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mode - CERN Accelerator School

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Transverse dynamics - Space<br />

charge<br />

→ Large numbers of particles per bunch ( ~10 10 ).<br />

→ CCoulomb l b repulsion l i between b t particles ti l ( (space charge) h ) plays l an iimportant t t role. l<br />

→ But space charge forces ~ 1/γ 2 disappear at relativistic velocity<br />

E<br />

B<br />

E<br />

r<br />

Force on a particle inside a long bunch<br />

with density n(r) traveling at velocity v:<br />

=<br />

e<br />

2πε r<br />

∫<br />

r<br />

0<br />

n(<br />

r)<br />

r<br />

dr<br />

F = e(<br />

Er<br />

− vBϕ<br />

) = eEr<br />

( 1−<br />

2<br />

2<br />

) = eE ( 1 β )<br />

2 r − =<br />

v<br />

c<br />

B<br />

ϕ<br />

eE<br />

γ<br />

r<br />

2<br />

=<br />

μ ev<br />

2π r<br />

∫<br />

r<br />

0<br />

n(<br />

r)<br />

r<br />

dr<br />

37

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