Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation...
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![Page 1: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/1.jpg)
Particle Physics SeminarTuesday 19 February 2008
Accelerator Physics Challenges Accelerator Physics Challenges in 3in 3rdrd Generation Synchrotron Light Sources Generation Synchrotron Light Sources
R. Bartolini
John Adams Institute and Diamond Light Source Ltd
![Page 2: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/2.jpg)
Particle Physics SeminarTuesday 19 February 2008
SummarySummary
Introduction:
synchrotron radiation
storage ring synchrotron radiation sources
Accelerator Physics challenges:
brightness, flux, stability, time structure
Conclusion:
future trends
3rd generation vs 4th generation
![Page 3: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/3.jpg)
Particle Physics SeminarTuesday 19 February 2008
What is synchrotron radiationWhat is synchrotron radiation
Electromagnetic radiation is emitted by charged particles when accelerated
The electromagnetic radiation emitted when the charged particles accelerated
radially (v a) is called synchrotron radiation
. It is produced in the synchrotron radiation sources using bending magnets undulators and wigglers
![Page 4: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/4.jpg)
Particle Physics SeminarTuesday 19 February 2008
storage ring synchrotron radiation sources (I)storage ring synchrotron radiation sources (I)
![Page 5: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/5.jpg)
Particle Physics SeminarTuesday 19 February 2008
storage ring synchrotron radiation sources (II)storage ring synchrotron radiation sources (II)
Courtesy Z. Zhao
![Page 6: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/6.jpg)
Particle Physics SeminarTuesday 19 February 2008
storage ring synchrotron radiation sources (III)storage ring synchrotron radiation sources (III)
Courtesy Z. Zhao
![Page 7: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/7.jpg)
Particle Physics SeminarTuesday 19 February 2008
synchrotron radiation sources propertiessynchrotron radiation sources properties
Broad Spectrum which covers from microwaves to hard X-rays: the user can select the wavelength required for experiment
High Flux and High Brightness: highly collimated photon beam generated by a small divergence and small size source (partial coherence)
High Stability: submicron source stability
Polarisation: both linear and circular (with IDs)
Pulsed Time Structure: pulsed length down to tens of picoseconds allows the resolution of processes on the same time scale
Flux = Photons / ( s BW)
Brightness = Photons / ( s mm2 mrad2 BW )
synchrotron light
![Page 8: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/8.jpg)
Particle Physics SeminarTuesday 19 February 2008
BrightnessBrightness
1.E+02
1.E+04
1.E+06
1.E+08
1.E+10
1.E+12
1.E+14
1.E+16
1.E+18
1.E+20
Bri
gh
tnes
s (P
ho
ton
s/se
c/m
m2 /m
rad
2 /0.1
%)
Candle
X-ray tube
60W bulb
X-rays from Diamond will be 1012 times
brighter than from an X-ray tube,
105 times brighter than the SRS !
diamond
![Page 9: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/9.jpg)
Particle Physics SeminarTuesday 19 February 2008
Life science examples: DNA and myoglobin Life science examples: DNA and myoglobin
Photograph 51 Franklin-Gosling
DNA (form B)
1952
Franklin and Gosling used a X-ray tube:
Brightness was 108 (ph/sec/mm2/mrad2/0.1BW)
Exposure times of 1 day were typical (105 sec)
e.g. Diamond provides a brightness of 1020
100 ns exposure would be sufficient
Nowadays pump probe experiment in life science are performed using 100 ps pulses from storage ring light
sources: e.g. ESRF myoglobin in action
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Particle Physics SeminarTuesday 19 February 2008
Brightness with IDs Brightness with IDs
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Particle Physics SeminarTuesday 19 February 2008
Time structureTime structure
rms bunch length (ps)
0
5
10
15
20
25
30
35
40
45
ESRFAPS
SPRING8
ALSTL
S
ELETTRA
PLSLN
LS
MAX-II
BESSY-II
NewSUBARU
SLSANKA
CLS
SPEAR3
SAGA-LS
ASP
Indus
-II
Diamon
dSoleil
Petra-II
I
SSRFALBA
SESAME
CANDLE
MAX-IV
NSLS-II
TPS
rms
(ps)
Time resolved science requires operating modes with single bunch or hybrid fills to exploit the short radiation pulses of a single isolated bunch
2/3 filling pattern
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800
bunch number
a.u.
312 ns
312 ns
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Particle Physics SeminarTuesday 19 February 2008
Accelerator Physics challengesAccelerator Physics challenges
Brightness, Flux
Stability
Time structure
Small Emittance
Insertion Devices (low gaps)
High Current; Control Impedance; Feedbacks
Control Vibrations; Orbit Feedbacks; Top-Up
Short Pulses; Short Bunches
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Particle Physics SeminarTuesday 19 February 2008
Brightness and emittanceBrightness and emittance
The electron beam emittance is a parameter of the storage ring that defines the source size and divergence
brightness 1 / emittance
NSLS-II
![Page 14: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/14.jpg)
Particle Physics SeminarTuesday 19 February 2008
Emittance in an electron storage ringEmittance in an electron storage ring
The quantum nature of the synchrotron radiation emission is responsible for the finite beam size, emittance and energy spread of the electron beam.
Transverse electron oscillations are excited by the emission of a photon and are damped on average when the electron travels through the RF cavities
Oscillation damping and excitation counterbalance and an equilibrium emittance is reached
![Page 15: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/15.jpg)
Particle Physics SeminarTuesday 19 February 2008
Small emittance latticesSmall emittance lattices
The horizontal emittance is determined by the dispersion generated by the main bending magnets.
dipolex
x HJ
2
2222 ''2 xxxxxxxx DDDDH
Low emittance and adequate space in straight section to accommodate long
Insertion Devices are obtained in the so called
DBA and TBA lattices
Theoretical Minimum Emittance
33
2
min,
10
bb
xx NJ
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Particle Physics SeminarTuesday 19 February 2008
Commissioning of small emittance optics (I)Commissioning of small emittance optics (I)
During commissioning the Accelerator Physicists have to ensure that storage ring operates successfully in the nominal linear optics.
Linear optics studies are based on the analysis of the closed orbit response matrix (LOCO-like approach)
Using the Singular Value Decomposition (SVD) of the Response Matrix R we can invert R and correct
the closed orbit distortion
The orbit response matrix R is the change in the orbit at the BPMs as a function of
changes in the steering magnets strength
y
xRy
x
measuredmodel
H
V V
H
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Particle Physics SeminarTuesday 19 February 2008
Commissioning of small emittance optics (II)Commissioning of small emittance optics (II)
The response matrix R is defined by the linear lattice of the machine, (dipoles and quadrupoles), therefore it can be used to calibrate the linear optics of the machine
ji
BPMsBPMsijBPMsBPMs GQRRGQ,
2modelmeasuredij
2 ,...),,(,...),,(
The quadrupole gradients are used in a least square fit to minimize the distance 2
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Particle Physics SeminarTuesday 19 February 2008
Quadrupole gradient correctionQuadrupole gradient correction
LOCO varies the quadurpoles individually to fit the measured RM;
Initially the quadrupole variations generated by LOCO could reach 4%;
Quads variation reduced with better closed orbit correction, BBA and SVD threshold for LOCO;
Within each family quads variations are less than 2 % with respect to the mean for each quad family. (Up to 5 % with respect to the nominal calibration)
![Page 19: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/19.jpg)
Particle Physics SeminarTuesday 19 February 2008
Implementation of small emittance opticsImplementation of small emittance optics
Residual beta-beating can be reduced to 1% or less
The optic functions measured at the BPMs location (circles) agree very well with the measured one
(crosses)
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Particle Physics SeminarTuesday 19 February 2008
Emittance measurements with two pinhole cameraEmittance measurements with two pinhole camera
Emittance
2.78 (2.75) nm
Energy spread
1.1e-3 (1.0e-3)
Emittance coupling
0.5%
Measured emittance very close to the theoretical values confirms the optics
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Particle Physics SeminarTuesday 19 February 2008
Small emittance and nonlinear beam dynamicsSmall emittance and nonlinear beam dynamics
Small emittance Strong quadrupoles Large (natural) chromaticity
strong sextupoles (sextupoles guarantee the focussing of off-energy particles)
strong sextupoles reduce the dynamic aperture and the Touschek lifetime
additional sextupoles are required to correct nonlinear aberrations
[Consider the effect of realistic errors (and define magnetic error tolerances)]
Courtesy A. Streun
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Particle Physics SeminarTuesday 19 February 2008
Chromatic (energy dependent) effectChromatic (energy dependent) effect
Optics functions vary with relative energy offset
The betatron tunes crosses a wide range of resonances with
relative energy offset
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Particle Physics SeminarTuesday 19 February 2008
Nonlinear beam dynamics optimisation (I)Nonlinear beam dynamics optimisation (I)
It is a complex process where the Accelerator Physicist is guided by
• (semi-)analytical formulae for the computation of nonlinear maps, detuning with amplitude and off-momentum, resonance driving terms
• numerical tracking: direct calculation of non linear tuneshifts with amplitude and off-momentum, 6D dynamics aperture and the frequency analysis of the betatron oscillations
Many iterations are required to achieve a good solution that guarantees a good dynamic aperture for injection and a good Touschek lifetime
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Particle Physics SeminarTuesday 19 February 2008
Nonlinear beam dynamics optimisation (II)Nonlinear beam dynamics optimisation (II)
Frequency Map Analysis
allows the identification of dangerous non linear resonances during design and
operation
ALS measured ALS model
The Dynamic Aperture problem
Strongly excited resonances can destroy the Dynamic Aperture
Vacuum chamber
![Page 25: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/25.jpg)
Particle Physics SeminarTuesday 19 February 2008
Touschek lifetimeTouschek lifetime
ringC
accxyxrings
be
Touschek
dsssss
C
C
cNr
023
2
)()()()(
1
8
1
Synchrotron radiation light sources require a large off-momentum aperture
The full 6D dynamic aperture has to be optimised
Electrons performing betatron oscillations may scatter and be lost outside the momentum aperture available from RF voltage and the 6D dynamic aperture
![Page 26: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/26.jpg)
Particle Physics SeminarTuesday 19 February 2008
How to achieve and even smaller emittanceHow to achieve and even smaller emittance
Reduce the emission of radiation in bending magnets with either lower energy or weaker magnetic field → larger circumference (NSLS-II, Petra-III, PEP, Tristan). The radiated energy is proportional to E2B2
Damping wiggler in the storage ring (NSLS-II, PETRA-III): beam dynamics still manageable; sub-nm emittance looks feasible !
Tailor the magnetic field in the dipole – azimuthal dependence - in order to reduce the integral of the dispersion invariant in the dipole (studies ongoing at ESRF, SLS, Soleil): Dynamic Aperture correction quite complicated;
![Page 27: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/27.jpg)
Particle Physics SeminarTuesday 19 February 2008
Closed Orbit correction and orbit stabilityClosed Orbit correction and orbit stability
The beam orbit is corrected to the BPMs zeros by means of a set of dipole corrector magnets: the BPMs can achieve submicron precision and the orbit rms is corrected to below 1 m:
![Page 28: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/28.jpg)
Particle Physics SeminarTuesday 19 February 2008
Closed orbit disturbancesClosed orbit disturbances
• ground settling
• tidal motion
• day/night (thermal variations)
• re-injection
• thermal drifts of the electronics
• insertion device gap movements
• ground vibrations
• air conditioning units
• refrigerators, compressor (cooling systems)
• power supplies
• cooling water flow
• high current instabilities
Courtesy C. Bocchetta
![Page 29: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/29.jpg)
Particle Physics SeminarTuesday 19 February 2008
Stability requirements in 3Stability requirements in 3rdrd generation light generation light sourcessources
mmx 3.121231.0 radradx 4.2241.0'
mmy 6.04.61.0
xx 1.0 '1.0' xx yy 1.0 '1.0' yy
Beam stability should be better than 10% of the beam size and divergence
For Diamond nominal optics (at the centre of the short straight sections)
radrady 4.041.0'
but IR beamlines will have tighter requirements
Courtesy L. Farvacque
![Page 30: Particle Physics Seminar Tuesday 19 February 2008 Accelerator Physics Challenges in 3 rd Generation Synchrotron Light Sources R. Bartolini John Adams Institute.](https://reader037.fdocuments.in/reader037/viewer/2022110321/56649cdb5503460f949a5ace/html5/thumbnails/30.jpg)
Particle Physics SeminarTuesday 19 February 2008
Beam vibrations induced by Beam vibrations induced by ground and girder vibrationsground and girder vibrations
Integrated H Ground PSD 0.018 um Integrated H Beam PSD 2.41 um
Integrated H Girder 1 PSD 0.090 um Integrated H Girder 2 PSD 0.088 um Integrated H Girder 3 PSD 0.072 um
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Particle Physics SeminarTuesday 19 February 2008
At ID source point
Horizontal Vertical
Long StraightStandard Straight
Long StraightStandard Straight
Position (μm)
Target 17.8 12.3 1.26 0.64
No FOFB 4.24 (2.4%) 3.08 (2.5%) 0.70 (5.5%) 0.36 (5.6%)
Angle (μrad)
Target 1.65 2.42 0.22 0.42
No FOFB 0.49 (2.9%) 0.61 (2.5%) 0.14 (6.2%) 0.24 (5.8%)
Beam stability at the source points (1-100Hz bandwidth) Beam stability at the source points (1-100Hz bandwidth)
We are within 10% of the beam size and divergence without FOFB
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Particle Physics SeminarTuesday 19 February 2008
Performance of Diamond FOFBPerformance of Diamond FOFB
Significant improvement up to 100 Hz; higher frequencies performance limited mainly by the correctors power supply bandwidth
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Particle Physics SeminarTuesday 19 February 2008
At ID source point
Horizontal Vertical
Long StraightStandard Straight
Long StraightStandard Straight
Position (μm)
Target 17.8 12.3 1.26 0.64
No FOFB 4.24 (2.4%) 3.08 (2.5%) 0.70 (5.5%) 0.36 (5.6%)
FOFB On
0.89 (0.5%) 0.63 (0.5%) 0.19 (1.5%) 0.11 (1.7%)
Angle (μrad)
Target 1.65 2.42 0.22 0.42
No FOFB 0.49 (2.9%) 0.61 (2.5%) 0.14 (6.2%) 0.24 (5.8%)
FOFB On
0.10 (0.6%) 0.13 (0.5%) 0.04 (1.7%) 0.07 (1.7%)
Beam stability at the source points (1-100Hz bandwidth) Beam stability at the source points (1-100Hz bandwidth)
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Particle Physics SeminarTuesday 19 February 2008
Long term drifts (30 minutes) SOFB OFFLong term drifts (30 minutes) SOFB OFF
3 m maximum drift over 30 minutes
H rms < 0.7 m
V rms < 0.4 m
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Particle Physics SeminarTuesday 19 February 2008
Long term drifts (30 minutes) SOFB ONLong term drifts (30 minutes) SOFB ON
SOFB running at 0.2 Hz
H rms < 0.5 m
V rms < 0.3 m
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Particle Physics SeminarTuesday 19 February 2008
Improving stability: Top-Up operation (I)Improving stability: Top-Up operation (I)
Top-Up operation consists in the continuous (very frequent) injection to keep the stored current constant
Top-Up improves stability
• constant photon flux
• constant thermal load on components
provides more flexibility
• Lifetime less important
• Smaller ID gaps
• Lower coupling
Already in operation at APS and SLS
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Particle Physics SeminarTuesday 19 February 2008
• Total current stable at 128.4mA to 0.1%
• Hybrid bunch stable at 0.43mA to 3.2%
Pk-pk ~ 0.2mA
σ ~ 0.06mA
Improving stability: Top-Up operation (II)Improving stability: Top-Up operation (II)
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Particle Physics SeminarTuesday 19 February 2008
Beam-line safe for top-up if:
1. Electrons travelling forwards from straight section cannot pass down beam-line
2. Electrons travelling backwards from beam-line cannot pass through to straight section
3. Electrons travelling in either direction do not have same trajectory at any intermediate point
Safety case for Top-Up operationSafety case for Top-Up operation
Machine Interlocks have to be defined to prevent a top-up accident under faulty
conditions:
BTS energy ILK and stored beam ILK are adequate for Diamond
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Particle Physics SeminarTuesday 19 February 2008
AP challenges: Time structureAP challenges: Time structure
Diamond present layout:
Injector and timing allow a very flexible fill pattern control (single bunch – camshaft, etc)
but bunch length limited to 10 ps
Rep rate higher than 533 kHz
2/3 filling pattern
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800
bunch number
a.u
.
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10
I (mA)
z
/
z0 a
nd
/
0
312 ns 312 ns
The bunch length and energy spread, increase with current due to the
"microwave instability":
Current Bunch length Lifetime
0.1 mA 10 ps 92.3 h
0.5 mA 12 ps 22.7 h
0.8 mA 13 ps 15.5 h
4 mA 18 ps 4.3 h
10 mA 25 ps 2.4 h
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Particle Physics SeminarTuesday 19 February 2008
Generation of short radiation pulses Generation of short radiation pulses in a storage ringin a storage ring
Low – alpha
Higher Harmonic Cavities
RF voltage modulation
Femto – slicing
1) shorten the e- bunch 2) chirp the e-bunch + slit or optical compression
3) local energy-density modulation
e– bunch
Crab Cavities
Synchro-betatron kicks
There are three main approaches to generate short radiation pulses in storage rings
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Particle Physics SeminarTuesday 19 February 2008
dzVdf
c
RFsz /2
3
Bunch length (low current)Bunch length (low current)
= 1.710–4; V = 3.3 MV; = 9.6 10–4 z = 2.8 mm (9.4 ps)
z depends on the magnetic lattice (quadrupole magnets) via
(low_alpha_optics) 10–6
6101 ds
D
Lx
z 0.3 mm (1 ps)
We can modify the electron optics to reduce
The equilibrium bunch length is due to the quantum nature of the emission of synchrotron radiation and is the result of the competition between quantum excitation
and radiation damping. If high current effects are negligible the bunch length is
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Particle Physics SeminarTuesday 19 February 2008
Low alpha opticsLow alpha optics
When the bunch is too short Coherent Synchrotron Radiation generates further instabilities
Microbunch instability (Stupakov-Heifets)
for Diamond the Microbunching threshold is about 10 A per bunch at 1 ps rms length
Single bunch: 10 A; 1 ps; rep. rate 530 kHz
Full fill: 10 A * 936 bunches; 1 ps; rep. rate 500 MHz
Bessy-II data
Bessy-II, ALS and SPEAR3 have successfully demonstrated low-alpha operation with few ps bunches for Coherent THz radiation
Courtesy P. Kuske
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Particle Physics SeminarTuesday 19 February 2008
Crab Cavities for optical pulse shorteningCrab Cavities for optical pulse shortening
Courtesy M. Borland (APS)
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Particle Physics SeminarTuesday 19 February 2008
A possible implementation of crab cavities at A possible implementation of crab cavities at DiamondDiamond
4 in V420 rad V kick
Crab cavities are located at 1.1 m from the centre of the long
straight
Looks feasible to get sub-ps x-ray pulses with very good transmission (80%)
Emittance degradation is modest
Impedance issues have still to be addressed (machine impedance,
LOM and HOM in crab cavity)
This scheme is yet unproven
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Particle Physics SeminarTuesday 19 February 2008
Femto-second slicingFemto-second slicing
A.A. Zholents and M.S. Zolotorev, Phys. Rev. Lett. 76 (1996) 912.
wiggler
spatial or angular separation in a dispersive section
(b)
electronbunch
femtosecondlaser pulse
W
fs pulse
fs pulse
“dark” pulse
electron-laser interaction in the modulator
(a)
femtosecondelectron bunch
fs radiation pulses from a radiator
(c)
BESSY-II, ALS and SLS have successfully demonstrated the generation of X-ray pulses with few 100 fs pulse length
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Particle Physics SeminarTuesday 19 February 2008
Energy modulation generated by a short laser pulseEnergy modulation generated by a short laser pulse
Natural energy spread 0.1%
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Particle Physics SeminarTuesday 19 February 2008
Separation of the radiation from the two Separation of the radiation from the two modulated bunchletsmodulated bunchlets
max 1.5 % energy modulation
Pulse stretching at radiator 35 fs
separation x = 1.8 mm (w.r.t. 200 um beam size rms)
separation x’ = 0.6 mrad (w.r.t. 0.3 mrad opening angle of radiation)
Radiation pulses of 35 fs can be generated;
modulatorradiator
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Particle Physics SeminarTuesday 19 February 2008
Comparison of options for short radiation pulsesComparison of options for short radiation pulses
Crab C.
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Particle Physics SeminarTuesday 19 February 2008
AP challenges: high current operationAP challenges: high current operation
The beam and its electromagnetic field travel inside the vacuum chamber while the The beam and its electromagnetic field travel inside the vacuum chamber while the image charge travels image charge travels onon the chamber itself. the chamber itself.
Any variation on the chamber profile, on the chamber material, breaks this Any variation on the chamber profile, on the chamber material, breaks this configuration.configuration.
The beam loses a (usually small) part of it is energy that feeds the electromagnetic The beam loses a (usually small) part of it is energy that feeds the electromagnetic fields that remain after the passage of the beam. Such fields are referred as fields that remain after the passage of the beam. Such fields are referred as wake wake
fieldsfields
Wake fields generated by beam particles, mainly affect trailing particles in previous Wake fields generated by beam particles, mainly affect trailing particles in previous bunches (long range wakes) or in the tail of the same bunch (short range wakes)bunches (long range wakes) or in the tail of the same bunch (short range wakes)
NegativeNegativeCharged BeamCharged Beam
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Particle Physics SeminarTuesday 19 February 2008
AP challenges: High currentAP challenges: High current
Collective effect are usually categorised as
Multi-bunch and Single-bunch;
Transverse and Longitudinal;
Main causes in synchrotron light sources are
Resistive Wall impedance (narrow gap chambers, SS vacuum chambers)
Ion related instabilities (Ion Trapping; Fast Ion Instability)
Poor design of vacuum chamber elements (tapers, bellows, BPMs, …)
RF cavities High Order Modes (HOMs)
Main cures are
Operation with high positive chromaticity
Bunch lengthening (low voltage RF voltage, Harmonic cavities)
Feedback systems (TMBF, LMBF)
better design of vacuum chamber elements (SCRF, HOM damping, …)
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Particle Physics SeminarTuesday 19 February 2008
Multi-bunch modesMulti-bunch modes
V instability visible at 17 mA for zero chromaticity
Onset of sidebands not too far from predicted RW threshold (40 mA)
Increasing chromaticity counteract the instability
Beam is stable up to 110 mA with chromaticity +2 in both planes
60 mA
2/3 fill
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Particle Physics SeminarTuesday 19 February 2008
AP challenges: High currentAP challenges: High current
Measurements at 160 mA (Chromaticity +2/+2)
Vertical betatron lines appears at about 12 MhZ
Some evidence of ion related instabilities
Fill pattern and chromaticity dependence are under investigations.
Tracking shows that chromaticity > 5 impacts injection efficiency (95% to 65%)
TMBF is required to damp these instabilities
160 mA
2/3 fill
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Particle Physics SeminarTuesday 19 February 2008
Current thresholdsCurrent thresholds
Ion related instabilities are clearly visible in the initial stage of commissioning. They become less important with vacuum improvement due to synchrotron radiation
cleaning of the vacuum chamber, but a TMBF is required.
Diamond Soleil
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Particle Physics SeminarTuesday 19 February 2008
Transverse Multibunch Feedback at DiamondTransverse Multibunch Feedback at Diamond
The TMBF system detects coherent betatron oscillation bunch-by-bunch and damps them with a pair of stripline kickers
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Particle Physics SeminarTuesday 19 February 2008
Single Bunch Longitudinal collective effects: Single Bunch Longitudinal collective effects: the microwave instabilitythe microwave instability
Bunch length at zero current 17 ps
(with 1.9 MV; = 1.410–4)
Z||/n ~ 0.4
nZe
EEI ECpeak
//
2002
When the current per bunch is larger than the instability threshold:
the single particles get excited by the wakes on exponentially growing
longitudinal oscillations. Because of non-linearities, the oscillation frequency changes with amplitude limiting the
maximum amplitude and in most of the cases no particle loss happens.
The net effect on the bunch is an increase of the energy spread above
threshold with a consequent increase of the bunch length
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Particle Physics SeminarTuesday 19 February 2008
Transverse mode coupling instabilityTransverse mode coupling instability
The transverse impedance of the machine can generate an instability of internal
modes of oscillation of a bunch (head-tail instability real part of the impedance)
or shift the frequency of the modes until they coalesce
(transverse mode coupling instability imaginary part of the impedance)
It can be cured with increasing chromaticity and the voltage
It cannot be cured simply by the TMBF system
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 0.5 1 1.5 2
current (mA)
Re
( -
ws)/w
s
Vertical beam blow-up at diamond
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Particle Physics SeminarTuesday 19 February 2008
Conclusions (I)Conclusions (I)
Third generation light sources provide a very reliable source of high brightness, very stable X-rays
Medium energy machines (~ 3 GeV) performances are now covering the needs of a wide user’s community and the number of beamlines per facility is increasing;
Future developments will target
even lower emittance < 1 nm
higher stability tens of nm over few hundreds Hz
short pulses < 1 ps
higher current > 500 mA
more undulator per straights (canted undulators)
Technological progress is expected to further improve brightness and stability (IDs, BPMs, …)
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Particle Physics SeminarTuesday 19 February 2008
Conclusions (II)Conclusions (II)
It is generally believed that 3rd generation light sources will not be replaced by SASE-FEL (4th generation light sources) but rather they can coexist.
3rd generation will remain unrivalled in terms of stability and cost effectiveness, and will still be competitive in terms of average brightness, tunability, reliability.
4-th generation light sources will be superior in their peak brightness and time structure, providing fs and sub-fs radiation pulses.
Although it is a mature technology and one cannot expect many order of magnitude improvements in the coming years, upgrades and new ideas are continuously proposed and new light sources are under commissioning (SSRF) or under constructions (ALBA) or planned (NSLS-II, …)
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Particle Physics SeminarTuesday 19 February 2008
Conclusions (III)Conclusions (III)
3rd generation light source are still fashionable…