Field

The present invention relates to apparatus, systems and methods for the recovery and purification of Hydrogen isotopes and fusion by-products. More particularly, the present invention relates to an ion Separation System and in particularly, a Cross-Field H-lsotope Separation System.

Background

Tritium-operated Fusion reactors present a challenge when recovering and purifying Hydrogen isotopes and fusion by-products.

The recovery of expensive tritium and deuterium from fusion exhaust gases emitted by tokamaks or any other fusion reactor are composed of a range of light gases including hydrogen isotopes. Given the small fraction of tritium ( ³ H) burnt per cycle (predicted to be 1% in ITER), the tritium may have to go through the reactor 100s of times before its fully converted into energy by the fusion reactor. Thus, high recovery rates of tritium and deuterium per fuel cycle from the exhaust gas is critical to the economics of the fuel cycle.

Prototype Isotope separation plants based on both Cryogenic distillation (CD) and Gas Chromatographs (GC) have been built as part of the Joint European Torus tokamak project (JET) active gas handling system. The CD system was designed for 30g of tritium 60g deuterium and achieved high purity (99.989% of tritium). Said CD system consisted of 3 columns (with 100 stages each) each 8m tall operating at cryogenic temperatures (21K). The recent H3AT plant tender at UK Atomic Energy Authority UKAEA has focused on CD, as has the ITER project. Cryogenic processes are hugely energy intensive.

Cryogenic distillation (CD) is a known method of tritium and deuterium recovery from fusion reactor exhaust gasses. CD plants also can’t operate continuously as they require consumable materials which must be replaced periodically. CD plants are inherently large with distillation towers measuring up to 20 meters or more in height and processing equipment taking a whole building. In contrast, each CHISS system can be as small as 1m ³ in volume.

The capital costs for volume CD plants are estimated at over £10m for 30g / day system by JET. Such a system also presents a single point of failure for a fusion reactor, perhaps requiring 2 plants to be built. A CHISS system generates 1.2g/d of tritium which would require 25 CHISS systems at an estimated cost of £6.25m (@£0.25m each, 1.2g/day tritium capacity). However, if the throughput of the machines can be doubled, which is a realistic proposition with development and optimization, this becomes more attractive and also the modular nature would allow maintenance and continuous operation.

The permanent magnet version of the current invention is estimated to cost under £150k per unit and does not require electricity for the electromagnet further improving efficiency with a capital cost estimated to be around £3.75m for a 30g plant.

The CHISS system can also be used to economically recover hydrogen isotopes from the secondary vacuum jackets used to prevent environmental leakage of hydrogen isotopes and increasing the recovery fraction achievable. The combination of CHISS intelligently applied to the fuel cycle with appropriate vacuum pumps could result in a recovery rate nearing 100%. Environmental legislation on tritium leakage from future fusion power plants have not been fixed but based on current indications they could be set at 3g per year making 100% recovery a key factor.

The isotope monitor may also find commercial opportunity as part of the hydrogen economy. As the fuel cycle is a common problem for all fusion reactor systems it is likely that there would be considerable global export potential. As fusion energy becomes reality efficiency and cost of operation will be key to success in a competitive market. Fusion reactors require an accurate ratio of deuterium and tritium in their fuel. Thus, efficient and accurate separation of isotopes and monitoring are key for recycling exhaust for remixing as fuel for reinsertion into the reactor.

Thus, the current invention seeks to provide a cost effective, continuously operable hydrogen isotope recovery system that is both efficient, compact and cost effective without requiring any consumables other than the mixed ion input gas stream. The current invention provides an economic, continuous cycle solution with a recovery rate of 99.999% of the H isotopes contained within a mixed ion gas stream. This is highly competitive.

The exhaust gas feed from a reactor is at similar pressures to that required for the input to a CHISS system, therefore, reducing the need for extra energy intensive pressure conversion steps required by the legacy processes. Per pass and an estimated cost of tritium recovered by the current invention based on the electrical power used is less than a twentieth of known systems such as cryogenic distillation (CD) processes. Summary of Invention

The present invention provides a system that can separate a beam of mixed ions into separate beams provide means to purify a gas mixture. Its main application is the separation of Hydrogen isotopes for the operation of Fusion reactors, including from blanket fluid and environmental contamination, with particular emphasis on tritium recovery. A magnetic field perpendicular to the follow of ions, and optionally crossed by an electric field, separate the ionic beam and direct the resulting beams to separate extraction ports. A magnetic field mirror is employed to maintain beam focusing and ensure stability of operation. The required magnetic field over the operating volume is provided by a C-frame electromagnet or a permanent magnet system. Although the main focus of the proposed invention is the separation and purification of hydrogen isotopes, the system can be engineered to process all those heavier elements and their isotopes that can be injected in gas form.

According to a first aspect, there is provided an ion separation system comprising a vacuum enclosure, including an operating volume therein; an ion beam source configured to supply a beam of mixed ionic species; magnetic or ferromagnetic pole pieces; and focusing optics operating in the vacuum enclosure; wherein, the operating volume is subject to a “Dee”-shaped magnetic field directed perpendicular to the plane of the ion beam and configured to separate a beam of mixed ionic species into distinct beams.

Optionally, the ion beam source is an engineered Anode-Layer, Electron impact, Plasmatron or Duoplasmatron source for producing high-intensity beams of mixed atomic and molecular species.

Optionally, the magnetic pole pieces include ferromagnetic baffles for shaping the magnetic field in the operating volume within the vacuum enclosure for providing a magnetic mirror effect able to confine the ion beam in the direction parallel to the magnetic field.

Optionally, further comprising a set of semi-circular electrodes along the beam path to provide a controllable electric field perpendicular to the magnetic field lines for controlling the direction and focusing of the corresponding ion beam.

Optionally further comprising a series of extraction ports in the main vacuum vessel including a beam neutraliser and an extraction port for neutralization of the ion beam and the recovery of the atomic and molecular species in gas form. Optionally, wherein the extraction ports include an electron gun for neutralising the ion beam.

Optionally, further including a pumping system connected to the extraction port for recovery of the atomic and molecular species in gas form optionally the pumping system includes a combination of pumping methods.

Optionally, further including an electromagnet assembly shaped to accept the above system, comprising a ferromagnetic C-frame, electromagnet coils, wherein the electromagnet assembly is configured to provide the required uniform magnetic field over the entire operating volume, inside the main vacuum vessel.

Optionally, further including a magnet assembly shaped to accept the above system comprising a ferromagnetic C-frame and permanent Rare-Earth magnets able to provide the required uniform magnetic field with no energy consumption during operation.

Optionally, the C-frame is manufactured from mild steel, iron or soft iron.

Optionally, further including an optical diagnostics system. The optical diagnostic system may be include a Raman spectrometer to employ Raman spectroscopyand/or a Doppler- shift spectrometer to employ Doppler-shift spectroscopy using to analyse and monitor continuously the ion beams and determine relevant information such as at least atomic or molecular species contained in said ion beam and/or energy distribution.

In a further aspect of the current invention an electromagnet assembly shaped to accept the CHISS system comprising a magnetic C-frame, electromagnet coils and configured to provide the required uniform magnetic field over the entire operating volume inside the main vacuum vessel.

In a further aspect of the current invention a magnet assembly shaped to accept the CHISS system comprising a magnetic C-frame and permanent Rare-Earth magnets able to provide the required uniform magnetic field with no energy consumption during operation;

In a further aspect of the current invention an optical diagnostics system that can integrate with the CHISS system. The optical diagnostic system may include a Raman spectrometer to employ Raman spectroscopy and/or a Doppler-shift spectrometer to employ Doppler-shift spectroscopy to analyse and monitor continuously the ion beams in order to determine relevant information such as at least atomic or molecular species contained in the beam and/or energy distribution. Brief Description of Drawings

Embodiments will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which: Figure 1 shows an ion separation System according to the current invention including an Electromagnet configured to provide a D-Shaped magnetic field;

Figure 2 shows an ion Separation System according to the current invention including permeant magnets configured to provide a D-Shaped magnetic field; and

Figure 3 shows ion Separation System according to the current invention with the frame, magnets and lid of the vacuum chamber removed.

Specific Description

The present invention is aimed at tackling the challenge faced by Tritium-operated Fusion reactors on recovery and purification of Hydrogen isotopes and fusion by-products. The Cross-Field H-lsotope Separation System (CHISS) 100 provides a means for separating Hydrogen isotopes from a gas mixture using the action of a magnetic field preferably crossed with an electric field in a highly ionized atomic and molecular beam 2, 3, 4 provided by an ion beam source 10.

The system can be used in, but it is not limited to, two main applications:

1) Tritium recovery from blanket and plasma fluid;

2) Tritium recovery from environmental leakage. The first application requires a system that can cope with a high throughput to process the circulating Tritium inventory of a typical Fusion reactor. The second application does not require high throughput, but it does require high selectivity and the ability to separate and monitor trace quantities of Tritium in a gas mixture dominated by heavier elements, including Nitrogen, Oxygen and Carbon Dioxide. A typical tritium inventory of a fusion reactor can be estimated to be 30 g/day and the necessary recovery from environment contamination to be 0.1 g/day [1,2]

Although the main focus of the proposed invention is the separation and purification of hydrogen isotopes, the system can be engineered to process all those heavier elements and their isotopes that can be injected in gas form.

The present invention is based on a concept similar to traditional mass-spectrometers and gas analysers, in which elements are separated according to their charge and mass. The basic operation is as follows. An ion beam injection system 101 including an ion source 10 and an ion optic system 11 housed within a gas injection and ion beam source chamber 8 provide an ionized beam of mixed elements (atomic and molecular) that is injected in direction D into a vacuum vessel 1 with appropriate energy into a region of space in which a perpendicular magnetic field is present in direction M. Due to the action of the Lorentz force on the charged ions, each atomic species follow a circular path with the radius of curvature defined by [3]: mv i qB where m is the mass of the ion, q is the elementary charge, v _± is the velocity component perpendicular to the magnetic field B. Therefore, by shaping the magnetic field in the appropriate way it is possible to separate the different atomic species into separate beams which can then be directed towards an external collection and storage system.

The main components of the CHISS system are:

• Ion beam injection system 101.

A low-pressure gas mixture, containing all the isotopes of interest and impurity gasses is injected by a gas injector 17 into a gas injection chamber 8 where one or multiple ion sources 10 generate a beam of ionized gas, whilst removing the electrons from the system. Ion beam source 10 can be Anode-layer, Electron impact, Plasmatron, Duoplasmatron or variations of the above. The ion beam 2, 3, 4 containing multiple species is then injected into a low-vacuum region within a mixed species ion beam transport region 7 in which focusing and acceleration optics 11 allows the beam to achieve a high current density and the required energy (at this point, partial selection of the species to recover is possible by rejecting very heavy atoms if necessary using a combination of electric and magnetic field drift and a series of rejection plates 16 with appropriate apertures 16). Once the ion beam is focused and accelerated, it is injected into the main vacuum vessel 1 where interaction with the magnetic field leads to the separation of the species into different ion beams 2, 3, 4. In a preferred embodiment these different ion beams 2, 3, 4 are a Hydrogen Ion Beam 2, a Deuterium Ion Beam 3 and a Tritium Ion Beam 4.

A pre-treatment system 30 can be introduced before the Ion beam source. Such system can include a regulator to reduce the pressure and the flowrate of the incoming gas and a purifier to perform an initial purification of the mixture. For example, a gas input containing a large amount of Nitrogen or CO2 from environmental contamination in Air can be pre-treated by cryogenic freezing of Nitrogen and other heavy species so that only the light elements are left and can be introduced in the low-pressure ionization chamber 8.

• Main vacuum vessel 1.

In a preferred embodiment, this is a cylindrical vacuum chamber 1 of -500 mm diameter and -200 mm height, evacuated to a pressure <1e-9 mBar. The main vacuum vessel 1 is designed such that it can fit within the external magnet pole-pieces 2c and have a sufficient number of ports 9, 14 to allow beam injection, extraction of H- isotopes and rejection of heavier elements, as well as the required number of optical and electrical diagnostics feedthroughs 42.

• Magnet 2, 2a, 2b.

In a preferred embodiment, the CHISS system specifies a required magnetic field strength between 0.08 T and 0.15 T in the median plane X of the vacuum vessel 1. Preferably, the direction D in which ion beam is introduced is in the plane X. The magnetic field will have to be uniform over an air gap of at least 200 mm and a radius of 250 mm (excluding the effects of the magnetic baffles 5a). A Magnetic field generator is provided including a ferromagnetic C-frame and a source of magnetic flux. This can be achieved using a mild steel C-frame 2 as part of an electromagnet 2a as shown in figure 1. Given the small amount of magnetic field required, a variant to the proposed design can be engineered to use permanent magnets 2b (NdFeB, SmCo and similar) and a smaller iron C-frame 2 as shown in figure 2. Such approach requires no power to operate. Preferably the magnetic pole pieces 5 are located in the top cover 1a and base 1b of the vacuum chamber 1 for supplying said magnetic field in the direction M across the vacuum vessel 1 perpendicular to the direction D of the electron beam. The External magnet pole-pieces 2c of the C-frame are shape to interface with the pole pieces 5 and configured to provide the required uniform magnetic field over the entire operating volume 50 inside the main vacuum vessel 1. A C-frame 2 is a C shaped frame. The C-frame includes rounded corners to provide a smooth flux path. The ends of the C-frame 2 are external pole pieces 2c. The external pole pieces 2c are D shaped in profile to direct flux to the magnetic pole pieces 5. In figures 1 and 2 it can be seen that the quadrilateral profile of the C-frame 2 changes to D shaped at the external pole pieces 2c. Preferably there is little or no air gap in the flux path between the external pole pieces 2c and the main magnetic pole pieces 5 to maximise flux transfer between said pole pieces.

• Magnetic pole-pieces 5.

In a preferred embodiment, the main magnet pole-pieces 5 will be shaped as a “Dee” in order to create a Dee shaped magnetic field across the operating volume 50. For the purposes of the current invention “Dee” shaped means in the shape of the letter D. The magnetic pole-pieces 5 may each have a face 5b facing the face 5b of another magnetic pole piece 5 across the operating region 50 in the vacuum chamber 1. This configuration enables the separated ion beams to be extracted at 180 degrees with respect to the injection port (alternatively, also a 90 degrees geometry is possible using “half-Dees”). In order to achieve a strong ion confinement, a magnetic mirror system is shown whereby a set of baffles 5a are included on the pole-pieces in order to create a non-uniform B flux in the vertical direction M (perpendicular to the beam deflection plane). The non-uniform vertical B flux or magnetic field acts as a trap for charged particles, therefore maintaining the confinement of the beam in the deflection plane [3] The non-uniform field produced by the baffles 5a is stronger closer to the pole pieces and a weaker in the median plane X, Preferably the ferromagnetic baffles 5a protrude from the face 5b of the pole piece and further preferably perpendicular to the face 5b of the pole piece into the operating volume 50 within the vacuum vessel 1. In figure 3 the ferromagnetic baffles 5a are shown having a rectangular profile however it will be understood that any profile is possible including a quadrilateral profile, a pentagonal profile, a tapered profile or any other profile that provides the required magnetic non-uniform vertical B flux. The ferromagnetic baffles 5a are preferably semi circular in plan view. The baffles 5a may be located along the path of the ion beams 2, 3, 4 when viewed in the direction M of the magnetic field. The set of baffles 5a may be machined onto magnetic pole-pieces 5, however, it will be understood that any arrangement that allows flux to flow in the baffles is possible. • Deflection electrodes 13.

The magnetic mirror formed by the magnetic pole-pieces 5 including ferromagnetic baffles 5a acts to confine the ions in the deflection plane, however, to ensure the beam density is maintained along the whole deflection path 2, 3, 4, semi-circular deflection electrodes 13 are introduced along the curved beam path 2, 3, 4 and they are used to produce a controlled electric field perpendicular to the direction of the magnetic field lines M. This electric field allows to maintain the beam alignment and apply small corrections to the trajectory to maximize the system throughput (hence, creating a cross-field system). Furthermore, the application of a crossed electric and magnetic field allows the selection of specific ion species based on their charge/mass ration, effectively working as a secondary filter for beam purity.

• Beam extraction ports and Neutralizers 9, 14

Once the ion beams 2, 3, 4 have been separated and they reach the space region where no magnetic field is present, they are neutralized by an electron-gun 12. In figure 3, 12a shows the shape of the ion beam 2, 3, 4 when neutralised by the electron gun 12. Once the atomic species have been neutralized, they can be collected by different pumping systems 32 via extraction ports 15 . An important fusion by-product is ³ He which, due to its mass, is deflected in the same beam as Tritium (doubly-ionized 3He can be deflected by the crossed electric field of the defection electrodes 13 to a separated collection port 9, if the ³ He undergoes only single-ionization this is not possible). In the case ³ He undergoes only single-ionization two option are available: 1) Oxidation of Tritium will allow the separation of the two gasses (since ³ He does not react with Oxygen) or 2) introduce an electron beam system 32 that can create doubly ionized ³ He which can then be deflected by a separate cross-field system into another extraction port. This secondary ionization system 32 can be embedded inside the main vacuum vessel 1 or as part of the Tritium extraction line which is the path taken by the tritium ion beam 4.

⁴ He and heavier elements are be deflected at different radii by the cross-field system, allowing for purification of the Hydrogen beams and recycling of any technologically relevant by-products such as Li, Be, etc.. at Heavy elements extraction ports 14. Molecular ionic species, including hydrogen H2, deuterium D2 and tritium T2, can be extracted from appropriate ports placed in such way to intersect the curvature radius. There are three beam extraction ports and neutralisers 9 and three heavy elements extraction ports 14 shown in figure 3. Each extraction port and neutraliser 9 including a beam neutraliser 12, preferably incorporating an electron gun 12 and a neutral beam extraction port 15. The ports 9 shown in figure 3 are a Hydrogen extraction line 9a; a Deuterium extraction line 9b, and a Tritium extraction line 9c. It will be understood that further extraction ports can be included as required for different ions and molecules.

• In-situ monitoring system 40.

It is paramount to be able to monitor the flowrate, beam current and purity using an in- line real-time monitoring system 40 including In-situ beam-line inspection and diagnostics ports 42. To this end, the CHISS incorporates a set of non-invasive optical methods to perform such analysis including, but not limited to: Raman spectroscopy, Langmuir Probe and Doppler-shift spectroscopy.

Below we summarize the expected preliminary specifications for the system: ! -

Input Gas Flow 1 - 100 seem 1 - 100 seem !

FIGURE 1

Figure 1 shows an ion System 100 in an Electromagnet Configuration including a Magnetic “Cee” frame 2; Electromagnet Coils 2a; Main CHISS System 20; ln-situ beam-line inspection and diagnostics ports 42.

FIGURE 2

Figure 2 shows an ion System 100 in a Permanent Magnets Configuration including a Magnetic “Cee” frame 2; Rare-Earth permanent magnets assembly 2b, Main CHISS System 20; ln-situ beam-line inspection and diagnostics ports 42.

FIGURE 3

Figure 3 shows a section view of the main CHISS system 20 to reveal parts (section views for illustration only). Figure 3 includes a main vacuum vessel 1 (with top cover 1a removed, see Figures 1 and 2); a Hydrogen Ion Beam 2; a Deuterium Ion Beam 3; a Tritium Ion Beam 4; Shaped magnetic pole pieces 5 with baffles 5a; a main vessel pumping ports 6; a mixed- species Ion Beam transport region 7; a gas injection and Ion beam source chamber 8; a plurality of Extraction port and beam neutralizers 9; an ion Source 10; an ion optic system 11; a beam neutralising electron gun 12; deflection electrodes 13; heavy elements extraction ports 14; Neutral beam extraction ports 15; Beam rejection plates and vacuum apertures 16.

Any system feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure.

Any feature in one aspect may be applied to other aspects, in any appropriate combination. In particular, method aspects may be applied to system aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspects can be implemented and/or supplied and/or used independently.

REFERENCES:

[1] Nuclear Fusion, Edward Morse, Springer.

[2] Hydrogen Isotope Separation in the JET Active Gas Handling System during DTE1, R Lasser et al, JET-CP(98)48.

[3] Principles of Plasma Physics, Umran S. Inan and Marek Golkowski, Cambridge University Press. said references incorporated herein by reference