GB2136197A

GB2136197A - Improvements in or relating to gyrotron devices

Info

Publication number: GB2136197A
Application number: GB08307510A
Authority: GB
Inventors: Maurice Esterson; Arnold Hugh William Beck
Original assignee: English Electric Valve Co Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1983-03-03
Filing date: 1983-03-18
Publication date: 1984-09-12
Also published as: GB8307510D0; GB2136197B

Abstract

A gyrotron device is provided in which electromagnetic energy generated in the resonant interaction cavity 4 thereof is conducted out of said cavity by a path which is separate from the collector 5 provided to collect residual beam electrons. As shown, said path comprises a waveguide 13 extending parallel to the axis of the cavity 4, and coupled thereto by means of a coupling slot 14, and tapers 6 and 11 are provided at the beam entrance and exit of the cavity 4 to inhibit the passage of generated electro-magnetic energy towards the collector 5 and the magnetron gun 8. Variable short circuit 16 permits adjustment of the power level transmitted to output window 15. <IMAGE>

Description

SPECIFICATION Improvements in or relating to gyrotron devices This invention relates to gyrotron devices, that is to say devices in which an annular electron beam is caused to interact with the electromagnetic field generated in an interaction cavity which is resonant at the cyclotron frequency, or integral fractions thereof, of an applied axial magnetic field whereby a net transfer of energy occurs from said electrons to said generated electro-magnetic field. This transfer is enhanced by a relativistic change in mass of the electrons in said beam.

Referring to Figure 1, a cylindrical magnetron injection gun (not shown) is arranged to project an annular beam of electrons along the axis 1, in the direction of arrow 2, through a tapering drift tube section 3 which opens out into a cylindrical resonant cavity 4, through which said beam also passes. Cavity 4 opens out into an output waveguide 5 which is constructed to act also as a collector. At the end of output waveguide 5 remote from cavity 4 is an output window (not shown). Energy reflecting tapers 6 and 7 are provided respectively at the entrance and exit of cavity 4.

In operation, the annular electron beam from the gun (not shown) is accelerated by an electric field into the drift tube 3, and focussed by a magnetic field which is increased in the direction of the axis 1 in the region of the drift tube 3. The diameter of the annular beam decreases and the annular velocity of rotation of the electrons about their drift paths increases as the electrons flow along the drift tube 3.

The axial magnetic field through the cavity 4 is adjusted so that the cyclotron frequency (or an integral fraction thereof) is close to a resonant frequency of the cavity. The rotating electrons entering cavity 4 from the drift tube 3 interact with the-transverse electric field in the cavity and enhanced by the relativistic change in mass of the electrons, there is a net transfer of energy from the electrons to the electromagnetic field generated in the cavity 4.

Taper 6 at the entrance to cavity 4 is designed to provide complete reflection of the electromagnetic energy generated in the cavity 4 whilst taper 7 is designed to provide partial reflection of such energy. Thus most of the electro-magnetic energy generated in the cavity is coupled into the output guide 5 from whence it transmitted via the aforementioned microwave window (not shown).

As has already been mentioned, output guide 5 acts as a collector. In the region of the output guide 5 the strength of the axial magnetic field is arranged to decrease gradually so that the annular electron beam diverges along the length of the guide 5 to contact the wall thereof thus dissipating residual beam energy.

With a gyrotron device as described above, the output waveguide has to transmit electromagnetic energy as output to the waveguide window and to act as an electron collector. The higher the frequency of operation, the smaller in diameter will the output waveguide normally be.

However, the smaller the diameter of the output waveguide the less internal surface area is there available for electron collection and this limits the output power of the device.

One object of the present invention is to provide an improved gyrotron device in which the above difficulty is mitigated.

According to this invention in its broadest aspect, a gyrotron device is provided which means are provided for conducting jutput electromagnetic energy out of the resonant interaction cavity of said device via a path which is separate from means for collecting residual beam electrons exiting from said cavity.

According to a preferred feature of this invention a gyrotron device comprises electron collector means in the path of beam electrons exiting from the resonant interaction cavity of said device, means for inhibiting the passage of generated electro-magnetic energy out of such cavity in the direction of beam electrons towards said collector, and means for conducting said energy out of said cavity via a path separate from said collector means.

Normally as known per se means are also provided for inhibiting the passage of generated electro-magnetic energy out of said cavity in a direction contra to that of said beam electrons towards said collector means. Preferably said inhibiting means comprises, in each case, a taper, but other inhibiting means may be used for example a short length of cut-off waveguide.

Preferably said means for conducting said energy out of said cavity comprises a waveguide coupled to said cavity by an aperture.

Preferably said aperture is a slot having its height extending parallel to the axis of said cavity.

There may be more than one such coupling apertures, but preferably not more than two, spaced circumferentially one from another.

Preferably the, or each, aperture is of electrical length between said cavity and said waveguide at least substantially equal to A/2 or an integral multiple thereof where 1 is the wavelength at the frequency of the electro-magnetic energy desired to be derived as output from said cavity.

Preferably said last mentioned waveguide for conducting said energy out of said cavity is extensive in a direction parallel to the axis of said cavity and is closed at its end remote from said coupling aperture or apertures by a waveguide window.

Preferably again at the end of said waveguide adjacent to said coupling aperture or apertures is provided variable short circuiting means operative to adjust the level of power transmitted in the opposite direction towards the end of said waveguide remote from said coupling aperture or apertures.

The invention is further described with reference to Figure 2 of the accompanying drawings which represents a longitudinal section through one gyrotron device in accordance with the present invention. Like references are used in Figure 2 for like parts in Figure 1.

Referring to Figure 2, the gyrotron device consists of a magnetron injection gun 8 with its associated gun magnet 9. Gun 8 projects, in operation, an annular beam of electrons along the axis 1 in the direction of arrow 2.

Positioned in the path of said electron beam is a tapering drift tube section 3 which opens into a cylindrical resonant interaction cavity 4, through which said beam also passes. Cavity 4 in turn opens into a waveguide section 5 which, as previously, is constructed to form a collector.

At the entrance to cavity 4 is an energy reflecting taper 6 which corresponds to energy reflecting taper 6 of Figure 1. At the exit from cavity 4 is another energy reflecting taper 11 which differs from energy reflecting taper 7 of Figure 1 in that it is reflective in the opposite direction so that electro-magnetic energy generated within cavity 4 is inhibited from passing out of the cavity in the direction of the axis 1 towards waveguide section 5.

Provided to generate the required magnetic field in the region of tapered drift tube 3 and cavity 4 is a cryostat and super conducting magnet 12.

As has already been described with reference to Figure 1 the axial magnetic field provided is increased in the direction of axis 1 in the region of the drift tube 3 so that, with the effects of the tapering of the drift tube 3, the diameter of the annular beam decreases and the annular velocity of rotation of the electrons about their drift paths increases as the electrons flow along the drift tube 3.

Again as has already been described, the resonant frequency of the cavity 4 is close to the cyclotron frequency of the axial magnetic field therethrough and the rotating electrons entering cavity 4 from the drift tube 3 interact with the transverse electric field in the cavity. Enhanced by the relativistic change in mass of the electrons, there is a net transfer of energy from the electrons to the electro-magnetic field generated in the cavity to produce electro-magnetic energy.

Taper 6 at the entrance to cavity 4 and taper 11 at the exit to cavity 4 both act to inhibit the passage of electro-magnetic energy out of said cavity, in the one case in a direction contra to that of said beam electrons entering the cavity 4 and in the other in the direction of beam electrons exiting said cavity towards said collector waveguide 5.

Provided to conduct out of said cavity electro magnetic energy generated in said cavity and otherwise trapped therein by the tapers 6 and 11, is a waveguide 1 3. Waveguide 13 is coupled to cavity 4 by a coupling slot 14 having its height extending in a direction parallel to the axis 1. The electrical length of coupling slot 14 between cavity 4 and waveguide 13, in this example, is effectively equal to A/2 where A is the wavelength at the frequency of the electro-magnetic energy desired to be derived as output from the cavity 4.

At one end of waveguide 13, i.e. the end remote from coupling slot 14, is a dielectric coupling window 1 5. At the other end of waveguide 1 3, i.e. the end adjacent to coupling slot 14, is a variable short circuiting device 16, as known per se, operative to adjust the level of power transmitted in the opposite direction, towards said window 1 5.

It will be noted that the means for conducting output electro-magnetic energy out of cavity 4, i.e.

waveguide 13, is entirely separate from waveguide 5 into which residual beam electrons pass. The waveguide 5 does not require to terminate in a waveguide window and is in fact closed at its end remote from cavity 4 in the fashion of a classical collector. The collector end of waveguide 5 is housed in a water jacket 1 7 so as to be water-cooled in operation. The water jacket 1 7 and waveguide 5 are insulated from the main body of the gyrotron by means of an insulator 1 8.

Claims

1. A gyrotron device in which means are provided for conducting output electro-magnetic energy out of the resonant interaction cavity of said device via a path which is separate from means for collecting residual beam electrons exiting from said cavity.

2. A gyrotron device comprising electron collector means in the path of beam electrons exiting from the resonant interaction cavity of said device, means for inhibiting the passage of generated electro-magnetic energy out of such cavity in the direction of beam electrons towards said collector, and means for conducting said energy out of said cavity via a path separate from said collector means.

3. A device as claimed in claim 1 and wherein means are also provided for inhibiting the passage of generated electro-magnetic energy out of said cavity in a direction contra to that of said beam electrons towards said collector means.

4. A device as claimed in claim 2 or 3 and wherein said inhibiting means comprises a taper.

5. A device as claimed in claim 2 or 3 and wherein said inhibiting means comprises a short length of cut-off waveguide.

6. A device as claimed in any of the above claims and wherein said hollow member comprises a waveguide coupled to said cavity by an aperture.

6. A device as claimed in any of the above claims and wherein said means for conducting said energy out of said cavity comprises a waveguide coupled to said cavity by an aperture.

7. A device as claimed in claim 6 and wherein said aperture is a slot having its height extending parallel to the axis of said cavity.

8. A device as claimed in claim 6 or 7 and wherein there are two coupling apertures spaced circumferentially one from the other around the cavity wall.

9. A device as claimed in any of claims 6 to 8 and wherein the, or each, aperture is of electrical length between said cavity and said waveguide at least substantially equal to A/2 or an integral multiple thereof, where A is the wavelength at the frequency of the electro-magnetic energy desired to be derived as output from said cavity.

10. A device as claimed in any of claims 6 to 9 and wherein said last mentioned waveguide for conducting said energy out of said cavity is extensive in a direction parallel to the axis of said cavity and is closed at its end remote from said coupling aperture or apertures by a waveguide window.

11. A device as claimed in any of claims 6 to 1 and wherein at the end of said waveguide adjacent to said coupling aperture or apertures is provided variable short circuiting means operative to adjust the level of power transmitted in the opposite direction towards the end of said waveguide remote from said coupling aperture or apertures.

1 2. A gyrotron device substantially as herein described with reference to Figure 2 of the accompanying drawings.

New claims or amendments to claims filed on 28.6.1983 Superseded claims 1,2 and 6 New or amended claims:

1. A gyrotron device in which means are provided for conducting output electro-magnetic energy out of the resonant interaction cavity of said device via a path which is separate from means for collecting residual beam electrons exiting from said cavity said path comprising a hollow electromagnetic wave supporting member extending alongside said cavity and coupled thereto by at least one coupling aperture.

2. A gyrotron device comprising electron collector means in the path of beam electrons existing from the resonant interaction cavity of said device, means for inhibiting the passage of generated electromagnetic energy out of such cavity in the direction of beam electrons towards said collector, and means for conducting said energy out of said cavity via a path separate from said collector means said path comprising a hollow electromagnetic wave supporting member extending alongside said cavity and coupled thereto by at least one coupling aperture.