A short history of accelerators CHESS & LEPP. 4πε. 1919: Rutherford produces first nuclear reactions with natural 4 He 14

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Kerry Chambers
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1 17 A short history of accelerators 1911: Rutherford discovers the nucleus with 7.7MeV 4 He from 14 Po alpha decay measuring the elastic crossection of 197 Au + 4 He! 197 Au + 4 He. 14 Po 4 He 197 Au E = r e Z1eZ e 4πε d 0 =.8fm, = Z 1 Z m c e m c re, d = 0.511MeV d = smalles approach for back scattering e 1919: Rutherford produces first nuclear reactions with natural 4 He 14 N + 4 He! 17 O + p 191: Greinacher invents the cascade generator for several 100 kev Rutherford is convinced that several 10 MeV are in general needed for nuclear reactions. He therefore gave up the thought of accelerating particles.

2 18 198: Explanation of alpha decay by Gamov as tunneling showed that several 100keV protons might suffice for nuclear reactions The transmission probability T for an alpha particle traveling from the inside towards the potential well that keeps the nucleus together determines the lifetime for alpha decay. R T V 0 lnt Tunneling allows low energies Schroedinger equation: area lnt L V=0 L m[ V ( r) E] exp[! A R C E r u m ( r) =! V( r) = V0, L = dr] E V E R 0 r [ V ( r) R E] u( r), Log 10 [Lifetime -1 (s -1 )] T = u( L) u(0) 10 6 s 3µs s 3GYears 1 E( MeV )

3 19 Three historic lines of accelerators Direct Voltage Accelerators Resonant Accelerators Transformer Accelerator Voltage 1MV Charge Ze Energy Z MeV The energy limit is given by the maximum possible voltage. At the limiting voltage, electrons and ions are accelerated to such large energies that they hit the surface and produce new ions. An avalanche of charge carries causes a large current and therefore a breakdown of the voltage.

stripes) that are charged by influence are commercially available.

4 0 The Van de Graaff Accelerator 1930: van de Graaff builds the first 1.5MV high voltage generator Van de Graaff Today Peletrons (with chains) or Laddertron (with stripes) that are charged by influence are commercially available. Used as injectors, for electron cooling, for medical and technical n-source via d + t! n + α Up to 17.5 MV with insulating gas (1MPa SF 6 )

5 1 The Tandem Accelerator Two Van de Graaffs, one + one The Tandem Van de Graaff, highest energy 35MeV 193: Brasch and Lange use potential from lightening, in the Swiss Alps, Lange is fatally electrocuted

6 The Cockcroft-Walton Accelerator 193: Cockcroft and Walton 193: 700keV cascate generator (planed for 800keV) and use initially 400keV protons for 7 Li + p! 4 He + 4 He and 7 Li + p! 7 Be + n The Greinacker circuit Up to 4MeV, 1A NP 1951 Sir John D Cockcrof Ernest T S Walton

7 3 The Marx Generator 193: Marx Generator achieves 6MV at General Electrics Spark gaps or fast switches After capacitors of around uf are filled to about 0kV, the spark gaps or switches close as fast as 40ns, allowing up to 500kA. Today: The Z-machine (Physics Today July 003) for -pinch initial confinement fusion has 40TW for 100ns from 36 Marx generators

8 4 Three historic lines of accelerators Direct Voltage Accelerators Resonant Accelerators Transformer Accelerator Particles must have the correct phase relation to the accelerating voltage.

5 The Cyclotron 1930: Lawrence proposes the Cyclotron (before

Ernest O Lawrence USA 1901-1958 1934: Livingston builds the

9 5 The Cyclotron 1930: Lawrence proposes the Cyclotron (before he develops a workable color TV screen) 193: Lawrence and Livingston use a cyclotron for 1.5MeV protons and mention longitudinal (phase) focusing NP 1939 Ernest O Lawrence USA : Livingston builds the first Cyclotron away from Berkely (MeV protons) at Cornell (in room B54) M Stanley Livingston USA

10 6 F = m γω v = r ω 0 q = m γ B 0 The cyclotron frequency = qvb const Condition: Non-relativistic particles. Therefore not for electrons. Dee The synchrocyclotron: Acceleration of bunches with decreasing ω = q ( E ) m γ ( E) The isocyclotron with constant ω = Up to 600MeV but 0 0 q m γ ( E ) B B this vertically defocuses the beam ( r( E)) S N N S S N ω RF = ω 1938: Thomas proposes strong (transverse) focusing for a cyclotron

1 Accelerator Physics for an ERL x-ray Source

1 Accelerator Physics for an ERL x-ray Source 1. History of Accelerators 2. Synchrotron Radiation Sources 3. Linear Beam Dynamics 4. Emittances 5. Radiative Beam Dynamics 6. Photo Emission Guns 7. Space