Genealogy of Gas Cell for low-energy RI-beams

Michiharu Wada, RIKEN Nishina Center

• IGISOL as Roots

• DC and RF in Gas Cell

• Various Improvements

EMSI16 (2012) Matsue, Japan

HE≧100MeV/u

IGISOLJYFL LIS+IGISOL

Leuven

RF IGISOLINS

Gas Cell Genealogy

SLOWRI prototypeRIPS RIKEN

LEBIT MSU

FAIR-LEBGSI

RF IGISOLSendai

no RF

GARIS+RF IGISOLRIKEN

FRIBMSU

PALISRIKEN

CARIBOUANL

RF funnel

RF funnelCyclotron

RF carpet

GARIS+IGISOLINS - RIKEN

ATLASANL

Res. Ionization

SHIP TRAPGSI

SLOWRI2.0RIBF RIKEN

ME≈10MeV/u

LE≈1 MeV/u

Re-Acceleration

future plans

more selectivity

more yield

Cf fission source

En

ergy

Year

SHE-Mass

~personal view~

ISOLHigh Yield, but difficult for Refractory elements, Chemically active elements

thick target

ion source

stop in target, diffusion, evaporation

ionization in IS≈50 keV

p

H HHe He

Li LiBeB B

C CN N

O O OFNe Ne Ne

NaMgMgMg

AlSi Si Si

PS S S

ClS

ArClArK

Ar

CaKCa Ca Ca

ScCa

Ti Ti Ti Ti TiVCr Cr Cr

FeMnFeFe Fe

NiCoNi Ni Ni

CuNi

ZnCuZnZn Zn

GaGe

GaGe Ge Ge

SeAs

Ge

SeSe Se

KrBr

Se

KrBrKr Kr Kr

SrRb

Kr

Sr Sr SrYZr Zr Zr

MoNb

Zr

MoMoMo

Ru

MoMo

RuRu Ru RuRu

PdRh

Ru

Pd Pd Pd

CdAg

Pd

CdAg

Pd

Cd CdCd

SnIn

Cd

Sn Sn

Cd

SnSn Sn SnSn

TeSb

Sn

TeSb

Sn

TeTe Te

XeIXe XeXe

Ba

Xe Xe

BaCs

Xe

BaBa Ba

Ce

BaBa

CeLaCePrNd Nd

Sm

NdNd Nd

SmEu

SmEu

Sm

Gd GdGd

Dy

Gd Gd

DyTb

Gd

DyDy Dy

Er

DyDy

ErHoEr Er Er

YbTm

Er

YbYb Yb YbYbLu

Yb

Hf Hf Hf Hf Hf

WTaW

ReW

Os OsOs OsIr

Os

PtIrPt Pt Pt

HgAu

Pt

HgHg Hg HgHgTl

HgTlPbPb Pb

Bi

10^1 cps10^3 cps10^5 cps10^7 cps

ISOLDE (SC, Fact Sheet)

EMIS

comprehensive study of RI since ‘60s

≈700 RI

Isobaric contaminations

ISOLDE, OSIRIS, TRISTAN,TISOL ....

note: laser ion source just supports

ionization process, not in target

First Beak Through: IGISOL @JYFLJ. Ärje, K. Valli: NIM 179(1981)533.

ISOL for All Elements, Fast Extraction

Problems:1) Poor Emittance (Gas Collision)2) Low Efficiency @HI (Plasma Effect)3) Isobaric Contamination (Universal)4) Low Yield (Thin Effective Target)....

Buffer gas cooling & Bunching

Electric Field in Cell!

Ion Guide ISOL

RF Ion Guide

J. Ärje, J. Äystö et al: PRL 54(1985)99.

W-180 5.5ms Isomer

100-500V0.1 mbar

1) Poor Emittance (Gas Collision at Skimmer)

TT. Inamura, M. Koizumi et al, NIMB70(1992)226

Energy Spread vs Skimmer Voltageby Laser Spectroscopy

ΔU≈100V

SPIG @INS

We must transport through Skimmers

without Acceleration

SPIG: rf 6-pole Ion beam Guide

Transport through Skimmers without Acceleration,

Even Cooling Ions

H. Xu, M. Wada, I. Katayama et al: NIM A222(1993)274.

S. Fujitaka, M. Wada, I.Katayama et al: NIMB126(1997)386.

ΔE≈0.8 eV

Multiple Skimmers : Easy Pumping

Trapping in SPIG

Trap Efficiency:10% @10ms

>80% @ 0.3ms

2) Low ε @Heavy Ion: Plasma Effect

Plasma by Primary Beam: Space-Charge effect We must Isolate

Primary Beam and RI Beam!

GARIS-IGISOL T. Nomura et al, NIMA269(1988)23

Selected RI Beam

Primary Beam

Also a hint for Fragment Separator + Gas Cell

Separate RI Beam from Primary Beam

3) Isobaric Contamination (Universality)Yu. Kudryavtsev et al, NP A701(2002)465c

Laser Resonance re-Ionization in Gas Cell

High Element Selectivity

neutralize in Ar gas

M. Huyse, Lasers in gas cells and jets ...

4) Low Yield (Effective Target Thickness)

effective target thickness:stopping capability of gas

Large Cell? Slow Extraction!

Electric Field in Cell!

J.Ärje thesis

~ most serious problem ~

Big Gas Cells

FRS Gas Cell (1st gen.)

Gas Cell at RIPS

use a DC field in Gas Cell?

Drift Motion: Follow Electric Field Line

Cathode

Always terminated at Cathode Electrode

Even if Cathode is a Mesh

He: 100 mbar

if a point Cathode is virtually outside Cell

Surface Current

L. Weissman et al, NIMA 540(2005)245

Spherical Electrodes @LEBIT, MSU

38Ca Mass Measurement @NSCL (G. Bollen et al, PRL 96(2006)152501)

RF Ion Barrier on Cathode

ANL RF-FunnelG. Savard et al

CARIBOU @ATLASone of ReA3 @NSCL

@TAM

INS-RIKENRF Carpet

M. Wada et al

SLOWRI@RIBFKVI Cryo RF CarpetP. Dendooven et al

FRS@GSIcyclotron RF@MSUion surfing RF@MSU

Invention of electric curtain with standing & traveling wave, in 1972

• Invention of rf hopper, curtain• transport aerosol, organic cell ions in air

History of RF Ion Guide @INS-RIKEN

two stage rf

first off-line test for Ta at INS1997-1998

first on-line test for Li-8 at RIKEN

2000

2m cylinder and RF carpet

15cm

30cm

Laser Spectroscopy of Be 2005~

MRTOF 2011~

200 mmφ

RF-Carpet Ion GuideTM

nozzle 0.7mmΦHe 100Torr x 2m

～2MeV/u(0~10MeV/u)

++

++

--

--

EdcEeff

~RF gradient Field: Barrier

€

E eff in gasmax =

mµ 2Vrf2

er03

€

2r0 ≈ electrode distance

€

F = − e2

4m1

(Ω2 +1/ τ v2 )∇E rf

2 (r)

€

(E(r,t) = E rf (r)cos(Ωt), τ v : relax time)

M.Wada et al, NIM B204 (2003) 570.

0.7φノズル

0.28mm Intervalco-centric ring

electrodes

More Precise Analytical FormulationS. Schwarz, IJMS 299(2011)71.

feedback to IGISOL (Fission)

RF-IGISOL @SendaiT. Sonoda et al

FP > 1 MeV/u

T. Sonoda et al, NIMB 254 (2007) 295-299

Larger Cell Gain

Issues & Solutions

1. Space-charge effect due to ionized He

2. Contamination

3. Longer Stopping Length

4. Faster Extraction

5. ...

All UHV Materials: ANLCryogenic Gas Cell: KVI-GSI

Effective Volume Reduction

Cyclotron Gas Cell

Cyclotron Gas CellTraveling Wave

ρ0=5x10-18 C/mm3

ρ0=5x10-17 C/mm3

ρ0=5x10-16 C/mm3

N0=104 ions/s

N0=106 ions/s

N0=108 ions/s

Ion Trajectories under space-charge

1. space-charge effect

ρ0=5x10-18 C/mm3

ρ0=5x10-17 C/mm3

ρ0=5x10-16 C/mm3

N0=104 ions/s

N0=106 ions/s

N0=108 ions/s

Ion Trajectories under space-charge

1. space-charge effect

New Ion Guide Gas Cell

- Fully covered RF carpets (planer & cylindrical)- Cryogenic cooling by thermal isolation

21

1. space-charge effect & 2. contamination

M.Ranjan, thesisCryogenic Gas Cell

@KVI →GSI

W. Plaß, The FRS Ion Catcher

N

S

He

High EnergyIon Beam

ThinDegrader

RF-Rings

SPIG-TrapCyclotron-RF-Ionguide

I. Katayama et al. / Cyclotron ion guide for energetic radioactive nuclear ions 167

Figure 2. A trajectory of a 5 MeV/u 11Be4+ ion coming out of a proper Ta energy degrader at R = 50 cm

and 5000 Pa He gas. The ion starts with an azimuthal velocity of vx = 3.1 × 107 m/s and vz =4.2× 105 m/s at (x0, y0, z) = (−500, 0,−3) mm. The charge state of ion is assumed to follow a chargeequilibrium given in [8]. Magnetic field is taken to be Bz = B0(1 − 0.25r/R) and Br = 0.25B0z/Rwith B0 = 17 kG. The result shows (a) the ion orbit in (z, r)-plane, and (b) the ion orbit in (x, y)-plane.

dc field is also schematically shown in figure 1. Ions should drift along a line which

is perpendicular to the equipotential and come to the exit of the gas cell. Another

very crucial point in the present scheme is an employment of the potential barrier

(we call ion barrier) along the vessel wall generated by an rf field applied on ring

electrodes. Since the electrodes themselves form the local peak potential, so, if they

were at dc potentials only, quite a number of ions would be collected on the electrodes

and lost by neutralization. The hint of this structure comes from the so-called ‘electric

curtain’ which has been devised by Masuda and his group [10]. It has been used for

transportation of microparticles for industrial use. The ring structure of the present

scheme is discussed in the next section. The ions drifted to the exit of the vessel, then

extracted to vacuum in a usual way of ion guide method, go through the molecular

dissociator section and are collected by SPIG.

3. Ion barrier

Among several configurations of ‘electric curtain’, one example is such that an

infinite number of rod electrodes of diameter d are arrayed on a plane keeping adistance b between two surfaces of the neighbouring rods [11]. Every alternative rodis connected together in this case and is applied with the same phase of an ac potential.

The ion motions in the ac field are expressed with two components, i.e., a weak but

fast vibrating motion with the ac phase and a slow drift component. Due to a field

gradient generated by the rf field, the equation for the slow drift motion of the ion for

- Long stopping length >10 m- Short drift path < 30cm- Isolated high space-charge & drift path

Ideal condition for:Fast extraction &

High Intensity

I. Katayama, M. Wada et al, Hyp. Int. 115 (1998)165. (proc. Ferrara 1997)

3. longer stopping length

Cyclotron Gas Stopper @ MSU

G. Bollen et al, NIMA 550(2005)27, Eur. Phys. J. ST 150(2007)265.

CF. M. Sternburg, G. Savard, NIMA 596(2008) 257.

S. Schwarz, under construction

another evaluation for Cyclotron Gas Stopping Concept.

G. Bollen, IJMS 299(2011)131-138

Ion Surfing RF-Carpet using Traveling Wave

• no DC High Vol in He

• Faster Extraction

Superposition of Ion Barrier RF (Radio Freq.)and Ion Transport RF (Audio Freq.)

M. Brodeur,Traveling wave ...

4. faster extraction

HE≧100MeV/u

IGISOLJYFL LIS+IGISOL

Leuven

RF IGISOLINS

Gas Cell Genealogy

SLOWRI prototypeRIPS RIKEN

LEBIT MSU

FAIR-LEBGSI

RF IGISOLSendai

no RF

GARIS+RF IGISOLRIKEN

FRIBMSU

PALISRIKEN

CARIBOUANL

RF funnel

RF funnelCyclotron

RF carpet

GARIS+IGISOLINS - RIKEN

ATLASANL

Res. Ionization

SHIP TRAPGSI

SLOWRI2.0RIBF RIKEN

ME≈10MeV/u

LE≈1 MeV/u

Re-Acceleration

future plans

more selectivity

more yield

Cf fission source

En

ergy

Year

SHE-Mass

end

F2

Target

1) Stop & Neutralize in Ar (1 bar)2) Extract by Gas Flow3) Re-Ionize at Exit and SPIGnot universal, not very fast but

A/Z, Z, A separation

F1

PALISPArasitic slow RI-beam with gas catcher Laser Ion Source

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SLOWRI 2.0 floor plan

BigRIPSF2D2 D3

D4

PALIS Cell

RF-CarpetGas Cell

SD1

SD2

SD3

SD4

To be constructed in FY2012 (approved)

mass sepa

mass sepa

parasitic beam

main beam

SLOWRI Exp Hall

FODO BTL