what is the isolde cooler rfq cb - iscool h. frånberg
TRANSCRIPT
What is the ISOLDE cooler RFQ CB - ISCOOL
H. Frånberg
Where at ISOLDE
Installation
Principle
• Reducing energy spread– Thermalization ions loose energy through
interaction with a gas– Confinement by electric field
220
4
RF
RF
mr
QVq
Optimization through the Mathieu equation:
mass
Inner radius
Angular frequency of RF voltage
Amplitude on RF voltage
Particle charge
Condition for stability:q < 0.908Optimum ISOLDE:q = 0.6
Ion motions
Ions are interacting with a gas.
Through the collisions they loose energy and change direction.
Buffer gas
Ion motions
Adding a oscillating RF field confines the ions in the gas, along the axis of the quadrupole.
VRF ~
Continuous mode
1. Ions are interacting with a gas.2. Adding a oscillating RF field confines the ions in
the gas.3. The electrodes have all a potential to “drag” the
ions through the RFQ.
VRF ~
80eV5-2V/cm
~1E-2 mbar 4He10-2mbar l/s
EXTRACTIONINJECTION
Bunching mode
1. Ions are interacting with a gas.2. Adding a oscillating RF field confines the ions in
the gas.3. Pulsing the last electrodes (HRS.AX(23,24,25)
(A/B))
VRF ~
80eV5-2V/cm
~1E-2 mbar 4He10-2mbar l/s
EXTRACTIONINJECTION
Trapping 50V
Summary
RFV
Three elements:RF quadrupolar fieldRadial confinement
DC potentialsExtracting ion in bunches or in continuos mode
Buffer gas Ion motion cooling
Results• Transmission:
– 50 % A>23 – 80% for A>40.
• Space charge limit of 1E8 ions/bunch.– The maximum limit of ions in the
RFQCB before the ions are lost.
• Cooling time < 1msec– At ISOLDE short lived isotopes with
half-lives of a few ms are explored.
• Bunch width ~ 30 µsec– For the time window of the experiments.
0.00E+000 1.00E+009 2.00E+009 3.00E+009 4.00E+009 5.00E+009
0.00E+000
2.00E+007
4.00E+007
6.00E+007
8.00E+007
1.00E+008
1.20E+008
1.40E+008
Ext
ract
ed
ion
s
Injected ions
-200 0 200 400 600 800 1000 1200 1400 1600 1800-1
0
1
2
3
4
4.0x10-4
6.0x10-4
8.0x10-4
1.0x10-3
1.2x10-3
1.4x10-3
1.6x10-3
Bea
m g
ate
Time [s]
MC
P
-40 -20 0 20 40 60 80 100 120 140
-8x10-3
-7x10-3
-6x10-3
-5x10-3
-4x10-3
-3x10-3
-2x10-3
-1x10-3
0
1x10-3
2x10-3
MC
P s
igna
l
Time [s]
10 ms 100 ms 1000 ms
Why do ISOLDE need an ion cooler and buncher?
• Large beam emittance – Low transmission to
experiments– Low efficiency in mass
spectrometers
~35·mm·mrad 95% emittance
Why do ISOLDE need an ion cooler?
• Small beam emittance – High transmission to
experiments. During tests we had 100 % transmission between the RFQCB and LA2 beam line!
– High efficiency in mass spectrometers
• Mistral• ISOLTRAP
– Small beam spot• Decay/collection experiments.
~2·mm·mrad 95% emittance
Why do ISOLDE need an ion buncher?• Finite time definition of
beam pulses – Gating on the beam pulse
background suppression.– Decay experiment
• T1/2
• Charge particle decay spectran
• Background suppression factor~1E4– COLLAPS (less laser power) -7 -6 -5 -4 -3 -2 -1
0
20
40
60
80
100
120
140
160
180
200
Gat
ed c
ount
s
Tuning voltage
-7 -6 -5 -4 -3 -2 -1
490000
492000
494000
496000
498000
500000
502000
Tot
al c
ount
s
Tuning volts
Singles (continuous counting)
Bunched:12µs gated spectra