GAMMA BASED POSITRON
SOURCE OPTIONS FOR ILC
Klaus Floettmann
DESY
K. Floettmann
KEK, Nov. 13-15, 2004
Contents:
§ Basics of gamma based sources
§ Status of work
§ Who wants to Do What?
K. Floettmann
KEK, Nov. 13-15, 2004
Conventional vs. Gamma Based Source
Primary Beam
Target
Capture Optics
Photons 10-20 MeV
thin target: 0.4 X0
Electrons 0.1-10 GeV
thick target: 4-6 X0
K. Floettmann
KEK, Nov. 13-15, 2004
Parameters of existing and planed positron sources
rep rate
# of
bunches
per pulse
# of
positrons
per bunch
5 Hz
2820
2 · 1010
5.6 · 1013
NLC
120 Hz
192
0.75 · 1010
1.4 · 1012
SLC
120 Hz
1
5 · 1010
5 · 1010
DESY
positron
source
50 Hz
1
1.5 · 109
1.5 · 109
TESLA/ILC
K. Floettmann
# of
positrons
per pulse
KEK, Nov. 13-15, 2004
The Problem: Target Heating
T  2 N pos
Edep  2
Edep
c A
MeV  cm
g
1  capture efficiency

c  heat capacity
A  source area
K. Floettmann
KEK, Nov. 13-15, 2004
Number of Positrons / Source Area
Example of the rotating target for TESLA:
0.8 m diameter
1250 revolutions per minute
52 m/s on the circumference
4 cm in a pulse train of 0.8 ms
Conceptual design for a rotating feed-through:
“A Megawatt Electron Positron Conversion Target – A Conceptual
Design” 1st EPAC Rome 1988
K. Floettmann
KEK, Nov. 13-15, 2004
Heat Capacity of the Target Material
Low Z materials have a higher heat
capacity (Dulong Petit Rule)
but
high Z materials give a higher positron
yield.
K. Floettmann
KEK, Nov. 13-15, 2004
Positron Yield vs. Target Thickness for a Photon
based Source
"Structural Modeling of Tesla TDR Positron Target," Werner Stein,
John C. Sheppard, July 2002 (SLAC-TN-03-043)
K. Floettmann
KEK, Nov. 13-15, 2004
Radiation Damage Material Test at BNL
collaborative
effort of
SLAC and
other labs
NOTE: Gamma
based sources
produce
significantly less
neutrons than
conventional
sources.
K. Floettmann
KEK, Nov. 13-15, 2004
How to Increase the Capture Efficiency?
Increase the acceptance of the capture optics
requires a Predamping ring with large
acceptance
Improve the positron emittance
photon based positron source with thin target
K. Floettmann
KEK, Nov. 13-15, 2004
Transverse momenta
conventional
source
thin target
source
K. Floettmann
KEK, Nov. 13-15, 2004
Comments concerning the DR design
Present situation: on energy acceptance is ok, off energy acceptance is too
small
• improve off energy acceptance
• investigate possibilities to reduce the energy spread by scraping or
removing correlations
Better communication between DR people and positron people is required
• assumed positron distributions seem to be too pessimistic sometimes
• realistic distributions should be used as input
Operation of a gamma based positron source without predamping
ring should be possible
K. Floettmann
KEK, Nov. 13-15, 2004
Undulator Based Positron Source
• Undulator length depends on the integration into the system, i.e.
the distance between undulator exit and target which is required
for the beam separation:
• ~ 50-150 m
K. Floettmann
KEK, Nov. 13-15, 2004
Integration of the Source into the BDS of TESLA
Auxiliary and
Commissioning source
500 MeV
e- source
in linac
target &
capture
undulator
287 MeV
e+ bypass
e+ 5 GeV
injector linac
 dump
e+ ma
physics
detector
“Conceptual Design of a Positron Pre-Accelerator for the TESLA Linear Collider”
TESLA-99-14
“Conceptual Design of a Positron Injector for the TESLA Linear Collider” TESLA-00-12
K. Floettmann
KEK, Nov. 13-15, 2004
Low energy operation
2.5
2.5 Hz operation
5 Hz operation
2.0
positron/electron yield
safety margin
used positrons
1.5
1.0
0.5
0.0
50
K. Floettmann
100
150
160
Electron energy (GeV)
200
250
KEK, Nov. 13-15, 2004
Low energy operation
4.0E+34
3.5E+34
nominal
5 Hz operation
2.5 Hz luminosity
operation
Luminosity (cm-2s-1)
3.0E+34
g scaling (fundamental)
2.5E+34
High-energy
optimised
source
2.0E+34
1.5E+34
1.0E+34
Low-energy
optimised
source
5.0E+33
0.0E+00
100
150
200
250
300
350
400
450
500
Ecm (GeV)
NOTE: Higher currents are possible at lower energy if the source is
integrated into the BDS (limited by DR)
K. Floettmann
KEK, Nov. 13-15, 2004
Auxiliary and Commissioning Source
500 MeV
e- source
287
e+ b
target &
capture
undulator
 dump
500 MeV electron source provides low intensity
(~1%) e+ source but same bunch train
• commissioning source
• standby source for MD when e- system is down
• e-e- and gg physics options source
K. Floettmann
phy
dete
KEK, Nov. 13-15, 2004
Design of the Positron Preaccelerator
K. Floettmann
KEK, Nov. 13-15, 2004
The capture optics
Bi
B z 
1 g  z
gP
1
e  Bi
low frequency (L-band)
x’
x’
x
K. Floettmann
Ø
large iris radius
Ø
long wave length
x
KEK, Nov. 13-15, 2004
Adiabatic Matching Device - AMD
Very basic design considerations by BINP
Novosibirsk (internal report):
• long pulse seems to be possible
• problem is to achieve the required field
quality
K. Floettmann
KEK, Nov. 13-15, 2004
NC High Gradient Cavities (solenoid focusing)
Design by INR Troitsk
K. Floettmann
KEK, Nov. 13-15, 2004
Optical functions in the Separator Section
• separation of photons,
positrons and
electrons
• longitudinal
collimation of the
positron bunches
• transverse collimation
can be done in the
solenoid section
aim for no particle loss
during injection into
DR
K. Floettmann
KEK, Nov. 13-15, 2004
NC Low Gradient Cavities (triplet focusing)
Design by INR Troitsk
K. Floettmann
KEK, Nov. 13-15, 2004
Phase Space at the exit of the Preaccelerator
K. Floettmann
KEK, Nov. 13-15, 2004
Positron Transfer Line
K. Floettmann
KEK, Nov. 13-15, 2004
Acceleration to 5 GeV in SC Cavities
K. Floettmann
KEK, Nov. 13-15, 2004
Polarized Positron Sources
For the production of polarized positrons circularly
photons are required.
Methods to produce circularly polarized photons of
10-60 MeV are:
• radiation from a helical undulator
• Compton backscattering of laser light off an
electron beam
K. Floettmann
KEK, Nov. 13-15, 2004
Why polarized positrons
Physics potential beyond the scope of this
workshop but we can gain a factor of two in
the interaction rate (eff. luminosity) by using
polarized electron and positron beams
K. Floettmann
KEK, Nov. 13-15, 2004
Polarization Transfer in Pair Production
K. Floettmann
KEK, Nov. 13-15, 2004
Super Conducting Design
• Ribbon-wire wound in a double helix
Current
Current
K. Floettmann
KEK, Nov. 13-15, 2004
Polarization vs. Emission angle
K. Floettmann
KEK, Nov. 13-15, 2004
Model of the Prototype Helical Undulator at
Daresbury
K. Floettmann
KEK, Nov. 13-15, 2004
Model of the Prototype Helical Undulator at
Daresbury
K. Floettmann
KEK, Nov. 13-15, 2004
Compton Backscattering based Positron Source
K. Floettmann
KEK, Nov. 13-15, 2004
GLC Polarized Positron Source Design
K. Floettmann
KEK, Nov. 13-15, 2004
Multi Collision Point Layout
K. Floettmann
KEK, Nov. 13-15, 2004
GLC Collision Region
10 collision sections, with 20 collision points each:
200 collision points
K. Floettmann
KEK, Nov. 13-15, 2004
E-166 Demonstration Experiment for a Polarized
Positron Source
About 47 members from 17 institutions:
Brunel, CERN, Cornell, DESY, Daresbury, Durham,
Jefferson, Humboldt, KEK, Princeton, South Carolina,
SLAC, Tel Aviv, Tokyo M.U., Tennessee, Wasada,
Yerevan
K. Floettmann
KEK, Nov. 13-15, 2004
E-166 Demonstration Experiment for a Polarized
Positron Source
• Final Focus Test Beam (FFTB) at SLAC with 50
GeV Electrons.
• 1 m long helical undulator produces circular
polarized radiation of up to 10 MeV.
K. Floettmann
KEK, Nov. 13-15, 2004
Undulator Parameter for Polarized Positron Source
Parameter
Length
Beam
Period
B-field
Energy of first
Harmonic
Positrons/bunch
K. Floettmann
TESLA
~150 m
200 GeV
14 mm
0.7 T
E-166
1m
50 GeV
2.4 mm
0.76 T
20 MeV
9.6 MeV
3 · 1010
2 · 107
KEK, Nov. 13-15, 2004
Pulsed Undulator for E-166
• Inner diameter
0.89 mm
• Magnetic field:
0.76 T
• Pulsed current:
2.3 kA
• Rate 30 Hz
K. Floettmann
KEK, Nov. 13-15, 2004
E-166 Demonstration Experiment for a Polarized
Positron Source
• Conversion of photons to positrons in 0.5 X0 Ti-target
• Measurement of polarization of photons and positrons by
Compton transmission method
• Expected polarization ~50%
K. Floettmann
KEK, Nov. 13-15, 2004
E-166 Demonstration Experiment for a Polarized
Positron Source
• E166 is a demonstration of production of
polarized positrons for future linear colliders
• Uses the 50 GeV FFTB at SLAC
• Approved by SLAC in June 2003
• All components or prototypes work properly
• Installation of total experiment in FFTB tunnel in
August 2004
• First data taking run in October 2004
• Second data taking in February 2005
K. Floettmann
KEK, Nov. 13-15, 2004
Experiment@KEK
K. Floettmann
KEK, Nov. 13-15, 2004
Experiment@KEK
K. Floettmann
KEK, Nov. 13-15, 2004
Experiment@KEK
1.) Production of polarized γ‘s and polarized e+
• pol. γ: finished 2002
• pol e+: underway
2.) Polarimetry
• polarimetry of short pulse & high intensity γ
rays established
• same method applicable for polarized positrons
K. Floettmann
KEK, Nov. 13-15, 2004
Who wants to Do What? (to be completed)
ASIA
• contributions to E166
• conceptual design for a polarized positron source for ILC
(simulation study)
KEK: Y. Kurihara, T. Okugi, J. Urakawa, K. Yokoya, T. Omori
Tokyo Metropolitan Univ.: K. Dobashi
National Institute of Radiological Sciences: I. Sakai
Waseda Univ.: T. Aoki, M. Washio, T. Hirose
Sumitomo Heavy Industries: A. Tsunemi
• experimental production of polarized positron at ATF
KEK: Y. Kurihara, T. Okugi, J. Urakawa, T.Omori
Tokyo Metropolitan Univ.: A. Ohashi
National Institute of Radiological Sciences: M. Nomura, M. Fukuda
Waseda Univ.: I. Yamazaki, K. Sakaue, T. Saito, R. Kuroda, M. Washio, T. Hirose
K. Floettmann
KEK, Nov. 13-15, 2004
Who wants to Do What? (to be completed)
Europe
• EuroTEV (s. talk by E. Elsen)
• contributions to E166
• interest to continue work on preaccelerator:
beam dynamics, structures, diagnostics
INR Troitsk: V. Paramonov
• synergies with FEL work at DESY:
NC structure design, code development, beam dynamics
K. Floettmann
KEK, Nov. 13-15, 2004
Who wants to Do What? (to be completed)
USA
• E166
SLAC, collaborators: John Sheppard et al.
• conceptual positron source design
SLAC, collaborators: John Sheppard et al.
• material tests
SLAC and collaborators: John Sheppard et al.
• more from SLAC ??????
• beam dynamics simulations/experiment
ANL: Wei Gei et al.
Fermilab: Philippe Piot et al.
K. Floettmann
KEK, Nov. 13-15, 2004
Workshop Announcement
'Workshop on Positron Sources for the
International Linear Collider‘
This workshop will discuss relevant issues for positron production for the ILC
Daresbury Laboratory
11th to 13th April 2005
http://www.astec.ac.uk/id_mag/ID-Mag_Helical_ILC_Positron_Production_Workshop.htm
K. Floettmann
KEK, Nov. 13-15, 2004