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