 Now, in this iron sources, if you see, what are the, when you design, what are the things you look for? One is that, what kind of species can make negative ions and what kind, kind of intensity it can give, not all the species or not all the elements make negative ions. What kind of negative ions can be made by that iron source that will, and the beam quality. When we talk about, we talk of brightness as well as emittance and emittance is a most important parameter and in a layman language, you can say the emittance is nothing but similar to divergence. So if the, if the divergence of beam is large, then of course that emittance is similar to that, but it is in the phase space. And therefore, the emittance should be, like divergence should be small, emittance also should be small. Now, this is when we are talking of one dimensional or two dimensional trajectories, then we talk of divergence, when we, and when we are talking of phase space, six-dimensional phase, then we talk of magnetesis. This I have discussed in one of the lectures in great detail. Then of course, when ions are made out of any gas or material or element, what is the energization efficiency, reliability, material utilization efficiency is equally important because there are some cases where very small quantity in sometimes even the less than milligram of sample is available and you have to use it for pretty long time for, and therefore the efficiency, material utilization efficiency of the ion source should be as much as possible. Then of course, the, from the point of your operation and it should be easy to do that. So, we can do duty cycle, whether a particular ion source, we can run it for 100 percent time, duty cycle is 100 percent or it has to be passed, so that also is one of the characteristics and offered the source, source lifetime. So, these are some of the characteristics which define whether the ion source is good or an improvement is required. There are different kind of mechanisms which are responsible for, for example, for negative ions for mission which is very important. In fact, lot of R and D is being done on these negative ion sources today and you can see that one is radiative capture where any element, neutral element acts, picks up electron and makes a negative ion and emits a radiation H nu and it emits radiation or momentum transfer of third body. So, this is one type of ion source is process which is involved in it. So, this X prior, X negative that means initially it is formed in excited state and it will be emitting radiation here. Then polar dissociation, so I am, you can see that there are different processes which are able to make this negative ions and of course the cross sections of, cross section of each process will be different. Some of them will be very low that means in that case you can get intensities very small. In other case that may be very high, so you will get, you will be able to get, but normally negative ion yield is very small. So, you can see that it is a dissociative attachment or charge exchange. Now as I mentioned that alpha cross is based on this. So, initially you make positive ions and then pass through a electronegative gas, material of gas or vapours and then the, then it will pick up electrons. So, that is, so first is sputtering is done and then the electrons are picked up, you can see here. Surface ionization is another one. Now, you will see that Snick's ion source is very popular not only for research point of view, but of course from the point of view of applications. Because it can generate negative ions which are accelerated by protons and which are very useful for AMS, etc. Now in this case you can see that there is an ionizer here and the cesium is, cesium is deposited here from, what you do is that cesium is put here, which you heat it and that cesium goes and gets deposited at various places. For example, at ionizer and cathode. So, cesium is deposited at the surface and when the, when the, this is heated, then the cesium plus ions will be emitted out of it and they will, they will heat the sample here, which is a cathode and then by sputtering, the negative ions will be, so sputtering basically is of the neutral atom or male positive and those ones will pick up electrons from the cesium, which is coming here. And this cesium is very, as a good donor of electrons because this outermost orbit of the cesium has only one electron and the work function or the ionization energy of that electron is very small. So, electron can easily get attached with those either positive or the neutral ions which are coming out of this cathode. So, for example, suppose I want to have let's say carbon negative ions, so I put a carbon sample here, hit with the cesium and carbon will come out and it will pick up electrons from cesium vapors and cesium beams or the vapors and then it can form negative ions and which by proper voltage on the extractor you can extract. So, this is a very, very important and very, very famous ion source which is used is being manufactured, developed and manufactured by National Electrostatic Corporation and USA, which sells the peloton accelerators and the details can be found here. Now, there is another source called alfaterose, is equally important and why I am showing is that, see for example, in the case of palatron or tandem accelerator, we need negative ions to be injected. Now, you know that helium does not make negative ions in the ground state and there are a lot of experiments have to be done with the alpha particle beams, so how to generate that? So, this is a source which does that, what it does is it creates, first it creates the helium plus beam which is coming from here and then there is a, either cesium or rubidium vapors are put into here, either cesium or the rubidium here in the path of this H plus beam and they pick up electrons from there and then they are extracted. So, it is a charged H still, positive helium picks up electrons and then becomes negative ions. So, this is a boob to the low energy nuclear physics or nuclear physics people or even atomic physics people who want to use H E minus beam or H E plus also in palatron because H E plus means this H E negative, that means helium negative beam will be first accelerated in the first part of the palatron. Then in the stripper it will be, electrons will be stripped again and it will be again H E plus or it could be H E plus plus and it will be further accelerated. So, both beams will be available, low energy beams of this and high energy beams of this. Of course, in the palatron you can get only H E plus but these beams also will be available if it is suppose you have a single stage kind of accelerator then it will be possible to get this beam. So, this is very interesting. So, this is what is involved in it. So, it is a charge exchange and NEC again has developed this ion source for the experiments or with the alpha beams. This is very popular for low energy experiments and the process is again listed here that H E plus you can create from either duoblastometron or any, there are several ion sources which can create positive ion and then either you put in the, this will interact with either rubidium or cesium and then the H E minus beam or H E, even the other, this process is again used for even the proton beams for making the negative ion beams and even heavier beams, there is no problem. So, this is one, there is another source which is very popular and it is used not only at low energy but also at high energy accelerators and that is duoblastometron. See most of the gases, ions, positive ions or even negative ions, they are made by making the plasma and then you extract from this and I, plasma is always neutral that means it will contain not only positive ions but electrons but also some negative ions so you can extract negative ions from that. Now, prior to duoblastometron which was called plasmatron is single plasma was formed in single plasmatron ion sources, intermediate electrode and magnets were not there and hence the plasma density was low and low currents of the ions were extracted. In duoblastometron sources, intermediate electrode and magnets were put. So, what is done is that you feed the gas and then there is a filament here which emits electrons and the electron interacts with the gas and makes it a plasma here and plasma will have, let's say it is a hydrogen gas then plasma will have H plus, H minus and electrons also. So, but what happens in the first plasma, the density of the plasma is low so therefore the number of these particles, these ions, their density is low so what you can do is that if you put intermediate electrode and then you have anode like this so that is the structure of the duoblastometron so you have two plasmas here. In second plasma, the density of these ions is much higher and therefore you can get higher currents from this second one instead of so this plasma was not there when in the case of plasma cone. Now this you can display, so what actually you are doing by doing this is you put one magnet also here. So, what you are doing here is you are increasing the number of collisions to make it so if the number of collisions are increased then positive ions also will be increased density and even some negative ion number also will increase so you can see here that both in second plasma density of the plasma is high and there is one more advantage by putting this magnet. One is that it is increasing the number of collisions and secondly it is happening that magnetic field for example if you take the motion of the ions will depend on the magnetic field so for a particular magnetic field you will find that since the positive ions are slightly lighter than the negative ions so two electrons are added to this so you will find the structure of this plasma it is like this that at the center you have density of positive ions which is much higher and at the periphery there will be a ring sort of thing where there will be negative ions density also will be there of course as I said that as compared to positive ions the current of the probability of negative ions is only 1 to 2 percent only so this current will be very small this negative ion current will be very small but this itself you can see so what you can do is when you are extracting here if the axis of this axis of this was matched to the extractor here then you will see that you are basically extracting the beam from here so you will extract more of a positive ions now suppose you shift that axis of this extractor in such a way that this axis is facing this ring then you will find that more negative ions will be available and therefore the negative ions in current will be enhanced by shifting the y of axis extraction of the beam so this is what is basically is a dioplasma electron source so you introduce one intermediate electrode and also a magnet this I think I have discussed earlier also but just to remind you and repeat it because it is an important thing is that helium is an inert gas and it has two electrons in the outermost orbits so in fact if you see various ions positive, neutral and negative in principle if you go by the rules then the configuration should be that here it is now since the helium has two electrons so one is removed here so it is helium plus so it should remain in one axis while neutral is 1s2 and 1s can have only two so it is a neutral while if you want to make negative ions then there will be you have to add one extra Newton so then the question is whether this one extra electron will sit in 2s or it will be somewhere else this is the question and if it sits in this then negative H e negative will be forming one ground state but it does not happen it should be this but it is not the bound actually the calculations as well as measurements show that it is not a bound state here in fact on the other hand they found that this H e negative is formed in this case at 1s2s2p is metastable state it is a metastable state which has a lifetime of about 360 microsecond with the binding of the binding energy of 77 milli electron volt so that means if you want the alpha beam you form helium negative ions which will have lifetime of about 359 microsecond and you inject and accelerate it because if your beam takes much longer time more than this then this electron will detach and therefore before this time it should reach the high voltage terminal and it should get stripped off after acceleration so that is what is but this is a huge time in the 360 microsecond this beam can pass through the entire accelerator so I would like to give the summary of this lecture this is as follows so in this lecture we have discussed different types of ion sources mainly snicks, alpha-tross and deoplasmotron ion sources deoplasmotron ion sources can produce both positive and negative ions although helium is an inert gas it forms negative ion in metastable state with lifetime of 359 microseconds and binding energy of 77 milli electron volts nitrogen 14 does not form negative ion and thus is responsible for high sensitivity for carbon 14 to carbon 12 ratio measurements for AMS studies thank you