EBIS Charge Breeder for CARIBU...Sergey Kondrashev, EBIS Charge Breeder for CARIBU, High Mass RIB Workshop, June 22, 2012 13 Experimental Set-up Experimental set-up: 1 – EBIS e-gun,

EBIS Charge Breeder for CARIBU

Sergey Kondrashev, C. Dickerson, A. Levand, P.N. Ostroumov, G. Savard,

R. Vondrasek, J. Alessi, E. Beebe, A. Pikin, G.I. Kuznetsov, M.A. Batazova

June 22, 2012

Sergey Kondrashev, EBIS Charge Breeder for CARIBU, High Mass RIB Workshop, June 22, 2012

2

Content

• Motivation for EBIS charge breeder at CARIBU

• Design and parameters of CARIBU EBIS charge breeder

• Commissioning of EBIS charge breeder sub-systems:

- 6 T superconducting solenoid

- high-perveance e-gun

• Charge breeding efficiency measurements at BNL Test EBIS

• Summary


Motivation for EBIS Charge Breeder at CARIBU

3

EBIS vs ECR:

• Higher breeding efficiency (about factor 2)

• Better purity of beams (several orders)

• Shorter breeding time (factor 5-10)

Choice for CARIBU:

• “Classical” EBIS

- Proven technology (REXEBIS, CERN)

- Higher acceptance (larger electron beam size) than in case of EBIT

• BNL RHIC and Test EBIS are prototypes (the most advanced EBIS technology nowadays)

4

EBIS Charge Breeder – Principle of Operation


E-gun

Solenoid

Barrier drift tubes Collector


Main Parameters of CARIBU EBIS Charge Breeder

5

Low current e-gun will be used to study efficiency gain at shell closures


6

Off-line Commissioning Configuration

HV platform

E-gun

6 T superconducting solenoid

Rails

Electron collector

Einzel lenses and steerers

Acceleration tube

Bending magnet

Cs+ ion source

FC PP


7

Drift Tube Structure

Supporting tube (scaffold)

Drift tubes with longitudinal slots

Openings for pumping

NEG coating

Openings for potential leads

Potential leads (SS roads, Ø 3 mm)


8

Commissioning of 6 T Superconducting Solenoid

• Unshielded solenoid with warm bore • Supplier: Cryomagnetics, Inc. • Delivered: October 2011

6 T solenoid installed at HV platform In final position for on-site commissioning

Magnetic axis was aligned with mechanical axis of warm bore in real magnetic environment


9

Results of 6 T Solenoid Commissioning

Parameter Specification Measurements

Central Field 6.0 T 6.05 T @ 82.66 A

Maximum Field 6.6 T 6.6 T @ 90.17 A

Charge Time to 6 T 70 min 70 min

Field Homogeneity ± 0.4% over ± 30 cm on axis ± 0.2% over ± 30 cm on axis

Coil Inductance 195 H 193 H

Field Decay Rate < 1 ppm/hour < 0.01 ppm/hour

-400 -300 -200 -100 0 100 200 300 40059400

59500

59600

59700

59800

59900

60000

60100

Mag

net

ic F

ield

, G

Axial position, mm

Simulated

Factory

On-site

-800 -600 -400 -200 0 200 400 600 8000

10000

20000

30000

40000

50000

60000

Mag

net

ic F

ield

, G

Axial position, mm

Simulated

Factory

On-site


10

Electron Guns

Engineering model of e-gun (1 – IrCe thermionic cathode, 2 – anode, 3 – vacuum chamber, 4 – magnetic coil)

2 A and 0.2 A e-guns are exchangeable by exchanging cathode units

Supplier: BINP (Novosibirsk, Russia)

Delivered: April 2012

Parameter CARIBU (high current)

CARIBU (low current)

Current Up to 2 A Up to 0.2 A

Current density at the cathode

10–15 A/cm2 10–15 A/cm2

Magnetic field at the cathode surface

~ 0.15 T ~ 0.15 T

Cathode material IrCe IrCe

Cathode diameter 4 mm 1.6 mm

Radius of cathode convex surface

6.6 mm 1.8 mm

Expected cathode lifetime ~ 20000 hours ~ 20000 hours

IrCe thermionic cathodes demonstrated the longest live time


11

IrCe Thermionic Cathodes Tests

*


12

E-gun Commissioning Results

-2 0 2 4 6 8 10 12 14-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 55.8 W (4.985 V/11.2 A)

40.5 W (4.054 V/10 A)

33.6 W (3.536 V/9.5 A)

red line - I[A] = 2.6*10-6*U3/2[V]

Curr

ent,

A

Voltage, kV

-5 0 5 10 15 20 25 30 35-20

-15

-10

-5

0

5

10 Voltage

Current

Time, s

Vo

ltag

e, k

V

-1

0

1

2

3

4

5

Curren

t, APerveance is about 2·10-6 A/V3/2


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Experimental Set-up

Experimental set-up: 1 – EBIS e-gun, 2 – EBIS drift tubes, 3 – EBIS electron collector, 4 - 16-plate-wide aperture deflector/lens, 5 – Faraday cup (FC1), 6 – pepper pot emittance meter, 7 – gridded electrostatic lens, 8 – planar bender, 9 – spherical bender, 10 – quardrupole quadruplet lens, 11 - vertical and horizontal steerers, 12 – Cs+ surface ionization ion source, 13 - Faraday cup (FC2), 14 - 45° bending magnet, 15 – Faraday cup (FC3).

In blue – equipment manufactured and ordered for this experiment This equipment will be used for commissioning of CARIBU EBIS charge breeder


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Main Parameters of BNL Test EBIS

Parameter Nominal Used in experiment CARIBU EBIS CB

Superconducting solenoid: length/ field 1 m/5 T 1 m/4.7 T 1 m/6 T

Diameter of the IrCe thermocathode 9.2 mm 9.2 mm 4 mm

Electron beam current up to 10 A 1 A and 1.5 A 1 – 2 A

Electron beam energy up to 20 keV 19 keV 6 – 8 keV

Electron beam current density inside trap up to 575 A/cm2 (for 10 A) ≈ 51 A/cm2 and ≈ 76 A/cm2 ~ 500 A/cm2

Electron beam diameter inside trap 1.6 mm 1.6 mm 0.58 mm

Ion trap length 0.7 m 0.7 m 0.7 m

Trap capacity (in elementary charges) 5.1·1011 (for 10 A/20 keV) 5.2·1010 and 7.8·1010 1011

5.3 ms breeding time was chosen for all measurements by two reasons:

• To fully resolve highly charged Cs ions at the exit of magnetic spectrometer

• To reduce overlapping between highly charged Cs and residual gas ions


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Mass and Charge State Distributions

0 20 40 60 80 100 120 140 160-2

0

2

4

6

8

10

12

14

16

18

20

N, O, Cq+

Csq+

Ch

arge

, pC

Magnet current, A

with Cs+

injection

without Cs+

injection

H+

10 15 20 25 30 35 40-2

0

2

4

6

8

10

12

14

16

18

20

O2+

N2+

C2+

O3+

N3+

O4+

(C3+)

N4+

C4+

Cs12+

Ch

arge

, pC

Magnet current, A

with Cs+

injection

without Cs+

injection

H+

Mass and charge state distributions with (blue line) and without (green line) Cs+ ion injection into EBIS for 1.5 A electron beam current (measured downstream bending magnet with 2 mm output slit) .

Distribution is peaked at Cs9+.


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10 15 20 25 30 35 40 45 50 55 60 65 70-2

0

2

4

6

8

10

12

14

16

18

20

13+

12+

11+

10+

5+

6+

7+

8+

Ch

arge

, p

C

Magnet Current, A

9+

Spectrum of charge state bred Cs ions for 1.5 A electron beam current.

Charge State Distributions

2 3 4 5 6 7 8 9 10 11 12 130

5

10

15

20

25

Rel

ativ

e A

bu

nd

ance

, %Cs Charge State

- 1.5 A

- 1 A


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Electron beam current 1 A 1.5 A

Electron beam current density in the trap ≈ 51 A/cm2 ≈ 76 A/cm2

Most abundant charge state 7 8

Average charge state 6.6 8.5

Injection/extraction efficiency 75% 71%

Breeding efficiency into the most abundant charge state 16.7% 17.5%

Results on Breeding Efficiency

2 3 4 5 6 7 8 9 10 11 12 130

5

10

15

20

25

30

Rel

ativ

e A

bu

nd

ance

, %

Cs Charge State

Measured

CBSIM

3 4 5 6 7 8 9 10 11 12 13 140

5

10

15

20

25

Rel

ativ

e A

bu

nd

ance

, %

Cs Charge State

Measured

CBSIM1 A 1.5 A

S. Kondrashev, et al., Nucl. Instr. and Meth. A 642 (2011) pp. 18-24


Summary

• EBIS charge breeder is an excellent choice for acceleration of CARIBU beams

• Design of CARIBU EBIS charge breeder has been completed and manufacturing of different components is in progress

• 6 T superconducting solenoid and high-perveance e-gun have been recently commissioned and met all specified parameters

• Injection/extraction efficiency above 70% and breeding efficiency into the most abundant charge state ~17% have been measured at BNL Test EBIS for 1 A and 1.5 A electron beam currents over a breeding time of 5.3 ms

• Good agreement between measured and simulated (by CBSIM code) relative abundances of charge-bred Cs ions has been found for proper pulsed injection into EBIS

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