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Astro-Particle Physics 3Acceleration mechanisms

Manfred Jeitler

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man-made accelerators:

inside of an Alvarez-typeaccelerating structure

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r∝ peB

Cyclotron

r.............orbit radiusp...........particle momentume............particle chargeB............magnetic field

revolution frequency must be independent of the particle‘s momentum !

man-made accelerators:

operating principle of the cyclotron

stable magnetic field to keep particleson track

alternating electric field for acceleration

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betatron:

acceleration not by alternating electric field but by time-dependent magnetic field

used for small-scale medical accelerators

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reflection of particles from magnetic clouds

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collision not with individual particles but with the cloud as a whole

second-order Fermi acceleration

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cv

v

second-order Fermi acceleration

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injection problem

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crab nebula

remnant of supernova observed in 1054

shock front of expanding matter may accelerate particles (first-order Fermi acceleration)

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pulsars

neutron stars, remnants of supernova explosionsradius ~10 km

angular momentum conserved during collapse very high rotational speed

magnetic flux conservedduring collapse very high magnetic flux density

spin and magnetic axis not aligned (just like on Earth) moving magnetic field creates high electric field: E = v × B

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accretion disk(binary system)

matter from bigger partner is sucked intodisk around massive(compact) partner(neutron star, blackhole)

relativistic effect

gravitational energy of particles is transformed into kinetic energy(friction, transport of conserved angular momentum to the outside; supposed to be strong source of X-rays; exact mechanisms not yet completely understood)

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Hillas criterion:

E < q B R

R ~ 3.3 * p / B

for: singly charged particle (Z=1) R in meters p in GeV/c B in Tesla

A Toy Model of magnetic fields

Source

Milky way

Halo B ~ G

0.1 Mpc

weak deflection(Extra-galactic B ~nG)

Larmor radius: rL = 110 kpc Z-1 (E / 1020 eV) (B / 1 G)-1

Deflection angle for protons

~ few degrees

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