A%20LINEAR%20RFQ%20TRAP%20FOR%20COOLING%20AND%20BUNCHING%20OF%20RADIOACTIVE%20ION%20BEAMS

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A LINEAR RFQ TRAP FOR COOLING AND BUNCHING OF
RADIOACTIVE ION BEAMS
Ari Jokinen
University of Jyväskylä CERN / PS-division
Introduction RFQ Buffer gas cooling JYFL ion
cooler and buncher
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WHY BEAM COOLING ?
Emittance characteristic property of an ion
beam
for a given number of ions, want minimum beam
size, divergence and energy spread (hence, small
emittance)
Ion beam geometry
Phase space diagram
dx
q
dq
x
Liouvilles theorem area of dx by dq is
constant small divergence - large beam small
beam spot - large divergence
therefore to reduce emittance we need a
dissipative environment cooling
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COOLING TECHNIQUES
Storage rings

• stochastic cooling
• electron cooling
• laser cooling

Ion traps

• resistive cooling
• evaporative cooling
• laser cooling
• buffer gas cooling

(fast, universal -gt optimal technique for RIB)
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BUFFER GAS COOLING
Two initial energy regions
A. Elastic collisions, Eion gtgt Egas

• collision rate
• energy loss in single collision

B. Viscous damping, Eion Egas

• Origin long-range interaction between incoming
  ion and polarized buffer gas atoms -gt viscous
  drag
• Ions are damped to zero (in the model)
• In reality RF-heating, thermal movement, ...