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V. I. Mishin
Institute for Spectroscopy (ISAN)
Russian Academy of Sciences
Troitsk, Moscow, 142190 Russia
1st Topical Workshop and Users meeting 2013: Laser Based Particle Sources CERN, Switzerland 20 – 22 February 2013
TIME-of-FLIGHT TECHNIQUE
for RILIS SELECTIVITY
IMPROVEMENT
Neutralizer
Laser beams
Atomic beam
Ion Detector
А+
Protons
Target and Ionizer
А+ Mass separator
Laser Resonant Ionization Spectroscopy of Radioactive Isotopes in Atomic Beams (1982)
Minimal measurable isotope
flow
≈ 103 – 105 isotopes/s
ISAN & LNPI
COMPLIS – ISOLDE
MAINZ UNIVERSITY
ISAN / LNPI experimental setup
An excerpt from Mishin’s scientific log book
ions
laser
Laser Resonant Ionization of Atoms in a Hot Metal Pipe (1982) ISAN/Troitsk
1. Ionization in the pipe.
Photoionization Methods for
LNPI
f laser pulse
repetition rate
l cavity length
υ thermal velocity
of isotopes
atomsions +
Laser Resonant Ionization of Atoms in a Hot Cavity. Operating Principle (1984)
S.V. Andreev,
V.I. Mishin,
S.K. Sekatsky
Pi /Pa = 4fl/υKtr
laser beam
l = 1cm
Pi ηRILIS = ≈ 75% Pi + Pa
metalplates
HOT CAVITY
insulator ISAN/Troitsk
Laser Resonant Ionization of Atoms in a Hot Cavity. Operating Principle (198
Laser Resonant Ionization of Atoms in a Hot Cavity (1984 – 1988)
1. Rise in the efficiency of ionization of atoms by pulse-periodic lasersS. V. Andreev, V. I. Mishin, S. K. SekatskiySov. J. Quantum Electron., Vol. 15, Num. 3 (1985) 398-400 (English version)Kvantovaya Elektronika, Volume 12, 3 (1985) 611-614 (in Russian)
Abstract. The possibility is investigated of raising the efficiency of particle interception in the method of resonant photoionization of atoms by laser radiation in a closed hot cavity, located in vacuum, and subsequently employing an electric field to extract the ions formed through a small aperture in the wall. It is shown that for realistic laser radiation parameters (pulse duration ~ 15 nsec, repetition frequency 10 kHz) the cavity geometry can be chosen in such a way that the interception efficiency exceeds 50%. The possibility is demonstrated of completely extracting the ions formed by photoionization from the cavity.
2. High-efficiency laser resonance photoionization of Sr atom in a hot cavityS. V. Andreev, V. I. Mishin, and V. S. LetokhovOptics Communications, Volume 57, Issue 5 (1986) 317-320 Abstract. The possibility of high-efficiency photoionization of Sr atoms inside a hot cavity with lasers of high pulse repetition rate ( 104 pps) has been studied. The produced photoions were extracted from the cavity through a small hole in its wall for further analysis and counting. An overall photoion yield of about 0.2 has been achieved.
Laser Resonant Ionization of Atoms in a Hot Cavity. (1985 – 1988)
3. Laser resonant photoionization detection of traces of the radioactive isotope 221Fr in a sampleS. V. Andreev, V. S. Letokhov, V. I. MishinJETP Letters, Volume 43, Issue 12 (1986) 736-739 (English version)Pis'ma Zh. Eksp. Teor. Fiz., Volume 43, Issue 12 ( 1986) 570-572 (in Russian) Abstract. The hyperfine splitting of the D2 line of the isotope 221Fr (T1/2 = 4.8 min) has been measured. The ionization potential of the francium atom has been refined: Ei ≤ 4.154 eV.
4. Laser resonance photoionization spectroscopy of Rydberg levels in FrS. V. Andreev, V. S. Letokhov, and V. I. Mishin«Physical Review Letters»Phys. Rev. Lett., Volume 59, Issue 12 (1987) 1274-1276 Abstract. We investigated for the first time the high-lying Rydberg levels in the rare radioactive element francium (Fr). The investigations were conducted by the highly sensitive laser resonance atomic photoionization technique with Fr atoms produced at a rate of about 103 atoms/s in a hot cavity. We measured the wave numbers ofthe 7p2P3/2→nd2D (n=22–33) and 7p2P3/2→ns2S (n=23, 25–27, 29–31) transitions and found the binding energy of the 7p2P3/2 state to be T=-18 924.8(3) cm-1, which made it possible to establish accurately the ionization potential of Fr.
Laser Resonant Ionization of Atoms in a Hot Cavity. (1985 - 1988)
5. Rydberg levels and ionization potential of francium measured by laser-resonance ionization in a hot cavityS. V. Andreev, V. I. Mishin, and V. S. Letokhov«Journal of the Optical Society of America B: Optical Physics»J. Opt. Soc. Am. B, Volume 5, Issue 10 (1988) 2190- 2198 Abstract. A highly sensitive method of detecting atoms in samples has been used for spectral investigations of the rare radioactive element Fr. The method is based on laser-resonance photoionization of Fr atoms in a hot quasienclosed cavity. The investigations have been carried out with samples in which short-lived radioactive 221Fr atoms formed at a rate of approximately 103 atoms/sec. The data obtained, to our knowledge for the first time, on the energies of the high-lying Rydberg levels of the 2S½ and 2D series have made it possible to determine the electron binding energy of the 7p 2P3/2 state and to establish the ionization potential of Fr accurately.
Laser PhotonizationPulsed Sourceof Radioactive
Atoms (1984)
(V. S. Letokhov and V. I. Mishin)
V.S. Letokhov, V.I. Mishin
Laser Ion Sources(1985)
H.-Jürgen Kluge, and F. Ames,
W. Ruster, K. Wallmeroth
Invited talk, given
at the “Accelerated
Radioactive Beams
Workshop”
Vancouver Island, Canada4 – 7 September 1985
Selective Laser Ion Source
(1989) LNPI-ISAN
Высокоэффективная z-селективная
фотоионизация атомов в горячей
металлической полости с последующим
электростатическим удержанием ионов
Г. Д. Алхазов, В. С. Летохов, В. И. Мишин, В. Н. Пантелеев, В. И. Романов, С. К. Секацкий, В. Н. Федосеев
Письма в ЖТФ, том 15, выпуск 10 (1989) 63-66
Fig. 1. Schematic drawing of the selective laser ion source. The dashed area is the region of ionization.
High efficient z-selective photoionization of atoms in a hot metal cavity followed by electrostatic confinement of the ions
G.D. Alkhazov, V.S. Letokhov, V.I. Mishin,V.N. Panteleyev, V.I. Romanov, S.K. Sekatsky, V.N. Fedoseyev
Pis'ma Zh. Tekhn. Fiz., Volume 15, Issue10 (1989) 63-67
A laser ion-source for on-line isotope separation (1990)
ISAN ISOLDE-3 Synchrocyclotron
Proceedings of the Fifth International Symposium on “Resonance Ionization Spectroscopy and its Applications, RIS -90”, Varese, Italy (1990)
Abstract. A laser ion source has been developed for efficient production of isobarically pure ion beams at the on-line mass separator ISOLDE at CERN. In first off-line tests with radioactive Yb-169, an efficiency of about 15% was achieved. An elemental selectivity between 10 and 104 was observed. The maximum value could be obtained at the off-line separator with TaC as construction material. A first test at the on-line separator ISOLDE-3 was performed recently with Yb isotopes. The lasers produced a pulsed ion beam of about 10 ns pulse length. In order to suppress the continuous background due to surface ionization a pulsed deflector was used so that the selectivity was improved by a factor of 10.
V.I. Mishin, V.N. Fedoseev, Yu.A. Kudryavtsev, V.S. Letokhov,
H. Ravn, S. Sundell, H.J. Kluge, F. Scheerer
Study of Short-Lived 101-108Sn50 Isotopes with
RILIS
at Heavy Ion Accelerator UNILAC/GSI
(1992)
extraction electrode
50Cr
laser beams
on-line mass separator
40 particle•nA of
58Ni14+(5MeV/u)FEBIAD
Ø 1 mm
E = 0.01 V
E = 1.0 Vion beam 106-xSn + 2p + xn
+
+
++
T ≈
24
00
K
The acronym RILIS was enacted for the first
time
in 1993 at the ISOLDE/BOOSTER
by Slava Mishin, Valentine Fedosseev and
Ulrich Köster
Operation of a RILIS
TRAPPING of IONS by CAVITY PLASMA
laser beam
atoms
high-temperaturepipe
+ +
photo ionssurface ions
++ + ++
sourcecontainer
RESONANT LASER
IONIZATION
of an ATOM
n1
n2
A+
Ahotmetal
cavity+ +
+
++-
-
- - --
-
---
- ----
---- -
Two basic factors define RILIS selectivity: *** LASER IONIZATION of studied atoms
*** SURFACE IONIZATION of interfering atoms
Selectivity of the RILIS Hot Metal Cavity
ηLASER (Ag) S(Ag/In) = βSURFACE(In)
0
5
10
15
20
25
30
RIL
IS o
vera
ll ef
fici
ency
, %
Overall RILIS
efficiencies for elements
available at ISOLDE
ISOLDE
ηLASER (Ag)
S(Ag/In) =
βSURFACE (In)
Selectivity of the RILIS Hot Metal Cavity
Wall sticking times
)exp(0 kT
Edsorp Frenkel
equation
1/τ0 – frequency factor Ed – interaction energy of the atom with the surface
τ, c
TEMPERATURE, oC
J. Beyer, A. F. Novgorodov and V. A. Halkin.JINR preprint Р6 – 9917, 1976
The number of collisions of atoms with a wall of the RILIS ionizer prior to atoms fly out is
Swall = πDLN = = 4L/D Shole = πD2/4
L = 3 cm, D =3 mm (length and diameter of the
ionizer)
N = 40 Lifetimes of the Sc, Y, Zr, Hf and some lanthanide atoms on the polycrystalline Ta surface
Neutron Number N
Pro
ton N
um
ber
Z
Selectivity of a RILIS can be increased considerably providinglaser produced ions are separated from thermal ions T laser pulse-repetition intervalτions creation time = τlaser pulse duration
Maximum RILIS selectivity, which can be reached by laser ions separation
from thermal ions, is equal to S = T / τions
flaser = 104 pps
T = 1/flaser = 100 μs
τions = τlaser ≈ 10 ns
time
S ≈ 10000
It makes sense to hunt for this number
ISOLDE
RILIS
Laser beams in ionizer Laser beams in ionizer Laser beams in ionizer
TARGET
IONIZER
30 mm
≈ 140 mm
- 60 kV
Acceleration electrode Ground plate
≈ + 2 V
Repelling electrode
TARGET
IONIZER
30 mm
≈ 140 mm
- 60 kV
Acceleration electrode Ground plate
≈ + 2 V
Repelling electrode
TARGET
IONIZER
30 mm
≈ 140 mm
- 60 kV
Acceleration electrode Ground plate
≈ + 2 V
Repelling electrode
TARGET
IONIZER
30 mm
≈ 140 mm
- 60 kV
Acceleration electrode Ground plate
≈ + 2 V
Repelling electrode
Laser beams in ionizer
Ions to mass separator magnets
ISOLDE
COMPARISON of an ISOL Time-of-Flight RILIS and
the Time-of-Flight Mass Spectrometer
The Wiley-McLaren TOF mass spectrometer
An ISOL TOF RILIS
Ground Extraction Acceleration Detector plate grid grid
Source Drift region
Extraction Acceleration region region
- 1600 V - 1600 V
0.2 cm 1.2 cm 40cm
0 V- 64 V
++
++
++++
++++
Repelling electrode Ground grid Ground grid Acceleration electrode
- 60 000 V30 V
3 cm
++
++
+++
+
++++
3 cm
++++
80 cm
Source – Hot cavity Drift region Acceleration region
There is a significantdiscrepancybetween the TOF mass spectrometer and ISOL TOF RILIS
1. Initial ion spatial distributionsTOF MS ≈ 0.3 mmTOF RILIS 30 mm
2. Voltage applied to
the TOF electrodesTOF MS ≈ 5000 VTOF RILIS ≥ 50 V
3. linear dimensionTOF MS 40 - 200 cmTOF RILIS ≈ 12 cm
Ion packets width
τ ion peaks ≈ τ spatial distributions + τ thermal energy distributions
Broadening of ion packets by initial spatial distributions
acceleration region
E=0+V
field free drift-region
τ spatial distributionsVE
L
Broadening of ion packets by initial thermal energy distributions
acceleration region
VE
L
E=0
L
+V
field free drift-region
02v m
eEτturn-around time = t1 – t0
t0
t0t1
t1
τ turn-around time
υ0 - initial thermal velocity m - mass of ions e - charge of electron
Duration of ion packets at the outputof the mass separator in relation to the voltage drop across the RILIS ionizer
target
ionizer
30 mm
Uacceleration
- 60 kV Uionizer
J. Lettry et al. (2002) Δτ(Ag) ≈ 50 – 60 μs
M. Koizumi et al. (2002) Δτ(Al) ≈ 10 μs 0 10 20 30 40 50 60 700
5
10
15
20
25
30
35
40
45
50
Du
ratio
n o
f io
n b
un
che
s,
s
Voltage applied to the graphite ionizer, Volts
M = 100 a. e.
The voltage
range
affect
the mass
separator
resolution
τ spatial distributions + τ turn-around time
Melting Points and Resistivityof the Refractory Metals and Carbon
Niobium Molybdenum Tantalum Tungsten Rhenium
Melting point 2750 K 2896 K 3290 K 3695 K 3459 K
Resistivity
Tungsten 5.6×10−8 Ω•m at 20 °C
Carbon (crystalline) 2.5×10−6 to 5.0×10−6 Ω•m // basal plane
3.0×10−3 Ω•m ⊥ basal plane
Carbon remains solid at higher temperaturesthan the highest melting point metals such as tungsten or rhenium.
Carbon sublimation point about 3900 K.
The temperature of the crystallinegraphite pipe in relation to the voltage
drop
20 22 24 26 28 30 32
1000
1200
1400
1600
1800
2000
Tem
pera
ture
, o C
Voltage, V
The electrical resistance of the pipe about 2.7 Ω
35,5
crystalline graphite
amorphous graphite
Ø5
Ø3
Acceleration Ground Ground plate grid grid
+
+
+ +
+
+
+
+
+
s D = 2s
E = E0 E = 0 E = E1 ≈ 60 000 kV/L
Primary Space Focus for Single-Stage Source Region Configuration
τion peak ≈ τturn-around time
Source – Hot cavity Drift region Acceleration region
Experimental Setup
Ø3 mm
L = 37 mm
Carbon (amorphous)
3,7 cm 3,7 cm
D = 2ss
atomic vapoursource
Time-of-flight mass spectrum of Li+, Na+, K+ and Tm+
Tm (thermal) Tm (laser)LiNa
K
current generator triggering pulse
Tm (thermal) and Tm (laser) peaks are created through Tm ionization on the hot cavity surface or by the laser
photodiode response on the laser pulse
laser ablation of the grid
5 ms
Uionizer = 15.3 V
+
+
+ +
+
+
+
+
+
s D = 2s
Acceleration Ground Ground
plate grid grid
E = E0 E = 0
Primary Space Focus for Single-StageSource Region Configuration
0 10 20 30 40 50 600
5
10
15
20
25
30
35
40
Voltage applied to the ionizer, Volts
Dura
tion of
ion
peaks
, μ
s
Broadening of ion peaks by initial spatial distributions
Broadening of ion peaks by initial thermal energy distributions
= +
0 10 20 30 40 50 600
1
2
3
4
5
M = 100 a. e.
Summary
• • • The hot cavity made of crystalline graphite can
operate
stable at high temperatures (≥2000oC)
• • • The voltage applied to the cavity may be as
much as 30 V
• • • Short ion pulses approaching 3 μs can be
prepared
by the use of the crystalline graphite hot
cavity
• • • The RILIS selectivity can be increased by a
factor of
30 – 50 for isotopes of mass 100 with the
crystalline
graphite hot cavity and single-stage TOF
configuration
Recommended