PLASMA LIGHT SOURCE
The present invention relates to a plasma light source.
In European Patent No E 1307899, granted in our name there is claimed a
light source comprising a waveguide configured to be connected to an energy source
and for receiving electromagnetic energy, and a bulb coupled to the waveguide and
containing a gas-fill that emits light when receiving the electromagnetic energy from
the waveguide, characterised in that:
(a) the waveguide comprises a body consisting essentially of a dielectric material
having a dielectric constant greater than 2, a loss tangent less than 0.01, and a DC
breakdown threshold greater than 200 kilovolts/inch, linch being 2.54cm,
(b) the wave guide is of a size and shape capable of supporting at least one electric
field maximum within the wave guide body at at least one operating equency
within the range of 0.5 to 30GHz,
(c) a cavity depends from a first side of the waveguide,
(d) the bulb is positioned in the cavity at a location where there is an electric field
maximum during operation, the gas-fill forming a light emitting plasma when
receiving microwave energy from the resonating waveguide body, and
(e) a microwave feed positioned within the waveguide body is adapted to receive
microwave energy from the energy source and is in intimate contact with the
waveguide body.
In our European Patent No 2,188,829 there is described and claimed a light
source to be powered by microwave energy, the source having:
• a body having a sealed void therein,
• a microwave-enclosing Faraday cage surrounding the body,
• the body within the Faraday cage being a resonant waveguide,
• a fill in the void of material excitable by microwave energy to form a light
emitting plasma therein, and
• an antenna arranged within the body for transmitting plasma-inducing,
microwave energy to the fill, the antenna having:
• a connection extending outside the body for coupling to a source of
microwave energy;
wherein:
• the body is a solid plasma crucible of material which is lucent for exit of light
therefrom, and
• the Faraday cage is at least partially light transmitting for light exit from the
plasma crucible,
the arrangement being such that light from a plasma in the void can pass through the
plasma crucible and radiate from it via the cage.
We refer to this as our Light Emitting Resonator or LER patent. Its main
claim as immediately above is based, as regards its prior art portion, on the disclosure
of our EP 1307899, first above.
We have filed LER improvement and modification applications published
under Nos: EP 2 399 269, EP 2 438 606, EP 2 430 647, and WO201 1073623 (the
Improvement Applications).
In our European Patent Application No 08875663.0, published under No
WO2010055275, there is described and claimed a light source comprising:
• a lucent waveguide of solid dielectric material having:
• an at least partially light transmitting Faraday cage surrounding the
waveguide, the Faraday cage being adapted for light transmission radially,
• a bulb cavity within the waveguide and the Faraday cage and
• an antenna re-entrant within the waveguide and the Faraday cage and
• a bulb having a microwave excitable fill, the bulb being received in the bulb
cavity.
We refer to this as our Clam Shell application, in that the lucent wave guide
forms a clam shell around the bulb.
As used in our LER patent, our LER Improvement Applications, our Clam
Shell application and this specification:
• "microwave" is not intended to refer to a precise frequency range. We use
"microwave" to mean the three order of magnitude range from around 300MHz to
around 300GHz;
• "lucent" means that the materia], of which an item described as lucent is
comprised, is transparent or translucent;
• "plasma crucible" means a closed body enclosing a plasma, the latter being in the
void when the void's fill is excited by microwave energy from the antenna;
• "Faraday cage" means an electrically conductive enclosure of electromagnetic
radiation, which is at least substantially impermeable to electromagnetic waves at
the operating, i.e. microwave, frequencies.
The LER patent, the Clam Shell Applications and the above LER
improvement applications have in common that they are in respect of:
A lucent waveguide plasma light source, having:
• a fabrication of solid-dielectric, lucent material, having;
• a closed void containing electro-magnetic wave, normally microwave,
excitable material; and
• a Faraday cage:
• delimiting a waveguide,
• being at least partially lucent, and normally at least partially transparent,
for light emission from it,
• normally having a non-lucent closure and
• enclosing the fabrication;
• provision for introducing plasma exciting electro-magnetic waves, normally
microwaves, into the waveguide;
the arrangement being such that on introduction of electro-magnetic waves, normally
microwaves, of a determined frequency a plasma is established in the void and light is
emitted via the Faraday cage.
In this specification, we refer to a Lucent Waveguide Plasma Light Source as a
LUWPL.
Insofar as the lucent material may be of quartz and/or may contain glass,
which materials have certain properties typical of solids and certain properties typical
of liquids and as such are referred to as super-cooled liquids, super-cooled liquids are
regarded as solids for the purposes of this specification.
In the preferred embodiment of our LER patent, the void is formed directly in
the lucent waveguide, which is generally a quartz body. This can result in problems if
the plasma causes micro-cracking of the material of the waveguide, which then
propagate through the body.
In our Clam Shell application, this problem is not present in that a quartz bulb
having the void and excitable material is provided distinct from and inserted into the
lucent wave guide. The waveguide may be formed of two halves captivating the bulb
between them or a single body having a bore in which the bulb is received.
The object of the present invention is to provide an improved LUWPL in
which the benefits of the LER patent are achieved, with a structure akin to that of the
Clam Shell application.
According to the invention there is provided a lucent waveguide plasma light
source, having:
• a fabrication of solid-dielectric, lucent material, having;
• a closed void containing electro-magnetic wave, normally microwave,
excitable material; and
• a Faraday cage:
• delimiting a waveguide,
• being at least partially lucent, and normally atleast partially transparent,
for light emission from it,
• normally having a non-lucent closure and
• enclosing the fabrication;
,• provision for introducing plasma exciting electro-magnetic waves, normally
microwaves, into the waveguide;
the arrangement being such that on introduction of electro-magnetic waves, normally
microwaves, of a determined frequency a plasma is established in the void and light is
emitted via the Faraday cage, and wherein the fabrication includes:
• a lucent waveguide body having a bore and
• a lucent tube in the bore, the tube providing the closed void and the tube
having:
• a first closed end and a second closed end and
• a fusion between the body and the tube at an orifice of the bore at or close
to the first closed end of the tube
wherein the void extends at least to the fusion between the body and the tube at the
orifice of the bore.
Preferably, the tube is formed with a swelling at the fusion between the body
and the tube, at a position to locate the tube with respect to the body.
It is envisaged that the void can extend beyond the fusion and/or the swelling
of the tube. However, it is preferred that the void extends to the fusion and/or the
swelling of the tube.
Typically, one end of the tube will be closed before insertion in the bore.
It is possible in theory for the rube to be a bulb formed as such prior to being
fused to the waveguide body. However, it is preferred that the void be closed with the
excitable material captivated therein after the tube is fused to the body.
Whilst it is envisaged that the lucent waveguide body and the lucent tube can
be of different material, preferably they are of the same material, normally quartz.
In a first embodiment of the invention, preferably:
the bore is a through-bore,
the bore in the waveguide body is bored and polished to an internal diameter such
as to receive the tube with a sliding fit,
the tube is formed with a swelling/collar at substantially the length of the bore
from the end closure,
the tube is fused to the body at both bore orifices,
the tube was fused to the body at both bore orifices prior to filling with the plasma
material and closure.
In a second embodiment of the invention, preferably:
the bore in the waveguide body is bored and polished,
an annular gap is provided between the bore and the tube,
the tube is formed with a collar at a position to locate the tube with respect to the
body,
the second closed end of the tube is free within the bore,
the bore is closed and evacuated or filled with inert gas and
the tube was fused to the body at the orifice of the bore prior to filling with the
plasma material and closure.
To help understanding of the invention, a specific embodiment thereof will
now be described by way of example and with reference to the accompanying
.drawings, in which:
Figure 1 is a cross-sectional view of a Lucent Waveguide Plasma Light Source
according to the invention; and
Figure 2 is a similar view of a plasma void tube used in manufacture of the
light source of Figure .
Figure 3 is a cross-sectional view of a Lucent Waveguide Plasma Light Source
according to the invention; and
Figure 4 is a similar view of the lucent body and two attached tubes used in
manufacture of the light source of Figure 1.
Referring to Figures 1 and 2, a LUWPL 1 has a quartz waveguide body 2
which has a short, 20mm length and has a circular, 49mm outside diameter. It has a
central, 6mm through bore 3. The bore is polished to optical smoothness, but need
not be polished to the extent of removing all possibility of micro-cracks into the body
of the quartz. The bore has orifices 4,5 at its opposite ends, opening centrally of flat,
end faces 6,7 of the body. Between these the body has a circular cylindrical periphery
8.
After boring, a drawn quartz tube 0 is inserted into the body. It is of th
same nominal size as the bore, the one being a sliding fit in the other. It has a lmm
wall thickness. At the stage of its insertion, the tube had its one end 11 closed and a
collar 12 formed by upsetting 25mm from the dome 1 of the closed end. The collar
locates the tube in the bore and it is then fused to the faces 6,7, at the orifices of the
bore, by normal glass working techniques.
The tube has an extension by which it can be evacuated and charged with
excitable material 15 and closed as a sealed void 16. This can be done in the manner
of our earlier European patent No. 1,83 1,91 6 - our sealing patent. Shown in Figure 2
are distal and proximal necks 17, 18 of the tube for first and second sealing of the tube
- after it has been fused to the body.
Included in Figure 1 are a mesh, Faraday cage 1 and an antenna 22 in a bore
23 in the body for feeding microwave energy to the light source. The Faraday cage is
closed by a solid metal support 24, to the cage is clamped. When powered with
microwaves, typically as described in our LER patent and our International patent
application No. PCT/GB20 10/00091 , resonance is established in the wave guide and
a plasma is established in the void. Light from this radiates from the void and leaves
the waveguide and the Faraday cage radially of the periphery 8.
Referring to Figures 3 and 4, a LUWPL 101 has a quartz waveguide body 2
which has a short, 20mm length and has a circular, 49mm outside diameter. It has a
central, 6mm bore 103. The bore is polished to optical clarity, but need not be
polished to the extent of removing all possibility of micro-cracks into the body of the
quartz. The bore has an orifice 104 at its end, opening centrally of flat, end face 105
of the body. The other end face 106 has a closure 107 of the bore. Between the end
faces 105, 106 of the body has a circular cylindrical periphery 108.
After making the bore 3 through the body, a 6mm internal diameter drawn
quartz tube 1 0 is fused to the face 106 and to be formed into the closure 107 as
described below. Another 4mm internal diameter drawn quartz tube 1 is sealed and
domed off at one end 1 2 and formed with an upset collar 1 4, 17mm from the
domed end. The sealed tube 111 is inserted into the bore with the collar locating the
tube at the orifice 104 of the bore in the face 106. The collar is fused to the face at the
orifice.
The body now has two tubes attached, the smaller one extending into the
central bore and the larger one extending the bore. The smaller/inner one is evacuated
and charged with excitable material 115 and closed as a sealed void 6. This can be
done in the manner of our earlier European patent No. 1,83 1,91 6 - our sealing patent.
Shown in Figure 4 are distal and proximal necks ,11 of the tube for first and
second sealing of the inner tube - after it has been fused to the body. The larger one
0 is also evacuated, evacuating the space around the inner one, and possibly filled
with nitrogen. It is sealed in the same way as the inner one, but requires only one
neck 119.
The result is that the inner quartz enclosure formed by the inner tube has its
central void filled with excitable material and surround by a narrow circular
cylindrical cavity 120, which insulates the inner tube, allowing it to run hot.
Included in Figure 3 are a mesh, Faraday cage 1 and an antenna 2 in a
bore 3 in the body for feeding microwave energy to the light source. The Faraday
cage is closed by a solid metal support 124, to the cage is clamped. When powered
with microwaves, typically as described in our LER patent and our International
patent application No. PCT/GB201 0/000 1, resonance is established in the wave
guide and a plasma is established in the void. Light from this radiates from the void
and leaves the waveguide and the Faraday cage radially of the periphery 08.
The invention is not intended to be restricted to the details of the above
described embodiments. For instance, the bore can be drilled to be blind. The cavity
120 then remains filled with air, or any ambient atmosphere in which the inner tube is
sealed, possibly a vacuum. Alternatively the bore can be a through bore and left open,
again the cavity remains air filled. Air still provides appreciable insulation between
the inner tube and the main body. Further, whilst a reader familiar with our LER
technology will recognise the dimensions of the LUWPL fabrication of the preferred
embodiments to be suitable for the TM010 mode at 2.45GHz, the invention is
applicable to other frequencies and modes, such the TE1 mode. Such a fabrication
for 2.45GHZ would be 44mm in outside diameter and 64mm long, i.e. slightly smaller
in diameter but longer. This mode has the advantage of higher Q at a higher wattage.
CLAIMS:
1. A lucent waveguide plasma light source, having:
• a fabrication of solid-dielectric, lucent material, having;
• a closed void containing electro-magnetic wave, normally microwave,
excitable material; and
• a Faraday cage:
delimiting a waveguide,
• being at least partially lucent, and normally at least partially transparent,
for light emission from it,
• normally having a non-lucent closure and
• enclosing the fabrication;
• provision for introducing plasma exciting electro-magnetic waves, normally
microwaves, into the waveguide;
the arrangement being such that on introduction of electro-magnetic waves, normally
microwaves, of a determined frequency a plasma is established in the void and light is
emitted via the Faraday cage, and wherein the fabrication includes:
• a lucent waveguide body having a bore and
• a lucent tube in the bore, the tube providing the closed void and the tube
having:
• a first closed end and a second closed end and
• a fusion between the body and the tube at an orifice of the bore at or close
to the first closed end of the tube
wherein the void extends at least to the fusion between the body and the tube at the
orifice of the bore.
2. A LUWPL as claimed in claim 1, wherein the tube is formed with a swelling at
the fusion between the body and the tube.
3. A LUWPL as claimed in claim 1 or claim 2, wherein the void extends beyond the
fusion and/or the swelling of the tube.
4. A LUWPL as claimed in claim 1, claim 2 or claim 3, wherein the second closed
end of the tube is free within the bore.
5 . A LUWPL as claimed in claim , claim 2 or claim 3, wherein the tube has a
second fusion between the body and the tube at an other orifice of the bore, the bore
having been a through-bore.
6. A LUWPL as claimed in any preceding claim, wherein the bore in the waveguide
body is bored and polished to an internal diameter such as to receive the tube with a
sliding fit.
7. A LUWPL as claimed in any one of claims 1 to 5, wherein an annular gap is
provided between the bore and the tube.
8. A LUWPL as claimed in claim 7, wherein the bore is evacuated.
9. A LUWPL as claimed in claim 7 or claim 8, wherein the bore is filled with inert
gas.
10. A LUWPL as claimed in any one of claims 1 to 6, wherein the bore is open at at
least one end.
11. A LUWPL as claimed in any preceding claim, wherein the lucent waveguide body
and the lucent tube are of the same material.
12. A LUWPL as claimed in claims 1 to 10, wherein the lucent waveguide body and
the lucent tube are of different materials.
13. A LUWPL as claimed in any preceding claim, wherein at least one of the lucent
waveguide body and the lucent tube is of quartz.
14. A method of making a fabrication for a LUWPL, the method consisting in the
steps of:
• providing the lucent waveguide body with a bore;
• closing an end of the lucent tube;
• inserting the lucent tube into the bore in the body;
• fusing the tube to the body at a first orifice of the bore;
• charging the tube with the excitable material; and
• closing the other end of the tube.
15. A method of making a LUWPL as claimed in claim 14, wherein at least one end
of the tube is closed before insertion of the tube into in the bore.
16. A method of making a LUWPL as claimed in claim 14 or claim 15, further
consisting of the step of forming a swelling in the tube at a position to locate tube
with respect to the body.
1 . A method of making a LUWPL as claimed in claim , claim 5 or claim 16,
further consisting of the step of fusing the tube to the body at a second orifice of the
bore.
18. A method of making a LUWPL as claimed in any one of claims 14 to 17, wherein
the lucent tube is inserted into the bore and fused to the body of the waveguide at at
least the first orifice of the bore prior to charging the tube with the excitable material
and closing the tube.
19. A method of making a LUWPL as claimed in any one of claims 4 to 17, wherein
the lucent tube is inserted into the bore and fused to the body of the waveguide at at
least the first orifice of the bore after charging the tube with the excitable material and
closing the tube.
20. A method of making a LUWPL as claimed in any one of claims 4 to 19, further
consisting of the steps of:
• evacuating the bore, and
• closing the bore.
. A method of making a LUWPL as claimed in claim 20, further consisting of the
step of filling the bore with an inert gas before closing the bore.
22. A fabrication for a LUWPL of solid-dielectric, lucent material, the fabrication
having:
• a closed void containing electro-magnetic wave, normally microwave,
excitable material
wherein the fabrication includes:
• a lucent waveguide body having a bore and
• a lucent tube in the bore, the tube providing the closed void and the tube
having:
• a first closed end and a second closed end and
• a fusion between the body and the tube at an orifice of the bore at or close
to the first closed end of the tube
and wherein the void extends at least to the fusion between the body and the tube at
the orifice of the bore.