1. 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

2. WHY BEAM COOLING ? dx q dq x 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
Liouville’s 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

3. COOLING TECHNIQUES Storage rings: stochastic cooling electron cooling
laser cooling
Ion traps:
resistive cooling
evaporative cooling
laser cooling
buffer gas cooling
(fast, universal -> optimal technique for RIB)

4. BUFFER GAS COOLING Two initial energy regions:
A. Elastic collisions, Eion >> 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 -> viscous drag
Ions are damped to zero (in the model)
In reality: RF-heating, thermal movement, ...