How to match production schemes and ion traps efficiently?...F. Herfurth - Ion Beam Bunching RFQ cooler & buncher • Linear Paul trap i.e. radial RF, long. DC • Gas filled (at low

Ion Beam Bunchingor: Beam Handling with/for Ion Traps

How to match production schemes and ion traps efficiently?

F. Herfurth - Ion Beam Bunching

Introduction

– Scope of this lecture– Production of exotic ions– “Typical” exotic ion trap facility


Experiments with Exotic Ions

Exotic Ions- radioactive = short lived

- (heavy) highly charged ions (HCI)- antimatter

Experiments in Traps- precision spectroscopy (K. Blaum, F. Herfurth)- (heavy) highly charged ions (HCI) (J. Créspo)

- antimatter (N. Madsen, C. Surko)- watching them decay (F. Herfurth)

This Lecture


Production & Preselection of radioactive Ions – ISOL & Fusion Techn.

Target wheel

Primary beaml@ 1..10 MeV/u

Fusion productswith about 100 keV/u

SHIPTRAPJYFLTRAP

Fusion products selected in flight by velocity

Fission, Spallation and Fragmentation products selected by m/q

ISOLTRAPTITAN, SPIRAL2-Trap

8

8

20

20

50

50

126

82

82

28

28

Dipole magnet

Target – Ion source

Proton beam1 .. 1.4 GeV


Production & Preselection of radioactive Ions – Fragmentation in Flight

Fragmentation products from heavy beams selected by m/q and Z

LEBITMATS

8

8

20

20

50

50

126

82

82

28

28

Primary beam@ 100 to 1000 MeV/u

„Thi

n“ T

arge

t

FRS


Production of radioactive Ions

p

fusion

Target

projectile

60 keVup to 400 MeV/u

Kinetic Energyafter the reaction

~100 keV/u


Production of Heavy, Highly-Charged Ions

– stripping of all Electrons at high Energy– fast, efficient– up to 106 bare Uranium Nuclei per pulse but at 400 MeV/u

U72+ @ 1 GeV/u

Au

f

oi

l U92+ @ 400 MeV/u


Production of Heavy, Highly-Charged Ions

– stripping of all Electrons by energetic Electron Beam→ J. Créspo

U1+ @ eV U92+ @ eV

time

Intense, energetic Electron Beam


How to get these Ions into a Trap?

Why is it a problem?

Production energy >> trap potential

(We try to capture the results of an explosion in a card box)

Great variety of energies and species after production (It's a mess)

Exotic ions are rare!

(Just a few per measurement shall be enough)

They are delicate. (Some decay quickly and some dislike matter)


How to get those Ions into a Trap?

Solutions:

Production energy >> trap potential

Decelerate/Stop in matter and/or electrically.

Great variety of energies and species after production Cooling and Purification using trap-specific properties.

Exotic ions are rare! Be efficient!

They are delicate. Be fast and handle them carefully!


Trap Facilities for Exotic Ions

ISOLTRAPSHIPTRAPMATSand others(see talk tomorrow)

HITRAP

Production Beam Preparation (incl. Bunching)

Bunching required


“Bunching” vs. “Chopping”

Club

people

people

People pass in groups periodically Sooner or later everybody passes

People pass in groups periodically Some are diverted :-(

Traffic Light


“Bunching” vs. “Chopping”

Chopper

ions

ions

Ions are grouped (bunched) and then transported further in those bunches

The ion beam is interrupted for a certain time during which no transport takes place

Buncher


RFQ Cooler & Buncher

– Principle– World wide– Example facilities


RFQ cooler & buncher

• Linear Paul trap i.e. radial RF, long. DC• Gas filled (at low pressure ~ sub mbar)

- Used first in chemistry for reaction studies. D. Gerlich. “Inhomogeneous RF fields: a versatile tool for the study of processes with slow ions” Adv. Chem. Phys. 82, 1–176 (1992)

- Brought to nuclear physics applications by R. B. Moore from McGill, Montreal

RF drive

Upseudo

Ulong - DC


RFQs for short-lived Ions in the World

ISOLDE/CERN

TRIGA/Mainz

SPIRAL II/CaenLEBIT/MSU

TITAN/TRIUMF TRIμP

Riken

Jyväskylä

ISOLTRAP/CERN

CPT/ArgonneSHIPTRAP/GSI

Oak Ridge

LPC/CaenLanzhou


• Continuous beam cooling (COLETTE for MISTRAL, now at TRIGA Mainz, ISCOOL)

• Beam accumulation and bunching (ISOLTRAP, JYFLTRAP, LEBIT, TITAN ...)

Beam and Bunch creation (Louvain, JYFL, SHIPTRAP, CPT, LEBIT, SLOW-RI)

“Stop” and Bunch using RFQ cooler&buncher


The ISOLTRAP RFQA beam accumulator and buncher



Ion Puls Properties

longitudinal emittance

transversal emittance

overall efficiency (ISOLDE beam)


Cooling Time

Changing buffer gas pressure:

10-3

10-2

0

2

4

6

co

ol

in

g

ti

me

[

ms

]

Helium pressure [mbar]

133Cs

39K


Be aware of RF heating- cooling stops working when M

ion- ~ M

gas

(but you need microscopic model to realize)

Resonant charge exchange (neutralization)- can't cool He+ ions with He buffer gas

Buffer-gas cooling Limits in RFQs

K+

K+see example

He

at 0

.02

mba

rA

r at

0.0

05 m

bar


The JYFL Cooler/buncher

Buffer gas cell, pHe ~ 0.1 mbar

DecelerationCollisional cooling in an

RF-quadrupole Acceleration

Beam in Beam out

40 kV

Turbo pump500 l/s

Turbo pump1300 l/s

Turbo pump900 l/s

High vacuum 10-6 mbar

Intermediate vacuum 10-4 mbar Electrodes

HV isolator

IGISOL E ~40 keV, � E ~100 eVIGISOL E ~40 keV, � E ~100 eV

Buncher: Accumulation time 10 ms -10 s

(Typically 100 ms - 1 s)

FWHM 15 � s bunches

Buncher: Accumulation time 10 ms -10 s

(Typically 100 ms - 1 s)

FWHM 15 � s bunches

A dual mode beam cooler/buncher

DC-cooler: E ~ 40 keV, � E < 1 eV

Transmission, on-line > 60%

DC-cooler: E ~ 40 keV, � E < 1 eV

Transmission, on-line > 60%

A. Nieminen et al., Nucl. Instrum. Methods Phys. Res., A 469, 244 (2001).


The ISOLDE Cooler “ISCOOL”A modern multi-purpose continuous mode beam cooler

I Podadera et al., Nucl. Phys. A 746 (2004) 647c and E. Mane et al., Eur. Phys. J. A - DOI 10.1140/epja/i2009-10828-0


The LEBIT RFQ

Deceleration- few keV to few 10 eV

accumulation &bunching

μ - RFQ

Injection & cooling

RF1

RF1

RF2 RF2

DC1

DC1

DC2DC2

Cross - section

extraction

• Separation of cooling and bunching

• Regions with different buffer gas pressure

• Linear ion trap with novel electrode system

• Cryogenic system (80K)

S. Schwarz et al., Nucl. Instr. Meth. B204 (2003) 474

Advanced technology – Separation of functions


Advantages of a Cold RF Trap

-2.0 -1.0 0.0 1.0 2.0-3000

-2000

-1000

0

1000

2000

3000

vx [

m/s

]

x [mm]

-2.0 -1.0 0.0 1.0 2.0-3000

-2000

-1000

0

1000

2000

3000

vx [

m/s

]

x [mm]

T = 300 KT = 300 K T = 80 KT = 80 K

Transverse phase space, 23Na ion cloud in trap (simulated)

� 95% = � 1.45 m2/s � 95% = � 0.41 m2/s

Transverse emittance� 95% ~ 4.9 � mm mrad @ 2keV

- Considerable emittance reduction

- Increased buffer gas density – lower gas load to the pumps

- Cleaner environment – longer storage time

S. Schwarz et al., Nucl. Instr. and Meth. B 204 (2003) 474


The next Generation• Separation of cooling, bunching and mass separation

e.g. W. Plass et al.

(SHIPTRAP)

• Different solutions to solve the DC – RF coupling challenge

• Improved control of RF and DC

rectangular RF drive – TITAN (TRIUMF)

phase controlled switching and precise amplitude control – W. Plass et al.

Includes mass resolving power and extremely short bunches


The next Generation● Go to higher particle number

from nA to � A

● Present devices: Vpseudo

~ 10 eV – limits the current to nA

• Simulations done – mean field and PIC approach

Accepting higher Ion currents (� A)


Space Charge Simulation vs. Exp.

“Mean field”-code: (FH & SCS)RF + Buffer gas collisions + Coulomb interaction

T. Kim, R.B Moore, McGill, MontrealBeam size as a function of beam current ψιελδσ beam temperature assuming no space charge

Agreement for spatial distribution (0 - 1.2 nA)

& slow rise of beam temperature

0.8 2.3� 95% [� mm mrad @ 60 keV]

T. Kim (PhD thesis),

1 � A simulation:URF = 15 kV, fRF = 5 MHz, Ez = 10 V/cm

� 95% ∼ 3 � mm mrad @ 60 keV

• Cs+ in N2 at 8·10-2 mbar

• r0 = 6.9 mm

• 0.7 MHz, 300 V

• Axial drag field Ez = 1 V/cm

Slope = 17.0(3) meV/nAT. Kim exp.: 15(3)

Offset = 44.3(3)T. Kim exp.: 42(3)


The SPIRAL II High Current RFQ

- First experimental tests: R.B. Moore, O. Gianfrancesco,

Nucl. Instr. and Meth. B 204 (2003) 557–562

- Device realized and being tested: R. Boussaid et al.

Accepting higher Ion currents (� A)

VRF < 10 kVF < 8 MHz


Performance of linear RFQ - Buncher

efficiency up to 80%

cooling time ~ ms

bunch length > 70 ns

capacity ~ 104..5, nA’s improving

mass separation Some but improving

present


Penning Traps to cool and bunch

– Advantagesstorage capacity, mass selectivity

– Examples areREXTRAP@ISOLDE; ISOLTRAP, JYFLTRAP, SHIPTRAP, CPT …


REXTRAPBuffer gas filled cylindrical Penning Trap


Storage Capacity

F. A

mes

et a

l. / N

ucl.

Inst

r. an

d M

eth.

A 5

38 (

2005

) 17

Cyclotron Frequency


Mass Resolving Power

In buffer gas filled preparation trap In UHV precision trap

Rauth et al., Phys. Rev. Lett. 100, 012501 (2008)

Rauth et al. EPJ ST 150, 329 (2007)

147Er

147Ho147Dy

147Dy+I.S.

G.S.

No.

of

ion

s

Mea

n T

OF

/ �s

Excitation frequency / Hz Detuning frequency / Hz

SHIPTRAP measurements


Heavy, Highly – Charged Ions

– Production at high energy (stripping electrons off sending 400 MeV/u ionsthrough a foil)

– To get them into Traps:The HITRAP facility

– Challenges:• Extremely high energy• Cooling of HCI


HITRAP @ GSI

Beam that will be available to users:

type A/q < 3 (U92+ ...)ions/pulse 105

energy keV/q ... meV/qenergy spread ≥ 0.3 meV

Test Ion Source - EBIT:

Up to bare KAny element (charge breeding)105 per pulse and second


The HITRAP Energy Range


To the Experiments

DDBIH

Cooler Trap

7m

HITRAP – A linear Decelerator

RFQ

Beam Type A/q < 3 (U92+ ...)

Ions/Pulse 105

Energy keV/q ... meV/q

Energyspread ≥ 0.3 meV

Be

am

f

ro

m

ES

R


RF Bunching

Gap UGap

time/2�

ions

Ele

ctro

de

Ele

ctro

de

Typical frequency: 100 MHz i.e. ns bunches


RF Bunching @ HITRAP

Gapions

Ele

ctro

de

Ele

ctro

de

Typical frequency: 100 MHz i.e. ns bunches

F. Herfurth - The linear Decelerator Facility HITRAP

ee--ee--

UU92+92+

HITRAP – LEBT & Cooler Trap

4 MeV/u 0.5 MeV/u 6 keV/u

• catch the ions in flight

• cool them with combined electron and resistive cooling to ~ 4 Kelvin


HITRAP – LEBT & Cooler Trap

4 MeV/u 0.5 MeV/u 6 keV/u

4 M

eV/u

• trap installed in magnet – offline injection tests ongoing

• Extensive calculations done – resistive cooling possible but slower than expected


• in Coulomb collisions, ions transfer in Coulomb collisions, ions transfer energy to eenergy to e--

• electrons are rapidly cooled by electrons are rapidly cooled by synchrotron radiation to 4.2 Ksynchrotron radiation to 4.2 K

Approximations:Approximations:• instantaneous conversion Einstantaneous conversion Eionion → T → Tee

• no ion-ion collisionno ion-ion collision• isotropic eisotropic e-- distribution distribution

Warning: radiative recombination!Warning: radiative recombination!

Conclusions:Conclusions:ee-- cooling down to 10 eV possible within ~ cooling down to 10 eV possible within ~ 1 s and 10-20% ion losses1 s and 10-20% ion losses

* = G. Zwicknagel, in „Non-neutral Plasma Physics VI“, eds. M. Drewsen, U. Uggerhoj, H. Knudsen, AIP Conference Proceedings, 862, 281 (2006)

Electron cooling*Electron cooling*


Resistive cooling of an ion cloud

H. Häffner et al., Eur. Phys. J. D 22, 163 (2003)

CoM

internal motionsτ ~ 5 s

(experiment)

internal motionsτ ~ 0.52 s

B

q/m

B

q/mΔqimage=0 !

z

• cooling of Center of Mass motion N times faster• “invisible” internal modes?

→ asymmetric coupling and nonlinear contributions to image charge


Spectrogram of 30 C5+ from our PIC code

PhD

thes

is G

. Mae

ro


U92+ in the HITRAP cooler TrapSimulations with:

• 105 U92+

• Symmetric coupling

• Utrap = 100 V (trap depth)

• Axial oscillation frequency 400 kHz

yields a cooling time tail � ~ 3.7 s !


Ion Beam Bunching – Handling of rare Ions

– Traps are indispensable (both, Paul and Penning)

– The technical challenges are enormous

– A number of interesting experiments wouldn't be possible without → Tomorrow's Talk

Documents

How to match production schemes and ion traps efficiently?...F. Herfurth - Ion Beam Bunching RFQ cooler & buncher • Linear Paul trap i.e. radial RF, long. DC • Gas filled (at low