 In this lecture, we will be talking about ion sources which is the most important part of the any accelerators, so this information will be useful to all types of accelerators. Now a point which I want to discuss is that since you have seen that in the case of tandem accelerator and the palleton accelerator, negative ions are injected, therefore you should know what is negative ion and how they are generated. So proton accelerators use charge which is plus electron accelerators use charge which is minus u. Heavy ions will depend on how is the, what is the charge state. Now at this moment I would like to point out that in the case of negative ion, the only singly negative ions are have been obtained. It has been a lot of experiments have been done to see if W negative ions or multiple negative ions can be formed and it has not been successful. Otherwise suppose the W negative ions are also formed then it would be possible to accelerate ions to twice the energy in the first column itself. Therefore you can get higher energy but unfortunately it has not been possible and therefore the positive ions it is easy to remove. Suppose you take oxygen 16 which has 8 electrons remove all the 8 electrons then it will be oxygen 8 plus so Q becomes 8 times. So energy in the case of tandem or the palleton will be 1 plus 8 means 9 times of the voltage. Now what is this negative ions? How you get this negative ions? You can see that atom for example we can get additional electron then for example if you take H then it has only one electron and that will go to 1S1 that is the orbital. And suppose you have H e helium then in ground state neutral and it will be another electron will go into the S orbital and it will become 1S2 and S can have only 2 electrons so it will have this. While if you add one electron to hydrogen then that extra electron can still sit in the S orbital and it can easily accommodate one more so it will be 1S2 which is a stable configuration. While in the case of H e minus you try to add one electron then 1S2 is full so it will go to the next. Unfortunately this H e minus is not possible in ground state. However there is a metastable state where the negative ion of helium is possible and it is formed for a short period about 360 microsecond. In the case of for example oxygen if it is a neutral atom then the configuration will be 1S2 2S2 and 2P4 it has 8 electrons. So P can have still 2 more electrons therefore O minus is possible without any problem so if O minus if you take then it will have 2 plus 5. Still one more electron but unfortunately binding energy does not allow this to happen. So helium is an inert gas and has 2 electrons in the orbit, configuration is this. H minus should be 1S2 2S in ground state but it is not formed. Binding energy calculation show that. However simulations as well as the experiments have shown that there is a state is called 1S2S2P that means these electrons they get distributed to 1, 1 in L, 1S2S2P and that state is called 4P5.5 metastable state which has a lifetime of 359 microsecond. So the binding energy of 77 milliliter volts is very loosely bound. However in the case of ground state the binding energy is very very small so it is not possible to. So here I want to emphasize that the lifetime of this metastable state is about 359 microsecond and that has been measured very accurately and earlier by mistake I told by 70 microsecond. 70 microsecond is for some other state here for this metastable state it is 359 plus minus 0.7 so very accurate measurements have been done. However this time microsecond is good enough to accelerate the power. So in the case of in the case of pelatrons or even tandem this helium is accelerated further and so first column section the h e minus will be accelerated there in the terminal in the stripper it is possible to remove both electrons which were not possible in the case of bandegra and because of power limitation here it is possible so you get three times energy rather than two times. So that is the advantage of pelatron and palatron. Now this has tremendous amount of this negative ion formation thing in pelatron has tremendous amount of advantages because there are many atoms which do not form negative ions and that gives tremendous amount of advantages. All the negative in ground state all the inert gases do not form negative because their outermost orbits are completely full so the and if you want to form the negative ion that extra electron which you are putting in has to go to a next orbital which is the has a binding energy machine. So all inert gases do not form none of the none of the inert gases form negative ions for example inert gases are helium, neon, argon, xenon, krypton so on and in addition to this inert gases another atom this is nitrogen 14 also does not form negative ions and this is a bonus for scientific communities because this allows us to do a very accurate measurements as far as accelerator mass spectrometry is concerned where we measure the let us say for carbon 14 to carbon 12 ratio and since nitrogen is not forming negative ions so it does not interfere with the carbon 14 dating and we are able to do good measurements on this and not only that there since these inert gases do not form negative ions so that is again a advantage for various kind of measurements where carbon 14 negative and aluminum 26 or iron 55 or iodine 129 they are they are used in this because there is no interference from these isobars which are shown below that carbon nitrogen 14, magnesium 26, manganese 55 or zero 129 so because there is no interference from isobars that is why we are able to get much higher accuracy in measurements carbon 14 formed in the atmosphere for the reaction between cosmic rays, neutrons and nitrogen 14 this is the reaction and this nitrogen carbon dioxide with carbon 14 is taken by the plants as long as they are alive and so there will be a certain amount of carbon 14 there and as suratic plant dies this intake of this carbon 14 stops so by measuring the carbon 14 by carbon 12 ratios you can easily find out what is the age of that plant or living being similarly by measuring the ratio of iodine 129 to 127 you can also measure whether in that area any nuclear activity has taken place whether it could be nuclear leakage in the reactor or some device testing has been done in that area so by measuring this iodine 129 you can measure that so this whole process where we measure this is called the X-light or mass spectrometry and this tandem and palatons are used in fact these tandem and palatons are known as ultra sensitive mass spectrometers and this is a field which is very widely used and now dedicated palatone small energy accelerators palatone accelerators are built they are in thousands in number which are used for AMS work and very accurate measurements are possible. Accelerators now it is even 500 kV to 1 mV palatone accelerators are also built explicitly for AMS purposes and they are very effectively used for this purpose. This is as I said that this is a very important component of in fact 80% of downtime in any accelerator is because of malfunctioning of ion source therefore it has to be properly designed built and tested before it is installed in the accelerator. Now in earlier lectures we have discussed different kind of ion sources and in fact not only in basic research but also in applied research these things are very important for example negative ion sources are very useful in the field of accelerator mass spectrometry where the identification of various elements can be done with almost 10-15 sensitivity and therefore these negative ions some elements form negative ions other don't form and that is the characteristic of the property used in the case of tandem and palatone kind of accelerators and sensitivity of detection of many elements in accelerator mass spectrometry depends on that and since we have to inject negative ions in the case of tandem and palatone accelerators therefore they are called ultra sensitive mass spectrometers because now coming back to ion sources different techniques are used for different times and this is the field I think which has been studied and research R&D has been done to the maximum level on the ion sources so there are very large number of ion sources have been built and their performance has been improved considerably over the period of time. Now we talked about that there are main three kinds of ion sources one is electrons and they are not ions they are electrons and positive ions and negative ions. Positive ions are used in Vendigraf or anywhere including the Cockrope Walton but negative ions are used in the case of tandem and palatone accelerators and that is why these there is an advantage in using these and this I have discussed earlier then there is another kind of ion source is called neutral beams and these neutral beams are very useful and they are required for system like Tokamai. Recently in the recent past another kind of beams are required and they are called P var anti protons or anti particles so these beams are available for nuclear reaction studies or particle physics studies and they are available at few places for example in Tebatron as at Fermilab USA one Tv anti proton beam anti proton is P var that means P var it is defined like this so it is P var you can call it these are the reactions or the interactions which people study and that is available at Tebatron where the one Tv by one Tv beams are studied reaction and there is another facility and where again the anti proton beams are available for this facility itself is called facility for anti proton and ion research that is called Faire at GSI Germany where these beams will be available. Now coming to details of ion sources the easiest one and most studied one is electron sources and that is a very simple source and there are two techniques which are used one is thermodynamic emission that means you have a flammant here you can see flammant and if you pass the current then it will get heated temperature will go up and the electrons will come out and then you can focus them or you can guide them another way of doing is that you have a like a sharp point here and apply a voltage then as the gradient of the electron will come is inversely proportional to the tip radius so since it is almost like zero so it will be very high so field ionization will take place around this and lot of electrons will be coming out and of course different kind of crystals and different kind of things are used for depending upon their properties and then you can get lot of electrons so electron beams in even in amperes have been possible and they have been achieved so either by increasing the temperature of this or by field ionization field emission these electron beams are and they are as I said that they are the most studied sources among all the others and the reason being that electrons are used everywhere whether it is medical or it is national security of food irradiation and therefore they are studied well. Now let me just give a overview of ion sources how they are produced and what kind of ion sources are available mainly in addition to this electrons electron beams we have positive ion sources as I mentioned for example in the case of in the case of Vandy graph accelerator or Cockroach Walton they are positive ion beams ions are used we can also use negative ions there if the terminal is raised to the negative voltage or you can have a peloton and the tandem kind of things where negative ions are injected so what are the various techniques and what kind of ion sources are very famous for these two things see for example you can see a list of various types of ions so I am not going to discuss all of them but I would like to discuss few of them which are most popular for example there is one called Dioplasmatron which can produce both positive as well as negative ions see you can see they are listed at both the sides so Dioplasmatron is one which can create which can give you both positive and negative ions and then there is another very important ion source which is called Isniks ion source which is a is a must for any peloton accelerator and it is a source of negative ions using cesium sputtering and then there is another ion source which is called Alphatros which is again a source of negative ions and particularly developed for peloton accelerators and this is also pretty famous there are many other kind of things there are target ion sources for radioactive ion sources production and things like that so there are different techniques have been developed and lot of R and D has been done to develop this kind of ion sources for example charge exchange also is another in fact this is Alphatros ion source also is nothing but this charge exchange type