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Dawn of Particle Accelerator Technology Fundamental Concepts of Particle Accelerators . I : Dawn of Particle Accelerator Technology . .. Koji TAKATA KEK [email protected] http://research.kek.jp/people/takata/home.html Accelerator Course, Sokendai Second Term, JFY2013 Oct. 24, 2013 Contents x1 Dawn of Particle Accelerator Technology x2 High-Energy Beam Dynamics: (1) x3 High-Energy Beam Dynamics: (2) x4 RF Acceleration x5 Future of the High Energy Accelerators x6 References Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 2 / 1 Dawn of Particle Accelerator Technology Contents 1 discovery of artificial nuclear disintegration（1919 - 1932） and birth of particle accelerators 2 various types of early accelerators 3 from DC acceleration to RF acceleration 4 problems in RF acceleration 5 great progress along with World War II（1941 - 1945） Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 3 / 1 Discovery of artificial nuclear disintegration（1919 - 1932）and the birth of particle accelerators (1) Ernest Rutherford (Cavendish Lab, Cambridge, UK）discovered nuclear disintegration by the alpha (α) rays (1917 - 1919). • He confirmed that protons were produced in a nitrogen-gas filled box containing an alpha ray source. 14 ! 16 α + 7N p + 8O This discovery provoked strong demands to artificially generate high energy beams to study in more detail the nuclear disintegration phenomena. Thus started the race for developing high energy accelerators, and, naturally enough, Rutherford himself was a great advocator. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 4 / 1 Discovery of artificial nuclear disintegration（1919 - 1932） and birth of particle accelerators (2) The first disintegration of atomic nuclei with accelerator beams was achieved at the Cavendish Laboratory in 1932 by John D. Cockcroft and Ernest T. S. Walton, who used proton beams accelerated by a 800 kV DC voltage-multiplier. 7 ! p + 3Li α + α The multiplier was of a type invented by H. Greinacher (1919), a Swiss engineer, but was greatly improved by them. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 5 / 1 DC HV Accelerators DC Generators: two major methods Voltage-multiplier circuits with capacitors and rectifier tubes first used by Cockcroft & Walton. Belt-charged generators first constructed by Van de Graaff (1931). Electrostatic accelerators are still in use for the mass spectroscopy, because of their fine and stable tunability of the acceleration voltage. • analysis, for instance, of the ratio 14C/12C : an important tool for archaeology. • the time after a creature stopped breathing is estimated in 14C's half decay time 5; 730 years. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 6 / 1 Cockcroft & Walton's voltage-multiplier circuit V cos ωt V(1+cos ωt) V(3+cos ωt) V(5+cos ωt) AC 0 2V 4V 6V 0 Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 7 / 1 Cockcroft-Walton Accelerator (1) J. D. Cockcroft and E. T. S. Walton, Proc. Roy. Soc. (London) A137 (1932) p.229. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 8 / 1 Cockcroft-Walton Accelerator (2) J. D. Cockcroft and E. T. S. Walton, Proc. Roy. Soc. (London) A137 (1932) p.229. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 9 / 1 Cockcroft around 1932 Please see the figure in p.227 of ref.∗ ∗E. Segr`e, From X-rays to Quarks, p.227, (W. H. Freeman and Company, 1980) Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 10 / 1 Van de Graaff's 1:5 MV Belt-charged Generator Insulating Belt High Voltage for Acceleration Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 11 / 1 HV Limits in Electrostatic Accelerators DC acceleration is limited by high-voltage breakdown (BD). • Typical BD voltages for a 1cm gap of parallel metal plates Ambience Typical BD Voltages Air (1 atm) ≈ 30 kV SF6 gas (1 atm) ≈ 80 kV SF6 gas (7 atm) ≈ 360 kV Transformer oil ≈ 150 kV Ultra High Vacuum ≈ 220 kV • Wider gaps do not make drastic improvement in BD limits. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 12 / 1 High Voltage Breakdown Demonstration with a Van de Graaff generator ∗ ∗http://web.mit.edu/museum/exhibitions/mindhand.html Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 13 / 1 Intermediate stage towards RF Acceleration: D. W. Kerst's betatron (1940) Electric field due to time variation of the magnetic flux Φ.∗ • The AC transformers work on this principle. • Faraday's law in Maxwell's equation: @B r × E = − : @t • Integrate the tangential component of the electric field E along a closed boundary C of an area S: I ZZ @ @ E · dl = − B · n dxdy = − Φ; C @t S @t where dl: line element of the curve C, and n: unit normal-vector of the area dS = dxdy. ∗There had been an earlier proposal by Wider¨oe(1924). Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 14 / 1 Kerst's First Publication of the Betatron Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 15 / 1 First Linear Accelerator (Linac) by Wider¨oe Proposal by Gustaf Ising (Sweden, 1925). Trial study by Rolf Wider¨oe (Norway/Germany, 1928). VRF ∼ 25 kV (1 MHz) per gap ×2 with a drift tube. He convinced that the scheme can be repeated any number of times to reach ever higher beam energies. RF Ion Source Beam Drift Tube This is the prototype of the present-day drift tube linacs (DTL). Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 16 / 1 Ernest Lawrence's Cyclotron (1931) Trial study of the multiple RF acceleration of charged particles moving on a circular orbit in a magnetic field. • The first circular accelerator. • Multiple acceleration at the cyclotron frequency !c = eB?=m. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 17 / 1 Early Cyclotrons Please see the figure in p.229 of ref.a A cyclotron at RIKEN, Japan, accelerated aE. Segr`e, From X-rays to Quarks, p.227, protons to 9 MeV and (W. H. Freeman and Company, 1980) deuterons to 14 MeV (1939). Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 18 / 1 Circular Motion of Particles in the Cyclotron RF Generator dee dee Circular orbit of particles with charge e and mass m in magnetic field B （assuming β = v=c ≪ 1). mvc r r > r • n n+1( n) orbit radius: r = jejB . • jejB revolution frequency: fc = 2πm . • f depends only on B and neither on Magnetic Field Electric Field r nor on v. • beam cyclotron frequency: !c = 2πfc. dee dee Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 19 / 1 Demonstration of the Circular Orbit of Electron Beams in a Magnetic Field ∗ ∗http://en.wikipedia.org/wiki/File:Cyclotron motion.jpg Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 20 / 1 Problems in RF Acceleration 1 Linacs: • poor RF power sources: electron tube technology was not yet matured. 2 Cyclotrons: • relativistic increase of particle mass: → decrease of !c, → asynchronism with RF. 3 Betatrons: • It was very difficult to inject and trap electron beams correctly on the circular orbit in the donut. • Indispensable was the analysis of the transverse oscillations of particles. • It led to the present-day theory of the betatron oscillations. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 21 / 1 Breakthrough Innovations Just after World War II 1 Discovery of the phase stability principle in RF acceleration. • Vladimir Veksler (1944) and Edwin M. McMillan (1945). • Cyclotrons. ! synchrocyclotron, and eventually ! synchrotron. 2 Strong focusing: new idea for the transverse beam focusing. • Christofilos (1950) and Courant-Livingston-Snyder (1952). 3 Radars in practical use quickened the development of high power microwave tubes. • magnetrons and klystrons. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct. 2013 22 / 1.
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