High Brightness Negative Ion Sources with High Emission Current Density

1
High Brightness Negative Ion Sources with High
Emission Current Density

• Vadim Dudnikov
• Fermi National Accelerator Laboratory

SNS, Oak Ridge March 6, 2002
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Contents

• Introduction.
• Historical remarks.
• Change-Exchange injection.
• Negative ion production in surface- plasma
  interaction.
• Cesium catalysis.
• Surface Plasma sources- SPS.
• Discharge stability noiseless operation.
• Charge-exchange cooling. Electron
  suppression.
• Beam extraction, formation, transportation.
• Space charge neutralization. Instability
  damping.
• SPS design. Gas pulser, cesium control,
  cooling.
• SPS life time. SPS in accelerators.
• Further development.
• Summary.
• Acknowledgment.

3
History of Surface Plasma Sources Development
(J.Peters, RSI, v.71, 2000)
4
General diagram of the surface-plasma mechanism
for production of ions in a gas discharge
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SCHEMATIC DIAGRAM OF THE BASIC VERSIONS OF SPS
(a) planotron (magnetron) flat catode (b)
planotron geometrical focusing (cylindrical
and spherical) (c) Penning discharge SPS
(Dudnikov type SPS) (d) semiplanotron (e) hollow
catode discharge SPS with independent
emitter (f) large volume SPS with filament
discharge and based emitter (g) large volume SPS
with anode negative ion production (h) large
volume SPS with RF plasma production and emitter
1- anode 6- hollow
cathode 2- cold cathode emitter 7-
filaments 3- extractor with 8-
multicusp magnetic magnetic system
wall 4- ion beam
9- RF coil 5- biased emitter 10-
magnetic filter
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Emittance, brightness, ion temperature
d
y
Emission slit
l
Emittance
Normalized emittance
x
?x
Normalized brightness
?a
Half spreads of energy of the transverse motion
of ions
Reduced to the plasma emission slit
Characteristics of quality of the beam formation
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H- detachment by collisions with various
particles and resonance charge-exchange cooling
Resonance charge -exchange cooling
8
Discharge stability and noise
n,1016 cm-3
noiseless
Diagram of discharge stability in coordinates of
magnetic field B and gas density n
no discharge
n
noisy
Bmin
B, kG
µ
noiseless
The effective transverse electron mobility µ vs
effective scattering frequency ? and Larmor
frequency ?
? / ?
9
Discharge noise suppression by admixture of
nitrogen
no N2
QN2 0.46 sccm
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H- Beam Intensity of SPS
Years
Beam intensity vs discharge current for first
version of semiplanatron
Evolution of H- beam intensity in ISIS
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Simulation of H- ion beam extraction from the
slit magnetron
Current density
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Electrodes trajectories and equipotentials
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J, A/cm2
Y, mm
0
Y, mm
2
250
Emittance plot
0
0
10
5
X, mm
Slit 2x10 mm I87 mA U21 kV neutral 95
X, mrad
-250
-2.5
2.5
X, mm
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Computer Simulation of H- Beam FormationPBGUNS
Emittance plot
Electrodes, trajectories and equipotentials
25
12
R ,mrad
R, mm
0
6
-25
0

-50 0
50
R, mm
0 4 8 12
16 20 24 28
Z, mm
Aperture diameter 0.4 mm, I1.5 mA
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Beam Formation and Diagnostics of SPS with
Penning Discharge
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Discharge voltage
Noiseless operation
Discharge current
100 Hz
Extraction voltage
Tested for 300 hs of continuous operation
Extraction current
H- current after magnetic analizer
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Fermilab Magnetron with a Slit Extraction
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Discharge Parameters and Beam Intensity in
Fermilab Magnetron
200
time, mks
0
0
Beam current, mA
80
100
0
time, mks
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Beam Intensity vs Discharge Current and
Extraction Voltage in Fermilab Magnetron
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Extraction System of BNL Magnetron
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H- Current vs Extraction Voltage for Magnetron
H- Current, mA
Extraction voltage, kV
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Semiplanotron SPS with a Slit Extraction
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Beam Current vs an Arc Current for Different Slit
Geometries in the Semiplanotron
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DC SPS with a High Emission Current Density
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Typical Assembling of CSPS on the Vacuum Flange
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LEBT with Solenoidal Focusing ( BNL, LANL)
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Emittance Plots after Magnetic LBT
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Semiplanotron SPS with Slit Extraction for High
Intense NI Beam Production
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Summary
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