Introduzione agli acceleratori - prima parte

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1 Introduzione agli acceleratori - prima parte Corsi di Dottorato congiunti BO-FE-PD Corso di Fisica delle Alte Energie Aprile 2012 Per Grafstrom University of Bologna and CERN

2 Introduction-Introduzione Organizzazione Lorenz force: first and second term, basis of it all. La forza di Lorenz: le basi di tutto Phase stability Weak and strong focussing- focheggiamento forte e debole Quadrupoles and FODO cells RF cavities Cavita a Radio Frequenza Fixed target versus collider 2

3 Gli acceleratori nel mondo An accelerator is a device that produce particles (protons,electrons,ions) of a certain energy normally measured in potenses of ev Example: 1 Mev corresponds to the energy a charged particle has acquired after passsage in a voltage drop of 1 million Volts 1 MeV e l energia cinetica acquistata da un elettrone sottoposto ad una differenza di potenziale di un milione Volt There are about accelerators in the world used for many different aplications.the wast majority are used for ion implementation, surface modifications, sterilization or medical application. Material science, biology and medicine are the dominating sciences related to accelerators. However here will concentrate on the accelerators used in Particle Physics. These are a small minorities of the accelerators existing in the world. 3

4 Gli acceleratori nel mondo Insert the table 4

5 Perché acceleratori in fisica delle alte energie? 5

6 Il principio di de Broglie Una particella con impulso p puo essere vista come un onda elettromagnetica di lunghezza d onda λ Wavelength versus energy 6

7 Understanding the Universe comprendere l universo Unification? Electroweak Transition Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics 7

8 Big Bang Proton Atom Radius of Earth Earth to Sun Radius of Galaxies LHC Universe Super-Microscope Study physics laws of first moments after Big Bang increasing Symbiosis between Particle Physics, Particle Physics and Philosophy Astrophysics Maria in der Aue, March and 2011, Cosmology AMS Hubble VLT ALMA P. Jenni (CERN) Experimental Methods in Particle Physics 8

9 La storia.. non è solo la storia The most important step in the development also describes the underlying principles of accelerators today. Factor 10 each 7 year! Un incremento di 3 ordini di grandezza ogni 20 anni 9

10 La base di tutto-la forza di Lorenz Campo elettrico Campo magnetico We could stop here. Potremmo fermarci qui the rest are details. Il resto sono dettagli but the devil in the details il diavolo è nei dettagli 10

11 Utilizzare il primo termine in forza di Lorenz: F=q E La soluzione con un solo gap E =campo elettrico Cookroft Walton 11

12 Due possibilità Il passo successivo. Many gaps- one after each other- uno dopo altro LINEAR accelerators-acceleratori lineari The same gap- many times- il stesso gap volte CIRCULAR accelerator-acceleratori circolari 12

13 Il primo acceleratore lineare Wideroe-1928 The particles gain energy at each gap Length of drift tubes follow increasing velocity Spacing regular a v approach c 13

14 Utilizzare il secondo termine della forza di Lorenz: F= q( v x B ) B= campi magnetici Q =carica V= velocita r =mv/bq (raggio di curvatura) T =2π r/v = 2π m/ Bq T independente di v 14

15 Un semplice acceleratore circolare-cyclotron Magneto dipolo Campo magnetico uniforme Campo elettrico T independente di v the particle always arrives at the correct time to the accelerating gap 15

16 Il primo ciclotrone : Lawrence and Livingstone 1.2 MeV 1932 However.max energy ~ 10 MeV. 16

17 Einstein sostituire Newton..... T= 2π m/bq T=2π m /Bq T non indipendente di v più 17

18 Relativity velocity CPS c PSB 1 2 Newton: E = mv 2 Einstein: energy increases not velocity energy SPS / LHC } 2 E = mc R. Steerenberg, 10-Jan-2011 AXEL

19 Come essere in tempo...to the gap.? Vary the frequency of the voltage at the gap to compensate for the increase of mass. To start with this was thought to be impossible because of the precision of the frequency change that was thought necessary However. self-regulating The principle of phase stability discovered in the 1940th Synchrocyclotron Sincrociclotrone 19

20 Da sincrociclotrone di sincrotrone r =mv/bq the radius increase with energy Il raggio aumenta con l energia Too much iron in the end Troppo ferro, alla fine Max energy in range 500 MeV to 1 GeV 20

21 La soluzione: il sincrotrone Acceleration gap Only magnetic field along one well defined track. No iron in the middle Non c e ferro nel mezzo Change the field to keep constant radius Injector 21

22 Come essere stabile nello spazio The particles have to be confined both radially and vertically. The particles oscillate around its ideal path. The oscillations must be stable and not diverge 22

23 Come essere stabile nello spazio? Weak focusing in the 40 th Strong focusing (focheggiamento forte) discovered in the 50 th Alternate gradient Separate bending and focusing functions Opened the door to modern accelerators 23

is fullfilled: B= B 0 (r 0 /r) n where 0 n 1 weak

24 Weak focusing RADIAL VERTICAL Can be shown that we have weak focussing in both planes if the following condition is fullfilled: B= B 0 (r 0 /r) n where 0 n 1 weak focussing implies stable but LARGE amplitudes in the oscillations 24

Ready 1953. First machine above 1 GeV Energy 3.

Discovered K L The Cosmotron HOWEVER: Weak focussing implied big

25 Ready First machine above 1 GeV Energy 3.3 GeV Brookhaven National laboratory First external beams Discovered K L The Cosmotron HOWEVER: Weak focussing implied big magnets because of the large amplitudes. Going higher in energy would just require too much steel!! 25

26 Strong focusing The principle of strong focusing was discovered in the 50th. Recall the condition for weak focusing...but of course strong defocus in the radial direction IMPORTANT DISCOVERY: Combine n 1 and n 0 and the net effect is FOCUSING 26

27 Strong focusing machines The two first and most famous machines based on strong focussing: The PS at CERN 28 GeV in 1959 The AGS at Brookhaven 33 GeV in

28 Separate bending and focusing functions It was soon realized that there are advantages in separating the bending and focusing functions. Instead of using bending magnets with positive or negative field gradients it was better to separate the functions by using simple bending magnets with n=0 in combination with separate quadrupoles What is a quadrupole? Che cosa è un quadrupolo? 28

29 Quadrupole Magnet Magnete Focheggiante Quadrupolo A Quadrupole has 4 poles, 2 north and 2 south Magnetic field They are symmetrically arranged around the centre of the magnet There is no magnetic field along the central axis. Hyperbolic contour x y = constant R. Steerenberg, 10- Jan-2011 AXEL

30 Quadrupole fields Magnetic field On the x-axis (horizontal) the field is vertical and given by: B y x On the y-axis (vertical) the field is horizontal and given by: B x y The field gradient, K is defined as: ( By) d ( Tm ) 1 dx 30

31 Types of quadrupoles Force on particles This is a: Focusing Quadrupole (QF) It focuses the beam horizontally and defocuses the beam vertically. Rotating this magnet by 90º will give a: Defocusing Quadrupole (QD) R. Steerenberg, 10- Jan-2011 AXEL

32 Focusing and Stable motion Using a combination of focusing (QF) and defocusing (QD) will keep the beams focused in both planes when the position in the accelerator, type and strength of the quadrupoles are well chosen. By now our accelerator is composed of: Dipoles, constrain the beam to some closed path (orbit). Focusing and Defocusing Quadrupoles, provide horizontal and vertical focusing in order to constrain the beam in transverse directions. A combination of focusing and defocusing sections that is very often used is the so called: FODO lattice. This is a configuration of magnets where focusing and defocusing magnets alternate and are separated by non-focusing drift spaces. 32

33 FODO cell The FODO cell is defined as follows: QF QD QF L1 L2 Centre of first QF FODO cell Or like this Centre of second QF 33

34 34

35 The mechanical equivalent-l'equivalente meccanico The gutter below illustrates how the particles in our accelerator behave due to the quadrupolar fields. Whenever a particle beam diverges too far away from the central orbit the quadrupoles focus them back towards the central orbit. R. Steerenberg, 10- Jan-2011 AXEL

36 Abbiamo anche bisogno di accelerazione Abbiamo parlato di magnet curvante e quadrupoli MA naturalmente abbiamo anche bisogno di accelerazione Fornita da cavita a radiofrequenza 36

37 Che cosa è una cavità a RadioFrequenza? Basically hollow metal box providing electric field, in the right direction, with the right strength and the right time The cavity becomes an resonating structure and grow stronger and stronger at the right Frequency. Noise do not resonate. 37

38 Molti insieme 38

39 Osservare! The RF cavity requires a bunched beam 39

40 Ingredienti di base nel moderno acceleratore Bending magnets: dipoles to keep the particles in their circular track Quadrupoles: to keep the particles together and focussed in small areas. Accelerating gaps or RF cavities. 40

Quad Collision/ Dipole Experiment Collimator

Collimator Quad Dipole Dump/extraction line

highest number of collisions at the highest

and Philosophy Maria in der Aue, March 2011,

42 Pedagogical sketch of a hadron machines Injection Collimator Dipole Quad RF cavities Quad Collision/ Dipole Experiment Collimator Collimator Quad Dipole Collimator Collimator Collimator Quad Dipole Dump/extraction line Dump/extraction line Goal: producing the highest number of collisions at the highest energy, in the safest way Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics 42

43 Distinzione importante Fixed target versus collider 43

44 Different approaches: fixed target vs collider Fixed target Storage ring/collider 44

45 La storia.. non è solo storia... Un incremento di 3 ordini di grandezza ogni 20 anni Factor 10 each 7 year! 45

Corsi di Dottorato -Bologna. Corso di Fisica delle Alte Energie. Maggio Per Grafstrom University of Bologna and CERN

Corsi di Dottorato -Bologna. Corso di Fisica delle Alte Energie. Maggio Per Grafstrom University of Bologna and CERN Introduzione agli acceleratori - prima parte Corsi di Dottorato -Bologna Corso di Fisica delle Alte Energie Maggio 2014 Per Grafstrom University of Bologna and CERN Organizzazione Introduction Lorenz force: