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Zoran Andjelkovic
Johannes Gutenberg Universität MainzGSI Darmstadt
Laser Spectroscopy of Highly Charged Ions and Exotic Radioactive Nuclei(Helmholtz Young Investigator Group)
Laser cooling of Mg+ and laser spectroscopy of HCI @ SPECTRAP
Zoran Anđelković2
outlineoutline
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
ion production andion production and TOFTOF
• trap acceptance up to 500 V
0 10 20 30 40 500
500
1000
1500
2000
2500
N2
+
26Mg+
25Mg+
24Mg+
H2
+
ion
coun
tTOF / s
TOF - Channeltron 142 cm200 eV ion energy
H+
• TOF of produced Mg ions• typical energy 100 eV to 1
keV
Zoran Anđelković4
view of the trap and the magnetview of the trap and the magnet
injection of externally produced ionsinjection of externally produced ions
Zoran Anđelković5
• 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
Zoran Anđelković6
ion motion in a Penning trapion motion in a Penning trap
• in a harmonic trap all three motions are independent• energy transfer in a non-ideal trap
I
t
Zoran Anđelković7
resistive cooling and non-destructive resistive cooling and non-destructive detectiondetection
1. Passive: - detects ion current- cools the ion cloud
2. Active: - excite ions and induce corr. motion- heats the ion cloud
endcap
endcap
C R L
detect
excite
„FT-ICR“ Fourier-Transform Ion Cyclotron Resonance
I
f
z
Voltage/Current Amplifier
Pe nning Tra p(c ro ss se c tio n)
ra d ia lly sp lit e le c tro d eslit
FFTFou rie r-Transfo rm - spectra l analyser
excited ion
m agnetic fie ld
low noiseAm p.
timetime-domain frequency-domain
I
frequency
d P /d fion current signal
mass spectrum
FFT
q/mspectrum
ion currentsignal
reduced cyclotron frequencyreduced cyclotron frequency
Zoran Anđelković8
2552 2553 2554 2555 2556 2557 2558 2559
-105
-100
-95
-90
ampl
itude
/ d
B
frequency / kHz
+/2 = 2,555665 MHz
• 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
2554 2555 2556 2557 2558 2559
5,0k
10,0k
15,0k
20,0k
25,0k
30,0k
Flu
ores
cenc
e / cp
sfrequency / kHz
/2 = 2,55698 MHz
fluorescence and line profilefluorescence and line profile
Zoran Anđelković9
-600 -500 -400 -300 -200 -100 0 100 200 300
0,0
200,0k
400,0k
600,0k
800,0k
fluor
esce
nce
rate
/ c
pslaser detuning / MHz
~ 100 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
-600 -500 -400 -300 -200 -100 0 100 200 300
400
600
800
1000
1200
1400
fluor
esce
nce
/ cp
s
laser detuning / kHz
~ 1500 trapped ionsa single trapped ion
real line profile
trapping timetrapping time
Zoran Anđelković10
0 100 200 300 400 500
0
100
200
300
400
500
no. of
det
ecte
d io
ns
trapping time / ms
Equation y = A1*exp(-x/t1) + y0
Adj. R-Squa 0,9955
Value Standard Err
B y0 2,84013 4,31848
B A1 462,9551 9,50422
B t1 142,7690 6,93405
• 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
Graph showing ions ejected and counted with an MCP
• fast switched ejection electrode (adiabatic ejection)
• additional einzel lense
further planned measurementsfurther planned measurements
Zoran Anđelković11
Type Ion Transition [nm] A [1/s]
low q 207Pb+ 2P1/2 - 2P3/2 710.17 24
B-like 40Ar13+ 2P1/2 - 2P3/2 441.24 104
C-like 40Ca14+ 3P0 - 3P1 569.44 95
H-like207Pb81+ F=0 - F=1 1019.7 20209Bi82+ F=4 - F=5 243.9 2849
Li-like 209Bi80+ F=4 - F=5 1555 12
final accuracy limited by the Doppler broadening
• with resistive cooling /0 ≈ 10-6 to 10-7
• with sympathetic cooling /0 ≈ 10-7 to 10-82
0
2ln8
mc
TkBD
Zoran Anđelković12
Pb1+
pro-well known transition
- no “fancy” ion source needed- „short“ lifetime (41 ms)
- improvement of the magnetic moment
wavelength: 710.172 nm
contra- difficult to trap
- invisible for pickup detection- „long“ lifetime (41 ms)
- how many can we make?
3 P0
6 P1F=2
F=1
F=1
F=0
208Pb ( I=0 )
207Pb ( I=1/2 )
a b d ec
T=1600 K
X. Feng, …, G. Werth; PRA 46 (1992)
candidate no. 1candidate no. 1
candidate no. 2candidate no. 2
Zoran Anđelković13 Zoran Anđelković13
Ca14+
pro- known transition, but
- accuracy can be increased by 3-4 orders of magnitude
- “short” lifetime (10 ms)- easy to trap, easy to see
wavelength: 569.44 nm
contra-need an EBIT
- need a beamline from the EBIT- transported with 5 keV and
needs large deceleration
3P0-3P1... no hyperfine structure
transition known from emission spectroscopy
Zoran Anđelković14
pulsed elevator electrodespulsed elevator electrodes
Zoran Anđelković14
• no mag field – phase space conservation makes life difficult
with the magnetic field field – the ions are kept on axis by the field
300 eV; +200 V to -50 V; no mag. field
300 eV; +200 V to -50 V; with mag. field
Zoran Anđelković15
outlookoutlook
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+
HITRAP and its experimentsHITRAP and its experiments
Zoran Anđelković16
from ESR4 MeV/u
HITRAP parameters:
• IH deceleration to 0.5 MeV/u• RFQ deceleration to 6 keV/u• cooler trap decel. to 4 K• mass over charge ≤ 3• N of extr. part. 106