rfq - Chalmers

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REXEBIS
In the Electron Beam Ion Source (EBIS) the 1+ ions are charge
bred. The positive ions are trapped in an electron beam which
knocks out electrons from the ions.
• EBIS working principle
The positive ions are injected from the
right and confined
- radially in the potential well from a
dense electron beam which is focused
by a strong solenoidal magnetic field
- longitudinally by two electrical
potential barriers
Inside the beam the ions perform
axial, magnetron and cyclotron
motions in an entangled way, as well
as collide with other ions.
EBIS cross-view
Axial potential
Radial potential
• Charge development
During the confinement period (s
to seconds), the ions are
continuously bombarded with fast
moving electrons from the electron
beam. These knock out the
electrons from the ions. When the
desired charge state is reached, the
ions are extracted to the right by
applying an extraction voltage.
Obtained charge
state:
q  je  confinement
REXEBIS
The REXEBIS is based on a 2 T superconducting solenoid. An
immersed gun produces the electron beam and the electrons are
absorbed in an iron-shielded collector. After a confinement < 20 ms a q/A
> 1/4 is reached.
filling tower
racks
electron gun
position
collector position
insulator
injection/extraction
optics
magnet iron shield
turbo pumps
60/20 kV platform
• The REXEBIS platform is switched between 60 kV
(at injection) and ~20 kV (at extraction) to convert the
ISOLDE energy (60 keV) to ~20 keV·q in accordance
with accelerator specifications.
T=10 – 20 ms
40
20
0
100 s
injection
60
breeding
extraction
Uplatform (kV)
5V
5V
10-20 ms
t
100s
• REX-EBIS data
B=2T
Eelectron = 5 keV
confinement < 20 ms
Ie = 0.5 A
je = 250 A/cm2
Ltrap < 0.8 m
Warm bore
q/A ~ 1/4

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