EC potential impact to colliders Reaching a high start luminosity Very short i bunches achieved by longitudinal cooling in combination with SRF cannot be attained with stochastic cooling ID: 152083
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Slide1
MEIC Electron Cooler Design Concept Slide2
EC potential impact to colliders
Reaching a high start luminosity
Very short
i
-bunches
achieved by
longitudinal cooling
in combination with
SRF
(
cannot
be attained with
stochastic cooling
!)
make sense to design a
super-strong focusing (low beta) at IP
Short bunches
allow one to
employ
the crab-crossing beams, thus avoiding the parasitic b-
binteractions
Low transverse
emittance
+ high rep. rate
allow one to
minimize charge/bunch
Extending the luminosity lifetime
EC
suppresses beam heating
and
luminosity loss
caused by multiple and
Touschek
IBS Slide3
ion bunch
electron bunch
Cooling section
solenoid
HEEC basics
Magnetized e-gun
Injector
SRF
linac
Cooling time grows with
Therefore:
staged cooling
Cooling conditions:
Co-moving “cold” electron beam serves as
thermostat for a
hot ion beam
(
i
– e Coulomb collision exchange)Slide4
Parameter
(p/e)
Unit
Value
Beam energy
GeV
150/7
Energy of cooling beam
MeV
75
Bunch rep rate
GHz
1.5
Particles/bunch
10
10
0.2/1
Beam current
A
0.5/2.5
Cooling current
A
2.5
Horizontal
emittance
*
m
1/100
Vertical
emittance
*
m
0.01/1Number of interaction points
4
Total beam-beam tune shift
0.04/0.16
Laslett’s
tune shift in p-beam
0.02
Luminosity overall IP (10
35)
cm
-2
s
-1
2
Cooling/IBS time in p-beam core
min
5
Luminosity
Touschek’s lifetime
h
20
High luminosity colliding beams
Parameter
(p/e)
Unit
Value
Energy
GeV/MeV
20/10
Cooling length/ circumf.
%
1
Particles/bunch
10
10
0.2/1
Energy spread
**
10-43/1
Bunch length
**
cm
20/3
Proton emittance
, norm**
m
4
Cooling time
min
10
Equilibrium emittance, *
m
1
Equilibrium bunch length*
cm2
Laslett’s
tune shift
0.1
Initial electron cooling
** max. amplitude
* norm.
rms
* norm.
rms
Staged ECSlide5
Staged Cooling in Ion Collider Ring
Initial
after boost
Colliding
Mode
Energy
GeV
/MeV15 / 8.15
60 / 32.6760 / 32.67proton/electron b
eam currentA0.5 / 1.50.5 / 1.5
0.5 / 1.5
Particles/Bunch1010
0.416 / 2
0.416 / 2
0.416 / 2Bunch length
mm(coasted)10 / 20~30 10 /
20~30Momentum spread10-4
10 / 2
5 / 2
3 / 2Hori. & vert.
emittance, norm.µm4 / 4
0.35 / 0.07
Laslett’s tune shift (proton)0.002
0.0050.06Initial cooling after ions injected into the collider ring for reduction of
3d emittance before accelerationAfter boost & re-bunching, cooling for reaching design values of beam parameters in colliding mode
Continuous cooling during collision for suppressing IBS, maintaining luminosity lifetime Slide6
High Energy e-Cooler for Collider Ring
Design Requirements:
up to 10.8
MeV
for cooling at injection energy (20
GeV
/c)up to
54 MeV for cooling top proton energy (100 GeV/c)Cooling e-beam current :up to 1.5 A CW beam at 750 MHz repetition rate
About 2 nC bunch charge (possible space charge issue at low energy)Solution: ERL Based Circulator Cooler (ERL-CCR)
Must be an SRF Linac for accelerating electron beamMust be Energy Recovery (ERL)
to solve RF power problemMust be Circulator -cooler ring (CCR)
for reducing current from source/ERLERL-CCR is considered to
provide the required
high cooling current while consuming fairly
low RF power and reasonable current
from injector Slide7
Conceptual Design of Circulator e-Cooler
ion bunch
electron bunch
Electron circulator ring
Cooling section
solenoid
Fast beam kicker
Fast beam kicker
SRF Linac
dump
electron injector
energy recovery path
(Layout A)Slide8
ERL Circulator Electron Cooler
ion bunch
electron bunch
Cooling section
solenoid
(Fast) kicker
(Fast) kicker
SRF
Linac
dump
injector
(Layout B)Slide9
Optimized Location of Cooling Channel
10 m
Solenoid (7.5 m)
SRF
injector
dumper
Eliminating a long circulating beam-line could
cut cooling time by half, or
reduce the cooling electron current by half, or
Center of Figure-8
(Layout C)Slide10
Cooler Design Parameters
Max/min energy of e-beam
MeV
54/11
Electrons/bunch
10
10
1.25
bunch revolutions in CCR
~100
Current in CCR/ERL
A
1.5/0.015
Bunch repetition in CCR/ERL
MHz
750/7.5
CCR circumference
m
~80
Cooling section length
m
15x2
Circulation duration
s
27
RMS Bunch length
cm
1-3
Energy spread
10
-4
1-3
Solenoid field in cooling section
T
2
Beam radius in solenoid
mm
~1
Beta-function
m
0.5
Thermal cyclotron radius
m
2
Beam radius at cathode
mm
3
Solenoid field at cathode
KG
2
Laslett’s
tune shift @60
MeV
0.07
Longitudinal inter/intra beam heating
s
200
Number of turns in circulator cooler ring is determined by degradation of electron beam quality caused by inter/intra beam heating up and space charge effect.
Space charge effect could be a leading issue when electron beam energy is low.
It is estimated that beam quality (as well as cooling efficiency) is still good enough after 100 to 300 turns in circulator ring.
This leads directly to a 100 to 300 times saving of electron currents from the source/injector and ERL.Slide11
Issues
Space charge limitations in CCR
:
Coulomb interaction (non-linear
Laslett
detune)
CSRIntra- and Inter-Beam Scattering in CCRSource/Injector/ERL/CCR beam matching gymnasticsMagnetized cathode
Matching with cooling solenoids, straights and arcsBeam size at cathode and related canonical emittanceOther agendas? (space charge dominated beam in axial optics…) Fast kicker
(beam-beam or other) And more…Slide12
Backup slides Slide13
Parameter
Unit
Value
Max/min energy of e-beam
MeV
75/10
Electrons/bunch
10
10
1
Number of bunch revolutions in CR
100
1
Current in CR/current in ERL
A
2.5/0.025
Bunch rep. rate in CR
GHz
1.5
CR circumference
m
60
Cooling section length
m
15
Circulation duration
s
20
Bunch length
cm
1
Energy spread
10
-4
3-5
Solenoid field in cooling section
T
2
Beam radius in solenoid
mm
1
Cyclotron beta-function
m
0.6
Thermal cyclotron radius
m
2
Beam radius at cathode
mm
3
Solenoid field at cathode
KG
2
Laslett’s
tune shift in CR at 10
MeV
0.03
Time of longitudinal inter/
intrabeam
heating
s
200
ERL-based EC with circulator ring
Slide14
Technology: Ultra-Fast Kicker
h
v
0
v≈c
surface charge density
F
L
σ
c
D
kicking beam
A short (1~ 3 cm) target electron bunch passes through a long (15 ~ 50 cm) low-energy flat bunch at a very close distance, receiving a transverse kick
The kicking force is
integrating it over whole kicking bunching gives the total transverse momentum kick
Proof-of-principle test of this fast kicker idea can be planned. Simulation studies will be initiated.
Circulating beam energy
MeV
33
Kicking beam energy
MeV
~0.3
Repetition
frequency
MHz
5 -15
Kicking angle
mrad
0.2Kinking bunch lengthcm
15~50Kinking bunch widthcm
0.5
Bunch chargenC
2 An ultra-fast RF kicker is also under development.
V.
Shiltsev, NIM 1996Beam-beam kickerSlide15
Electron source
e-gun V 500
KeV
Pulse
duration
0.33 ns
Bunch charge 2
nC
Peak current 0.65 A
Emittance, norm 1 mm.mrad
Rep.rate
15 MHz
Average
current
30 mA
1st compressor
Prebuncher
frequency
500 MHzVoltage 0.2 MV
Energy gradient after prebuncher 2x 10%
1
st drift 2 m
Bunch length after 1st compression 1 cm
Beam radius (assumed value) 2 mm
Coulomb defocusing length 30 cm
1
st
accellerator cavity
Voltage 2 MVFrequency 500 MHz
Beam energy 2.5
MeV
2nd compressor
Buncher
frequency 1.5 GHz
Energy gradient 2 x 10% 2nd
drift 1.8 m
Bunch length, final 0.5mm
Beam radius 2 mm Coulomb defocusing length 35 cm
Estimates for Injector to ERL