the Transversely Deflecting RF-. Structure LOLA at FLASH (DESY). Michael Roehrs ,Holger Schlarb, Christopher. Gerth, Andy Bolzmann, Markus Huening,.
Time-resolved Measurements using the Transversely Deflecting RFStructure LOLA at FLASH (DESY) Michael Roehrs ,Holger Schlarb, Christopher Gerth, Andy Bolzmann, Markus Huening, Bolko Beutner
Outline • Principle of measurements with LOLA • LOLA and its integration into the FLASH-Linac • Recent / possible measurements : – Longitudinal density profile – Slice emittance – Energy-time correlation
– Horizontal slice centroid shifts – 3-dimensional spatial particle distribution
Introduction e
−
σz
LOLA ~ σz .3.66 4 m
Vy(t)
Courtesy: H. Schlarb, M. Nagl, M. Ross et al.
• • Maximum streak at 500 MeV: ~6mm/ps • Streak depends on optics downstream of LOLA:
Some facts about LOLA •
•
• •
Originally used as a rf separator for secondary particles (1968) Named after its designers G. LOew, R. Larsen, O. Altenmueller Already used for beam diagnostics at SLAC Installation at DESY in 2003, in operation since 2005 Courtesy: M. Nagl
LOLA installation at FLASH Some important issues: • • • • • •
The installation team:
Klystron Modulator Water Cooling Synchronization Kicker Diagnostic screen
Courtesy: M. Nagl
Parameters of LOLA IV Type of structure Mode type Phase shift / cell Cell length Design wavelength Nominal operating frequency Nominal operating temperature Quality factor Relative group velocity Filling time Attenuation Transverse shunt impedance Deflecting voltage Nominal deflecting voltage Maximum operating power Length of structure Disk thickness Iris aperture Cavity inner diameter Cavity outer diameter
Constant impedance structure TM 11 (Hybrid Mode) 120° (2 Pi / 3) 35 mm 105 mm 2856 MHz 45 °C 12100 1.89 % 0.645 µs 0.477 N = 4.14 dB 16 MΩ / m Vo = 1.6 MV·L/m·(Po/MW)1/2 26 MV at 20 MW 25 MW 3640 mm (about 12 feet) 5.84 mm 44.88 mm 116.34 mm 137.59 mm
Courtesy: M. Nagl
LOLA in the FLASH beamline UND6
….
UND1
Collimator
LOLA
ACC5
ACC4
BC3
ACC2 ACC3 BC2 ACC1 GUN
Beam direction
Q9/10ACC6 Q9/10ACC5
Q9ACC7
Q9/10ACC4
ACC5
ACC4
LOLA Off-axis screen Horizontal Kicker
Courtesy: H. Schlarb
Screen Calibration •
For fixed power: measurement of the vertical beam position for different phases
•
For arbitrary power:
OTR17:vertical spike position versus time−delay
OTR17:phase−sensitivity for different power−values
800 data points Fit: 1/P(1) = −10.6234 fs/pixel
data points Fit: power−offset = 0.064708 MW (Δ y / Δφ)2 [(mm/degree)2]
700
0.2
600
y [pixel]
500 400 300 200
0.15
0.1
0.05
Klys.amp = 1.03
100 0 −3
−2
−1
0 Δ t [ps]
1
2
3
0 0
0.5
1 Power [MW]
1.5
2
Measurements with LOLA: Longitudinal density profile LOLA off:
132 fs (FWHM); 1
-6
0.23 nC Qspike = 0.230 ± 0.016 nC
0.6
(1nC bunch charge)
-4 -2 Y [mm]
0.8
norm. density
-8
Δ tspike = 132.8 ± 8.3 fs (FWHM)
0 2 4 6
0.4
8 -3
-2
-1
0.2
0 −2
0
2
4 Δ t [ps]
6
8
0 X [mm]
1
2
3
1
2
3
LOLA on:
10
-8 -6 -4
→ Resolution depends on the vertical beam size at the screen
Y [mm]
-2 0 2 4 6 8 -3
-2
-1
0 X [mm]
Measurements with LOLA: Horizontal slice emittance Results: ACC5
ACC4
Normalized horizontal slice emittance (100%) 15
εx [um]
screen
LOLA Kicker
10
5
0
2
Δ t [ps]
3
4
5
2
B
1.5 1 0.5 0
0
1
2
0
1
2
Δ t [ps]
3
4
5
3
4
5
150
100
x
reference point: peak in vertical Slice width: 0.4 mm (y) , 0.24 ps (z) profile
1
Mismatch with respect to the bunch Twiss parameters
Θ [degree]
→ scan of quadrupole(s) upstream of LOLA → measurement of horizontal slice widths → both BCs on, 4.5 deg from maximum compression Subdivsion into slices:
0
50
0
head
Δ t [ps]
tail
→ emittance blow up in the head → gradually changing twiss parameters along the bunch
Measurements with LOLA: Energy – time correlation •
Measurement on screen 5ECOL in a dispersive section
Dipole
Dispersion at 5ECOL; reference current I of D1ECOL: 111.5 A 0 500
Calibration of screen, measurement of horizontal dispersion → establish on x-axis and time on y-axis of the screen
450
400
x [pixel]
•
data points Fit: D = −29386.4972 pixel = −290.9263 mm
Energy-time correlation: BC3 on, ACC23 off-crest LOLA off:
ACC23−phase: −32 deg. 7 50
6
100
150
5
200
250
Δ E/E [%]
4
300
350
3
400
450
2
100
200
300
400
500
1
→ slice energy width
0 −1 −2
3
2
1 Δ t [ps]
CSR/ longitudinal space charge forces
0
−1
−2
→ Calculation of the peak current? → Comparison with
simulations
600
Scan of ACC23-phase ACC23−phase: −26 deg. ACC23−phase: −27 deg.
7
1.1
7 6
5
5
4
4 Δ E/E [%]
Δ E/E [%]
6
3
1.05 1
3 2
2
Δ E/E [%]
1
1
0
0
−1
−1
−2
−2
rms energy width for different ACC23 phases
3
2
1 0 Δ t [ps] −29 deg. ACC23−phase:
−1
3
2
1 Δ t [ps]
0
−1
−2
0.95 0.9 0.85
−2
0.8
ACC23−phase: −30 deg.
7 7
6
5
4
0.7 -34
4
Δ E/E [%]
Δ E/E [%]
0.75
6
5
3 2
1.1
0
0
-30 -28 ACC23-phase [deg]
-26
-24
2 1
1
-32
3
rms bunch length for different ACC23 phases
−1
1
−1 −2
−2
3
2
1 Δ t [ps]
0
−1
3
2
−2
1 Δ t [ps]
0
−1
−2
0.9 ACC23−phase: −32 deg.
ACC23−phase: −31 deg.
7
0.8
7
σz [ps]
6 6
5 5
4 Δ E/E [%]
Δ E/E [%]
4 3 2
2
0.5 0.4
0
0
−1
−1 −2
0.6
3
1
1
0.7
−2 3
2
1 Δ t [ps]
0
−1
−2
3
2
1 Δ t [ps]
0
−1
−2
-34
-32
-30 -28 ACC23-phase [deg]
-26
-24
Measurements with LOLA: Tomography •
Scanning the LOLA power allows to reconstruct the 3-dimensional spatial particle distribution → reconstruction of the vertical slice emittance? → combination with phase space tomography? 100
100
100
100
200
200
200
200
300
300
300
300
400
400
400
400
500
500
500
500
600
600 100
200
300
400
600 100
200
300
400
600 100
200
300
400
100
100
100
100
200
200
200
200
300
300
300
300
400
400
400
400
500
500
500
500
600
600 100
200
300
400
600 100
200
300
400
100
200
300
400
100
200
300
400
600 100
200
300
400
Measurements with LOLA: Slice centroid shifts Over-cpmressed beam with slice centroid shifts
•
Δ t [ps]
15
10
•
5
0
0
2
4 x [mm]
BC2 off, BC3 on, overcompression
6
8
10
Energy-loss due to coherent synchrotron radiation in the dipoles of the bunch compressors lead to horizontal slice centroid shifts Comparison with simulations (Bolko Beutner)
Summary and Outlook
• • • •
LOLA is a very powerful device especially well-suited for measurements of bunch length and the spatial particle distribution, slice emittance, energy-time correlations and for studies of CSR- and space charge effects Future plans: Measurement of slice-emittance and energy-time correlation under SASE- conditions ( planned for August 2006) Comparison with simulations Study of slice-centroid shifts (Bolko Beutner) Reconstruction of the complete spatial particle distribution by tomography
