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The REX-ISOLDE charge state breeder

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The REX-ISOLDE charge state breeder. Fredrik Wenander BE/ABP. ISOLDE Radioactive beam facility Since end of 1967, now 3 rd version 60 keV beams >70 elements and >700 isotopes. REX-ISOLDE Post accelerator to 3 MeV /u Room temperature Linac First experiment 2001.

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slide2

ISOLDE

Radioactive beam facility

Since end of 1967, now 3rd version

60 keV beams

>70 elements and >700 isotopes

REX-ISOLDE

Post accelerator to 3 MeV/u

Room temperature Linac

First experiment 2001

slide3

Electrostatic bender

Energy slit

IHS

7GP

9GP

RFQ

5keV/u

300keV/u

Magnet

Mass slit

2.2MeV/u

3MeV/u

1.2MeV/u

3m

A/q

separator

Linac

Type 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

* Upgrade to >5 MeV/u in progress

* Adding SC cavities after present NC linac

slide4

charge bred ions

EBIS

A/q separator

bunched 1+ ions

1+ ions from ISOLDE

selected q+ ions to Linac

Penningtrap

bunching/cooling/breeding

mass

separator

* A/q < 4.5

* beam intensity a few to 109 particles/s

* pulsed machine

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

RF-quadrupole

to linac

beam from

ISOLDE

bunched or semi-continuous

buncher/cooler

slide5

B

beam in

U

trap cylinders

REXTRAP principle

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

  • Radial Cooling
  • sideband excitation with a quadrupolar field in the transversal plane at the
  • cyclotron frequency
  • c = q/m B
  • coupling of magnetron and

reduced cyclotron motion

slide6

Trap data

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

Preparatory REXTRAP

Large Penning trap at REX

  • * Cooling (10-20 ms)
    • Buffer gas + RF
  • * (He), Li,...,U
  • * Efficiency 45-55 %
  • * Space charge limit
  • 108 ions/pulse
slide7

Beam out of REXTRAP

  • 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
slide8

Axial magnetic field

B

axial field

EBIS cross-view

Axial potential

Radial potential

EBIS basics

EBIS Electron Beam Ion Source

 High Charge States

 Very low Rest Gas Contamination

 Variable CSD via Breeding Time

 Restricted in Beam Intensity

* ~25% in one charge state

* More near closed shells

Extracted beam has a charge state distribution

Charge development

slide9

racks

collector position

insulator

electron gun position

injection/extraction optics

1+ ions in

magnet iron shield

q+ ionsout

turbo pumps

1 m

60/20 kV platform

The REXEBIS

REXEBIS

  • Super conducting solenoid, 2 T
  • Trap length <0.8 m
  • Semi-immersed gun (0.2 T)
  • Warm bore
  • Breeding time 3 to >300 ms
  • 50-400 us extracted bunches
  • Ramped HT potential 20-60 kV
  • What’s special with REXEBIS?
  • EBIS + radioactive ions
  • Few ions 200 to 108
  • Warm bore
  • The high efficiency requirement
  • Low residual gas ions
  • General properties
  • Run with low e-beam neutralisation
  • Total capacity 6·1010 charges
slide10

REXEBIS hardware

  • 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

Manne Siegbahn Laboratory / Chalmers University of Sweden

1.6 mm

The REXEBIS

The perforated and NEG coated drift tubes

The LaB6 <310> cathode

slide11

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.

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

q/A resolution ~150

slide12

500 us FWHM

Slow extraction, 190Pb44+ measured with Miniball detector

N2+

CO+

REX low energy - toolbox for ion manipulation

Slow extraction

Isobaric mass separation

In-trap decay

β±-decay

Molecular beams

Be

slide13

Issues / R&D

  • 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

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

Manufacturer

* AP-TECH

* before FEI Beam Technology

1. Reliability and simplicity

* new electron cathode type (IrCe, Kimball Physics)

2. Higher electron current/density

+ heavier elements

+ faster breeding

+ larger beam acceptance

-> new gun (and collector) design

3. Improved (quantitative) beam diagnostics

* tape station after REX mass separator

What to improve on EBIS?

1. shortening of the tbreeding

2. continuous injection

3. increased charge capacity

>500 mA and >250 A/cm2

slide14

Project 1 Setup the TwinEBIStestbench

  • a. Finalize design and installation of mechanical parts, 6 months
  • b. Re-commission superconducting solenoid
  • c. Produce a control system for power supplies, current readouts,
  • vacuum control system, interlocks. Labview experience, 6-9 months
  • d. 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

New IrCecathode

Modified

Wehnelt

electrode

Courtesyof T. Berg

TwinEBIStestbench

slide15

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.

slide16

Project 1c

A buffer trap as a debuncher

EBIS

Breeding to high charge states

Mass separation

In trap decay

Slow extraction

Buffer trap

CW

PseudoCW

RFQ cooler

1+

N+

Linear Paul trap

Using the energy spread

Post acceleration

A/q or TOF

separation

CW injection or bunching in a RF trap

Pulsed

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.

Problem with high intensity bunched beams

NUPNET collaboration

with e.g. GANIL

slide17

Project 3 HIE-EBIS design study

Path 1

Path 2

Large capacity, moderate charge state

Moderate capacity, very high charge state

EBIS test stand

Superbreeder for injection into Heidelberg Test Storage at ISOLDE

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

Skills needed:

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

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