Future Accelerators. DESY -MPY- Maria Laach Part I

Transcription

1 Future Accelerators DESY -MPY- Maria Laach 2007 Part I

2 References (Real Paper ) Accelerator Physics Courses Physik der Teilchenbeschleuniger und Synchrotronstrahlungsquellen, Klaus Wille, Teubner Verlag, Studienbücher, 2. Auflage 1996 Proceedings of CERN ACCELERATOR SCHOOL (CAS), Yellow Reports General Accelerator Physics, and topical schools on Vacuum, Superconductivity, Synchrotron Radiation, Cyclotrons, and others E.g. 5th General CERN Accelerator School, CERN 94-01, 26 January 1994, 2 Volumes, edited by S.Turner Accelerator Physics General Handbook of Accelerator Physics and Engineering, A.W.Chao and M.Tigner, World Scientific, 1998 Technology Topics Superconducting Accelerator Magnets, K.H.Mess, P.Schmüser, S.Wolff, WorldScientific 1996 RF Superconductivity for Accelerators, H. Padamsee, J. Knobloch, and T. Hays, John Wiley & Sons, The Superconducting TESLA Cavities, B. Aune et al., PRST-AB, 3, September 2000, Historical and Sociological Aspects A BRIEF HISTORY AND REVIEW OF ACCELERATORS, P.J. Bryant, CERN, Geneva, Switzerland, CERN 94-1 Pions to Quarks, edited by L. M. Brown, M. Dresden and L. Hoddeson, (New York: Cambridge Univ. Press, 1989). The Birth of Particle Physics, edited by L. M. Brown and L. Hoddeson (New York: Cambridge University Press, 1983). Galison, Peter u. Bruce Hevley (Hg.): Big science: the growth of large-scale research. Stanford Univ. Pr., 1992 Traweek, Sharon: Beamtimes and lifetimes: the world of high energy physicists. Harvard University Press 1988 Rhodes, Richard, Die Atombombe

3 References (Virtual) Wikipedia Accelerators Lecture by Rüdiger Schmidt (german) LHC: XFEL: ILC:

4 Outline History of particle accelerators Particle accelerators concepts New particle accelerators for HEP LHC ILC Technology challenges in particle accelerators e.g. Superconducting Magnets Superconducting Cavities Outlook

5 History of particle accelerators One can try to identify three main lines Electrostatic E.g. tandem accelerators Resonant acceleration Accelerating structures in virtually every accelerator built today E.g. RF Linacs Betatrons

6 Electrostatic Accelerators 1857 Heinrich Geissler Gas discharge tubes Julius Plücker First cathode ray tubes = electron sources 1886 Eugen Goldstein Kanalstrahlen = ion sources 1895 Lenard. Electron scattering on gases (Nobel Prize). < 100 kev electrons. One of the initiators of the Deutsche Physik in the 1930/40s 1913 Franck and Hertz excited electron shells by electron bombardment Rutherford bombards mica sheet with natural alphas and develops the theory of atomic scattering Rutherford publishes theory of atomic structure Rutherford induces a nuclear reaction with natural alphas Rutherford believes he needs a source of many MeV to continue research on the nucleus. This is far beyond the electrostatic machines then existing, but... Gamov predicts tunnelling and perhaps 500 kev would suffice Cockcroft & Walton start designing an 800 kv generator encouraged by Rutherford Generator reaches 700 kv and Cockcroft & Walton split lithium atom with only 400 kev protons. They received the Nobel Prize in 1951.

7 Rutherford s Dream It has long been my ambition to have available for study a copious supply of atoms and electrons which have an individual energy far transcending that of the alpha- and beta-particles from radioactive bodies. I am hopeful that I may yet have my wish fulfilled.... E. Rutherford: Proc. of the Royal Society of London, 117:300 (1927)

8 Cathode Ray Tubes (Railway tube Crookes)

9 Kanalstrahlen

10 Van de Graaff Generator 1. hollow metallic sphere (with positive charges) 2. electrode connected to the sphere, a brush ensures contact between the electrode and the belt 3. upper roller (for example in plexiglass) 4. side of the belt with positive charges 5. opposite side of the belt with negative charges 6. lower roller (metal) 7. lower electrode (ground) 8. spherical device with negative charges, used to discharge the main sphere 9. spark produced by the difference of potentials Tandem concept with stripping for doubling the voltage

11 25 MV Tandem (Oak Ridge)

12 Towards Resonant Acceleration Electrostatic accelerators are limited to a few Megavolts because therefore use resonant acceleration Accelerating structures in virtually every accelerator built today E.g. Radiofrequency (RF) Linacs Power Sources are readily available (e.g. klystrons from radar or TV) 1924 Ising proposes time-varying fields across drift tubes. This is "resonant acceleration", which can achieve energies above that given by the highest voltage in the system Wideröe demonstrates Ising's principle with a 1 MHz, 25 kv oscillator to make 50 kev potassium ions Lawrence inspired by Wideröe and Ising, conceives the cyclotron Livingston demonstrates the cyclotron by accelerating hydrogen ions to 80 kev Lawrence cyclotron produces 1.25 MeV protons and he also splits the atom just a few weeks after Cockcroft and Walton (Lawrence received the Nobel Prize in 1939). Sparking during conditioning the 25 MV Tandem in Oak Ridge

13 Linear Accelerator (LINAC) l 1 l 2 l 3 l 4 l 5 l 6 l 7 Teilchen quelle Driftröhren aus Metall Particles from the source are accelerated towards the first drift tube While passing through the tube the potential changes the sign When leaving the first drift tube they will be accelerated towards the second drift tube As the speed increases the distance between tubes increases (and their length ~ HF-Sender mit fester Frequenz

14 + l i Energy of the particles after tube i: E i = i e 0 U 0 sin( Ψs ) sin 1.1 ( r ) π Sine function x r, r, r 2 π U 0 maximum Voltage of the HF source, and Ψ s the average phase during the passage between the tubes of the particle sin 1.1 ( r ) π Sine function x r +, r, r 3 π Consequence: No continuous beam can be accelerated, Need particle bunches Length: from few 10 um upto 1m

15 Linac at FERMILAB 1971, upgraded in 1993 Linac can accelerate beam to 400 MeV Low energy end of the Fermilab linac is an Alvarez style drift tube linac. The accelerating structures are the big blue tanks shown in the photo. The five tanks of the low energy end take the beam from 750 KeV to 116 MeV. The resonant frequency of the cavities is 200 MHz.

16 FERMILAB Linac

17 FLASH (VUV-FEL) Facility at DESY TTF / FLASH RF gun accelerator modules collimator undulators Laser bunch compressor bunch compressor 4 MeV 150 MeV 450 MeV 1000 MeV bypass FEL experimental area 250 m

18 Circular Accelerators: Betatrons Basic idea A time varying magnetic field induces a circular electrical field 1923 Wideröe a young Norwegian student, draws in his laboratory notebook the design of the betatron Two years later he adds the condition for radial stability but does not publish Wideröe makes a model betatron in Aachen, but it does not work. Discouraged he changes course and builds the linear accelerator (see above) 1940 Kerst re-invents the betatron and builds the first working machine for 2.2 MeV electrons Kerst builds the world's largest betatron of 300 MeV.

19 Circular Accelerators: Cyclotron Principle B z s Particle moving in perpendicular magnetic field: results in a circular motion: F = m a = q v B dv m = q v B dt dv = q v B dt m F v x Equilibrium of Lorentz- and centrifugal forces: Revolution time is constant, thus the frequency of the acclerating field Independent of energy and velocity F Lorentz = q v B 2 F = m v Zentrifugal R R = m v / q B v mit ω = gilt : ω = R q m B If B constant, R will increase!

20 History Excursion: Ernest Orlando Lawrence Born: August 8, 1901 Died: August 27, : 4 inch cyclotron 1932: 27-inch 1945:184-inch Relativity speed limit, frequency ramp needed

21 N.B.: Tubealloy was the WW II code word for uranium History Excursion: Ernest Orlando Lawrence Lawrence is one of the founders of what is called Big Science Big Science as opposed to the small laboratory work has certain features Big budgets By government Big staffs: Diversification into specialist areas Big machines: See slide before. Big laboratories: Big national labs in the US, CERN, DESY, Several methods for getting money to built larger machines were explored by Lawrence Medical application e.g. cancer treatments already before world war II (WW II) Military applications e.g. Isotope separation with the Calutron and isotope production with the cyclotron during WW II

22 Vertical Focusing in the Cyclotron People just got on with the job of building them. E.Wilson Lectures 2001 Then one day someone was experimenting The Figure shows the principle of vertical focusing in a cyclotron In fact the shims did not do what they had been expected to do Nevertheless the cyclotron began to accelerate much higher currents

23 Lutz Cyclotron Lilje DESY -MPY-at CERN

24 Cyclotron at PSI Medical cyclotron for proton therapy at PSI 90 t and 3,2 m diameter Protons with 60 % of speed of light Superconducting coils Work of Michigan State University, PSI and Accel Instruments GmbH

25 Early Synchrotrons Synchrotrons RF frequency is changed Magnetic field is ramped Energy is increased Early Synchrotrons with only weak focussing (see below) Large aperture magnets Avoid saturation Large vacuum chambers Cosmotron (BNL, 1953) 3 GeV 2000 tons mainly for the magnets 288 C-shaped

26 Bevatron (Berkeley, 1954) 6 GeV, tons

27 Synchrophasotron (Dubna, 1957) Effectively a synchrotron 10 GeV tons Vacuum tube 150 x 40 cm

28 Beam Optics and Focussing Particles with different initial conditions (position, angle) will depart from each other Assume a divergence between two particles of 10-6 rad After 10 6 m they would have a distance of a meter E.g. LEP (circumference m) after 50 turns (5 ms) Compensate Gravity Need defined conditions at interaction point (IP) Small dimensios desirable for higher interaction rate (luminosity) Different energy particles should reamin together

29 Geometrical (Weak) Fokussing in Homogenous Dipole Field B z v F s Particle A B Particle B Two particles with identical energy at the same position with slightly different angle will meet evry half turn Fokussing only perpendicular to magnetic field In the other direction there is no focussing and particles would diverge A focussing force is needed x Nominal orbit

30 Dispersion in Dipole field B Two particles with different energy and the same momentum will come back to initial position after each turn. Nominal Orbit Momentum p 0 Dispersion orbit with momentum p 1 ),, ( ),, ( z s x 1 q p z s x R z 0 0 B = ),, ( ),, ( z s x 1 q p z s x R p p p z B = + δ = p D s x x D δ = ) ( x D (s)

31 Strong Focussing 1950 Christophilos 1952 Courant, Snyder, Livingston Alternate magnet types e.g combined function magnets Provide focussing Smaller vacuum chambers (e.g. compare Cossmotron with AGS) From: M.C. Crowley-Milling Rep. Prog. Phys 46,1983, 51ff.

32 Early Strong Focusing Synchrotrons PS (CERN) GeV AGS (BNL) GeV 4000 tons

33 z Magnet Types z x x Dipole Field Quadrupole field Today accelerators mainly use seperated function magnets: Dipole magnet constant Field in Aperture Quadrupole magnet Zero Field in center, linear increase Lense like in light optics Sextupole magnet - Zero Field in center, quadratic increase Chromaticity correction Off-energy particles

34 Dipole magnet B z N Iron Yoke Parallele poles N Coil S S Vacuumchamber z Iron yoke z Coils Quadrupole magnet S N N S x S N N S x Vacuumchamber Hyperbolic Pole shoes

35 Real Life: Dipole magnet and Quadrupole magnet

36 Beam s eye view of an SNS half cell. From front to back: corrector, quad polefaces, sextupole faces the dipole Magnet for SNS

37 Summary of History Part Several accelerator types were developed in the third decade of the last century Other applications like medicine were also considered, but were of minor importance in the early years Driving force was primarily nuclear physics Particle accelerators are an excellent example for Big Science The main type of accelerator used today are Radiofrequency Accelerators with bunched beams Especially as power sources are readily available e.g Klystrons from radar or TV applications Several important principles known until mid of last century E.g. Strong focussing in modern synchrotrons Most of the building blocks of modern accelerators have been described But of course there is more (not in this lecture..) Space-charge Collective effects Beam-beam effects.. In the next lecture, we look at how people to put these pieces together Accelerator concepts

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