ALPHA Storage Ring

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ALPHA Storage Ring

• Indiana University
• Xiaoying Pang

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Summary

• Purpose
• Wiggler design
• Injection and Extraction
• RF cavity
• Touschek lifetime
• Vacuum
• Photon source

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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.

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Design

• Typical operational energy
• 20MeV 100MeV,
• maximum 600MeV
• Dipole (existing)
• 1) effective length 2m
• 2) bending radius r 1.273m
• 3) edge angle 12 ? vertical focusing
• Wiggler (three dipoles)
• 1) modify damping partition number ?
  horizontal betatron motion stable (without
  wigglers Jx -0.3 )
• 2) tune momentum compaction factor

3m
C 20 m T 66.6 ns
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Wiggler Design

• Three gradient rectangular dipoles with
• B1 /B01.9 m-1 , where B1(dBz /dx)x0
  
• The minimum vertical gap is 40mm.
• Maximum field strength is 1.67 kG at 25MeV, 6.7kG
  at 100MeV.

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Wiggler Design
A linac beam can be debunched of its rf
structure in one turn if ac0.5 When
the wiggler is turned off, rw8
Qausi-isochronous condition
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Wiggler Design
25MeV
At 50 MeV , the horizontal damping time can be
10s.
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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

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septum
dipole
kicker 1
kicker2
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At the kickers location f21 p 180?, b1/
b22.185/2.185 ? q1/q2 1 At the
septums location bs 0.818, q1
q2 24 mrad ? Xco(septum) ? 32 mm
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Injection Scheme (Accumulation)
Septum
x
X0
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Injection Efficiency vs Fractional Tune
n 0.73
n 0.75
When tune is off 0.75, the ideal 4-injection-turn per closed orbit location is not guaranteed
n 0.77
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Number of Injection Turns per Closed Orbit Location
n 0.667
n 0.6 or 0.8
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Number of Injection Turns per Closed Orbit Location
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Number of Injection Turns per Closed Orbit Location
x
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Total number of Injection Turns
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Kicker Strength
Electrostatic kicker will be used
For one turn injection and extraction, the
integrated field strength is 0.60 MV at 25 MeV
electron beam energy. Choosing a length of
L0.5 m, the applied voltage on two plate is 60
kV.
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Kicker Strength
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Sample Injection
Watch the beam at septum
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Beam profile evolution around the ring
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Considering the aperture
Lets 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
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Extraction by Lambertson extraction magnet
The Lambertson septum is used to extract beam.
Injection
Extraction
Septum
1.4m
1.4m
0.2m
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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 h1, f15MHz

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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
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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
  h6 (or 494 MHz, h33)in order to achieve a bunch
  length of the order of 10ps for short-pulse
  X-rays

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Touschek lifetime

• Toucheck lifetime is sensitive
• to 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,
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Vacuum
Emittances are dominated by pressure in low
energy, become natural emittances at high energy.
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Compact Photon Source

• The X-ray is generated by laser- electron
  scattering at the chicane magnet.

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X-ray

• The energy of the scattering photon is
• where, EL is the laser energy, bc is the
  electron speed, q is angle of the scattered X-ray
  photon, q is the crossing angle of the laser
  and the electron beam, for head on collision,
  qp.
• is a small correction
  term.
• The scattered X-ray photons are confined to a
  cone of 1/g 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.

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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/sx2sz2

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Quadrupole Triplet
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Fitting results

• Best results

• Parameters

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• Currently the ALPHA ring is under construction.
• We will start the experiments on RF cavity soon.