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ALPHA Storage Ring. Indiana University Xiaoying Pang. Summary. Purpose Wiggler design Injection and Extraction RF cavity Touschek lifetime Vacuum Photon source. Our Purpose. Provide radiation effect experiments for NASA Debunch the rf linac beam bunches - PowerPoint PPT Presentation
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ALPHA Storage Ring
Indiana UniversityXiaoying Pang
Summary
• Purpose• Wiggler design• Injection and Extraction• RF cavity• Touschek lifetime• Vacuum• Photon source
Our Purpose• Provide radiation effect experiments for NASA Debunch the rf linac beam bunches
• Compact X-ray photon source based on Inverse Compton scattering (ICSX)
Advantage: low cost, easy operation. Difficulties: long damping time,
negative horizontal damping partition, space charge effect, beam lifetime issue.
Design Typical operational energy : 20MeV ~100MeV, maximum : 600MeV
Dipole (existing) 1) effective length 2m 2) bending radius = 1.273m 3) edge angle 12⁰ vertical focusing
Wiggler (three dipoles) 1) modify damping partition number horizontal betatron
motion stable (without wigglers Jx = -0.3 ) 2) tune momentum compaction factor
C = 20 mT = 66.6 ns
3m
Wiggler Design
• Three gradient rectangular dipoles with B1 /B0=1.9 m−1 , where B1=(dBz /dx)x=0
• The minimum vertical gap is 40mm.• Maximum field strength is 1.67 kG at 25MeV, 6.7kG at
100MeV.
0.1m 0.1m
0.2m
zero momentum compaction factor
positive horizontaldamping partition number
Wiggler Design
A linac beam can be debunched ofits rf structure in
one turn if |c|≥0.5
When the wiggler is turned off, w=∞
Qausi-isochronous condition
Wiggler Design25MeV
At 50 MeV , the horizontal damping time can be 10s.
Injection• Two bumpers and a Lamberston septum are
used • Use electrostatic kickers with kicker rise time
10ns• Beams are injected from a linac with 25MeV
(up to 60 MeV)• Phase space painting
kicker 1 kicker2
iii
ico ss
sx
)(cossin2
)()(
2
1
0sinsin
0coscos
:orbit closed localizedfor Condition
212211
212211
and 2
11221
dipole
21
septumseptum
At the kickers’ location:
At the septum’s location:
s = 0.818, mrad Xco(septum) 32 mm
beam pipebeam pipe
25mm 2-5mm
1mm 5mm or 2mm
2mm
X=0
BSeptum
Amax = 25mm
75.1x
x
mm1.0Injection Scheme (Accumulation)
Injection Efficiency vs Fractional Tune
= 0.75
= 0.73
= 0.77
When tune is off 0.75, the ideal 4-injection-turn per closed orbit location is not guaranteed
= 0.667
= 0.6 or 0.8
Number of Injection Turns per Closed Orbit Location
Number of Injection Turns per Closed Orbit Location
x
x ’
Septum5 injections per ellipse
x
x ’
Septum4 injections per ellipse
More Ellipses!
Number of Injection Turns per Closed Orbit Location
Total number of Injection Turns
co, max
A = 21 mm
Beam Size = 42 mm
x = 25 mm
co, max
A = 25 mm
Beam Size = 50 mm
x = 32 mm
Electrostatic kicker will be used:
Kicker Strength
field electric gapE
light of speed c
kicker theoflength L
MeV 60at ][2.0
where,
TmB
Bc
LEk
For one turn injection and extraction, the integrated field strength is 0.60 MV at 25 MeV electron beam energy. Choosing a length of L=0.5 m, the applied voltage on two plate is 60 kV.
Kicker Strength
32
50
5
142
2.84 /
co
gap
x mm
L cm
g cm
V kV
E MV m
Sample Injectionsconstraint aperture without )injection turn 10( 75.1xv
Watch the beam at septum
Beam profile evolution around the ring
Considering the aperture: Let’s take into the consideration of the apertures at the bending dipoles and electrostatic kickers. Set the aperture radius at dipoles to be 100mm = 0.1m, at kickers to be 25mm. The total injection numbers will decrease.
With about 10 turns of injection, 50ns bunch length and 0.5A linac current, we can achieve:
JMVnCQEEnergy
nCnsAQ
6.1560250
25010505.0
Extraction by Lambertson extraction magnet
100MeV.at 1.02T and MeV, 25at 0.25T Bstrength field The
dipole.adjacent theavoid toseptum by the deflected 35' need we
'
.2/sept.)(kick
wherespacedrift theof middle in the septum put the We
x
B
lBx z
3535
The Lambertson septum is used to extract beam.
InjectionSeptum
Extraction
1.4m 1.4m0.2m
35
RF cavity
• Revolution frequency 15MHz• In the operational mode of debunching no RF
cavity is needed.• For beam physics study with quasi-
isochronous condition, we can modify the existing MPI cavity to make it operate at h=1, f=15MHz
MPI Cavity• Was built for proton acceleration with frequency from 2 to 10MHz• A quarter-wave –like cavity, is loaded with 10 ferrite rings with
quadrupole field bias.• Major RF tuning is achieved by parallel external capacitors. With an
external capacitance Cext =290 pF , the cavity was tested up to 11.4MHz, the resulting shunt impedance was about 1k.
Diameter of the cavity ~0.55m; Length ~0.6m
In the future
• For 15MHz operation, we need to reduce the external capacitance to about 120pF or the number of ferrite rings in the cavity.
• Reconfigure the ferrite rings to maximize the shunt impedance for a possible 3kV voltage.
• We will built a 90 MHz rf cavity for harmonic h=6 (or 494 MHz, h=33)in order to achieve a bunch length of the order of 10ps for short-pulse X-rays
Touschek lifetime Toucheck lifetime is sensitiveto the parameter:
is the rf bucket height, is the horizontal momen-tum spread can range from 0.001 to 1.
we will need a lifetime of 1h or more.
It can also be varied by changing the momentum compaction factor
where,
Vacuum
energy. offunction
a as emittance mequilibriu the
calculatecan we,2.9
25MeV,for 9.48 Choosing
)()/(
)/(
:emittance mequilibriu The
CO 40% H 60%
:ncompositio Vacuum
n compositio
vacuumon the depends :g
pressure. vacuum:P
emission.photon to
due excitation quantum :G
time.damping :
where,2
12
:equationevolution emittance The
dilution. emittance of source
another is scattering gas Beam
1
0
50
10
20
2
mg
nTorrPg
gPGdt
d
g
Emittances are dominated by pressure in low energy,become natural emittances at high energy.
Compact Photon Source
• The X-ray is generated by laser- electron scattering at the chicane magnet.
X-ray• The energy of the scattering photon is:
where, EL is the laser energy, c is the electron speed, is angle of
the scattered X-ray photon, * is the crossing angle of the laser and the electron beam, for head on collision, *=.
is a small correction term.
• The scattered X-ray photons are confined to a cone of 1/ with respect to the electron beam direction
• The bending angle of the chicane magnet can vary from zero to 110mrad.
• The scattered X-ray can easily be separated from the circulating
electron beam at a distance 25cm from the collision point.
Photon Brilliance
• The brilliance of the back scattering X-ray photon is:
• The X-ray flux is given by: where L is the luminosity. For head-on
collision, the luminosity is:• Brilliance 1/x
2z2
Quadrupole Triplet
Fitting results
Best results Parameters
• Currently the ALPHA ring is under construction.
• We will start the experiments on RF cavity soon.