A radio-frequency ion trap and quadrupole mass spectrometerfor atomic and molecular physics at ASTRID2

A. Svendsen, L. Lammich, K.E. Nielsen, J.E. Andersen, H.K. Bechtold, F. Mikkelsen E. Søndergaard, and H. B. PedersenDepartment of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark

A new experimental setup for studying photophysics of atomic and molecular ions in the XUV range is currently under development at Aarhus University. The XUV light will be provided by the AMO beamline, a photon beam line at the new synchrotron ring, ASTRID2, at Aarhus University. The end station comprises an electrostatic storage ring and a radio-frequency ion trap followed by a quadrupole mass spectrometer. The two complementary setups at the end station allow to study both the details of the molecular break-up as wellas the spectroscopy of molecular ions at a well-de�ned temperature. Here, the �rst test experiments with the trap and quadrupole mass spectrometer setup are presented.

Radiofrequency ion trap:

Ground

“Ground” ofhigh voltage platform

20151050

U [e

V]

6040200z [mm]

r0

Trap electrode End cap

Lensp1 p22πz0

Axial trapping potential

p1p2

1.00.80.60.40.20.0

Ueff

[eV]

543210r [mm]

Radial trapping potential

Trapping potentials

Demonstration of trapping

Trapping time [ms]

10

20

30405060

100

Inte

nsity

0.1 1 10 100

-400 V applied to entrance end cap -25 V applied to entrance end cap

Ion lifetime in trap

Ion time-of-flight spectra

3002001000-100

Time [µs]

Exit end cap

Ion chopper

Trapping time

Entrance end cap

Time [µs]

Ion bunch width

Inte

nsity

3002001000-100

Trapping

Guiding

Trap depth model

1.00

0.75

0.50

0.25

0.00

Trap

dep

th, U

trap

[eV]

300250200150100500

RF amplitude, V0 [V]

model 1

model 2

22-pole trap

r trap

[mm

]

5

4

3

2

1

0300250200150100500

RF amplitude, V0 [V]

model 2

Effec

tive

pote

ntial

, Ueff

[eV] 1.1

z / z0

1.0

0.9

0.8

0.00 π/2 π 3π/2 2π

Utrap

model 2

Utrap

model 1

0.362

0.360

0.358

0.356

0.354

0.000

r [m

m]

0 π/2 π 3π/2 2πz / z0

rmax

model 2

model 1

h(r,z/z0) = hmax

h(rmax,z/z0) < hmax

Trapping boundary

Effective potential at boundary

Radius of trapping volume

Trap depth

Adiabatic ion motion:

Smooth drift motion Rapid oscillatory motionmicromotion

Equation of motion:

Approximative solution (adiabatic approximation):

Equation of motion for R:

Effective potential:

Adiabaticity parameter:

Adiabatic approximation valid andion motion stable if η<0.3

Trap depth = maximum Ueff in volume with η<0.3

Experimental setup:

Radiofrequency ion trap: . Photofragment spectroscopy of cold ions . Manipulation/storage of ions before injection into ring

Electrostatic storage ring, SAPHIRA: . Crossed and merged beams setups . Detection of charged and neutral fragments as well as electrons

Transfer beamline

Ion sourcemounted on accelerator

Radiofrequencyion trap

+Quadrupole mass spectrometer

for fragment analysis

SAPHIRA electrostaticstorage ring

Crossed beamssetup

Synchrotron lightfrom ASTRID2

Electronspectrometer

Fragmentanalysis

Magnet for mass analysis

Residing on HV platformto trap ions from fast beam

Quadrupole mass spectrometer:

x

zy +U+V cos(ωt)

-U-V cos(ωt)

Equations of motion for ion in quadrupole:

DC

volta

ge, U

RF amplitude, V

∆m

∆res

Ions rejected

Ions transmitted

Stability diagram

∆m = -20 ∆m = -70 ∆m = -120 ∆m = -220

∆res = -500 ∆res = -1000

∆res = 0

250

200

150

100

50

0

Inte

nsity

7065605550RF amplitude, V [V]

Resolution tests with Cl-

First photodissociation experiments:

Cl2 + hν (532 nm) Cl- + ClCl-2

50

40

30

20

10

0

Inte

nsity

120011001000900800700600500

Quadrupole mass command [arb. units]

x10

Cl-

Cl-Cl2Laser onLaser off

Mass spectrum

4

3

2

1

0

Inte

nsity

4035302520151050

Trapping time [ms]

Laser fires

Laser onLaser off

Time dependence of Cl- signal

0.04

0.03

0.02

0.01

0.003002001000

Cl-

Inte

nsity

Laser onLaser off

0.4

0.3

0.2

0.1

0.03002001000

Time [µs]

Cl-Cl2

Inte

nsity

Laser onLaser off

Arrival time distributions

Status and future plans:

Trapping of ions in radiofrequency ion trap demonstratedMass selection in quadrupole mass spectrometer achievedFirst photodissociation experiments performed

Next:Explore further the trap characteristicsImplement cryocooler for the ion trapConstruction of the electrostatic storage ring

Funding:

Carlsberg FoundationLundbeck FoundationThe Danish Council for Independent Research in Natural Sciences (FNU)Faculty of Science and Technology, Aarhus University

Undulator Parameters The undulator has been ordered from Kyma.

�u 53 mm

43

No. poles 87

BMax 1 T

Minimum gap 14 mm

0 50 100 150 2000

2x1014

4x1014

6x1014

8x1014

1x1015

Flux

Photon Energy / eV

Gap: 20 mm