Transcript Slide 1

Laser cooling of Mg+ and laser
spectroscopy of HCI @ SPECTRAP
Zoran Andjelkovic
Johannes Gutenberg Universität Mainz
GSI Darmstadt
Laser Spectroscopy of Highly Charged
Ions and Exotic Radioactive Nuclei
(Helmholtz Young Investigator Group)
outline
Introduction:
– overview of SPECTRAP?
– trapping cycle
Results from ion trapping and laser cooling:
– fast fourier transfom ion cyclotron resonance
– single and multiple ion fluorescence
– trapping time
Further plans:
– for the not so near future
– and two immediate spectroscopy candidates
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ion production and TOF
2500
24
Mg
TOF - Channeltron 142 cm
200 eV ion energy
2000
ion count
+
1500
25
Mg
1000
+
26
Mg
+
+
+
H
500
N2
+
H2
0
0
10
20
30
40
50
TOF / s
• TOF of produced Mg ions
• typical energy 100 eV to 1
keV
• trap acceptance up to 500 V
view of the trap and the magnet
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injection of externally produced ions
• dynamic ion capture cycle
• low energy and TOF allow
selection of captured ions
Option with a cooling mechanism:
Stacking of successive ion
bunches
• 2 s gate
• up to 5 Hz
• almost no ion loss
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ion motion in a Penning trap
• in a harmonic trap all three motions are independent
• energy transfer in a non-ideal trap
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resistive cooling and non-destructive
FFT
low noise
Fourier-Transformdetection
Amp.
spectral analyser
„FT-ICR“
q/m
spectrum
Fourier-Transform Ion Cyclotron Resonance
I
I
ion current
signal
ed ion
dP/dfI
mass spectrum
FFT
slit
ion current
radially split electrode
t
signal
time-domain
f
frequen
time
frequency-domain
endcap
1. Passive:
2. Active:
- detects ion current
- cools the ion cloud
- excite ions and
induce corr. motion
- heats the ion cloud
C R
endcap
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detect
L
excite
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reduced cyclotron frequency
30,0k
-90
25,0k
Fluorescence / cps
amplitude / dB
+/2 = 2,555665 MHz
-95
-100
/2 = 2,55698 MHz
20,0k
15,0k
10,0k
-105
5,0k
2552
2553
2554
2555
2556
frequency / kHz
2557
2558
2559
2554
2555
2556
2557
2558
2559
frequency / kHz
• around 500 trapped and cooled 24Mg ions, excitation ~ 100 mVpp
• measured via electronic pickup and fluorescence reduction
• a small frequency shift due to the magnetic field imperfection
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fluorescence and line profile
1400
a single trapped ion
fluorescence rate / cps
fluorescence / cps
1200
800,0k
1000
800
600
~ 1500 trapped ions
400,0k
~ 100 MHz
200,0k
real line profile
0,0
400
-600
600,0k
-500
-400
-300
-200
-100
0
laser detuning / kHz
100
200
300
-600
-500
-400
-300
-200
-100
0
100
200
laser detuning / MHz
• identified single ion signal via quantized fluorescence jumps
• natural linewidth 42 MHz => final temperature < 1 K
• if fully saturated => detection efficiency ~ 5*10-5 
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300
trapping time
Graph showing ions
ejected and counted
with an MCP
• fast switched
ejection electrode
(adiabatic ejection)
• additional einzel
lense
500
Equation
Adj. R-Squa
400
no. of detected ions
y = A1*exp(-x/t1) + y0
B
B
B
300
0,9955
y0
A1
t1
Value
Standard Err
2,84013
4,31848
462,9551
9,50422
142,7690
6,93405
200
100
0
0
100
200
300
400
500
trapping time / ms
• if ejected after a long time the radial component gets too big
• fluorescence showed that the real trapping time is much longer
• estimated t1 ~ 100 s => in-trap vacuum ~ 10-11 mbar
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further planned measurements
l [nm]
A [1/s]
- 2P3/2
710.17
24
40Ar13+
2P
2
1/2 - P3/2
441.24
104
40Ca14+
3P - 3P
0
1
569.44
95
207Pb81+
F=0 - F=1
1019.7
20
209Bi82+
F=4 - F=5
243.9
2849
209Bi80+
F=4 - F=5
1555
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Type
Ion
low q
207Pb+
2P1/2
B-like
C-like
H-like
Li-like
Transition
final accuracy limited by the Doppler broadening
• with resistive cooling Dn/n0 ≈ 10-6 to 10-7
• with sympathetic cooling Dn/n0 ≈ 10-7 to 10-8
Dn D
8k BT ln 2

n0
mc2
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candidate no. 1
X. Feng, …, G. Werth; PRA 46 (1992)
Pb1+
208Pb
( I=0 )
207Pb
( I=1/2 )
F=2
6 P1
wavelength:
710.172 nm
T=1600 K
F=1
c
a b
d e
F=1
3 P0
F=0
pro
contra
-well known transition
- no “fancy” ion source needed
- „short“ lifetime (41 ms)
- improvement of the magnetic
moment
- difficult to trap
- invisible for pickup detection
- „long“ lifetime (41 ms)
- how many can we make?
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candidate no. 2
Ca14+
wavelength:
569.44 nm
3P - 3P
0
1
... no hyperfine structure
transition known from emission spectroscopy
pro
contra
- known transition, but
- accuracy can be increased by 3-4
orders of magnitude
- “short” lifetime (10 ms)
- easy to trap, easy to see
-need an EBIT
- need a beamline from the EBIT
- transported with 5 keV and
needs large deceleration
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pulsed elevator electrodes
• no mag field – phase space conservation makes life difficult
300 eV; +200 V to -50 V; no mag. field
with the magnetic field field – the ions are kept on axis by the field
300 eV; +200 V to -50 V; with mag. field
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Anđelković
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outlook
current status:
• UHV system and superconducting magnet in operation
• ion trap with cryogenic electronics finished and working
• demonstrated laser cooling of Mg+ to sub K temperature
• fluorescence detection functioning
• successfull ESR measurements of both Bi82+ and Bi80+
further plans:
• install a He recovery system
•improve the UHV system (cryopums)
• perform cooling and laser spectroscopy on Pb+
• new ion sources – EBIT, MEVVA, HITRAP
• measurements on forbidden transitions in mid-Z ions
• finally, high precision measurements on Bi82+ and Bi80+
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HITRAP and its experiments
HITRAP parameters:
• IH deceleration
• RFQ deceleration
• cooler trap decel.
• mass over charge
• N of extr. part.
to 0.5 MeV/u
to 6 keV/u
to 4 K
≤3
106
from ESR
4 MeV/u
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