Transcript WG3a Sources Summary Jim Clarke on behalf of John Sheppard, Masao Kuriki, Philippe Piot and all the contributors to WG3a.

WG3a Sources Summary
Jim Clarke
on behalf of
John Sheppard, Masao Kuriki, Philippe Piot
and all the contributors to WG3a
Goals for WG3a
• Review ILC electron and positron source requirements.
• Review proposed source designs.
• Make recommendation for the baseline reference
design.
• Develop list of R&D tasks.
• Discuss design options.
• Propose a timeline for the development of the ILC
sources which includes criteria and milestones for
technology selection.
• Make a list of current activities; make a list of institutional
interest in future development activities.
ILC Source Requirements
Parameter
Symbol
Particles per bunch
nb
Bunches per pulse
Nb
Tb
f rep
E0
A=2J
E/E
Fc
Pe
Pp
Bunch Spacing
Pulse Repetition Rate
Energy
DR Transverse Acceptance
DR Energy Acceptance
Overhead Factor
Electron Polarization
Positron Polarization (option)
Value
2 x1010 ( 1x1010 )†
2820 (5600) †
Units
e- or e+
number
~300
5
ns
Hz
5
0.04
1
1.5
>80
~60
GeV
m-rad
%,FW
number
%
%
Electron source
• 2 sessions dedicated to electrons
• 7 presentations
• Type of gun
– DC or RF
– What DC voltage to use
– What RF scheme to use
• Photocathodes
• Lasers
N Yamamoto, Nagoya
OPCPA system for generation of trains
of femtosecond pulses with ~800 nm wavelength
Ti:Sa oscillator
Piezo
primary
synchronization loop
grating stretcher
t  100 fs
t = 15 ps
G > 5 000
photo
diode
mixer
1.3 GHz
master clock
f = 1.3 GHz
grating
compressor
three-crystal
OPA
synchronized
Nd:YLF Burst-Mode laser
pumping the OPA
G ~ 20
t = 12 ps
(FWHM)
picosecond-pulse
output channel:
pulse trains, 800 ms long
t = 150 fs (FWHM)
Emicro = 50...100 mJ
@ f= 1 MHz
output
pulse trains
800 ms long,
l = 790 ...
830 nm
l = 523 nm
I. Will, H. Redlin, MBI Berlin
• OPCPA system generates trains of
picosecond or femtosecond pulses
t = 150 fs .. 20 ps (FWHM)
• pulse energy:
Easily stretched
Emicro = 50…100 mJ
Etrain = up to 80 mJ Far more
energy than
• Available wavelength:
needed
l = 790…830 nm
up to 900 us
Output pulse train
of the OPCPA
K Floettmann, DESY
ILC polarized electron source, Baseline Recommendation!
DC gun(s)
laser
room-temperature
accelerating sect.
sub-harmonic
bunchers + solenoids
Laser requirements:
pulse energy: ~ 2 mJ
pulse length: ~ 2 ns
# pulses/train: 2820
Intensity jitter: < 5 % (rms)
pulse spacing: 337 ns
rep. rate: 5 Hz
wavelength: 750-850 nm
standard ILC
SCRF modules
diagnostics
section
DC gun:
120 keV HV
photocathodes:
GaAs/GaAsP
Room temperature linac:
Allows external focusing
by solenoids
Same as e+ capture linac
Positron Source
• 4 sessions dedicated to positrons
• 13 presentations
• 3 alternative schemes were considered in
detail
• Lively discussion on pros and cons of
each scheme !!
“Conventional” Scheme
Conventional Target
Target material WRe
56kW absorbed
Target rotates at
360m/s
Operates at fatigue
stress of material
W Stein, LLNL
Positron Yield
Positron yield is defined as the ratio of the number of captured
positrons to that of incoming electrons striking the conversion target.
Specification
is 1.5
no safety
margin
W Gei, ANL
Undulator Based Source
Many options for undulator placement etc
Schematic Layout – Undulator @ 250GeV & Transfer Paths
Primary esource
Beam
Delivery
System
5 – 100 GeV eBypass line
Positron Linac
250 GeV
IP
150 – 250 GeV e- Photon
Transfer Line Collimators
eDR
Electron
100 GeV
Target eDump
Helical
Undulator
Linacs
e+
DR
Photon
Beam
Dump
150 GeV
2nd e- Source
D Scott, Daresbury
Auxiliary eSource
Photon
Target
Adiabatic
Matching
Device
e+ preaccelerator
~5GeV
Undulator Prototypes
14mm SC, Rutherford Lab
10mm SC, Cornell
14mm PM, Daresbury
D Scott, Daresbury
Target and Yield
• Target
– Material is Ti
– 18kW absorbed
– Rotates at 100 m/s
– Factor of 2 safety margin in fatigue stress
• The value of positron capture for
undulator-based source is 3-4 larger than
that of electron-based source because of
better positron beam emittance after
target. (Y Batygin, SLAC)
E-166 Experiment
E-166 is a demonstration of undulator-based production
of (polarized) positrons for linear colliders:
- Photons are produced ~in the same energy range and
polarization characteristics as for ILC;
-The same target thickness and material are used as in the
linear collider;
-The polarization of the produced positrons is the same as in a
linear collider.
-The simulation tools are the same as those being used to
design the polarized positron system for a linear collider.
- Number of gammas per electron is lower ~210 times,
however: (150/1)(2.54/10)(0.4/0.17)2.
A Mikhailichenko, Cornell
E-166 at SLAC
Undulator
Undulator table
table
Positron
Positron table
table
Gamma
Gamma table
table
A Mikhailichenko, Cornell
Vertical
Vertical soft
soft
bend
bend
E166 Undulator Area
A Mikhailichenko, Cornell
E-166 Results
• Number of photons agrees with expected
• Gamma polarisation agrees with theory
82-99.3 %±10-20%
• Number of positrons agrees with expected
• Positron Polarisation = 95 %±30%
• Simulated 84%
A Mikhailichenko, Cornell
Compton Scheme
Compton ring
Electron storage ring
to main linac
T Omori, KEK
positron stacking in main DR
laser pulse stacking cavities
Proof of Principle at KEK
T Omori, KEK
Summary of Experiment
1) The experiment was successful.
High intensity short pulse polarized
e+ beam was firstly produced.
Pol. ~ 80%
2) We confirmed propagation of the
polarization from laser photons ->
g-rays -> and pair created e+s & e-s.
3) We established polarimetry of short pulse &
high intensity g-rays, positrons, and
electrons.
T Omori, KEK
Compton Scheme for ILC
• Electron storage ring
• Laser pulse stacking
• Positron stacking ring
• Two versions, based on either CO2 or
YAG laser
• Expect 60% polarisation
Schematic View of Whole System (CO2)
~2.5A average
current
One laser feeds 30 cavities in daisy chain
T Omori, KEK
0.03
-0.03
dEnergy/Energy
e+ stacking in Damping Ring (simulation)
i-th bunch on
j-th DR turn
1st bnch on 1st trn
5th bnch on 5th trn
10th bnch
on 10th trn
e+ in a bucket
Time
-0.4
0.4
Longitudinal Pos. (m)
~110 msec
T=0
before 11th bnch on
941st trn
11th bnch on 942nd trn
15th bnch on 946th trn
~10 msec
20th bnch
on 951st trn
before 21st bnch on
1882nd trn
~10 msec + 110 msec
stacking loss = 18%
in total
T Omori, KEK
~20 msec
100 bnchs on 9410th trn
~110 msec
100th bnch
on 8479th trn
~100 msec + 110 msec
100 bnchs on 18820th trn
~200 msec
Open Issues for Positron Sources
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L-band warm structure 1ms operation : U , LC and Cv.
Target damage : Cv.
Radiation damage on target : U,LC
Thermal load of the capture section: Cv.
Damage by the operation failure : U (MPS)
Damage or failure by the instabilities : U
Degrade the electron beam quality: U
Positron Stacking in DR : LC
e beam stability in Compton Ring: LC
Vacuum pumping : U
Stability of integration of optical cavity : LC
Radiation loss, heat load in DR : LC
Fast Kicker operation with large kick angle for DR injection : U, LC and
Cv (DR problem)
• Mechanical failure on the rotation target: Cv and U
Cv: Conventional U: Undulator LC: Laser Compton
Baseline
• Baseline not yet agreed
• A number of issues for each scheme will
be examined in detail (next week)
• Need some interaction with other groups
(eg Damping Ring)
• Generate Performance & Issues List
• Aim to make recommendation for baseline
(and alternative) next week