Microsoft PowerPoint - ppt_Jayakar_Thangaraj_Berkeley_2012exchange beamline at the A0 photoinjector
J. C. T. Thangaraj
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III. Experimental results of emittance exchange with chirped beam
Next-generation emittance exchangers
beam*
emittance. Typically asymmetric emittances.
Emittance exchange can swap transverse with the Emittance exchange can swap transverse with the
longitudinal emittance.
longitudinal modulations : Beam shaping application
• Can also be used to suppress microbunching
instability** 3 *P. Emma et al. , Nature Photonics 4, 641 - 647 (2010) ; **M. Cornacchia and P. Emma, PRSTAB 5, 084001 (2002)
Emittance exchange beamline
Condition for EEX
L Lc Lc Lc
η α α
S2
Q1 Q2
Q3 SpectrometerStreak
Energy 14.3 MeV
Rep. rate 1 Hz
• Beam size: OTR and YAG screens
• Bunch length: Streak or Interferometer
• Energy spread: Spectrometer magnet and a screen
• Transverse emittance: Multi-slit method
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7
X3
X21
RF gun
Q1 Q2
Q3 SpectrometerStreak
camera1
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1 RF – scan to locate minimum energy spread i.e. no chirp
2 Streak camera to measure bunch length (Longitudinal emittance)
3 X-Slits and Y-slits to measure the transverse emittances (X3)
4 Tune quadrupoles to maximize CTR radiation thus minimizing the
bunchlength. Tune quadrupoles to minimize energy spread at XS4.
Finer scan along the minimum values.
5 X-slits and Y-slits to measure outgoing transverse emittance (X23)
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by Timothy W. Koeth
XS4D2 D3
through a bending magnet.
radiation wavelength.
Number of electrons in the bunch
( ) 1 for
e e
P
p
N
f
e e B
r
L
The A0 beamline
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Bunch length measurement: Experimental Setup
XS4D2 D3
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D1
D1
Skew
quad
screen
21 * Using a Skew Quad in a Chicane to Temporally Resolve the Transverse Effects of CSR – P. Emma ( uBI 2010)
Twin pulse at the cathode
10.2 ps
2.6ps 3.1ps
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Y
X
Skew QUAD OFF Skew QUAD ON
O N
C S R
Skew QUAD OFF Skew QUAD ON
Charge 300pC
Emittance-exchanger
Emittance-exchanger
Z
δ
How to minimize thick lens effect?*
:
' :
:
:
:
:
λ
δ
α
Minimize this term: [ 2 ]z D D zα δ α δ< > + < > + < >
2 2 2 2 2 2then : 2
1 willmake this termzero.
h D
α α
In other words, set Chirp to -1/R56
* P. Emma, Z. Huang, K. - J. Kim, P. Piot, “Transverse-to-longitudinal emittance exchange to improve performance of
high-gain free-electron lasers”, Phys. Rev. ST Accel. Beams 9, 100702 (2006), 28
Minimize thick lens effect: Add energy chirp
Look for bunch length, transverse beam
size, emittances (x and z)
Chirp RF-phase
0 -30
2.0 -35
4.5 -40
7.7 -45
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0
= = +
Chirped beam study: Streak camera b u n c h l e n g th
a ft
e r
E E
b u n c h l e n g th
a ft
e r
E E
• Pyro signal increases ~ by a factor of 2 31
Interferometer measurement
CSR Power (pyrometer) Vs RF Phase (bunchlength)
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Energy 13.2 MeV
Charge 400 pC
34250 pC; PRL 106, 244801 (2011) * IPAC 2012
Emittance exchange simulation with GPT
Energy 13.2 MeV
Charge 400 pC
Next generation EEX: upgraded Classic EEX*
• Use two (or one) more deflecting cavity to compensate thick lens effect
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39 A. Zholents & Zolotorev
• Chicane style EEX : Cornacchia and Emma (2002)
• Double dogleg EEX: Kim and Sessler (2005)
• A0 emittance exchange beamline commissioned
• Beam shaping results : Yin-e et. al (2010)
• Emittance exchange result: Jinhao et. al (2010)
• EEX for tailoring current distributions: Piot (2011)
• EEX for HHG: B. Jiang (2011)
• Double EEX proposal : Zholents & Zolotorev (2011)
• Use of EEX as a bunch compressor : Carlsten (2011)
• Chicane style EEX: Xiang and Chao (2012)
• Terra incognita ……………………..
emittance exchange beamline.
improved performance. Emittance dilution still exists.
• Next generation EEX has to take into account the thick
lens cavity with modification to exchange lattice.
• A chicane-style emittance exchange looks promising and
is planned to be tested at the Advanced Superconducting
Test Accelerator (ASTA) facility @ 40 MeV
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