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