Transcript Accelerator Design Summary • There are presently two designs, eRHIC and ELIC. – For eRHIC, the Ring-Ring option with an electron ring 1/3

Accelerator Design Summary
• There are presently two designs, eRHIC and ELIC.
– For eRHIC, the Ring-Ring option with an electron ring
1/3 the size of RHIC is the present point design,
however,
– the Ring-Linac option will be maintained and developed.
– ELIC is a “green-field” design being optimized for spin
preservation & handling and for potentially higher
luminosity than eRHIC.
eRHIC Ring-Ring
5-10 GeV static electron ring
recirculating linac injector
V. Ptitsyn, BNL
RHIC
e-cooling
EBIS
LINAC
BOOSTER
AGS
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
eRHIC Ring-Linac
V. Litvinenko, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
ELIC Layout
L. Merminga, Jlab
IR
IR Solenoid
IR
3-7
3
-7 GeV electrons
Snake
30--150
30
150 GeV light ions
Electron Injector
CEBAF with Energy Recovery
Beam Dump
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Design Parameter comparison
eRHIC
Ring-Ring
eRHIC
Linac-Ring
ELIC
Luminosity (ep)
4.4…1.5E32 1E33…1E34 1E33…1E35
Ions
…U92+
…U92+
…6Li+++
Ep (GeV)
50…250
50…250
30…150
Ielectron (A)/ppb
0.45/1E11
0.1…1E11
2.3…4.1/1E10
ppb (proton)
1E11
1…2E11
4E9
fcoll (MHz)
28
28
1500
lb (p/ion)(cm)
20
20
0.5
lb (e–) (cm)
1…2
1
0.5
p
.0065
.005
.01
e
.08
–
.09
ß*p/e (m)
.27/.27 (y)
.26/0.3…1
5
0.005
U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Presentations
• We heard presentations on
– Electron and ion sources and polarization
(Farkondeh, Poelker, Roser, Derbenev &
Dudnikov, Barber)
– Cold and intense beams (Skrinsky, Kroc,
Derbenev, Dudnikov)
– Energy recovering linacs (Litvinenko, Calaga,
Krafft)
– “Luminosity” (Hoffstaetter, Wei, Lebedev,
Montag, Hyde-Wright, Wang, Masuzawa)
• I will emphasize the WG contributions
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Sources
• Polarized Proton & ion sources
– BNL has the KEK-TRIUMF-BNL OPPIS
– 1.6 mA (1E12 pp) H– @ 90% polarization
– EBIS for 3He++ under development at BNL,
2E11, 70…75% polarization
– Atomic-beam Ion Sources (ABS) may yield
somewhat higher polarization at lower current
– 2D source: 90% Pz and Pzz vs 50…60%
– a 6Li+++ source also may be feasible.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Polarized
D
and
++
He
ion sources
•Vector spin polarized D- ion beam in excess of 1.0 mA can be produced in the
OPPIS, as well as in the atomic beam source with resonant plasma ionizer.
•J.Alessi and A.Zelenski proposed to use an EBIS (Electron Beam Ion Source
under development at BNL) for nuclear polarized 3He gas ionization to 3He++
ions. The polarized 3He will be produced by conventional technique of optical
pumping in metastable states. The expected beam intensity is about 2•1011
3He++ ions/pulse, polarization 70-75%.
T. Roser, BNL
EBIS test stand
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Sources (cont’d)
• Electron Sources
– Irradiate a GaAs cathode with circular
polarized laser light (≈800 nm) & collect pol e–.
– Strained lattice & superlattice cathodes have
largely overcome the surface charge limit (e.g.
SLAC), => no issue for eRHIC ring-ring
– For ring-linac, ELIC at issue are rep. rates for
the laser, up to 100 MHz lasers now available,
combination of power & rep. rate not yet.
– Increase area on cathode to increase charge
– eRHIC: using FEL => large-scale project
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
ELIC e-Beam
Specifications
Typical parameters;
•
•
•
•
I
Ave injector gun current 2.5 mA (and then 25 mA)
Micropulse bunch charge 1.6 nC
M. Poelker, Jlab
Micropulse rep rate 150 MHz (and then 1.5 GHz)
Macropulse rep rate ~ 2 kHz, 0.5 ms duration.
1/fc
CCR/c
~100 CCR/c
Injector
I
CCR= 1.5 km
Circulator Ring
t
t
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Continuing Trend Towards Higher Average Beam Current
JLab FEL program with
unpolarized beam
M. Poelker, Jlab
100
ELIC with
circulator ring
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Series1
Series2
Series3
1
First low polarization,
then high polarization
at CEBAF
0.1
0.01
1970
1980
1990
2000
2010
2020
2030
2040
Year
First polarized beam
from GaAs photogun
Source requirements for ELIC less demanding
with circulator ring. Big difference compared
to past talks. Few mA’s versus >> 100 mA of
highly polarized beam.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Polarization,
–
e
• Electron polarization (eRHIC):
– Significant progress has been made (10 GeV):
• Feasible design for spin rotators incl. spin
matching.
• eRHIC electron ring spin tracking studies
(incl. spin rotators, excl. detector)
• may produce >80% polarization, pol≈20 min
(small e– ring helps!)
• will require excellent alignment & orbit
correction (50µm rms)
• at lower energy: some shift of pol. vector
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
ELIC Polarization vs Energy
D. Barber, DESY
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Polarization: ELIC,
–
e
• “Figure 8” design elegant way to control spin
– Polarization axis given by “controlled imperfection”
(e.g. solenoid).
– Smaller no. of snakes required
– Potentially up to 4 IPs with longitudinal poln.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
(Slide of Fig. 8 ring with snake)
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Polarization: p
• Polarized protons demonstrated in RHIC
(30%)
– dominated by AGS depolarization
• AGS upgrade program to increase
polarization
• Development of helical spin rotators/snakes
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Polarization survival in RHIC (store # 3713)
T. Roser, BNL
Acceleration and
squeeze ramp
Spin rotator ramp
Some loss during
accel/squeeze ramp
(Tune too close to ¼)
No loss during
spin rotator ramp and
during store
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
e-Cooling
• eRHIC ring-linac and ELIC proposals require ecooling to work. eRHIC ring-ring would profit
– e-Cooling is necessary to
• combat IBS (beam emittance)
• shorten the bunches (5 mm for ELIC)
– Can make flat beams (ELIC)
• effect of IBS greatly reduced
• All cooling schemes require high power electron
beams (50…75 MeV, ≈1 A)
– Factor 10 beyond FNAL Recycler cooler
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Electron Cooling (cont’d)
• Because of the high beam power involved
– Electron ring & energy recovery are required.
– Stringent requirements on beam quality &
collinearity of e and p beams
– “Hollow” electron beams may help reduce
recombination rates (Skrinsky).
• Highly ambitious R&D projects, Recycler
experience will be invaluable.
– BNL is launching R&D project to demonstrate
feasibility for RHIC upgrade.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
R. Calaga, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Schematic Layout of the
Recycler Electron Cooling
T. Kroc, FNAL
Electron Cooling System Parameters
Parameter
Value
Units
Electrostatic Accelerator
Terminal Voltage
4.3
MV
Electron Beam Current
0.5
A
Terminal Voltage Ripple
500
V (FWHM)
Cathode Radius
2.5
mm
Gun Solenoid Field
600
G
Cooling Section
Length
20
m
Solenoid Field
150
G
Vacuum Pressure
0.1
nTorr
Electron Beam Radius
6
mm
Beam angular spread
≤ 80
µrad
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Energy Recovering Linacs
• ERLs are essential in most scenarios
– Directl: ELIC, eRHIC ring-linac
– Indirect: in the electron cooler
• Principle demonstrated in Jlab FEL
at low energy, recently at CEBAF at 1 GeV, 80 µA.
• High-current high-energy operation remains to be
demonstrated
• Cavities for high-current ERL are being designed.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
R. Calaga, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Luminosity Considerations
• Everything else being equal, luminosity is
prop. to I•/ß*.
• The linac scenarios gain on e by allowing
high tune shift (disruption) of the e– beam.
• The ring-ring scenario somewhat makes up
by higher I.
• However, how much beam loss (e.g. from
halo generation) can the energy recovery
replenish?
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Gedanken Experiment
For round, equal sized beams, the following scaling applies:
I e  e e
L
e  * re
G. Krafft, Jlab
Comparing linac-ring colliders and ring-ring colliders, what can change
for the better?
1.
2.
3.
4.
5.
6.
Maximum Ie/e is set by ION ring stability. The same in the two cases
e set by the physics. The same in the two cases
Minimum ß* is set by IR region design issues. Can it be too much
better for linac-ring? Should not be any worse than for ring-ring
re is set by (God, Yahweh, Allah, …); YOU cannot change it
If there are to be luminosity enhancements to be found for linac-ring
designs compared to ring-ring designs, they must arise because one is
allowed to make the equivalent tune shift e bigger for linac-ring
colliders.
Finding the physical phenomena that determine the maximum  e are
extremely important for evaluating the linac-ring idea.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Luminosity (cont’d)
• Beam-beam simulations are underway to
reach insight
• Two approaches:
– Coulomb Sum
– PIC
• Benchmark: HERA!
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
G. Hoffstaetter, Cornell
Simulated coherent modes
ex  0.041
*
ey  4.0m +
ey  0.272
dQex  0.027
why?
 exm  0.009
dQey  0.082
how ?
 eym  0.013
(From work with Jack Shi, KU)
 px
 py
f x / f0
f x / f0
 eysim  0.013
 exsim  0.003
 ex  ex
 ex
f x / f0
 ey
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 ey  ey
2nd EIC Wkshp, Jlab
f x U.
/Accel.
fWienands,
0 Design Summary, 15-Mar-04
Luminosity
G. Krafft, Jlab
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
The electron beam parameters
F. Wang, Bates
Requirement
Reason
Concerns & Measures
Beam emittance
(uncoupled x, nm)
40-60 (10 GeV)
50-90 (5GeV)
Match ion beam
Arc lattice
Wiggler || superbend
Beam y/x emittance ratio
~0.2
High luminosity
70% polarization ?
High Peq ~ high Ke, HERA
update? study
Damping decrement
Damping time < ~25
ms at 5GeV?
Less beam-beam limit
reduction at low E
Wiggler || superbend
for low E operations
Bunch intensity
(120 bunches)
11011
High luminosity
Vacuum chamber (syn.
radiation), RF, instability
…
Injection
On energy, top-off or
continues
Integrated luminosity.
High e b-b limits lead to
short lifetime
On energy Injection,
flexible bunch-bunch
filling.
Beam-beam tune shift limit
y ~ 0.08
B-factory achieved
Working point near
integer(spin), study
Increase instability region
?
Study
Coherent b-b effect in
Unequal-circumference
collider
(0.45A)
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Scratch of a “super-bend” for radiation enhancement at 5 GeV
F. Wang, MIT Bates
All bends
on
Center
bend on
only
 (m)
70.3m
23.4
P
(MW)
~0.35
~1.06
x
~54.5
~18.1
Red: normal bend
Blue: center bend only
(msec)
y reduction ~ 20%
(Compare to 10 GeV)
*Total path length increase:
~4.47cm.
* Linear rad. power at 10
GeV ~14kW/m
e-ring path length adj. requirement (with super-bends)
-5
e-p(GeV)
5/250
032
10/250
20cm
U. Wienands, 2nd EIC Wkshp, Jlab
10/50
Accel. Design
Summary, 15-Mar-04
Intra-beam phenomena in RHIC
• IBS: intra-beam small-angle Coulomb scattering
 primary luminosity limiting factor in an heavy-ion storage ring
Rutherford scattering cross section ~ Z4 / A2
J. Wei, BNL
Luminosity
degradation
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Flat colliding beams equilibrium
Ya. Derbenev, Jlab
At low coupling, cooling results in flat beams
x – emittance is determined by the IBS vs horizontal cooling
y – emittance is limited by the beam-beam interaction

Luminosity is determined
by the beam area

IBS effect is reduced
by a factor of the beam size
aspect ratio
y
e
P
x
Multiple IBS
Touschek
scattering

Cooling effect at
equilibrium can be enhanced
by flattening the electron
beam in cooling section
solenoid
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
IBS in the Tevatron
V. Lebedev, FNAL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Tevatron Measurements
V. Lebedev, FNAL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Crossing Angle
• Non-zero crossing angle causes luminosity
loss (geometry) and synchro-betatron
coupling limiting intensity, thus luminosity.
• “Crab crossing” aligns the bunches in space
such that they collide head-on, albeit in a
transversely moving system, thus allowing a
crossing angle, simplifying IR design greatly.
• 1st test of scheme likely at KEKB.
– One cavity/ring only => c.o. for head of bunch is
different than for tail, crabbing everywhere
• Integral part of ELIC (100 mr crossing angle)
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Superconducting Crab Cavity
KEK Crab Cavity R&D Group
K. Hosoyama, K. Hara, A. Kabe,
Y. Kojima, Y. Morita, H. Nakai
A. Honma, A. Terashima, K. Nakanishi
MHI
S. Matsuoka, T. Yanagisawa
M. Masuzawa, KEK
Input Coupler
I.D. 240
I.R. 90
I.D. 120
I.D. 188
I.R.241.5
Coaxial Coupler
866
I.R. 20
I.D. 30
Monitor Port
0
100
50
150
483
scale (cm)
38
K.Hosoyama (MAC 2004)
U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Crab Crossing for ELIC
• Short bunches also make feasible the Crab
Crossing:
• SRF deflectors 1.5 GHz can be used to
a
Ya.create
Derbenev,
Jlab
proper bunch tilt
E  100 GeV
 cr  2 f  2 t
eB l
t  t t
E
F

F 3 m
2
  20 cm
Bt  600 G
 cr  0.1
(1.5 GHz
(  20 MV / m )
 t  5  104
lt  4 m
 f  1 mm
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
IR issues
• IR design is critical for colliders
– Electron beams esp. challenging due to handling
of synchrotron radiation
– It is imperative that detector and accelerator
people work together to reach a feasible design
• Physics equirements (e.g. small-angle
detectors, low backgrounds)
• Machine requirements (beam separation,
focusing, vacuum)
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
C. Montag, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
C. Montag, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
V. Litvinenko, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Physics Requirements
• The IR design will need more physics input:
– (C. Hyde-Wright, ODU)
• Forward tagging
• Hadron beam tagging
• Recoil protons
• Neutron detection
•…
• Most of these require detector access to
small/zero angle, spectrometer magnets etc.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
C. Hyde-Wright, ODU
• First few elements in lattice should be
designed with thought to detection of forward
fragments
• Compact detectors near 0deg can enhance
physics program.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Electron-cloud effect
– Positively charged beams are subject to
electron-cloud formation & emittance blowup
• ISR, PSR, B-Factories, RHIC, BINP rings,…
– Solenoids work well in drift regions, but are
unlikely to work in magnets.
– Electron rings are not safe either: fast ion
instability can affect even the linac scenarios.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Models of two-stream instability
•
•
•
The beam- induces electron cloud buildup and development of two-stream e-p instability is one of major
concern for all projects with high beam intensity and brightness [1,2].
In the discussing models of e-p instability, transverse beam oscillations is excited by relative coherent
oscillation of beam particles (protons, ions, electrons) and compensating particles (electrons,ions)
[3,4,5].
For instability a bounce frequency of electron’s oscillation in potential of proton’s beam should be close
to any mode of betatron frequency of beam in the laboratory frame.
1. http://wwwslap.cern.ch/collective/electron-cloud/.
2. http://conference.kek.jp/two-stream/.
3. G.I.Budker, Sov.Atomic Energy, 5,9,(1956).
4. B.V. Chirikov, Sov.Atomic.Energy,19(3),239,(1965).
5. M.Giovannozzi, E.Metral, G.Metral, G.Rumolo,and F. Zimmerman , Phys.Rev. ST-Accel.
Beams,6,010101,(2003).
V. Dudnikov, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Instability in RHIC, from PAC03
V. Dudnikov, BNL
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
R&D issues for ELIC and LR-eRHIC
 High intensity polarized and unpolarized electron gun
• Currently a few mA
G. Hoffstaetter, Cornell
 Up to 450 mA / 16nC
• Currently a few 100 mA of polarized beam GaAs photo injector at 80% pol.




Up to 450 mA electron current at 80% pol.
Methods to overcome the surface charge limit for 16nC/bunch
Beam emittance control for 16nC/bunch and a large source diameter (14mm)
Test and improvement of cathode lifetimes
 Electron Cooling at high energies
Currently a frew 100MeV, soon 8.9GeV/c pbar at the FNAL recycler
 For LR-EIC: Cooling of Au or light ions up to 100GeV, p at 27GeV
 New technology: ERL cooling + cooling with bunched e-beam
 Limits to the ion emittance with e-cooling (especially vertically) and with all
noise processes.
 Allowable beam beam parameters for ions, especially with electron cooling
•
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
R&D issues for ELIC and LR-eRHIC
 IR design, detector integration, saturation in special magnets, optimization …
 Halo development by beam disruption, especially at low electron energies
 Impact of beam disruption on following IRs
 Ion-beam dynamics with crab cavities
G. Hoffstaetter, Cornell

High current ERLs
Currently strong influence of small e-beam oscillations on p-emittance in HERA
 Stabilization of the e-beam + influence on the ion beam
 Current limits by multi-pass Beam-Breakup instability
 CW operation of high filed cavities, stabilization, heat loss
 Influence of HOMs with large frequencis (>2GHz)
 R/Q and Q agreement with calculations including absorbers
•
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
G. Hoffstaetter, Cornell
R&D specific to ELIC






Spin resonances in Figure 8 rings
Stability of non-vertical polarization in figure 8 rings and in the ERL
Stable beam in a 100 turn circulator ring
Crab cavity R&D and crab cavity beam dynamics
Beam beam resonance enhancement when operating close to the hourglass effect
Limits to the bunch length, since this limits the beta function
R&D specific to LR-eRHIC
 1kW FEL at 840nm
 Heating of the cathod / problems associated with large spot size (14mm)
 Production of very high polarized e-beam
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
Issues for further Study
• Both proposals:
– Interaction region, at different energies, with spin rotators
• eRHIC
– Hirata-Keil coherent
beam-beam modes
– Restriction on e- beam
energy (pol, lumi)
– effect of different ion
energy on electron orbit
– maximize no. of bunches
in RHIC
• ELIC
– Parameters have been
pushed into new
territory…
• ß, lb, ring shape, crab
crossing,…
– benefits of circulator
ring vs “real” storage
ring
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04
At last…
• There has been much progress over the last years,
the eRHIC design is maturing.
• ERL technology demonstrated at CEBAF at 1 GeV
• A rigorous e-cooling R&D program est’d. at BNL
• ELIC proposes some very elegant and innovative
features worth further investigation.
• Thank you to all speakers and the organizers for a
very lively workshop.
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U. Wienands, 2nd EIC Wkshp, Jlab
Accel. Design Summary, 15-Mar-04