun g significantly reduced.

Der Aufwand könnte noch weiter vermindert werden, wenn statt der drei Magnetspulen nur eine Magnetspule auf der Beschleunigerröhre befestigt würde und die Emission der Teilchenquelle 4 in Abhängigkeit des Stromes durch die Magnetspule so gesteuert wird, daß sie nur bei aufgebautem Magnetfeld erfolgen kann. Es wäre auch möglich statt der von Wechselstrom durchflossenen Magnetspulen ein konstantes Magnetfeld, beispielsweise eines Permanentmagneten zu verwenden. In diesem Fall würden die Sekundärelektronen genauso abgefangen, nur würde die thermische Belastung des Strahlenaustrittsfensters nicht vermindert.The effort could be further reduced if, instead of the three magnetic coils, only one magnetic coil were attached to the accelerator tube and the emission of the particle source 4 is controlled as a function of the current through the magnetic coil so that it can only take place when the magnetic field is built up. It would also be possible to use a constant magnetic field, for example a permanent magnet, instead of the magnetic coils through which alternating current flows. In this case, the secondary electrons would be intercepted in the same way, only the thermal load on the radiation exit window would not be reduced.

Claims (6)

1. A linear accelerator (1) for charged particles for X-ray therapy, with an evacuated accelerator tube (2) which possesses walls of non-ferromagnetic material, with a device (5) which serves to accelerate the charged particles in a forwards direction, the particles thereby forming a particle beam of radiation pulses with a predetermined pulse frequency, and with an outlet window (8) for the accelerated particles, which window seals the accelerator tube (2) in vacuum-tight fashion, characterised in that in the vicinity of the outlet window (8) there is arranged an electromagnetic device known per se which serves to repeatedly deflect the beam of charged particles, that the device comprises three magnetic coils (14, 16, 18) which are offset relative to one another by 120° and are arranged around the beam of charged particles at the outer periphery of the walls of the accelerator tube (2) which consist of non-ferromagnetic material, where the axes (24, 26, 28) of the three magnetic coils (14, 16, 18) intersect one another at a common point on the axis of symmetry (6) of the accelerator tube (2), and that the three magnetic coils (14, 16, 18) are connected to a three-phase mains supply (U, V, W) whose frequency is lower than the aforementioned pulse frequency of the radiation pulses, as a result of which the electromagnetic device generates a changing magnetic field which deflects the point of impact (15) of the beam of charged particles on the outlet window (8) in a circular fashion.
2. A linear accelerator as claimed in claim 1, characterised in that the electromagnetic device is arranged at that end of the accelerator tube (2) which faces towards the outlet window (8).
3. A linear accelerator as claimed in claim 1 or 2, characterised in that where the interval between the magnetic coils (14, 16, 18) is non-uniform relative to the axis of symmetry (6) of the accelerator tube (2), each magnetic field (25) of these three magnetic coils (14, 16, 18) is maintained at the same value in the region of the outlet window (8) by virtue of the setting of the connected voltage and/or the selection of a different coil size.
4. A linear accelerator as claimed in one of claims 1 to 3, characterised in that the magnetic coils (14, 16, 18) are electrically connected in a triangle (fig. 6).
5. A linear accelerator as claimed in one of claims 1 to 4, characterised in that the three-phase mains supply (U, V, W) is the public mains with a frequency of 50 or 60 Hz.
6. A linear accelerator as claimed in one of claims 1 to 5, characterised in that the form of the magnetic coils (14, 16, 18) is adapted to the shape of the accelerator tube (2) (fig. 2).
EP81102176A 1980-03-31 1981-03-23 Linear accelerator for charged particles Expired EP0037051B1 (en)

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DE3168429D1 (en) 1985-03-07
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JPH0356440B2 (en) 1991-08-28
EP0037051A1 (en) 1981-10-07

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