FETS H- Ion Source Experiments and Installation

Scott Lawrie, Dan Faircloth, Alan Letchford,Christoph Gabor, Phil Wise, Mark Whitehead,

Trevor Wood, Mike Perkins, Mick Bates, Pete Savage, David Lee, Juergen Pozimski, Rafael Enparantza

Front End Test Stand (FETS)

Beam Parameter

ISIS Ion Source

FETS Ion Source

Total Energy 35 keV 65 keV

Current55 mA

(35 mA to LEBT)

60 – 70 mA

Rep. Rate 50 Hz 50 Hz

Pulse Length 200 μs 2 ms

Normalisedx emittance

0.9 π mm mRad 0.5 π mm mRad

Normalisedy emittance

0.8 π mm mRad 0.5 π mm mRad

Main Modifications

• Post extraction acceleration gap

• Analysing dipole magnet

• Extraction electrodes

• Power supplies

250µs Pulsed Extraction

Power Supply +

17kV-

90° Analysing Magnet

35 keV H- Beam

55 mmPost Extraction

Acceleration Gap

Platform Ground

Platform DC Power Supply

Laboratory Ground

-35 kV

+-

18 kV

Extraction system

ISIS Ion Source

2ms Pulsed Extraction

Power Supply +

25kV-

90° Analysing Magnet

65 keV H- Beam

9mmPost Extraction

Acceleration Gap

Platform Ground

Platform DC Power Supply

Laboratory Ground

-65 kV

+-

40 kVExtraction

system

FETS Ion Source Proton Suppressor

Post ExtractionAcceleration Gap

ISIS LEBT Line

Ion sourcePost

Extraction Acceleration

Solenoid 1 Solenoid 2 Diagnostics Sol. 3

FETS LEBT Line

Ion source

Post Extraction

Acceleration PLUS

Diagnostics

Solenoid 1 Solenoid 2 Diagnostics Sol. 3

Steel mounting and pumping flange

Laser diagnosticsdipole apparatus

Electrode and mu-metal shielding assembly

Ion source, analysing dipole magnet and cold box

Electrode Spacer Assembly

Analysing Sector Magnet

Reasons For Use of Dipole

• Analyse out co-extracted electrons

• Allow caesium to collect in cold box

• Modify beam from slit to round shape

• Weakly focus beam to LEBT entrance

• Convenient 90° loading geometry

Field Stronger

Field Weaker

Field Stronger

Field Weaker

Axial Beam

Size

Angle Around Dipole

90°0°

Angle Around Dipole

Radial Beam

Size

90°0°

dR

dB

B

Rn

e

eMagnetic Field Index:

n > 1n = 1n < 1

Predicted beam profiles

Measured beam profiles

n > 1 n = 1 n < 1

Extraction Electrode Setup

Beam Parameters Determined by Extraction

System:• Ion species (H-)

• Current needed for application (70 mA)

High current density at plasma apertureHigh extraction voltage:

• Low divergence angle (ε < 0.5 π mm mRad)

Concave plasma meniscusFocussing electrostatic lens geometrySpace charge compensationLow ion temperature

2

3

VI

Standard ISIS Extraction Geometry

Pierce-Style Extraction Geometry

AlternativePierce-Style Geometry

Overview of Experimental Work

Norm. εh = 0.82 π mm mRad Norm. εv = 0.75 π mm mRad

ISIS Ion Source

46.6 mA

Norm. εh > 0.69 π mm mRad Norm. εv > 0.45 π mm mRad

ISIS Ion SourceReduced

Post-Extraction Acceleration Gap

+

56.0 mA

Norm. εh = 0.68 π mm mRad Norm. εv = 0.42 π mm mRad

ISIS Ion SourceReduced

Post-Extraction Acceleration Gap

+Improved Sector

Magnet Good Field Region

+

49.6 mA

Norm. εh = 0.57 π mm mRad Norm. εh = 0.39 π mm mRad

ISIS Ion SourceImproved Sector

Magnet Good Field Region

+Reduced

Post-Extraction Acceleration Gap

+Pierce-Style Extraction Geometry

+

42.6 mA

FETS Ion SourceInstallation Progress

Questions?Ion Source Latest Status:

•Commissioning timing signals

•Mains operable on platform

•Platform 70 kV imminent

•Extract power ready

•Beam due very soon!