The REX-ISOLDE charge state breeder

110Sn injected

0

20

40

60

80

100

120

140

160

77 79 81 83 85 87 89

B-field (mT)

Exra

cte

d c

urr

en

t (p

A)

110Sn27+

28+

29+

26+

25+

24+

23+

A/q=4

14N3+

Fredrik WenanderBE/ABP

ISOLDERadioactive beam facilitySince end of 1967, now 3rd version60 keV beams>70 elements and >700 isotopes

REX-ISOLDEPost accelerator to 3 MeV/uRoom temperature LinacFirst experiment 2001

LinacType normal conducting

6 accelerating cavities

Length 11 m

Freq. 101 MHz (202 MHz for the 9GP)

Duty cycle 1 ms 100Hz

Energy 300 keV/u, 1.2-3 MeV/u (variable)

A/q <4.5

RFQIHS 7GP 9GP

A/qseparat

or

5keV/u 300keV/u

1.2MeV/u 2.2MeV/u 3MeV/uMagnet

Energy slit

Mass slit

Electrostatic bender

3m

* Upgrade to >5 MeV/u in progress* Adding SC cavities after present NC linac

* A/q < 4.5

* beam intensity a few to 109 particles/s

* pulsed machine

* repetition rate <100 Hz, linac duty factor <10%

bunching/cooling/breeding

buncher/cooler

bunched or semi-continuous

to linac

massseparator

RF-quadrupolebeam from ISOLDE

Penningtrap

EBIS

A/q separator

bunched 1+ ions

charge bred ions

1+ ions from

ISOLDE

selected q+ ions to Linac

B

Utrap cylinders

beam in

REXTRAP principle

transversal cooling by side-band excitation of c= q/m B

* Cooling (10-20 ms)Buffer gas + RF

* (He), Li,...,U* Efficiency 45-55 %* Space charge limit108 ions/pulse

Preparatory REXTRAP

Large Penning trap at REX

-800 -600 -400 -200 0 200 400 600 800

-500

100

200

300 trapping

ejection

ion energy

z [mm]

10-5

10-4

10-3

Buffer Gas Pressure

Electric Potential

Trapping Electrodes

Trap data•Super conducting solenoid

magnetic field B = 3 T • Length 90 cm• Buffer gas 10-3 mbar Ar, Ne, (He)

50 100 150

0

1000

2000

3000

4000

5000Cs

Ne

ion

s

TOF [s]

2.5 10-3 mbar

1.5 10-3 mbar

7.5 10-4 mbar

From ISOLDE• Semi-continuous (release several 100 ms)• ΔE a few eV• ε ~30 mm mrad (95%) @ 60 keV• Not isobarically nor molecularly clean

After REXTRAP

• Bunched beam (t·E ~ 10 s·eV)

• Emittance >10 mm mrad @ 30

keV

Beam out of REXTRAP

EBIS basics

EBIS cross-view

Axial potential

Radial potential

axia

l fi

eld

B

Axial magnetic field

EBIS Electron Beam Ion Source

Charge development

Extracted beam has a charge state distribution

* ~25% in one charge state

* More near closed shells

High Charge States Very low Rest Gas Contamination Variable CSD via Breeding Time Restricted in Beam Intensity

High Charge States Very low Rest Gas Contamination Variable CSD via Breeding Time Restricted in Beam Intensity

REXEBIS

General properties• Run with low e-beam neutralisation• Total capacity 6·1010 charges

General properties• Run with low e-beam neutralisation• Total capacity 6·1010 charges

• Super conducting solenoid, 2 T• Trap length <0.8 m• Semi-immersed gun (0.2 T)• Warm bore

racks

magnet iron

shield

turbo pumps

insulat

or collector position

60/20 kV platform

electron gun position

injection/extraction

optics

1 m

1+ ions in

q+ ionsout

The REXEBIS

What’s special with REXEBIS?

• EBIS + radioactive ions• Few ions 200 to 108

• Warm bore• The high efficiency requirement• Low residual gas ions

• Breeding time 3 to >300 ms• 50-400 us extracted bunches• Ramped HT potential 20-60 kV

• Breeding time 3 to >300 ms• 50-400 us extracted bunches• Ramped HT potential 20-60 kV

REXEBIS hardware

The REXEBIS The perforated and NEG coated drift tubes

Manne Siegbahn Laboratory / Chalmers University of Sweden

The LaB6 <310> cathode

1.6 mm

• Electron beam energy 3-6 keV

• Perveance 0.87 A/kV3/2

• 0.5 mm beam diameter (simulated)

• Reached Ie=460 mA, normally <250 mA

• Normally je=100-125 A/cm2

q/A resolution ~150

Nier-spectrometer – an achromatic separator to select the correct A/q and separate the radioactive ions from the residual gases.

Nier-spectrometer – an achromatic separator to select the correct A/q and separate the radioactive ions from the residual gases.

Charge bred beam

Extracted beams from REXEBIS as function of A/q showing residual gas peaks and charge bred 129Cs. The blue trace is with and the red trace without 129Cs being injected.

Slow extraction, 190Pb44+ measured with Miniball detector

500 us FWHM

Molecular beams

β±-decay

In-trap decay

Slow extraction

Be

N2+

CO+

Isobaric mass separation

REX low energy - toolbox for ion manipulation

1. Reliable electron cathode-> test alternatives to LaB6 cathodes

2. Increase electron current to >500 mA -> modify drift tube structure

3. Increase electron beam energy to >10 keV-> modify electron gun

4. Increased (> 1 ms) or decreased (<30 us) beam extraction time-> modify drift tube structure

Issues / R&D

Manufacturer* AP-TECH* before FEI Beam Technology

Data* LaB6* Diameter 1.6 mm* Mini Vogel Mount* Crystal orientation <310>* Work function 2.5-2.7 eV* Heating power: without shunt 8-10 W

with shunt 6-7 W* Calibration from manufacturer: Temperature vs power calibration No e- emission vs temperature curve

* Cathode heating current limited in most cases

New IrCe cathode

ModifiedWehneltelectrode

Courtesy of T. Berg

TwinEBIS testbench

Project 1 Setup the TwinEBIS testbench

a. Finalize design and installation of mechanical parts, 6 monthsb. Re-commission superconducting solenoidc. Produce a control system for power supplies, current readouts, vacuum control system, interlocks. Labview experience, 6-9 monthsd. Commission the source, test alternative cathode and gun types,increase electron beam current and energy. Electron beam simulations. >12 months

Experienced student(s)Contact person: F. Wenander

Project 1b Dedicated investigation of cathode problems

Work description

The PhD student should make use of the TwinEBIS setup (or REXEBIS during 2013 if possible) in order to understand the 'poisoning effect' of the electron gun cathode and suggest modifications to mitigate the problem. The student should also experimentally evaluate the performance of the IrCe cathode. Furthermore the student should simulate the electron beam and design an electron gun capable of delivering higher (10-15 keV) electron beam energies. If time permits, the student should investigate what is limiting the storage time inside REXTRAP and what can be done in order to improve it.

A buffer trap as a debuncherEBIS

RFQ cooler

Mass separationIn trap decay

Breeding to high charge states

Buffer trap

Slow extraction

Pseudo CW

Linear Paul trapUsing the energy spread

CW

Pulsed

A/q or TOF separation CW injection or

bunching in a RF trap

1+ N+

Problem with high intensity bunched beams

Post acceleration

Goal: to design a debuncher for high intensity bunched beams (from EBIS).

Concept: based on linear RFQ widely used either as beam guides and coolers/bunchers.

NUPNET collaborationwith e.g. GANIL

Project 1c

Project 3 HIE-EBIS design study

Superbreeder REXEBISElectron current >5 A 0.3Electron current density >20 kA/cm2 150 A/cm2Electron beam energy >100 keV 5 keVSolenoid field >6 T 2 TFull-field trap length >50 cm 80 cmTrap region pressure <1E-13 mbar 1E-11 mbar

Main design parameters for an upgraded EBIS/T charge breeder aimed to produce VHCI for injection into TSR.

Superbreeder for injection into Heidelberg Test Storage at ISOLDE

EBIS test stand

Path 2Path 1

Skills needed:EBIS/T design, 5 A electron beams, cryogenic design, 100 kV design, XHV

Large capacity, moderate charge state Moderate capacity, very high charge state