PROBLEM:Determination of optimal compression of BC1 and BC2and longitudinal feedback system .
PROPOSED SOLUTION: Power monitor of CSR emitted from compressors
•Pyroelectric detector measures the CSR power in THz region.
•The emitted power increases as the bunch gets shorter.
•RF accelerating phases before compressor are changed to find the optimal compression.
•Applications to longitudinal feedback system
References:TTF2 Linac- Y.Kim et al. FEL2005 pg 518LCLS Linac - J.Wu et al. SLAC-PUB- 11275 and11276 May, 2005
M.Veronese, M.Ferianis
Radiation sources for diagnostic purposes: signals evaluation for FERMI
+COHERENTRADIATION EMISSION
ShortBunches
•Synchrotron Radiation
•Transition radiation
•Diffraction Radiation
I N particles I N2 particles
•d2 I/dd tot = [N+N(N-1)|F|2] d2 I/dd single e–
•|F|2 = |dr (r)e-irk|2 Coherence enhancement factor:
|Fourrier Transform of longitudinal electron distribution|2
M.Veronese, M.Ferianis
Medium Bunch Long Bunch
S. Di Mitrisimualtions
after BC1
after BC2
at LINAC end
Enhancement factors:
medium bunch long bunch
M.Veronese, M.Ferianis
Comparison between step function and expected bunch
The peaks enhance high frequencies
M.Veronese, M.Ferianis
Synchrotron Radiation angular spectral distribution
References:H.Wiedemann “Particle Accelerator Physics” SV, NY 1993O.Grimm single electron synchrotron radiation emission from TTF2-BC2
Integrating over the solid angle:
M.Veronese, M.Ferianis
Incoherent Synchrotron spectrum for medium and long bunches
M.Veronese, M.Ferianis
CSR spectra for expected MEDIUM bunch @(BC1,BC2)
gau
ssia
n
gau
ssia
n
VIS
IBL
E
VIS
IBL
E
M.Veronese, M.Ferianis
gau
ssia
n
gau
ssia
n
CSR distributions for expected LONG bunch @(BC1,BC2)
VIS
IBL
E
VIS
IBL
E
M.Veronese, M.Ferianis
Vacuum Chamber low frequency cut-off
Warnock PAC1991 pg1824: 2 Parallel perfectly conducting planes
cutoff =2*h3/2/R1/2
shielding function
Dohlus and Limberg NIMPR-A v407 pg278 y1998
M.Veronese, M.Ferianis
CSR shield from 2 Perfect conduct. planes: cutoff< < bunch,
cutoff =2*h3/2/R1/2
bunch=2**z (z =rms bunch length)-gaussian approximation
location/
bunch type
R[m] h[m] cutoff/cutoff bunch/bunch RMS LB[m]
exit BC1
medium
7.38 0.01
0.02
0.03
0.74[mm]-0.41[THz]
2.08[mm]-0.14 [THz]
3.8[mm]-0.078 [THz]
2[mm]-0.144[THz] 1.1 [ps]
0.33 [mm]
exit BC1
long
7.38 0.01
0.02
0.03
0.74[mm]-0.41 [THz]
2.08[mm]-0.14 [THz]
3.8[mm]-0.078 [THz]
4.5[mm]-0.067 [THz] 2.4 [ps]
0.71 [mm]
exit BC2
medium
9.35 0.01
0.02
0.03
0.65 [mm]-0.46 [THz]
1.85[mm]-0.16 [THz]
3.4[mm]-0.088 [THz]
0.59[mm]-0.506 [THz]
0.31 [ps]
0.094 [mm]
exit BC2
long
6.17 0.01
0.02
0.03
0.80[mm]-0.37 [THz]
2.30[mm]-0.13 [THz]
4.2[mm]-0.072 [THz]
1.5[mm]-0.197 [THz] 0.8 [ps]
0.24 [mm]
M.Veronese, M.Ferianis
Proposed layout for BC1/BC2 CSR THz extraction
TTF2 design adapted to FERMI BC1: -bigger chamber height -> 30 mm-CSR detection ->no transport line-> as near as possible pyroelectric detector to avoid water absorption-angle of extraction 0.045rad
M.Veronese, M.Ferianis
Angular distribution for CSR extraction from BC1 e BC2.
For low frequencies <<c the angular distribution becomes wider.The critical angle at which the SR decrease by 1/e is qc:
Example at: BC1: R=7.38m and cuoff=0.07 THz then c =65 mrad BC2: R=6.17m and cuoff=0.07 THz then c =69 mrad
Considering extraction of Thz radiation after 1m one gets:chamber width = at least 65-69mm !!
Note that average opening angle: q =1/BC1[E=0.22GeV] =2.33mrad------- BC2[E=0.6GeV] =0.85mrad
c=(3*c/R)1/3 where R is the bending radius.
M.Veronese, M.Ferianis
Suitable window materials for Far infrared (and visible)
z-cut Quartz
Material Vacuum Environment Spectral Range
z-cut quartz: UHV 0.15 <l< 3.5mm 100mm<l<2mm
HDPE
(high density polyethylene)
HV 16mm <l< 2mm
TPX
(polymetylpentene)
HV 0.35 <l< 1.1mm
200mm <l< 2mm
M.Veronese, M.Ferianis
Other diagnostics usable radiation sources:
CTR - Coherent Transition Radiation
destructivesimplehas useful intense optical emissionmature experience in diagnostics
CDR - Coherent Diffraction Radiation
non destructive !!weak optical emissionless mature but promising
Transition Radiation = lim (h->0) of Diffraction RadiationSame detection scheme for both CTR and CDR
M.Veronese, M.Ferianis
TR and DR angular spectral distribution
References:Castellano et. al. PRST-AB 1 pg062801 (1998)Murokh et al. NIMPR-A 410 pg452 (1998)Rule et al. NIMPR-B 173 pg 67 (2001)
a slit of height “h” between infinite perfectly conducting semi-planes
•Transition radiation spectral distrib: approx. constant for >200nm
•DR less intense than TR in visible spectral region
•Coherent Enhancement factor is the same for both CTR and CDR.
R=h/(*X=xY=y
M.Veronese, M.Ferianis
Diffraction Radiation Far field X,Y angular distributions
Transition radition
R=2
R=0.5R=0.5
R=2
R=h/(*
orthogonal polarization
parallel polarizationM.Veronese, M.Ferianis
CDR-CTR Targets design
Castellano group design for TTFVariable height rectangular slit at 45°
Very flexible but complex
OTR + fixed DR slits
TR-screen
e- beam
1 mm slit
2 mm slit
Less flexibleSimple extension ofTR- screen
M.Veronese, M.Ferianis
EOS bunch arrival monitor diagnostics:
A non destructive shot-to-shot bunch arrival time in needed
It will be placed at the end of linac (E=1.2GeV)
Desired time resolution 100 fsec
Time window 10-20 ps
Our choice is EOS sampling based diagnostics
M.Veronese, M.Ferianis
Spectral distribution function:
dI/d=k*|Ey()|2 where Ey()=F(Eyt(z))= F(Ey(z))*F((z)) with Ey
t(z)=Ey(z)*(z)
Typical Electric Field frequencies for FERMIless than 1 THz Phonon frequency of EO crystal (about 5.3THz ZnTe,11THz GaP)
40
e(x2+ y2 +2 z2)
xEx=
40
e(x2+ y2 +2 z2)
zEz=
40
e(x2+ y2 +2 z2)
zEy=
Transverse electric field of electron bunch
z
y
b
fs laser
EO crystal
e- bunch
Ex=0
40
e(b2 +2 z2)
zEz=
40
e(b2 +2 z2)
bEy=
on-axis
References:A.Cavalieri et al. PRL 94, 114801 (2005)S. Casalbuoni et al. TESLA Report 2005-01J.D.Jackson “Classical Elctrodynamics” M.Veronese, M.Ferianis
Estimated EOS signal
EOcrystal
/4pol. WollastonPrism
Balanced Detector
e-beam
EO Signal=|A1|2-|A2|2=sin()
where
= (d/0)n03r41Easqrt(1+3cos2())
M.Veronese, M.Ferianis
Transverse Electric field intensity (Gaussian)
Medium Bunch Long Bunch
M.Veronese, M.Ferianis
Bunch arrival EOS Layout
We need a single shot EO scheme ->, two main options:
BBO
EO
20ps
30fs
CCD
TEMPORAL DECODING
CCD
fs-laserEO
20ps
30fsSPATIAL DECODING
fs-laser
Spatial decoding (SPPS,VUV-FEL-proposed)
Temporal decoding(FELIX,TTF2):
Needs high power laserAppealing if seed laser branchcould be used
No need of high power laserPre-compensated fiber transmissionfrom MLO
M.Veronese, M.Ferianis
Future work:CSR/CTR/CDR:
Transverse beam size,Low frequency cutoffs (vucuum chamber) simulations Impact of optics and detector on the signalComparison of available detectors (Diode, Golay cells, Pyroelectric)Feasibility of CDREvaluation of CTR EO autocorrelator for single shot measurementsEvaluation of single shot polychromator
EOS:Study effect of simulated bunch profile on EOSSimulation of THz and Laser propagation through the optics.Re-scaling of single shot scheme of SLAC to our case.
COTR: as bunching intra- undulator diagnostics has to be evaluated
Instrumentation:Choice of Laser for EO operation diags (800nm-30fsec): independent phase locked laser or MLO derived pulses.Set-up of laser test bench at Elettra including 800 nm, 30fs pulsed laser (Ti:Sa or Fiber Laser), FROG, GaAs THz wide area source,etc.
M.Veronese, M.Ferianis