1 Preliminary Analysis of GTF Longitudinal Emittance Experiment D. Dowell SLAC July 18, 2001.
14
1 Preliminary Analysis of GTF Longitudinal Emittance Experiment D. Dowell SLAC July 18, 2001
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Transcript of 1 Preliminary Analysis of GTF Longitudinal Emittance Experiment D. Dowell SLAC July 18, 2001.
1
Preliminary Analysisof
GTF Longitudinal Emittance Experiment
D. DowellSLAC July 18, 2001
2
I. Description of Experimental Technique
II. Data Analysis
III. Experimental Results
IV. Summary and Conclusions
Talk Outline
3
BoosterGun
Spectrometer
Energy Screen
Description of the Experimental Technique
booster
Determine Longitudinal-Space at Exit of Gun
Longitudinal : Measure Energy Spectra Vs. booster
Transverse: Measure Beam Size Vs. Quad Current
Technique similar to quadrupole scan of transverse emittance
4
Longitudinal Beam Ellipse:
t t E E2 22
Longitudinal Beam Matrix:
11 12
12 22
11 Uncorrela ted Bunch Length
22 Uncorrela ted Energy Spread
Definition of Initial Phase Space Parameters, Including Correlations
Include correlated emittance by distorting the ellipse boundary using quadratic and cubic terms:
E t tt
a t b t
2 2
2 3
E E Ebooster1 0booster
(cos( t0 booster ) cos( )) ; t t1 0
Uncorrelated Bunch Length
Uncorrelated Energy Spread
Randomly populate and ray-trace down the booster:
5
27 28 29 30 310
500
1000
1500Booster Phase = -33 degrees
27 28 29 30 310
500
1000
1500Booster Phase = -28
27 28 29 30 310
200
400
600
800
1000Booster Phase = -23 degrees
27 28 29 30 310
200
400
600
800Booster Phase = -18
27 28 29 30 310
500
1000
1500Booster Phase = -13 degrees
27 28 29 30 310
500
1000
1500
2000Booster Phase = -5 degrees
27 28 29 30 310
500
1000
1500
2000Booster Phase = 0 degrees
27 28 29 30 310
500
1000
1500
2000
2500Booster Phase = 5 degrees
27 28 29 30 310
1000
2000
3000
4000Booster Phase = 10 degrees
May, 2001 Longitudinal Emittance Scan
6
20
QuadraticDistortion
12 = 0a > 0, b = 0
CubicDistortion
12 = 0a = 0, b > 0
Undistorted Phase Space12 = 0
a = 0, b = 0
E (keV)
t (ps)
Distortions of the Longitudinal Phase Space Ellipse
7
30.4 30.5 30.6 30.7 30.8 30.9 31 31.1 31.20
500
1000
1500
2000
Booster Phase = 0 degrees
2 1 0 1 20.4
0.2
0
0.2
0.4Booster Phase = 0 degrees
Time (ps)
En
erg
y (
MeV
)
Curvature Terms are Needed to Fit Ends of Energy Spectra
Head
Tail
8
30.4 30.5 30.6 30.7 30.8 30.9 31 31.1 31.20
500
1000
1500
2000Booster Phase = 0 degrees
30.56 30.58 30.6 30.62 30.640
200
400
600
800
Booster Phase = -13 degrees
4 2 0 2 40.4
0.2
0
0.2
0.4
E1ip
t0ip
4 2 0 2 40.1
0
0.1
E2ip
t0ip
2 0 2
0.2
0
0.2
Longitudinal Distribution After Gun
Time (ps)
Ene
rgy
(MeV
)
On Crest Min Energy Spread
9
27.6 27.8 28 28.2 28.4 28.60
500
1000
Booster Phase = -33 degrees
28.2 28.4 28.6 28.8 29 29.20
500
Booster Phase = -28 degrees
29.2 29.4 29.6 29.8 30 30.20
500
Booster Phase = -23
29.6 29.8 30 30.2 30.40
200
400
600
30.4 30.5 30.6 30.7 30.80
500
Booster Phase = -13 degrees
30.5 30.6 30.7 30.8 30.9 310
1000
2000
Booster Phase = -5 degrees
30.4 30.6 30.8 31 31.20
1000
2000
Booster Phase = 0
30 30.2 30.4 30.6 30.8 31 31.20
1000
2000
Booster Phase = 5 degrees
30 30.2 30.4 30.6 30.8 31 31.20
1000
2000
Booster Phase = 5 degrees
29.8 30 30.2 30.4 30.6 30.80
1000
2000
3000
Booster Phase = 10 degrees
Fits to Longitudinal Emittance Scan
Fit
Data
10
2 0 2
0.2
0
0.2
Longitudinal Distribution After Gun
Time (ps)
En
erg
y (
MeV
)
4 2 0 2 40
100
200
Pulse Length
Time (ps)
0.2 0 0.20
20
40
Energy Spectrum
Energy (MeV)
Phase Space Out of GunCorrelated Length and Energy Spectrum
2.9 ps fwhm
Tail
Head
11
2 0 2
0.2
0
0.2
Longitudinal Distribution After Gun
Time (ps)
En
erg
y (
MeV
)
Uncorrelated Energy Spread
15 keV
12
0 2 4 6 8 10 12 140
5
10
15
20
25
30
350 2 4 6 8 10 12 14
0
5
10
15
20
25
30
35
[2.6 + 2.1 (nC/cm2)] mm-keV
Unc
orre
late
d L
ongi
tudi
nal E
mitt
ance
( m
m-k
eV)
Surface Charge Density (nC/cm2)
The Uncorrelated Longitudinal Emittance Grows Linearly with Surface Charge Density Below the Space Charge Limit
-Results from 1994 Experiment for 144 MHz Gun-
Ref: D. H. Dowell, S. Joly and A. Loulergue, “The Dependence of Longitudinal Emittance Upon Surface Charge Density in a RF Photoinjector”, Proc. Of 1997 Particle Accelerator Conf., Vancouver, BC, Canada
13
0 2 4 6 8 10 12 140
2
4
6
8
10
120 2 4 6 8 10 12 14
0
2
4
6
8
10
12
0.81 keV + 0.66 (nC/cm2) keV
Unc
orre
late
d E
nerg
y Sp
read
(ke
V)
Surface Charge Density (nC/cm2)
In These Experiments Most of the Emittance GrowthResults From Increased Energy Spread
-Results from 1994 Experiment for 144 MHz Gun-
1 Spread
Ref: D. H. Dowell, S. Joly and A. Loulergue, “The Dependence of Longitudinal Emittance Upon Surface Charge Density in a RF Photoinjector”, Proc. Of 1997 Particle Accelerator Conf., Vancouver, BC, Canada
14
Summary and Conclusions
-Curvature Terms Needed to Fit Energy Spectra
-Fits Poor for Large Phases--> More careful analysis
-Large Energy Correlation for 50 deg Launch Phase(Relative to Peak Field)
-Compression Observed from 4 ps to 2.9 ps
-Model-Independent Analysis (Tomography) Needed
