Koji TAKATA KEK. Accelerator Course, Sokendai. Second Term, JFY2011. Oct.

Transcription

1 .... Fundamental Concepts of Particle Accelerators I : Dawn of Particle Accelerator Technology Koji TAKATA KEK koji.takata@kek.jp Accelerator Course, Sokendai Second Term, JFY2011 Oct. 27, 2011 Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

2 Contents 1 Dawn of Particle Accelerator Technology 2 High-Energy Beam Dynamics 3 High-Energy Beam Dynamics: Advanced Topics 4 RF Technology 5 Future of the High Energy Accelerators 6 References Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

3 Dawn of Particle Accelerator Technology Contents 1 discovery of artificial nuclear disintegration and birth of particle accelerators 2 various types of early accelerators 3 from DC acceleration to RF acceleration 4 problems in RF acceleration 5 rapid progress of RF technology around World War II Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

4 Discovery of artificial nuclear disintegration and birth of particle accelerators (1) Ernest Rutherford (Cavendish Lab, Cambridge, UK discovered nuclear disintegration by the alpha (α) rays ( ). He confirmed that protons were produced in a nitrogen-gas filled container in which a radioactive source emitting alpha rays was placed. α N p O This discovery provoked strong demand 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 Rutherford himself was a great advocator. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

5 Discovery of artificial nuclear disintegration 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 800 kv proton beams accelerated by a DC voltage-multiplier. They revised the multiplier circuit first invented by H. Greinacher (1919). p Li α + α Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

6 DC HV Accelerators DC Generators two major methods Cockcroft & Walton s 800 kv voltage-multiplier circuit with capacitors and rectifier tubes. Van de Graaff s 1.5 MV belt-charged generator (1931). Electrostatic accelerators are still in use for the mass spectroscopy, because of their fine and stable tunability of the acceleration voltage. analysis of the ratio 14 C/ 12 C : an important tool for archaeology. the time after a creature stopped breathing is estimated in 14 C s half decay time 5, 730 years. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

7 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 / 1

8 Cockcroft around 1932 Refer to From X-rays to Quarks, page 227, by E. Segrè, (W. H. Freeman and Company, 1980) Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

9 Glass Tube with Beam Acceleration Gaps Refer to Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

10 750 kev Cockcroft-Walton Accelerator Used at KEK in 1980s Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

11 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 / 1

12 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 SF 6 gas (1 atm) 80 kv SF 6 gas (7 atm) 360 kv Transformer oil 150 kv Ultra High Vacuum 220 kv Making the gap wider makes not so drastic improvement in BD limits. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

13 High Voltage Breakdown of a Van de Graaff generator Refer to: van der graaf generator on Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

14 Intermediate stage towards RF Acceleration Donald 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: E = B t. Integrate the tangential component of the electric field E along a closed boundary C of an area S: E dl = B n dxdy = C t S t Φ, where dl: line element of the curve C, and n: unit normal-vector of the area ds = dxdy. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

15 Kerst s First Publication of the Betatron Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

16 First Linear Accelerator (Linac) by Wideröe Proposal by Gustaf Ising (Sweden, 1925). Trial study by Rolf Wideröe (Norway/Germany, 1928). V RF 25 kv 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 So urce Beam This is the prototype of the present-day drift tube linacs (DTL). Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

17 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 ω c = eb /m. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

18 Early Cyclotrons Refer to From X-rays to Quarks, page 229 by Segrè, E. (W. H. Freeman and Company, 1980) Lawrence with the first cyclotron (ca. 1932). A cyclotron at RIKEN, Japan, accelerated protons to 9 MeV and deuterons to 14 MeV (1939). Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

19 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). Magnetic Field r n rn+1 (> r n) Electric Field orbit radius: r = mvc e B. revolution frequency: f = e B 2πm. f depends only on B and neither on r nor on v. dee beam dee cyclotron frequency: ω c = 2πf. Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

20 Demonstration of the Circular Orbit of Electron Beams in a Magnetic Field Search for the key word Cyclotron in Koji Takata (KEK) Fund. Conc. Part. Acc. 1 Acc. Course, Oct / 1

21 Problems in RF Acceleration 1 Linacs poor RF power sources: electron tube technology was not yet matured. 2 Cyclotrons 3 Betatrons relativistic increase of particle mass: decrease of ω c, asynchronism with RF. 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 / 1

22 Great Progress 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 / 1