FR2586139A1 - ION DIODE WITH MAGNETIC MIRROR - Google Patents

Abstract

MAGNETIC MIRROR DIODE. THE DIODE INCLUDES AN ANODE 20, A CATHODE 22 AND A WINDING 24 CREATING, BEHIND THE ANODE, A DIVERGENT MAGNETIC FIELD. THE ELECTRONS WHICH CROSS THE ANODE ARE PUSHED TOWARDS THE ANODE. APPLICATION AS A SOURCE OF IONS.

Description

ION DIODE WITH MAGNETIC MIRROR

  The present invention relates to a magnetic mirror ion diode. It finds many applications in particular as an ion source and as a means of depositing high density energy on a substrate to create dense and hot plasmas as is sought in physics and in particular in

  thermonuclear fusion studies.

  To generate the high intensity ion beams required for inertial fusion, many laboratories around the world have designed and developed ion diodes. The design of these devices is

  always guided by the fundamental problem of eliminating

  nation of the electron current, which is inevitable-

  present with an intensity still much greater (10 to 100 times) than the current of ions. This problem is very important since it conditions the

  energy efficiency of the device.

  There are two ways to remove the

  electron beam in an ion diode:

  1) by applying a magnetic field in the diode

  perpendicular to the accelerating electric field.

  which curves the electronic trajectories to

  prohibit the electrons from crossing the

  accelerator, 2) by making a diode which has a very thin anode with an electric mirror placed at

  the rear, which creates a "reflex" structure in the-

  which electrons oscillate a very large number of times on both sides of the anode before being stopped

in this one.

  These two solutions are described in an article

  synthesis paper by S. HUMPHRIES entitled "Intense Pulsed Ion Beams for Fusion Application" published in the

  Nuclear Fusion review, vol.20, n 12, (1980) pp 1549-

  1572. Many diodes exploit the first principle. But the present invention retains the second and utitise a device "reflex". An ion diode according to this known principle is shown in FIG. 1. It comprises an anode 10 in the form of a claw, a

  first cathode 11 disposed in front of the anode and a second

  conde cathode 12 disposed behind the anode. Its function

  The following is the next. The electrons e extracted from the cathode 11 are accelerated by the electric field present between the anode and the cathode and are directed towards the anode 10 through which they pass. They are decelerated by the electric field behind the anode (which is symmetrical with the accelerator field). The second

  cathode thus behaves like an electric "mirror".

  The electrons turn back and head again

  calf to the anode that crosses in the opposite direction.

  They are again decelerated and the process is

  follows until complete absorption by the anode. It forms around this a plasma 14 that generates

  ions 1, which are accelerated, cross the

  of 11 and are then directed to a cibte.

  Such a device has many disadvantages

  The ion current is emitted in fact by the two faces of the anode and as it can only be used on one side. The efficiency of the diode is divided by 2. diode does not permit focussing of the ion beam, - the electric "mirror" formed by the second cathode is subject to cleavages which, in practice,

  make the system difficult to use.

  The device according to the invention avoids these

  disadvantages thanks to the use of a "mirror"

  gnetic which: - is not subject to breakdowns, - makes it possible not to have an electric field behind the anode and thus to accelerate the ions only on one side, - allows a quasi-spherical configuration

  which makes it possible to focus the ion beam.

  More precisely, this magnetic mirror is obtained by a winding traversed by a current,

  this winding being coaxial with the anode and the cathode

  of. It is placed behind the anode, instead of

  the second negative electrode of the prior devices

laughing.

  In any case, the invention will be better

  taken from the description which follows, of a

  example given for explanatory purposes and no

  limiting effect. This description refers to

  attached drawings in which: - Figure 1, already described, shows a diode according to the prior art, - Figure 2 shows, in section, a diode

according to the invention.

  The device represented in FIG.

  takes an anode 20 brought to a high positive voltage + V delivered by a source 21, a cathode 22 connected to

  the mass, and behind the anode, a coiled coil 24

  xial at the anode and the cathode. This winding is supplied with current by a generator 26. The lines of

  Magnetic field are referenced 28. They are strong-

  diverging towards the anode (or convergent

  if you consider the opposite direction). In addition

  very terms the field is strongly non-homogeneous.

  It will be observed that the anode and the cathode pre-

  feel like spherical caps whose concave

  is directed to a target 30. In this way,

  the ion beam 32 has a certain focus

  tion. The operation of this device is as follows. The portion between the anode and the cathode operates as in the prior art. Electrons

  are extracted from the cathode, are accelerated in the

  internode, fall on the anode and pass through

  feels. These electrons are then subjected to the magnetic field

  of the coil 24. Their trajectories are

  slow around the field lines and lie down towards

  the axis of the diode. The electrons end up rebrous-

  be sure to fall back on the anode and cross it again.

  The interelectrode electric field decelerates them first, makes them turn back again and then accelerates them again towards the anode that they cross again. The magnetic field bends their trajectories again to finally direct them back to the anode, etc. The electrons oscillate a large number of times around the anode. At each pass, they give energy to the anode, which helps to create a plasma around it. The ions are extracted from this

  plasma and accelerated forward by the electric field.

  than interelectrode. Since there is no elec-

  at the rear of the anode, only an ion beam

  32 is emitted forward towards the target 30.

  The presence of electrons in the vicinity of the anode creates, in the vicinity of the anode, a charge

  of negative space that compensates for the posi-

  of the ion beam, itself responsible for the

  current limitation. This effect is therefore beneficial.

  The electric field between the anode and the cathode is as large as 200 kV / cm at 2 MV / cm. He is

continuous or impulsive.

  In an alternative embodiment, the cathode 22 is a gate and a heated filament 33 is used in connection with a current source 34. The electrons from the filament 33 diffuse to the gate 22, then enter the interelectrode space o they are accelerated. The process is then the same as that described above. Various embodiments are possible for the anode and the cathode. They can be gastight and thus delimit watertight chambers.

  there are reduced gas pressures (a few torr).

  But they can also be realized in the form of

metal grilles.

  Moreover, the anode may include in its

  mass or in the form of a superficial layer, the species

  these atoms must constitute the ion beam.

Claims (7)

  An ion diode comprising an anode (20) and a cathode (22) and means (21) for creating between   they have an electric field, the cathode (22) being sufficient   the ion which has been accelerated by this field, this diode further comprising a means located behind the anode for repelling the electrons which, coming from the cathode, have passed through the anode, characterized in that this middle east   constituted by a winding (24) traversed by a neck   rant and creating a magnetic field (28) strongly   extending towards the anode (22), this winding (24), the anode (20) and the cathode (22) having a same axis of symmetry.   2. Ion diode according to claim 1, characterized in that the anode (20) and the cathode (22) are spherical caps having a concavity turned away from the coil (24) towards a target ( 30) where the ions are directed in beam form focused.   3. Ion diode according to claim 1, characterized in that it further comprises a   heated electro-emissive filament (33) disposed proximate mity of the cathode (22).   4. An ion diode according to claim 1,   characterized in that the anode (20) and the cathode (22) are gastight and delimit chambers   leakproof o have reduced gas pressures.   5. Ion diode according to Claim 1, characterized in that the anode (20) and the cathode (22) are metal grids.   The ion diode according to claim 1,   characterized in that the anode (20) has in its mass or in the form of a superficial layer, the   atomic species to be the ion beam.   7. Ion diode according to claim 5, characterized in that is maintained in space   between the anode and the winding, a pressure con-   venable of a gas including the atomic species ahead constitute the ion beam.