Particle accelerators with special reference to their early history

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Particle accelerators with special reference to their early history
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Thermodynamic equilibrium Particle Avro Canada CF-105 Arrow Separation process Photodissoziation Electron Refractive index Power (physics) Cyclotron Boat Flight Direct current Fahrgeschwindigkeit Mass Plane (tool) Gradient Screen printing Orbit Heisenberg, Werner Storm Cosmic distance ladder Hot working Force Fire apparatus Linear particle accelerator Arbeitszylinder Band gap Rutschung Spare part Radiation Forging Spaceport Video Spannungsmessung <Elektrizität> Centrifugal force Magnetization Particle accelerator Intensity (physics) Electronic component Kilogram Machine MOST-Bus Synchrotron Nyquist stability criterion Gentleman Sizing Gamma ray Inertial navigation system Radiant energy
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i had got mine and dominant hebburn that is about as far as i can venture into the german language.
i am very bad language as and so i feel very sorry for interpreters and hence i was still be fairly closely to my script this will also help me perhaps to keep closely to the time schedule. in the time of my disposal it would be impossible to cover in any detail the large field which comes under the title of particle accelerators i should limit myself to giving a general outline of those principles which have led to significant advances. and also to a somewhat more detail discussion of the early work about which i can speak with more authority because i was then engaged on several of the b.b.c. types of accelerator and say shall not sure you pretty slides of modern giant excel. creators nor make any significant reference to the nuclear knowledge obtained by the use of accelerators.
the urge to produce particle accelerators a roast out of rather ford's work on the artificial transmutation of one element into another nineteen hundred nineteen he used and natural life of particles from radioactive substance is to bombard night to. surgeon and the founder that swift protons were emitted occasionally slide one shows the well known picture taken by black it and the ease of such an event as revealed by a wilson clout chamber you would see up near the top. all of the picture a case of where one of the many alpha party could shown has struck and nitrogen nucleus and a proton comes out towards the left but there is no sign of the alpha particularly coming out and at that time it could be deduced that.
that no other particles did come out because the new trim was not know now this is at type of disintegration which we call a half the proton type and for more than a dozen years this was the only type of nuclear.
gration known but it was obviously desirable that there should be available for disintegration experiments streams of high energy particles in large numbers and of various sorts indeed this was mentioned in rather for its anniversary address to the royal. society in nineteen twenty seven in theory such particles could be produced by applying a few million volts to an evacuee to choose the current involved would be small for example and microgram pair of helium ions corresponding know. more to the total after a particularly mission from about one hundred grams of radium. however the difficulties appeared to be very great by the standards of that time such bull teaches where expensive to produce and no one had succeeded in making a vacuum tube capable of withstanding more than about one tenth of the voltage believe. to be necessary and spiegel began to think about possible methods are producing fast particles by indirect or trick methods which would avoid the use of high voltages.
there are in this audience young people whose career lies ahead of them and whose field of work is as yet undetermined it may interest some of them to hear how one gets involved in special scientific feeds on so i will say in a few. words what happened to me i went to cambridge as a research student in nineteen twenty seven and after a few months in the nursery as it was called where we learnt some new techniques rather for called me to his room to discuss my. kind of research on being asked if i had any suggestions to mate i put forward the idea of accelerating electrons by letting the move round that many times in a circular electric feed as in a modern be to try he suggested a modification. nation which appeared more practical than my scheme and this is shown in slide to you see at and evacuated chub there with a coil one round the middle of it. and the tungsten filament to give some electrons. this arrangement as rather for pointed out at the time was really just a modification all the arrangement used by j.j. thompson in his work on the effect roadless ring discharging gases high frequency current from a spark discharge.
was sent through the coil chill mare. this gave a rapidly changing magnetic trucks and hence an alternating electric speed was produced in the two it was hoped that the alternating magnetic field together with a steady feed produced by an electromagnet might produce suitable conditions for the acceleration of. the electrons but no trace of evidence was found for the presence of fast electrons calculations were carried out which showed that the magnetic field present was of the wrong type to give really instability to the motion of the electrons defeat. increased from the center out to the coin. the calculation showed that really instability would be produced by a field decreasing inversely with the radio this means provided that a suitable high frequency a radial electric field was also present experiments along these. lines were not successful because the arrangements were too crude and also because no provision was made for stability in the axle direction.
now these experiments were really quite nice wants to start with they had one very great advantage as far as i was concerned in that before starting on the work one had not got to read perhaps several hundreds of papers which had gone before in fact at the time i. but nor the single paper to be read on the subject and that is a great advantage and i did discover later on that the with one paper i might have read it happen to be have happened specification. when the failure of this method became evident another method was suggested to rather for it was the method utilized in what is now called linear accelerator the principle is shown in slide three. and it is that the particles acquire the energy as a result of receiving a large number of success of cushions in between these pushes which they receive is the problem from one of the cylinders to the next to shown in the diagram they pass through. conducting cylinders and artist on affected by any changes made in the potential use of the cylinders. i shown in the diagram the odd numbered cylinders are connected together and so what are the even numbered ones the two sets of cylinders are connected to the output of a high frequency generator. if the lengths of success of cylinders the increase in the correct way it is possible always to have an accelerating the present as the group of particles move between success of cylinders. experiments on this carried out in nineteen twenty eight at cambridge failed for two reasons. the high frequency voltage was generated by a crude spark gap arrangement. and at the same time very little was known about the focusing of charged particles indeed the hands of the cylinders were covered with calls in order to ensure that feed for the space inside them. and this effectively removed the natural focusing action which occurs in the gap between two cylinders with a potential between them. late in nineteen twenty eight and important paper by vietor or appeared in the archive for electric technique in his he described experiments to verify the basic principle of accelerating a particle in the circular electrical field produced by it. changing magnetic looks he was able to follow the electrons one and a half times around the circle this was not the first publication on the be to try on the principle had been described by slepian in a statement taken out in the united states in nineteen twenty. twenty two businesses do not normally read these papers specifications. the generals paper also describe some experiments in which i n's were given to accelerate asians in a linear accelerator arrangement he had developed further the idea of the linear accelerator first put forward by the sing in a swedish journal in nineteen. twenty four it is interesting to note at this early date a failure in communications about which we hear so much at the present time although cambridge at the time was regarded by many as the world center for the atomic physics as it was then called no one there. they're not even rather for himself appeared to have heard of he sings paper the next light shows a diagram of the method suggested by using this proposal involved the breakdown of a spark gap and the application of the impulse of potential.
reduced to various cylinders through suitable the lady lines it's interesting to note that he included in his diagram the goal was this at the end of the cylinders which were included four years later independently and wrong way in the experiments at cambridge the to roast. a par was important in another respect it was responsible for directing lawrence's attention to the problem are accelerating particles to high energies at a time when he was looking around for the new line of research he came upon the to roast paper are quite act. identity he said that he knew very little german but was able to understand what the paper was about by studying the diagrams the result was that by nineteen thirty one he and sloan were able to report the production of mercury irons of one point two six. six million electron volts using an accelerating potential of only forty two thousand volts in a linear accelerator arrangement has shown in the next slide in see the series of cylinders up at the top the rest of the diagram is. connection with the measurement of the energies. the limits imposed by the electrical capacity of the cylinders in this method then became evident and saw lawrence was led to invent the cyclotron which in effect uses the same pair of cylinders over and over again. fortunately the disintegration of elements by artificially accelerated particles did not have to await the development of the indirect methods which had been suggested in nineteen twenty eight gamma off and independently continent bernie apply. by the then new way of mechanics to account for the details of the emission of alpha particles from radioactive substance it explained the statistical character of the mission and the well known relation between the energy of the alpha particles and a half life. of the radioactive substance cup croft in cambridge so that the theory could be applied in reverse to the penetration of charged particles into the nuclei of atoms calculation showed that protons are quite moderate energies. had a reasonable chance of penetrating into the interior of nuclei if they did so one might expect that in a proportion of the cases this integrations might follow immediately estimates indicated that the current other hundred micrograms.
pairs of protons accelerated by a few hundred thousand volts should produce an ample number of this integrations for easy observation the next slide shows cop croft and damn have evidently well pleased with the result of these. discussions are crossed on the left them off on the right approach should be so results to rather ford and it was decided to test the theory by the use of fast protons accelerated directly by the application of a high voltage it was further decide. i did that cop croft would abandon his experiments on that the position a metallic vapors onto surfaces school to low temperatures. and that i would abandon work on indirect methods and that we should work jointly on the new project. when planning to use the direct method employee at high voltage sometimes referred to as the brute force method the first matter to be settled is the type of high voltage generator to be employed the next slide shows the possibilities.
at that time to be a has shown there is the induction coyle which had a long and honorable place and physical a bar or trees the impulse generator is used by bashing langer the tesla coil resonant transformer has used the carnegie institute by bright tube and dial.
or power transformers used by lots and in the united states or a transformer and rectifier or electronic machines most of these methods produced voted just which vary with the tide and just when used to accelerate ions big is a beam contain. the ions with a wide range of energy's electricity i think machines tend to give a high voltage low current output and this is just what is required for new clearest work furthermore they usually give a steady voltage and of dust capable of producing a stream of iowans all. all of identical energy. the best type of electors static machine was introduced by band the graph in nineteen twenty nine and has been a valuable to in nuclear research its main use has been in the range off from about one million to about twenty million votes for your vote. to just the circular type developed at a novel of the leech he has been found to be very suitable than the graft machine works on very simple principles which are well known an actual not discuss them here. nineteen twenty eight the most suitable method of producing a high steady vote each have a few hundred kilowatts with an output of a few million pairs appeared to be a power transform our with its output rectified and smoothed by a suitable capacitor this was the method. chosen for the experiments in cambridge. some development work had first to be done on the construction of high boteach continuously a back to it that wrecked the fires and on the problems which arose when they had to be used in series fortunately the problems were greatly simplified by the use of a modification of a circuit. reduce by schenkel in ninety nine team using this it was possible to multiply the output of the transform our an even number of times and to produce at the same time as steady i could go to church. it enabled the rectifier is to be placed one above the other to form a large glass pillar which could be evacuated by a diffusion pump placed at birth attention as shown in the neck slide.
you can see the tall column of gas cylinders their the middle of the picture here and this is the accelerating chew over there. now with this arrangement also ensured that they reversed voltages across the various rectifier where equalised automatically. the apparatus is known as a bone to multiply and was used in nineteen thirty two in the first disintegration experiments using artificially accelerated particles montages of up to nearly eight hundred kilobits could be generated with this apparatus the next slide shows a wilson chamber. photograph up some of the disintegration produced you can see a lot of alpha particles coming out from the center of the picture the east of produce by the bombardment of lithium with some fast protons. and you can see that there are large number of these particles which were actually emitted in a time of something like one fiftieth of a second indeed at this lithium reaction is so easy to observe that the experiments could have been performed ten years earlier for this by twenty thousand volt. this would have sufficed but no one would have dared to do it at that time because anybody seen attempting to do this would have been more or less laugh that because he would have been an ignoramus quite on conversant with the nature of the electric fetus.
is near the nucleus of a natter there's something to be said all the same for trying what i sometimes called as a of foods experiment provided that it can be done quickly easily and quietly in a room which can be kept locked so that no one will know about the experiment it is not. successful. the cambridge voltage multiplier apparatus was capable of disintegrating some of the light elements and of producing artificial radioactivity another's these results gave great encourage men to those working on the indirect methods for these were the only. one is likely to provide particle sufficiently energetic to disintegrate the heavier elements seem to be no doubt that a gateway to large on explore area was open to anyone who had available a beam of high energy particles at this stage i returned to the indirect methods. and consider the major problems involved and the limits to the energy attainable in each case the the to drama kinetic induction accelerator already mentioned his have used only for the acceleration of electrons.
the reason for this is the particle acquires only a small addition to its energy during each revolution and so the particle most travel around the circular electric field perhaps a million times while a flux increases from zero to its maximum value. electrons by reason of their small mass some high velocity can do this but positive buy ins with their much larger masses will make a much smaller number of revolutions and apply only a small energy in the time as the electrons have to travel perhaps a million times around the circle it is essential that the. he should be not merely and equilibrium or but for the electrons but that it should also be a stable world otherwise any slight the storms would cost the particles eventually to move off the equilibrium orbit and be lost this problem of orbital stability is fundamental. to all machines in which particles during acceleration must remain near to a definite past the problem can be split into two separate parts stability in the direction of the magnetic field are actually instability and stability in the plane of the orbit or really instability the. first of these arose in larne says work on the cyclotron the next slide shows the sort of magnetic field that you get near the edge of the port pieces and the arrows on that show the direction of the forces acting on the particle going into the plane of the screen. they're and you can see that these forces about components tending to bring the particles back to the central plains of the apparatus if a particle wanders from the axiom direction it is obvious that it would be brought back again. the magnetic field must be curbed outwards have shown and this entails a magnetic field which decreases in the redirection mathematically it means that if the magnetic field is proportional to one over our to the yen then and must be greater than not and equal to or not would correspond to a uniform feed. the condition or for stability in the radial direction is that if the particle starts to move on an orbit of slightly larger radius the magnetic field must be strong enough to cause this particle to move in a circle of smaller radius the not have the new orbit hand as the centrifugal force falls off in. mostly what the radial distance the magnetic field must fall off less rapidly and dos we see that if the magnetic field is proportional to one over our to the and then a man is less than one knows for stability in both directions this index this feat index a.
and most lies somewhere between north and want the full mathematical theory of this was given in nineteen forty one by kirsten serb are who also dealt with the damn thing out of such associations might occur. an understanding of the results enabled cursed to construct the first practical be to draw on which is shown in the diagram on the next flight. now i'm not going to the details of that i just want you to notice the dimensions the with of that apparatus is something like half a meter and yet with this very simple apparatus he was able to produce two point three million volt electrons in sufficient numbers to produce. it's a gamma ray intensity equivalent to those that emitted by one gram of radium. the largest be to try and constructed to gives three hundred million electron vote electrons and was designed by kirsten others and nineteen fifty it may well be the largest to be built for at this size many practical problems become severe more important still a fundamental imitation. the rises and electronic in its orbit is being accelerated all the time to the center and so we get a continuous radiation of electromagnetic energy this last is proportional to the fourth power of the energy of the particle and sore point is rapidly reached when the loss of energy per. pollution by radiation becomes as great as the energy or revolution given to the particle by the be to try and action fortunately the electron synchrotron by reason of the great a radius of the electron orbiting it and the much greater energy added per revolution. can give electrons have much greater energy it turned out to the linear accelerator in dealing with the be to try and i spoke about the need for or but the stability of the electrons we need also was similar stability in a linear accelerator so the particles can not wonder too far from the. axis of the cylinders. hence it is perhaps more natural to talk about the focusing of the party indeed this terminology has been extended to cover both linear accelerators and orbital accelerators it to a new grades at the end of the cylinder some focusing occurs naturally as can be seen in the next lied. these dotted lines represent the at lines of electric force the full lines represent the part of the particle as the particle enters into this gap you can see that there's a force acting down this way along the direction of the lines blech force and a particle get sick.
celebrated up then there's a deep focusing force here due to this line of electric force tending to pull the article away from the axis but the particle is then moving faster this force acts for shorter time and the overall effect is of focusing on. now the details are this were worked out by rosen wilson in nineteen thirty eight for the cyclotron the same period place to the linear accelerator its equivalent optically to a large number of contacts lenses one after the other. now the next slide shows the type of result that we get at arising from this focusing action this is the axis of the accelerator and you have a particle starting off this way there are no focusing action it would go off like that. with the selector static focusing action we get a path like this for the party or one of increasing amplitude and increasing wavelength. and we see initially there's quite helpful action in keeping the particularly of the axis but ultimately the electorate static focusing is of no use the article is going too fast for the electric lenses to be have any significant effect.
now unfortunately the a year. there were as should have said that perhaps that the electrical focusing that can be increased by having a varying attention one which decreases as the particles cross the gap and in that case we get a stronger lands but unfortunately we get phase be focusing in. the linear accelerator. the plant lawrence realized the limitations of the linear accelerator the device the method of the cyclotron and the first publication was by lawrence an age of servant in nineteen thirty eight verified the basic principle of the site to try on. the next slide. here we have really to hollow electrodes in the shape of these between which an alternating voltages applied and these two hollow electrodes behave like the first two cylinders in a linear accelerator and just as if we use them over and over again. now the particles in the psych the tron i haven't time to go into the details start somewhere near the middle and spiral out words as the acquire energy each time they crossed the gap between the two d. shaped electrodes.
now at the same elect a static focusing a course in near the center all the cyclotron but it's of no significance as you move out for its at large and small introduced a magnetic focusing out there so we have this combination of electric and magnetic focusing and in action in. the site to chop it now lawrence built a number of cycle trans of increasing size the largest planned having a poll diameter of four point six meters and this would produce about three hundred and fifty million electron volts particles now there is at a difficulty which arises because. as he had to use a decreasing magnetic field to produce focusing but this means that the particles get out of step with the alternating voltage as the move into this region of decreasing magnetic feet and it meant that to get over this you would have to apply. very large go to church between the disease. it was span for this large cyclotron that something like a million votes alternating potential would be applied between the disease and this would have raised very great technical problems fortunately a better solution turned up in nineteen forty five million in the united states and. dexter in russia.
independently drew attention to the existence of they spoke to sing which cars are under suitable conditions to understand what this means let us think of a linear accelerator designed to accelerate particles which crossed the gap at a certain place on each radio frequency oscillation next. it's like trees. we imagine that the machine has been designed so that of particles cross here then when they go through the cylinders they reach the next gap just at the same heart all the oscillation let's see what happens if a particle arrives with the right energy but a little bit later. up here it means that it acquires more energy than the normal particularly and so at the next chapter derives a little bit earlier it doesn't get quite as much additional energy is this got but still it gets some additional energy and it arrives still earlier at the next chapter shown over here so the particle moves back. towards this point on the oscillations that actually over shoots the mark and also it's about now this meant that if you had in the cyclotron a group of particles going round crossing the gap between the disease at this point here where there's no vote. each that these could continue on round in i started without requiring any energy what if you decrease the frequency then they would start to come in at another point and acquire some energy come in here and acquire some energy and they would move back again to. this proper place for this meant that by simply reducing the frequency you could expand this said one to particles which are circulating in a circle or watches the same thing you could change the magnetic feet and the circuit would expand out to meet thing you can. missions this in a few words is the basis of this idea faced ability and it enabled to this large plants like the conferences to be used not as a straight site the tron but ask what we call that sin course like the trial where the frequency was changed to match the. changing frequency of revolution in the week of parts of the magnetic feet. i'm here i'm afraid the at the time is getting on and so i'll have to just make some cuts in what i have written out here now in the electron synchrotron we can introduce a great ceiling in the cost of the machine because we can reduce. the volume of the magnetic feet instead of having part of spiralling of words from the centre they are all the time kept on at circle of constant radius and you can do this if you increase the magnetic field with time here again in the electron synchrotron the year.
sensible have faced ability works and that one can produce very high energy particles in this way it's rather interesting that the central tron works for the very reason that the cyclotron fails to work at the height energies you haven't the cyclotron to live. patients one the necessity to decrease the magnetic field is your wife words and the all our the fact that the particles acquire additional mass as they speak up and this has the same effect as the decreasing magnetic field they get out of step rather quickly. if we just consider the synchrotron so you can also have a proton centers drawn by varying both the frequency and the magnetic field. we want to see how you can put up the energy of the particles produced at normally one would simply build a bigger magnet so if you had a larger circuit for the particles to move around on what if you can reduce the gap then it is possible that to keep the mag. and that i reasonable sachs now it's possible to reduce the gap if you can introduce additional stability into the motion of the particles and this was the next advance the next big idea in the year history of the development of the subject it meant that one needs a stronger focusing.
action than one have got previously now this focusing action this new focusing action called strong focusing on alternating grading focusing was the first of our suggested by current and livingston across night or in nineteen fifty two who found to that the same by the year.
had been suggested and get a bit earlier in a paper and five by chris to five loss in nineteen fifty now and the full of the theory of this method is difficult there are a few simple examples of a given in most of the books that described the action. the optical and loeb of where you have a series of concave and contacts lenses and you get an overall are focusing effect there are sometimes mechanical and the locals are given such as the way in which the stability of the pendulum can be increased by breaking the point to support. up and down now this without going into detail is this principle of alternating brady and focusing where in the axle direction you have a series of regions where you have strong focusing followed by strong be focusing and the actions are directly related direction you get the opposite. effect now this means that in both the axle and the radio direction one gets very strong focusing you can reduce the size of vacuum tube you can reduce the gap and a magnet and you can keep the cost of the magnet on the size of the magnet down. now this is the arrangement used in the largest machines which we have to create such as the brookhaven one or the one at sir are already you one that's just come into operation in russian and these give energies of varying amounts from about thirty thousand. million electronic votes at up to that sort of value now if we look at happy would turn to a slight number twenty one i don't fancy. this is a diagram due to livingston showing the progress of many eric celebrators over the years here are the d.c. methods write about nineteen hundred and thirty this is a scale of the energies of the party comes clotted logarithmically this is one million electron. votes here and you see the cars tend to turn over then later on we have the development of the electorate that method the band the graft me she and you can see that car begins to turn over when you get up to a few million electronic books then we have this linear protonix salary. later and here we have the site to try are we have a beta drawn up here and the synchrotron up here. and the proton centric trot up here which is the type of the machines i've just been mentioning now all of these show what kind of opera limit lived roughly allow this car and if congress bonds to a very rapid rate of increase involved teach. with time. these are the years mark here and it's curious how you get very nearly a straight line on this semi logarithmic plot but if we look to the future see what's going to happen next. you've got to go up to very high energies indeed beyond the limits of that core and it's obvious that one is getting to the stage when one needs a new idea.
and the idea that various ideas have been suggested and that i just mention one that has come to the fore in recent months this is a suggestion put forward in the pan play by baxter and good cop way back in nineteen fifty.
six. the basis of what is that if we can hold a cloud of electrons together and inject protons into it so the number of protons is about one percent of the electrons press and then these protons will be very firmly attached to the cloud by electricity at force if the cloud is. accelerated to high speed the protons will also be accelerate because the mass of the protons is much greater than the electron mass the energy of individual protons will be much greater than the energy of the individual electrodes some of the details of the scheme shown in the next flight. the problem is it to hold the love of electrons together because they are they tend to fly apart with the recalls of forces between the negative charges and this is down in this projected met and think some experimental work is being done have already. by getting the cloud in the form of a ring you have fast moving electrons this helps because you have to pinch effect at if you have to ireland cards going the same direction we can to move towards each other. so you start off with a ring of electrons in the cross-section shown here and here ring comes right around like this and its head in this ring by a magnetic field which to base the usual be to try and conditions now what you do is you have these electrons going round with.
i'm a few millions of electron volts energy and then you shrink this ring down by increasing the magnetic feet and you can shrink down at the same time they can be drawn action increased in for the energy of the particles as the robot drive and you end up with this ring like this and you have electrons go. when round rapid are held together and that's about one percent of protons make stuff then you accelerate this ring up in that direction by putting it through what is in effect a linear accelerator you can push it out here by reducing the field due to the current in this coin coin. dr here that opens this magnetic field out in the ring gets pushed out and six celery that about just as an individual pocket might be and the protons of course go live with now they said introduces the possibility of getting protons. our energies very much higher than the energies of the individual electrons that are accelerated in that ring fact if you started off with slowly moving electrons one would get protons of nearly two thousand times the energy of the electrons at in the ring which is an excel or.
rated up a preliminary experiments have shown a method to be promising. even if machines of this type are successful the energy is given to particles are likely to be very small in comparison with that possessed by some of the cosmic rays we do not know the mode of art in of these they may indeed be formed in some vast natural for more of. magnetic and electric fields in space which would surely be entitled to be told a celestial ultra high energy particles accelerator. wow crew.