E. Beebe Test EBIS Results EBIS Project Technical Review 1/27/2005 An EBIS-based RHIC Preinjector - Test EBIS Results Ed Beebe Preinjector Group Collider-Accelerator

E. BeebeTest EBIS Results

EBIS Project Technical Review1/27/2005

An EBIS-based RHIC Preinjector -

Test EBIS Results

Ed Beebe

Preinjector GroupCollider-Accelerator Department



Linac-based Preinjector - Source “requirements”

1. Intensity for 1.2 x 109 Au ions/bunch in RHIC : ~ 3.4 x 109 Au32+

ions/pulse from the source

2. No stripping before Booster injection : q/m > 0.16 (Au32+, Si14+, Fe21+)

3. 1-4 turn injection into Booster : pulse width 10-40 s

(Note - 1 & 3 result in a Au32+ current of 1.7 - 0.42 mA)

4. Rep rate : ~ 5 Hz

5. Emittance : 0.2 mm mrad, normalized, rms (for low loss at Booster injection)

Parameter RHIC EBIS Test EBIS e-beam current 10 A 10 A e-beam energy 20 keV 20 keV e-beam density ~575 A/cm2 ~575 A/cm2 Ion trap length 1.5 m 0.7 m Trap capacity (charges) 1.1 x 1012 5.1 x 1011 Yield positive charges 5.5 x 1011 2.6 x 1011 Yield Au32+, design value 3.4 x 109 ions/pulse Yield U45+, design value 2 x 109 ions/pulse

Test EBIS - 1/2 length prototype, but with the full power electron beam

EBIS Test Stand (prototype)

Test EBIS

Test EBIS - showing ion injection arm and extraction to Time-of-Flight Spectrometer

External ion source

SteerersQuadrupole triplet

Horizontal benders

Einsel lens

Einsel lens

Ion beam chopper

Steerers

Gridded lens

Ion extractor

Electron collector

EC magnet coil

Removable Faraday cup (FC2)

Ion currenttransformer

(Location of former FC1)

Gridded lens

Time of flight mass-spectrometer (Mamyrin type)

Drift tube

Removable Faraday cup(FC3)

•Non-destructive current measure of injected and extracted beams can be made on current transformer.

•Low resolution in-line TOF (between ion beam chopper and FC2)

•High resolution TOF in energy focusing Mamyrin spectrometer

Ion injection arm

Some Principles for a Reliable, Low Maintenance EBIS

The basic principle that has been followed is to separate the functions of source components and remove as much of the action as possible from the high vacuum ionization region.

Provide beam current loss monitoring on all elements in beam path

Avoid magnetic shims and shields where possible; allow for external corrections or reshaping of magnetic geometry

External ion injection:EBIS acts as a charge state multiplier, low contamination, high reliability

Test EBIS performance represents more than an order of magnitude improvement over past EBIS sources. At the same time, operation has been very reproducible and stable. Some of the key features, almost all of which are unique to this EBIS, are the following:

•A novel electron gun design from Novosibirsk. Convex LaB6 & IrCe cathodes

•A warm bore, unshielded superconducting solenoid for the main trap region

•Careful vacuum separation of the trap region from the electron gun and electron collector regions

•Large bore (31mm) drift tubes have been used (pumping, reduced alignment precision, fast extraction, reduced RF coupling)

•The use of auxiliary (warm) solenoids & many transverse magnet coils for steering corrections

•The electron beam is pulsed to reduce the average power on the electron collector

•Very versatile controls allow one to easily apply a time dependent potential distribution to the ion trap

Design Choices for a Reliable, Low Maintenance EBIS 2



Cathode unit

Anode

Electron gun magnet coil

8" gate valve

HV feedthroughs of electron gun

Pumping port

First drift tube

E-Gun Chamber and Cathode Unit

Electron Gun chamber with gate valve installed at Test EBIS

Electron gun cathode unit with LaB6 cathode is shown above.



Electron Collector and Vacuum HousingView from ion extractor end

(extractor not installed)



Drift Electrode Structure of the Test

EBIS Ionization Region

Close-up of electrical leads (right).

Drift electrode structure spans the length of the central vacuum chamber within theTest EBIS Superconducting Solenoid bore (above).



Low Energy Vacuum Arc Source (LEVA)

Hollow Cathode Ion Source (HCIS)

External Sources used for Primary Ion Injection at

the Test EBIS

8 A, 100 ms Electron Beam Pulse


Development of the 10 A electron gun – This was a key element, since previous EBIS operation was typically at 0.5 A or less. Collaboration with BINP on the development of a LaB6 –based electron gun. This gun has produced currents of up to 13A, has a good lifetime, and excellent beam optics. The unique optics for extraction and matching into the strong magnetic field allows a very stable operation over a broad range of electron beam currents.

Propagation of a 10 A electronbeam through the EBIS trap

Gun and E-beams 2

IrCe Gun, Gate Valve, and Anode Modification

• Cathode replacement and electron gun upgrades without disturbing ionization volume ultra-high vacuum.

• Anode/Drift Tube geometry eliminates need for an additional auxiliary solenoid

• Electron beams up to 10A, 100kW have been propagated with very low loss, using IrCe Cathodes from BINP, Novosibirsk.

• 10 A electron gun with IrCe cathode meets the RHIC EBIS requirements, with an estimated lifetime of >20,000 hours

Gold Injection from Leva: FC2 Current andCharge Extracted from EBTS

( Ie = 4A, Tinj ~ 200 s, Tc = 2ms )

Gold injection From Leva

Top trace: Extracted current without ion injection

Middle trace: Extracted current after Gold injection from LEVA source

Bottom trace: integrated charge (13.3nC) extracted from EBIS 2ms after gold injection from LEVA

5.5 x 1011 charges/pulse are required for RHIC. By doubling the EBIS trap length to 1.5 m, we will exceed this requirement. (The ion yield has been shown to scale linearly with trap length).


Time-of-flight spectrum peaked at Au 34+

Charge Extracted from BNL EBIS

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 2 4 6 8 10

Electron Current (A)

Ch

arg

es

/pu

lse

(q

x 1

011

)

Goal

Au

RHIC requirement scaled to EBTS

trap length

Results from Test EBIS ( ½ Length of RHIC EBIS)

Comparison of experimental and predicted ionization time of Au34+

1.3(jT)Theory=101.3=19.95

Experiment:

Au34+ produced in 50ms,with 7.2A, 20.5keV e-beam

For Test EBIS,

10A e-beam j10A~575 A/cm2

Then J8A~0.72*575=414A/cm2

TTheory =( jT)Theory/J8A=0.048sec

So the experimental production of Au34+ with a 50 ms confinement period is in good agreement with the 48ms predicted time. This means that the Au ions are confined well in the EBIS electron beam.

Computer calculation of successive ionization of Au with a 20keV electron beam:

Excellent ion yields from the trap, with very high beam neutralization efficiencies have been achieved

Ion Ie Charges/pulse E-beam

Neutralization Au 8 A 3.4 x 1011 85% (est. 70%

due to Au) Xenon 7 A 1.9 x 1011 55%

5.5 x 1011 charges/pulse are required for RHIC, from a trap length of 1.5 m, and assuming operation at 10 A electron current. (The ion yield has been shown to scale linearly with trap length and electron current).

Extraction of ions from the EBIS trap

The design goal of the Test EBIS is that 50% of the electron beam charge be neutralized by the ion species of interest (e.g. gold ions).

Routine

Extraction 100/200 s*

Extraction 40s

Fast Extraction

10s

Test EBIS 8A e-beam 0.7m trap

55 A 138 A 550 A

RHIC EBIS 10A e-beam 1.5m trap

85 A 425 A 1700 A

Au32+ Pulsed Ion Currents

By manipulation of the EBIS trap electrodes (Fast extraction), the EBIS extracted charge can be delivered in pulse widths necessary to meet single to multi-turn injection requirements of the synchrotron.

*(Typical extraction pulse widths without fast extraction)

Fast Extraction of Ions from the EBTS (for single turn injection into Booster)

A 3.2mA, 12s FWHM, (40nC) ion pulse was obtained at the source exit toroid using a 6.8A e-beam and Au external ion injection, after a 15ms confinement. (85 nC required for RHIC)

Faster extraction has been obtained earlier by applying a graded potential distribution to the trap drift tube electrodes during extraction. In the RHIC EBIS, the pulse shape will be tailored by applying an appropriate voltage pulse to the well.

Fast Extraction of Ions from the EBTS

Inline Time-of-Flight

• Full ion beam sampled and collected on Faraday Cup

• Ie= 7A; • 10 ms confinement• Au = 83%; C&O = 15%; H = 2%

12.7

16.5

20.3

24.1

27.9

31.8

35.6

39.4

43.2

47.0

50.8

54.6

58.4

62.2

66.0

-37.2

-30.2

-23.3

-16.3

-9.3

-2.3

4.7

11.6

18.6

25.6

32.6

Position (mm)

Ang

le (

mra

d)

Emittance of a 1.7 mA extracted beam from EBIS, with Au injection. (n, rms)= 0.1 mm mrad.All charge states, peaked around Au25+.

Measured Emittance for a 1.7mA Gold Beam

The emittance of light ions from EBIS is expected to be less due to less heating by the electron beam during relatively short confinement times necessary to reach charge states of interest.

Electron collectorMagnet shield

Ion extractorSuppressor

Bucking coilSolenoidDrift tubes

Electron gun

Bucking coil

1 2 3 4 5 6 7 8 9 10 11 12

Short trap

Long trap

0

3

6

9

12

-150 -100 -50 0 50 100 1500

1

2

3

4

5

6

L - cm

Axi

al m

agne

t fie

ld -

T

Bea

m r

adiu

s -

mm

Experimental conditions: Iel=7.5 A, Lshort=71 cm, Llong=107 cm, Btrap=4.6 T, Bmin=0.19 T

Geometry of EBTS electro-optical system (top) and axial magnet field distribution with simulated radial

profile of electron beam (bottom).

Ion output vs Ion Trap Length

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Tconf, ms

Qio

n, n

C

Time evolution of the total extracted ion charge (nC) with Au injection for the long

trap (solid line) and short trap (dashed line).

a b

Charge state spectra of ions extracted from the long (a) and short (b) traps after confinement time 2.5 ms for = 7.5 A. Cursor for both cases is on Au19+.

The capacity of ion trap is proportional to the length of the trap (as typically observed in any EBIS). The loss of ionization factor for a long trap, as observed in the spectra, is due to very low magnetic field on the peripheral parts of the long trap and will be avoided in the RHIC EBIS by maintaining the full field throughout the trap.

The ion intensity is expected to double with the doubled trap length in the RHIC EBIS.

Hollow Cathode Ion Source at Test EBIS

• Cu+1 >25A, Ne >80A

• PEBIS~2x10-10 mb for PHCIS~1mb, 10ms, 1Hz shutter operation

P~4x 10-8 mb P~4x 10-6 mb P~8x 10-5 mb P~0.8mB

Electronically Controlled Shutters

Electronically controlled shutters are used to help provide differential pumping in the ion injection beam line. (25mm aperture, 6ms minimum open time)

•The controller coordinates the application of all time dependent voltages and timing references associated with EBIS operation with a time resolution of 1 s, such as:

•Time dependent ion trap HV

• Electron beam ramping

•Table Driven Beamline Optics for Ion injection from Multiple sources and EBIS ion beam extraction

EBIS Voltage and Timing Controller

Multiple Ion Species (PPM)

• The EBIS highly charged ion beam species and charge state can be selected on a pulse to pulse basis

• Voltage Controller is hardware configured for 3 independent cycles with a repetition factor of up to 15 each

• Software presently allows for use 16 independent beamline optics tables for selecting injection from various external sources or EBIS beam propagation to various diagnostic devices (RFQ, TOF, emittance analysis, etc).

Test of unregulated electron collector supplyIn the normal Test EBIS setup, a highly regulated supply provides both electron collection and cathode biasing functions.

A test was performed to test the feasibility of using separate collector and cathode biasing (accelerator) supplies:

• An unregulated, high current supply for electron beam collection• A low current regulated supply to provide: 1) stable e-beam launch 2) Independent acceleration voltage 3) Electron beam fault protection

Results using a 50F Capacitor as a Collector Supply:• 4A electron beam, 50ms pulse: droop ~3.7kV from nominal 10kV good e-beam propagation• Lower Cost Unregulated Collector Supply can be used in RHIC EBIS

(Ion Injection and extraction will be locked to repetitive waveform to minimize optical effects)

Experimental Test & Rhic EBIS Configuration

Normal Test EBIS Configuration

EBIS Results and Rhic design Parameters

Achieved RHIC

Ion Au32+ Au32+

Ie 10 A 10 A (20)

Je 500 A/cm2 500 A/cm2

tconfinement 35 ms 35 ms

Ltrap 0.7 m 1.5 m

Capacity 0.51 x 1012 1.1 x 1012

Au neutralization 70%* 50%

% in desired Q 20% 20%

Extracted charge 55 nC 85 nC

Ions/pulse 1.5 x109 (Au32+)* 3.3 x 109 (Au32+)

Pulse width 10-20 s 10-40 s

* Estimated result for data with 8A e-beam

With Test EBIS, more than an order of magnitude improvement in EBIS performance has been achieved.

The ion output scales with length, ion charge state is achieved within design confinement times, and the ion electron system has been shown to be stable for ion trap length up to 107cm. The RHIC EBIS design will be very similar to the present Test EBIS operating at BNL.

No significant improvement in performance is required, other than the straightforward scaling of ion output with an increase in trap length. Beyond this, changes to the Test EBIS design, which was a device built to demonstrate feasibility, will make the RHIC EBIS an “operational” device, i.e. simpler to maintain, and more reliable due to increased engineering margins on components.

Summary

Documents

E. Beebe Test EBIS Results EBIS Project Technical Review 1/27/2005 An EBIS-based RHIC Preinjector - Test EBIS Results Ed Beebe Preinjector Group Collider-Accelerator