- Slides: 26
Claudio Pellegrini in Frascati Oct. 2, 2010 S. Tazzari
Introduction I can not possible properly review here all of Claudio’s copious production on accelerators in Frascati. Also, great part of his work, essential for the progress of the accelerator construction and operation, is documented, as usual, in internal, unpublished notes only. I have therefore chosen to dwell on papers, not necessarily all published, that - from the point of view of an experimentalist having to run the accelerators - I personally remember our projects having most profited from. Finally, because accelerator development in Frascati in the early years was dedicated to the design, construction and exploitation of the first e+e- storage rings, Ad. A and Adone, I shall (once more) show a few slides about them.
1955 The Frascati Laboratory 1. 1 Ge. V electron synchrotron, at the time the world highest energy one in its class, started first operation for Physics on May 15 1955. The laboratory had been built on a green field next to Frascati in four years by a team averaging between 23 and 25 years of age , the project leader, Giorgio Salvini, being 33.
Claudio’s Frascati days Claudio received his "Laurea" degree from the University of Rome “La Sapienza” in the year 1958 dicussing a thesis on the design of part of an apparatus for a physics experiment to be performed at the newly built synchrotron. Like several of the approximately ten Physics students graduating every year in the Rome University “La Sapienza” at the time, he was hired to start working in the new Frascati Laboratory, belonging to CNEN (National Centre for Nuclear Energy), the Particle and Accelerator physics and technology being supervised by INFN (National Institute for Nuclear Physics). But very soon he decided he would rather work on theory and was allowed to spent a year and a half abroad, working on general relativity problems. Once back, in 1960, he joined the small accelerator group that pioneered work on electron-positron colliders, first on the 250 Me. V Ad. A and later on the 1. 5 Ge. V Adone. He remained in Frascati working on accelerator Physics until 1974 when CNEN dispatched him to the British Culham laboratory to help the ongoing work on JET (Joint European Tokamac) and in 1978 he eventually joined Brookhaven.
1960 First step towards e+ e- colliders: Ad. A The first step in the electron-positron direction was taken in Italy, the key personality behind it being the outstanding theorist Bruno Touschek of the University of Rome. During a famous seminar he gave in Frascati on March 7, 1960, he outlined the scientific potential of electron positron annihilation compared to e-e-. E. Amaldi, CERN 81 -19, 1981
The accelerator 1961 ADA in Frascati Diameter 2 m Beam Energy 250 Me. V The first beam was successfully stored in Ad. A in spring 1961 It was a very simple design with toroidal vacuum chamber and a toroidal magnet and could be built very fast. Injection was made, using the electron-synchrotron , by converting an in-coming gamma-ray beam on a target that protruded slightly into the vacuum chamber. The synchrotron radiation process would allow a small fraction of the e+ e- pairproduced on the converter to be trapped in the chamber. The machine had a very low injection rate, low circulating currents and therefore very low luminosity. …. . ”
1963 -1964 1963 ADA in Saclay Given the very low circulating current obtainable in Frascati because of its poor injector, ADA was shipped to the LAL Laboratory in Orsay, near Paris, where a high energy, high intensity injector linac was available. With some 107 stored particles per beam, e+e- events could be observed at a reasonabe rate at the beginning of 1964 and luminosity production proven. During commissioning the “Touschek effect” (loss of particles because of intra-beam scattering) was discovered and promptly explained by Touschek.
1960 Adone draft proposal
early 1961 ADONE feasibility study From an Internal Adone document:
Birth of Colliders: challenges In those times the existing conventional accelerators did operate with very low density particle beams and fast cycling. On the contrary radiation damping in electron storage rings brought the bunch particle density to very high values, down to circulating currents as low as fractions of a m. A and, in addition beams had to be stored for hours. From the end of the 1950’s to mid 1970’s Frascati accelerator builders had therefore to solve a whole set of new theoretical and technical problems. An example !. . . LNF Internal Note
The radiation damping problem 1961 Frascati internal document 3) - The radiation damping Many calculations have been done on the effects of the radiation on the motion of electrons in cyclic acclerators. They all agree on the value of the damping constants for a constant gradient, isomagnetic accelerator; they also agree on the existance of an anti-damping effect on the radial betatron oscillations in an isonmagnetic strong focusing accelerator. Where they do no longer agree is on the changes to be made in a strong focusing machine to damp the radial betatro oscillations. Robinson and Tarazov find that one needs changing the magnetic field along the orbit, without changing the focussing properties of the structure, while Kolomenski finds the focussing parameters need not be changed. C. Bernardini and C. Pellegrini are now working on this problem, which is of course a fundamental issue for a storage ring; for the time being they have not arrived at a clear-cut solution.
1961 Radiation effects solution A calculation of Radiation Effects on Electron Oscillations in a Circular Accelerator C. PELLEGRINI Laboratori Nazionali del C. N. E. N. - Frascati (Roma) Problem solved….
1965 Transverse Resistive Wall Instability “Vacuum chamber resistive walls induce tune shifts depending on beam current, and are therefore liable to producing single and coupled bunch instabilities. ” C. Pellegrini, “Istruments of discovery, from Adone to the X-ray free-electron laser” IL NUOVO CIMENTO VOL. LXIV B , N. 2 11 Agosto 1966 The Transverse Resistive - Wall Instability of Extremely Relativistic Beams od Electrons and Positron E. FERLENGHI, C. PELLEGRINIi and B. TOUSCHEK Laboratori Naziona. Ii di Frascati del C. N. E. N. - Frascati Istituto Nazionale di Fisica Nucleare - Sezione di Roma “Intensive work was started and much correspondence exchanged particularly between the interested parties in californian Italy and the Brookhaven National Laboratories. A summer study group organised at Stanford did much to clarify the situation, so that today it can be said that the transverse instability observed in Stanford is indeed due to the finite resistivity of the walls of the acceleration chamber and that it can be cured either by the application of a feedback or by the introduction of nonlinearities, which inhbit the build up of large amplitudes of betatron oscillations. …. Most of the foundations of this work were laid independently of the work of other groups, so that in spite of the recent intense exchange of information, the present paper can be considered as corroborative evidence for at least part of the results obtained elsewhere. ” C. Pellegrini
1967 Coherent beam phenomena TRANSVERSE COHERENT BEAM PHENOMENA IN COLLIDING BEAM DEVICES C. Pellegrini and A. M. Sessler CERN 67 -19 Intersecting Storage Rings Division, 18 July 1967 " A general formalism is developed for the analysis of the transvers coherent motion of beams in a strong focusing storage ring. Both coherent and incoherent forces arising from either direct or wake fields are included in the analysis. The beams, in the absence of coherent motion, may move along different orbits which have both time and/or space crossings. The analysis applies to beams with arbitrary longitudinal density variations. We recover the well known results for a single coasting or bunched beam, but now generalized to include the relative minor influence of an A. G. structure. Our previous results for two bunched beams which were strongly dependent on the assumed azimuthal symmetry of the machine are now significantly modified. The analysis leads to simple ways to evaluate the coherent motion, for any given structure and for bunched (electron) and unbunched (proton) beams. One intersting result is that, for a suitable choice of the number of bunches and of the Q value, all coherent modes are stable. The anlysis also shows that a strong beam with a small coherent amplitude can drive a week beam to large amplitudes. "
1967 Curvature effects
1967 “Linear Theory of Motion in Electron Storage Rings ” C. Bernardini and C. Pellegrini LNF ANNALS OF PHYSICS 46, 174 -199 (1968) “The (single-particle) motion of electrons or positrons in storage rings is studied, giving special attention to the effects determining the beam size in general magnetic structures. …is a delicate matter calling for a unified treatment. …… even restricting the subject to… linear approximation, the description of the various effects determining for instance the beam size is not easy, especially when considering the two transverse betatron modes of oscillation to be strongly coupled. ”
1965 ADONE HALL DURING FINAL ASSEMBLY The two 5 m diameter, 10 MHz, double RF-cavities (arrows) were the cause of most Adone’s instabilities. They were eventualy replaced by a single 50 MHz cavity.
1968 The Head-Tail Instability When, in 1968 we started injecting single beams into the ADONE ring for the first time we met with a very nasty surprise. While the design stored current per beam was nominally 100 m. A it was found that there was no way to inject stable currents exceeding fractions of a m. A. Currents in excess would decay at a rate roughly proportional to the amount exceeding the above threshold. Several weeks were spent studying the phenomenon until Claudio and Matt Sands, then visiting in Frascati, came up with the right idea: the Head-Tail instability.
1968 Head-tail : new class of instabilities A 1968 new class of collective instabilities had been discovered. IL NUOVO CIMENTO VOL. LXIV, N. 2, 21 Novembre 1969 On a New Instability in Electron-Positron Storage Rings (The Head-Tail Effect) C. Pellegrini Laboratori Nazionali del CNEN - Frascati (Roma) In Claudio's words: “ I remember discussing with Touschek and Matt Sands in the control room of Adone, what could be the explanation of what we were seeing. Those discussions led to the Head-Tail instability theory which needed the combination of synchrotron oscillations, betatron oscillations and wake fields present in the ring vacuum chamber. ”
1968 More about the Head-Tail Instability The cause of the instability was rightly attributed to the presence inside the rather wide Adone vacuum chamber of a number of large clearing electrodes and other not properly (we learned!) terminated objects. In Claudio’s words : “. . the instability is due to the regenerative effect introduced by synchrotron oscillations, which enhances the action on the beam of rapidly decaying electromagnetic signals excited by the beam itself in its surrounding media. The results obtained show that the effect can produce instabilities for small (in the m. A range) currents, and that it can be influenced and reduced by properly choosing some parameters of the storage ring. ” Nuovo Cimento Vol. 44 A, n. 2. According to theory, correcting the lattice chromaticity eliminates the head-tail instability dipole mode. A confirmation of theory was thus obtained by temporarily installing a sextupole on Adone. Once the cause known, besides later improvements in the design of items inside the chamber, the problem could also promptly be solved by installing appropriate feed-backs.
1968 Linear theory of RF cavity bunched beam interaction C. Pellegrini Adone Internal Note T-21, June 1968 “Coherent phase oscillations have been seen in both the Orsay and the Frascati storage rings. These oscillations appear also when the RF system is properly tuned following the rule found by many authors for the case of a single bunch- RF system interaction. Another characteristic of the coherent phase oscillations in Orsay and Frascati is that , if the cavity is tuned according to the known rules and there is ony one bunch in the ring, the bunch is stable. In this paper we present a calculation of the interaction between a bunched beam with more than one bunch and an RF cavity, taking into account the presence, inside the cavity, of high frequency parasitic resonant modes. The calculation shows that when in the cavity there are parasitic resonances at frequencies close to multiples of the revolution frequency but not of the main RF voltage one, instabilities can arise with oscillation modes in which the center of mass of all bunches stays still. ”
1969 Colliders status C. Pellegrini
1969 Adone first 2 beam operation
1969 "Beam Amplitude Behaviour Upon Crossing a Linear Coupling Resonance with Damping in one Dimension" M. J. Lee, E. D. Courant, Brookhaven National Laboratory Upton, New York, C. Pellegrini, Lab. Nazi di Frascati, Rome, Italy A. M. Sessler, Lawrence Radiation Laboratory, Berkeley, California “A small coupling perturbation in a synchrotron cause instability of the particle motion as a beam is being accelerated through a resonance. Such a resonance may occur whenever n 1 v 1 + n 2 v 2 = n 3 where n 1, n 2 and n 3 are integers and vl and v 2 are the ratios of the frequencies of horizontal and vertical betatron oscillations to the frequency of revolution. Recently, large growth of beam dimensions in the horizontal direction relative to the vertical direction has been observed in the ZGS for some acceleration routes in which several resonances were crossed. The experimental observation suggests that the damper used for the vertical beam instability may be responsible for this effect. A study has been conducted to investigate theoretically the effects of vertical damping on the betatron oscillations for particles passing through a resonance. This report describes a calculation for a single-particle model and for the case of the v. I + v 2 = 1 resonance. ”
1 9 7 4 1974 Longitudinal instabilities The study is about longitudinal instabilities for the case (Adone) of a ring with two counter-rotating beams each having three bunches. It was aimed at finding the rules to design a novel feedback system to suppress modes of beam oscillations plaguing Adone. Much work was done by A. Renieri, who succeeded following Claudio’s suggestion and guidance, in designing the workable scheme eventually successfully implemented. All common work done on the subject between 1972 and 1974 has been eventually documented in the above Internal Note.
1975 Anomalous Bunch Lengthening: Helping out into the future. “Turbulence and anomalous bunch lenghtening in storage ring beams” “It has been seen that in e+e - storage rings the bunch length depends on the bunch current and on the beam energy. . . . A letter from Alberto Renieri: “At that time (1974)…. Claudio left the Adone Group to work on JET in Culham, on behalf of CNEN. During his stay there we had lengthy discussions on the anomalous lengthening phenomenon and on some ideas of mine (a kind of “ante litteram” SASE FEL) that could explain it. In December 1974 I actually travelled to Culham to discuss them with Claudio once more. As a result, I could write up the model (Adone Memo T-71) that would later become the basis of my work on FEL Physics, leading to the so called “Renieri Limit“ for storage ring-based FEL’s. ”