Patent Application
20140010958
The invention relates to a device for producing solid hydrogen and/or deuterium targets continuously and at cryogenic temperatures.
Recent progress made by high-power lasers enables use of the latter to be envisaged in several fields, in particular in fields using a proton beam. For example, protontherapy is a particular radiotherapy technique the aim of which is to destroy cancerous cells by irradiating them with a proton beam.
The protons can be accelerated by focusing a high-intensity pulsed laser on a target comprising pure solid hydrogen and/or deuterium, at a frequency of about 10 Hz.
It is therefore interesting to provide a system continuously producing a solid hydrogen and/or deuterium film having a small thickness (1 to 10 μm), deposited on a gold or aluminium strip. By using this type of strip, the protons, mainly originating from the solid hydrogen and/or deuterium film, can be accelerated by the intense electric field generated by interaction of an intense laser with the gold or aluminium strip.
Formation of solid hydrogen and/or deuterium films is generally performed on gold or silver foil sheets. The article [“Experimental setup for X-ray spectroscopy of muonic atoms formed from implanted ions in solid hydrogen”—P. Strasser and al. —Nuclear Instruments and Methods in Physics Research A, 460 (2001), pp. 451-456] describes an X-ray spectrometer emitted by muonic atoms. In this device, the muonic atoms are generated by ion implantation in a solid hydrogen film. The spectrometer comprises a cryogenic chamber comprising a support of a silver strip and a diffuser of a gas mixture having a hydrogen and deuterium base. The pressure and volume of the gas mixture inlet to the diffuser produce a dosed distribution of the gas mixture on the silver strip. Maintaining the silver strip at a temperature of 3 K and dosed distribution of the hydrogen and deuterium gas mixture thereby enable formation of a solid hydrogen film on the silver strip.
Interaction of a laser with solid targets can be used in other fields, for example in extreme ultraviolet lithography (13.5 nm wavelength). In the article [“Laser-Plasma Extreme Ultraviolet Source Incorporating a Cryogenic Xe Target”—S. Amano—Recent Advances in Nanofabrication Techniques and Applications, December (2011), pp. 353-368], Laser-Produced Plasma (LPP) constitutes the source of the extreme ultraviolet beam. This article describes a device using Xe as solid target for creation of the LPP plasma. Indeed, Xe enables a strong emission around 13.5 nm. In addition, as Xe is an inert gas, it prevents deposition of residues. The device comprises a cylindrical copper drum filled with liquid nitrogen designed to cool the outer surface of the drum. The Xe in gas phase is then injected onto the outer surface of the cylindrical drum in rotation. The Xe in gas phase thus condenses to form a solid film of Xe with a thickness ranging from 300 to 500
In certain applications, a requirement exists to provide a device for continuous deposition of a solid hydrogen and/or deuterium film on a strip that is easy to produce and to use.
This requirement tends to be satisfied by providing a device for performing continuous deposition of a film of solid hydrogen or deuterium, or of a mixture of the two, comprising:
A method is also provided for continuous deposition of a solid hydrogen or deuterium film comprising the following steps:
Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given for non-restrictive example purposes only and represented in the appended drawings, in which:
As represented in
Device 1 also comprises a strip 6 on which a solid film of hydrogen and/or deuterium is advantageously deposited in continuous manner. Strip 6 is a metal strip and it is preferably gold- or aluminium-based. What is meant by continuous deposition of a film on strip 6 in cell 2 is that device 1 enables a film to be deposited on strip 6 whereas it is moving inside cell 2. Strip 6 is passing through the cell 2 via first 3 and second 4 openings. Furthermore, strip 6 is configured to move in cell 2 from the first opening to the second opening. This movement does not exclude provisional stopping of strip 6 being performed in cell 2.
Device 1 further comprises movement means 7 configured to perform movement of strip 6 in cell 2 from first opening 3 to second opening 4. Movement means 7 can comprise a first fixed reel 7a and a second fixed reel 7b around which strip 6 can be wound. First reel 7a can be located at the level of first opening 3. Second reel 7b can thus be located at the level of second opening 4 so that cell 2 is arranged between first reel 7a and second reel 7b. The location of first 7a and second 7b reels is chosen so as to be able to move strip 6 in cell 2. Movement means 7 can comprise a motor 7m designed to make second reel 7b rotate around its axis so as to unwind strip 6 from first reel 7a and to wind it around second reel 7b. Advantageously, motor 7m also enables first reel 7a to rotate and to perform movement of strip 6 in the opposite direction, i.e. from second opening 4 to first opening 3. Another motor can also be associated with first reel 7a.
In general manner, condensation of a gas at cryogenic temperatures requires precise adjustment of the pressure and temperature of the gas that is to be condensed. However, depending on the configuration of cell 2, control valve 5r cannot on its own maintain a constant pressure of the gas inlet to cell 2. The gas inlet via opening 5 can in fact escape from cell 2 through first and second openings 3 and 4. For this reason, to adjust the pressure of the gas to be condensed, device 1 further comprises a pumping device 8 configured to place a volume 9 of cell 2 at a first pressure P1. Said volume 9 is defined in cell 2 and strip 6 runs through the latter.
The pumping device can comprise one or more pumps 8a and a sealed chamber 8b containing cell 2 and strip 6. Pumping device 8 further enables any parasitic condensation of the gas outside said volume 9 to be prevented, by sucking the gas escaping from cell 2.
Cell 2 also comprises a first heat exchanger 10 configured to maintain strip 6 in said volume 9 of the cell at a first cryogenic temperature T1. What is meant by cryogenic temperatures are temperatures lower than about 120 K. First heat exchanger 10 is preferably located in the walls of cell 2 so as to be in contact with the molecules of the gas inlet to cell 2. For simplification reasons, in the remainder of the text, first heat exchanger 10 will also designate the part of cell 2 defining said volume 9 of the cell. The contact between the molecules of the gas and first heat exchanger 10 enables the temperature of the gas comprised in said volume 9 to be easily adjusted. Heat exchanger 10 is preferably controlled by a thermostat. On account of the molecular heat exchange phenomenon between gas and strip 6, heat exchanger 10 thus enables strip 6 and the gas inlet to said volume 9 of the cell to be maintained at the first cryogenic temperature T1. For continuous deposition of a solid hydrogen film on strip 6, the inlet gas is a hydrogen gas and the first temperature T1 is preferably equal to 7 K. For continuous deposition of a solid deuterium film on strip 6, the inlet gas is a deuterium gas and the first temperature T1 is preferably equal to 12 K.
Device 1 is able to define the temperature of the gas and of strip 6 in cell 2 by means of first heat exchanger 10. In order to also define the pressure, device 1 comprises a control circuit of pumping device 8 and of control valve 5r. Said control circuit is configured to adjust the first pressure P1 to a value P1c. The pressure value P1c is higher than the value of the saturated steam pressure Ps of the material to be deposited, at the first cryogenic temperature T1. This adjustment of the first pressure P1, is performed so as to respectively condense a solid film of hydrogen or deuterium or of a mixture of the two, on strip 6 in movement in said volume 9 of the cell. Advantageously, adjustment of the first pressure P1 by the control circuit also depends on the speed of movement of strip 6 in said volume 9 of the cell and on the thickness of the solid film that is to be condensed on strip 6.
Device 1 enables a film of solid hydrogen or deuterium to be deposited on a moving metal strip. The metal strip can then be bombarded by a laser beam, preferably a pulsed laser beam, thereby generating a proton beam due to the interaction of the laser with the metal strip. In order to generate the proton beam, the laser interacts directly with the metal strip to generate a gold or aluminium plasma with a high electronic density. The solid hydrogen or deuterium film is thus preferably arranged on one of the two main surfaces of the strip only. The laser then bombards the surface devoid of a solid hydrogen and/or deuterium film. The intense electric field generated by the metal laser interaction enables protons located at the level of the surface of the strip comprising the solid hydrogen and/or deuterium film to be accelerated.
Device 1 according to the first embodiment enables a solid film of hydrogen and/or deuterium to be condensed on the two main surfaces of strip 6 in said volume 9 of cell 2. Consequently, to prepare strip 6 for a possible interaction with a laser beam, device 1 can comprise means designed to eliminate the condensed film on one of the two main surfaces of strip 6. For example purposes, device 1 can comprise a scraper, not represented in
Continuous deposition of a film of solid hydrogen or deuterium on a metal strip facilitates continuous generation of a proton beam. In advantageous manner the device can be configured so that the speed of movement of strip 6 is chosen according to the frequency of the pulsed laser bombarding strip 6. For example purposes, by using first 7a and second 7b reels which have a diameter of 40 mm, and a speed of movement of strip 6 of 5 mm/s, device 1 enables continuous production, during 24 hours, of a strip comprising a solid hydrogen film with a thickness of about 5 μm.
First heat exchanger 10 is preferably configured to be in contact with a main first surface 6a of strip 6. For example purposes, the elements enabling heat transfer with first heat exchanger 10 can be arranged salient with respect to the walls of cell 2 so as to be in contact with strip 6 when the latter passes through cell 2. The contact between first heat exchanger 10 and strip 6 enables a direct heat transfer to be performed between these two elements. Definition of the temperature of strip 6 is thereby more precise and the heat transfer is faster in comparison with a heat transfer performed by means of the hydrogen or deuterium gas comprised between first heat exchanger 10 and strip 6. Furthermore, first heat exchanger 10 also enables a heat transfer to be performed to the molecules of the gas contained in said volume 9.
According to a second embodiment illustrated in
Device 1 for performing continuous deposition according to this embodiment enables an efficient heat transfer to be achieved between first heat exchanger 10 and strip 6. Device 1 further enables a solid hydrogen and/or deuterium film to be deposited on main surface 6a of metal strip 6, leaving the opposite surface 6b of strip 6, designed to interact with a laser beam, uncovered.
In advantageous manner, movement means 7 are mechanically connected to a fixed support 7s by means of at least one spring 7r so as to fix the tension of strip 6, and the contact pressure between the strip 6 and first heat exchanger 10 in said volume 9 of the cell. Spring 7r can thus adjust a contact pressure between the strip 6 and inner wall 10p of first heat exchanger 10, which enables the heat transfer from the heat exchanger to strip 6 to be improved. Spring 7r also makes it possible to maintain a fixed tension of strip 6 during movement of the latter in cell 2, in particular when it is wound and unwound around reels 7a and 7b. In other words, the device 1 comprises at least one spring 7r mechanically connected to a fixed support 7s so as to fix the tension of the strip 6 and the contact pressure of the strip on the first heat exchanger 10 in said volume 9 of the cell 2. Maintaining a selected tension then makes it possible to avoid excessive stretching of strip 6 able to be the cause of deformation or even worse to result in breaking of metal strip 6.
In order to take account of a possible interaction between a laser beam and opposite surface 6b of strip 6, device 1 advantageously comprises a tightly sealed cryostat 15 inside which cell 2 and strip 6 are located. Cryostat 15 is shaped in such a way as to comprise a first window 16 configured to let an incident laser beam bombarding strip 6 pass, and a second window 17 configured to let the proton or neutron beam transmitted by strip 6 pass. For example, first window 16 can Sapphire-based and second window 17 can be Mylar-based. To achieve an efficient interaction between laser beam and strip 6 only, cryostat 15 also comprises an additional pump 18 configured to create a vacuum in the tightly sealed cryostat 15. The vacuum created within the cryostat prevents any parasitic condensation of the gas on opposite surface 6b of level strip 6 that might disturb interaction of the laser with metal strip 6.
For an improved thermal insulation between cell 2 and movement means 7, device 1 can comprise a heat shield fitted between these two elements. In other words, device 1 advantageously comprises a heat shield 19 separating movement means 7 and cell 2. Movement means 7 do in fact comprise mechanical parts maintained at 300 K which generate heat inputs by radiation. In the absence of a heat shield, these heat inputs may disturb the thermal stability of cell 2, and thereby condensation of the gas on strip 6. Preferably, the device 1 comprises a heat shield covering the cell 2, and comprising two apertures facing respectively the first and second openings. The said apertures configured to let the strip moving through the cell 2 via the first and second openings.
In advantageous manner, cell 2 comprises an upstream duct 21 arranged between first opening 3 and first heat exchanger 10 and extending along a longitudinal axis 21a. Upstream duct 21 is shaped in such a way that strip 6 passes through the duct when movement of the latter takes place in cell 2. Strip 6 thus respectively passes through first opening 3, upstream duct 21, and then first heat exchanger 10 when strip 6 moves in cell 2 from first opening 3 to second opening 4. Strip 6 preferably passes through upstream duct 21 in a direction that is identical to longitudinal axis 21a. Upstream duct 21 is connected to said volume 9 of the cell so as to form a first outlet opening 27 of the non-condensed gas on strip 6. In advantageous manner, cell 2 also comprises a second heat exchanger 22 preferably located in the walls of upstream duct 21. Second heat exchanger 22 is configured to keep strip 6 in upstream duct 21 at a second temperature T2 that is higher than first temperature T1. Second temperature T2 is fixed so as to maintain the hydrogen or deuterium gas, inlet to cell 2, in gas phase in upstream duct 21.
Upstream duct 21 enables strip 6 to be thermally prepared before passing into said volume 9 of the cell. Strip 6 is in fact initially wound around first and second reels 7a and 7b, which operate at a higher temperature, for example at a temperature close to the ambient temperature (about 300 K). Second heat exchanger 22 of upstream duct 21 enables the temperature of strip 6 to be lowered and maintained at second temperature T2, preferably close to first temperature T1. Upstream duct 21 thus enables first heat exchanger 10 to maintain the temperature of strip 6 in said volume 9 in rapid and precise manner, which improves the efficiency of condensation of the solid hydrogen and/or deuterium on strip 6.
In preferential manner, movement means 7 are configured for strip 6 to be devoid of contact with second heat exchanger 22 in upstream duct 21. Strip 6 being in contact with first heat exchanger 10, this arrangement enables any additional friction between strip 6 and cell 2 to be prevented. Indeed, repetitive friction may result in wear and mechanical fatigue of metal strip 6. The heat transfer between second heat exchanger 22 and strip 6 is then performed by molecular heat exchange. The latter is performed using flow of the non-condensed hydrogen and/or deuterium gas from first outlet opening 27 to first opening 3, via upstream duct 21. This gas flow is made possible by means of pumping device 8 which participates in regulating the pressure of the gas to be condensed in cell 2 and in particular in said volume 9 of the cell. To achieve a better control of this pressure, pumping device 8 advantageously comprises a first pump 23 configured to perform suction of the non-condensed excess gas flowing in upstream duct 21 downstream from second heat exchanger 22. First pump 23 is preferably arranged between first opening 3 and second heat exchanger 22. First pump 23 is connected to upstream duct 21 via one or more openings formed in an area of the inner walls of upstream duct 21. In advantageous manner, said area of the inner walls is formed by chicanes, thereby improving the aerodynamics of the gas when the latter is sucked in by first pump 23.
Cell 2 advantageously comprises a similar downstream duct 24 to upstream duct 21. Downstream duct 24 is arranged between first heat exchanger 10 and second opening 4, and it is formed in such a way that strip 6 passes through the latter when movement of the strip takes place in cell 2. Downstream duct 24 is connected to said volume 9 of the cell so as to form a second outlet opening 28 of the non-condensed gas on strip 6. In advantageous manner, cell 2 also comprises a third heat exchanger 25, preferably arranged in the walls of downstream duct 24. Third heat exchanger 25 is configured to maintain strip 6 in downstream duct 24 at a third temperature T3 that is higher than first temperature T1. Third temperature T3 is fixed so as to maintain the hydrogen or deuterium gas, inlet to cell 2, in gas phase in downstream duct 24. Second temperature T2 and third temperature T3 are preferably substantially equal.
Downstream duct 24 advantageously enables condensation of solid hydrogen and/or deuterium on strip 6 to be stopped, while at the same time maintaining thermodynamic conditions compatible with maintaining the hydrogen and/or deuterium film in solid state on strip 6.
In preferential manner, movement means 7 are configured for strip 6 to be devoid of contact with third heat exchanger 25 in downstream duct 24. The heat transfer between third heat exchanger 25 and strip 6 is performed by molecular heat exchange. The latter is performed by making use of flow of the non-condensed hydrogen and/or deuterium gas between second outlet opening 28 and second opening 4, via downstream duct 24. For better control of the pressure of the gas in cell 2, pumping device 8 advantageously comprises a second pump 26 configured to perform suction of the non-condensed excess gas flowing in downstream duct 24. Second pump 26 is preferably arranged between second opening 4 and third heat exchanger 25. Second pump 26 is connected to downstream duct 24 via one or more openings formed in an area of the inner walls of downstream duct 24. Said area of the inner walls is preferably formed by chicanes.
According to a particular implementation mode of continuous deposition of a solid hydrogen and/or deuterium film on a metal strip, the deposition method uses one of the devices illustrated in
The deposition method further comprises a step of injection of a gas formed by hydrogen or deuterium in cell 2. During this gas injection step, strip 6 is maintained in a volume 9 of the cell at first cryogenic temperature T1. The gas is further maintained at a first pressure P1 in cell 2. During this injection step, the first pressure P1 is adjusted so as to have a first value P1i that is lower than the saturated steam pressure Ps of the gas at first temperature T1.
In order to condense the gas on metal strip 6, the deposition method comprises a step of increasing the first pressure P1 of the gas in said volume 9. After injection of the gas in said volume 9 of the cell has been performed, first pressure P1 of the gas is in fact increased from the first value P1i to a second pressure value P1c. The second pressure value P1c of the gas in said volume 9 is chosen so as to be higher than the saturated steam pressure Ps of the gas to be condensed, at first temperature T1.
The continuous deposition method according to the invention advantageously enables the constraint on the temperature parameter to be released in order to focus only on the “gas pressure” parameter when condensation takes place. Stabilization of the temperature of the strip and of the gas to be condensed can in fact prove more delicate than adjustment of the pressure of the gas in the condensation cell. The method according to the invention thus facilitates continuous condensation of a solid hydrogen and/or deuterium film on a metal strip.
According to a preferred implementation mode, the continuous deposition method uses device 1 illustrated in
Injection of the gas in cell 2 and adjustment of second 22 and third 25 heat exchangers enable strip 6 to be maintained at second T2 and third T3 temperatures, respectively in upstream duct 21 and downstream duct 24. These heat exchangers in fact take advantage of flow of the gas between said volume 9 and upstream and downstream ducts 21 and 24 to cool the strip by molecular heat exchange. Second and third temperatures T2 and T3 are chosen such as to be close to first temperature T1 and to maintain the gas to be condensed in gas phase in upstream and downstream ducts 21 and 24.
When the temperature of strip 6 and of the gas in said volume 9 is stabilized (equal to T1), the control circuit of pumping device 8 and of control valve 5r is configured to increase the pressure of the gas in said volume 9 from first value P1i to a second pressure value P1c that is higher than the saturated steam pressure Ps of the gas to be condensed at the first temperature T1. This pressure increase then enables a solid hydrogen and/or deuterium film to be deposited on strip 6 in movement in said volume 9 of the cell. The control circuit adjusts the first pressure P1 according to the gas involved (hydrogen or deuterium), the speed of movement of strip 6 in said volume 9 and the thickness of the layer to be deposited on strip 6.
Advantageously, the deposition method comprises a final step consisting in heating cell 2 and cryostat 15, for example to a temperature of 25 K. This heating enables all the undesirable condensates in cell 2 and in cryostat 15 to be removed in order to prepare the deposition device for a new in condensation of hydrogen and/or deuterium on metal strip 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12 01923 | Jul 2012 | FR | national |
