a radio-frequency ion trap and quadrupole mass ...astrid2.pdf · the end station comprises an...
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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