Mass Spectrometry & Spectroscopy
Mass Spectrometry for Fusion Applications Dr Dane Walker, Hiden Analytical Ltd, Nuclear Fusion
In a rapidly developing world where demand for energy is ever increasing, the importance of the discovery of a sustainable source of energy is becoming ever more imperative. Nuclear fusion allows a near inexhaustible supply of energy from widely available fuels. Waste produced is non-toxic and doesn’t contain CO2
greenhouse gases. The main by-product of the process is inert helium gas which is non-radioactive and useful for many industrial uses such as cryogenics and the production of some metals.
or harmful
Typical nuclear fusion reaction 2H+ 3H He (3.5 MeV) + neutron (14.1 MeV)
Mass Spectrometry for Fusion Applications
Nuclear fusion produces energy by controlling the fusion of atoms to produce around four million times the energy of chemical reactions, such as burning fossil fuels and over four times the energy of nuclear fi ssion. Fuels used in nuclear fusion reactors are easily obtainable and plentiful, for example, tritium is produced during the fusion process from lithium, which is in turn common enough to supply fusion reactors for over a thousand years from mineral supplies alone, ocean supplies will enable millions of years of operation. Deuterium, another fuel is present in all natural water supplies, and can be distilled from these.
The supply of energy from nuclear fusion reactions is predicted to be analogous to current nuclear fi ssion reactors, around 1 to 1.7 gigawatts, with a similar initial cost. As technology develops it is predicted that as outputs increase, costs will decrease signifi cantly. increase and costs decrease.
will
To obtain perfect conditions for nuclear fusion three parameters need to be optimised. In typical deuterium-tritium fusion reactions, temperatures in excess of 100 million degrees are needed. Typically, a range of heating systems are used in tandem to deliver the temperature required to sustain the fusion plasma allowing high energy collisions to occur. The plasma density is crucial to allow collisions to occur, this is a challenge in vacuum systems where the mean free path can signifi cantly limit collisions. In nuclear fusion reactors, electromagnets are employed with fi eld strengths in excess of 10 Tesla. Enabling confi nement of the plasma species, allowing collisions as well as preventing plasma ignition loss by keeping it away from the reactor wall. Confi nement time is also a crucial parameter, this is the time which the particles are confi ned within the plasma, in current technology this is in the order of a few seconds.
Nuclear Fusion Compounds
In nuclear fusion reactions two or more nuclei are combined forming one or more new nuclei along with subatomic particles. Elements smaller than iron generally have a large binding energy per nucleon. The main examples used for nuclear fusion are light elements such as hydrogen and helium isotopes, where the nuclear fusion reaction is highly exothermic.
Mass Spectrometry Quadrupole Mass spectrometry is a well-established analysis technique, routinely used for gas, vapour plasma and surface analysis. The spectrometer’s ionisation source is typically an electron impact ion source in which electrons from a heated fi lament are accelerated to 70 eV before impacting with the gas molecules. The emitted electrons ionise all molecules present, allowing them to be fi ltered by the integral mass fi lter and in-turn detected by the sensitive detection electronics. For general vacuum applications such as leak detection, vacuum and precursor quality, this technique offers high sensitivity and fast response. This is particularly useful in reaction monitoring where real time analyses of precursor and reaction products is readily available. For contaminant monitoring and vacuum quality at UHV, the inherent high sensitivity employed, where detection limits can be as low as 10-16 mbar. Improvements in ion source technology have allowed extremely low outgassing from ion source components, further improving detection capabilities.
Threshold Ionisation Mass Spectrometry (TIMS)
Hydrogen isotope separation is one of the most critical technological problems in nuclear fusion research, and, in order to assess accurately the performance of hydrogen isotope separation, quantitative analysis of hydrogen isotopes takes priority and becomes the fi rst essential problem to be addressed. However, since hydrogen isotopes have almost identical shape, size, and chemical properties, separation and analysis of hydrogen isotopes has historically have proved to be diffi cult, and in some cases intractable, using the conventional mass resolved mode of mass spectrometry. One method that has been employed successfully is the Threshold Ionisation Mass spectrometry (TIMS) technique. In conventional mass spectrometry, the ionisation energy of an electron impact ionisation source is set to a value of 70 eV to allow all species to be ionised by electron bombardment. The ability of some systems to control the electron energy allows another dimension of analysis to be carried out. The ability to use lower electron energies is advantageous to modify the ionisation of species. Controlling the electron energy allows improvements in species selectivity. The TIMS technique takes advantage of this technique in nuclear fusion research where it can selectively ionise deuterium from a mixed stream of helium and deuterium.
A typical quadrupole mass spectrometer.
LAB ASIA - APRIL 2022
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