Focusing and Space-Charge
Compensation of Beams with
Electron Columns
Kathrin Schulte
Institute for Applied Physics
NonNeutral Plasma Physics Group
Goethe University Frankfurt
FCC Week 2015
Washington DC, 23-27 March 2015
1. Electron Trap
1947 D. Gabor
+V
2.0e14
80e3
1.5e14
60e3
E / Vm-1
Important Features:
• applied magnetic field and
potential are used for electron
confinement solely
• strong electrostatic focusing
• space-charge compensation
• controlled electron distribution
ne / m-3
electron column
1.0e14
40e3
20e3
0.5e14
0
0
0
20
40
r / mm
60
80
0
20
40
r / mm
60
80
2. Focusing – Experiments
Target
Chamber
Transport Beam Line of H-mode Test LINAC (HTL) at IAP
Deflector
Ion
Source
Gabor Lens
Gabor Lens
High Current Test Injector (HOSTI) at GSI
Ion
Source
Emittance Scanner
High Voltage
Gap
Gabor Lens
Planned
connection
to IH-RFQ
2. Focusing – Results
Emittance Dominated Beam Transport:
measurement - output
measurement - input
40
y’ / mrad
20
Gabor lens parameters:
FA= 0 kV
Bz= 0 mT
-20
-40
-60
erms,n= 0.166 mm mrad
beam parameters:
He+
I = 3 mA
Wb = 50.3 keV
60
40
20
y’ / mrad
beam parameters:
He+
I = 3 mA
Wb = 50.3 keV
60
Gabor lens parameters:
FA= 20 kV
Bz= 10.8 mT
-20
-40
-60
erms,n= 0.321 mm mrad
Space-Charge Dominated Beam Transport:
measurement - output
measurement - input
beam parameters:
Ar+
I = 30 mA
Wb = 124 keV
40
y’ / mrad
20
-20
-40
-60
erms,n= 0.170 mm mrad
-40
-20 y / mm 20
40
Gabor lens parameters:
FA= 0 kV
Bz= 0 mT
beam parameters:
Ar+
I = 35 mA
Wb = 124 keV
60
40
20
y’ / mrad
60
-20
-40
-60
erms,n= 0.236 mm mrad
-40
-20 y / mm 20
40
Gabor lens parameters:
FA= 9.8 kV
Bz= 10.8 mT
3. Space-Charge Compensation
Space-Charge Compensation (SCC) in Intense Ion Beams Under the Influence of Beam Optics
Impact of compensation electron (CE) distribution on measured phase space distribution
CE distribution according to superposition of magnetic field
strength and beam potential
Magnetostatic Quadrupole
adjustable CE distribution due to
the confinement conditions
Superconducting Solenoid
Gabor Lens
60
40
y’ / mrad
20
-20
-40
-60
-40
@ Virtual National Laboratory for Heavy Ion Fusion
K+
I = 190 mA
Wb = 1 MeV
K = 7.71 10-4
-20 y / mm 20
40
@ R. Hollinger, GSI
Ta3+
I = 50 mA
Wb = 0.132 MeV
K = 5.25 10-3
Ar+
I = 35 mA
Wb = 0.124 MeV
K = 3.29 10-3
3. Space-Charge Compensation
Studies of Space-Charge Compensation in IOTA (FNAL)
space-charge effects studies and
compensation experiments
with 2.5 MeV protons at IOTA
Electron beam (Tevatron e-lens as an example):
Shiltsev et al., Phys. Rev. ST Accel. Beams 11, 103501 (2008)
Static electron column:
2.5-MeV
circulating
p-beam
G. Stancari, FERMILAB-CONF-14-314-APC
In collaboration with:
M. Chung, V. Shiltsev, G. Stancari,
J.C. Thangaraj, A. Valishev
using BPMs as electrode system
4. Ongoing Activities – SC Gabor Lens
Gabor Lens Filling Scheme under XHV - Conditions
Beam optics for SC LINACs
Reduced risk of quenching due to reduced
magnetic field strength
Cold emitter as an e-source
Courtesy of
F. Odorici, INFN Bologna
Prof. H. Podlech
CNT
Ion Beam
SC – Gabor Lens
SC – Cavity (DTL)
4. Ongoing Activities – Bunch Merging
In collaboration with
Prof. H. Podlech
Neutralized Merging of Bunch Trains by Gabor Lens
two beam RFQ
Gabor Lens
ion sources
Ion sources
& LEBTs
merging
& LEBT‘s
Shift of beam axis behind
electron column at t = 75 ms
bunching and acceleration
deflector
Gabor
lens
merging
matching
Two separted bunch trains at Crossover under full space
the exit of the RFQ
charge w/o e-column
y
y
x
x
He+
I = ~ 1 mA (each)
Wb = 0.18 MeV
f = 54 MHz
bunch spacing 6 ns
tbunch = 3 ns
4. Ongoing Activities – Diagnostics
Investigation of Electron Column Frequency Spectrum and RF-Response
RF-pick up
beam
antenna
e-column
5. Summary
Studies of
1. Electron column properties and dynamics
• Production and loss processes  equilibrium state
2. Interaction with beam
• Space-charge compensation / effects
• instabilities
3. Non-invasive diagnostics (also during beam
interaction)
Thank you for your attention!
In the name of the Frankfurt NNP group:
A. Ates, C. Beberweil, M. Droba, S. Klaproth, D. Noll, O. Meusel,
P. Schneider, H. Niebuhr, O. Payir, J. Wagner, C. Wiesner, K. Zerbe
My special thanks go to all members of the GSI ion source group
and
all colleagues from the FNAL Accelerator Physics Center.
4. Numerics
• GaborM
by J. Pozimski & O. Meusel
– fluid description
– steady state
er 2 Bz2
FA 
8me
• GabLensM2
by M. Droba
– 3D PIC code
– kinetic description
– dynamic processes
• bender
by D. Noll
– 3D PIC code
– kinetic description
– ionization of residual gas and secondary
electrons on surfaces implemented
State of the plasma column after 140 μs, U=9.8 kV, B=10.8 mT, 1e-3 Pa Ar+