Exchange of Transverse and
Longitudinal
Emittance
at the
A0
Photoinjector
Tim
Koeth
(this talk was initially prepared for TK’s
committee meeting of March 11, 2008)
Updated March 14
th
, 2008
Outline
•
Brief Photoinjector introduction
•
Motivation & Theory of Emittance Exchange
•
Exchange Apparatus at the A0 Photoinjector
•
Results to date…
•
Next Steps
•
Acknowledgements
The A0 Photoinjector
•
Laser energy 16
m
J/pulse @ 263nm
•
<5nC/bunch (have had >12 nC in the past)
•
Typically 10 bunches/RF pulse. 1 Hz rep rate
•
4 MeV gun output energy
•
16 MeV total energy
•
D
p/p ≈ 0.3%@ 16MeV (1nC)
•
Bunch length ≈ 2 mm (1nC)
•
ge
z
≈ 120 mm
-
mrad (RMS @ 1nC)
•
ge
x
,
ge
y
≈4 mm
-
mrad (RMS @ 1nC)
Next, Artur will talk about the low level
RF systems that keep the laser, two 1.3
GHz and one 3.9 GHz systems in sync.
The Idea:
Emittance
Exchange (EEX)
•
In 2002 M.
Cornacchia
and P. Emma proposed using a TM
110
deflecting
mode cavity in the center of a chicane to exchange a
smaller longitudinal
emittance
with a
larger transverse
emittance
for a FEL.
•
Kim &
Sessler
in 2005 proposed using a flat beam (
e
x
<<
e
y
) combined with a
deflecting mode cavity between 2 doglegs to produce a beam with very
small transverse
emittances
and large longitudinal
emittance
to drive an
FEL.
•
We are doing a proof of principle
emittance
exchange at A0 using the
double dogleg approach with a round beam (
e
x
=
e
y
) .
–
We’ll be exchanging a larger longitudinal
emittance
with a smaller transverse
emittance
.
–
Keep in mind that
emittance
is the area beam phase space,
•
Why ?
•
Basic and unique beam dynamics manipulation
–
proof of principle
•
FEL’s
-
low transverse
emittance
, large brightness
•
This phase space manipulation could have application in a linear
collider
2
2
2
'
'
xx
x
x
e
TM110 (Deflecting) Mode Cavity
•
No longitudinal electric field on axis.
•
Electric field imparts an energy kick
proportional to distance off axis.
–
Plan to use this to change the
momentum deviation in presence of
dispersion!
•
Electro
-
magnetic field provides
deflection as a function of arrival time.
•
This is the type of cavity used as a crab
cavity or for bunch length
measurement.
kx
(from Figure 1 of C&E)
Electric field at synchronous phase.
Magnetic field a quarter period later.
kz
x
'
aE
eV
k
0
k
is the integrated
longitudinal energy gain
at a reference offset
a
normalized to the beam
energy
E
.
a
Concept of Emittance Exchange
in
out
z
x
x
D
D
D
D
A
A
A
A
z
x
x
'
0
0
0
0
0
0
0
0
'
22
21
12
11
22
21
12
11
in
out
z
x
x
C
C
C
C
B
B
B
B
z
x
x
'
0
0
0
0
0
0
0
0
'
22
21
12
11
22
21
12
11
A typical non
-
dispersive transport matrix:
What we want to develop is a matrix like:
EEX: Linear Optics Model
final e
-
bunch
Initial e
-
bunch
D1
e
x
>
e
z
D2
D3
D4
3.9 GHz TM
110
First, break the EEX
-
line into three sections:
Magnetic dogleg before cavity: M
bc
TM
110
cavity (thin lens): M
cav
Magnetic dogleg after cavity: M
ac
1
0
0
0
1
0
0
0
1
0
0
1
D
D
D
L
M
M
ac
bc
1
0
0
0
1
0
0
0
1
0
0
0
0
1
k
k
M
cav
1
0
0
0
1
0
0
0
1
0
0
1
1
0
0
0
1
0
0
0
1
0
0
0
0
1
1
0
0
0
1
0
0
0
1
0
0
1
D
D
D
L
k
k
D
D
D
L
M
M
M
R
bc
cav
ac
and
To get:
EEX: Linear Optics Model
Dk
kL
k
Dk
ad
k
D
D
Dk
aDkL
Dk
D
D
Dk
Dk
k
Dk
DkL
Dk
D
D
kL
L
Dk
Dk
L
Dk
R
1
0
)
1
(
1
)
1
(
1
0
)
1
(
)
1
(
1
2
However, if we take the special case of k =
-
1/D = k
o
we get:
0
0
1
0
0
1
0
0
0
0
D
L
D
aL
D
D
L
D
D
L
R
All of the X
-
X and Z
-
Z coupling elements are zero !
Now if we take the trivial case of k =0 we get:
1
0
0
0
2
1
2
0
0
0
1
0
2
0
2
1
D
D
D
L
R
EEX: Linear Optics Model
With our k=k
o
D
C
B
A
D
L
D
aL
D
D
L
D
D
L
R
0
0
1
0
0
1
0
0
0
0
z
z
z
z
z
z
z
z
x
x
x
x
x
x
x
x
z
x
o
g
e
e
e
e
g
e
e
e
e
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
We can transports the initial uncoupled beam (sigma) matrix through the EEX line
via
T
o
R
R
a complete swap of the emittances is seen.
z
x
e
e
2
det
x
x
e
And remember
:
Then take the determinate of
σ
x
,
σ
z
and we get:
2
det
z
x
e
2
det
x
z
e
T
z
T
x
T
z
T
x
T
z
T
x
T
z
T
x
D
D
C
C
B
D
A
C
D
B
C
A
B
B
A
A
o
o
o
o
o
o
o
o
We know from above that A = D = 0, so this reduced to:
T
x
T
z
C
C
B
B
o
o
0
0
EEX Beam Line at the
Photoinjector
= Beam Position Monitor (BPM)
-
Transverse beam position
= Diagnostic cross: viewing screen(s) & digital camera
-
Measuring transverse beam size
= Slit/Screen pair for transverse emittances.
Not shown: Streak camera & Interferometer
–
e
-
bunch length, Phase Mon
–
e
-
TOF
= MagneticSpectrometer
–
P & ∆P
Diagnostics:
Vertical bend
avoids residual
dispersion of X
-
plane
EEX Beam Line at the Photoinjector
Beam
direction
Dipoles
Vertical
Spectrometer
TM
110
Cavity
Beamline Layout
Deflecting Mode Cavity
0
5
10
15
20
25
5
6
7
8
9
10
11
12
s(m)
beta (m)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
eta (m)
betax
betay
etax
etay
EEX Beam Line at the
Photoinjector
(
Cav
off)
TM110 Cavity Details
Construction:
5 cells (of CKM design)
Punched OFHC Copper
Vacuum brazed
Radio Frequency:
3.9 GHz (3x 1.3GHz)
Q
300K
=14,900
Q
80K
=35,600
Coupling (
β
) = 0.7
Req’d RF power @ full gradient: 50kW
Cavity
Polarizaton
and Field Flatness
Red: theory
Black: fit cell 2
Blue: fit cell 3
Green: fit cell 4
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
230
235
240
245
250
255
260
265
270
275
280
285
290
295
300
305
310
315
320
325
330
335
340
345
350
355
•
Longitudinal electric field vs angle in
cells 2
-
4 determined by bead pull.
•
Cavity polarization is set by input
coupler
•
Bead pull results of cavity field
flatness tuning.
Vertical
-10
-8
-6
-4
-2
0
2
4
6
0
50
100
150
200
250
300
350
400
450
TM
110
Cavity: 1
st
Deflection
The induced kick is about 70% of what was expected for the input power, however, sufficient
contingency was built into the cavity to accommodate this.
Operating phase
for exchange
BPM26
•
Preliminary investigations showed
encouraging results. For instance, as
we increased the TM
110
cavity
strength we saw a reduction in
momentum spread…
Early Vertical Spectrometer Images
Cavity: OFF
Cavity 10%
Cavity 20%
Cavity 30%
Cavity 40%
Cavity 50%
Cavity 60%
Cavity 70%
Cavity 80%
Cavity 100%
Spectrometer Screen
~ 550keV
Measuring the EEX Line Matrix
There is exciting evidence that the cavity was indeed modifying the momentum
spread, so we have begun to systematically measure the EEX beam line matrix.
in
out
z
y
y
x
x
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
z
y
y
x
x
'
'
'
'
66
65
64
63
62
61
56
55
54
53
52
51
46
45
44
43
42
41
36
35
34
33
32
31
26
25
24
23
22
21
16
15
14
13
12
11
Again, describing the beam line with linear optics we have:
Adjusting one input parameter at a time and measuring all output parameters we can
map out the transport matrix. For example, introducing a momentum offset yields
the 6
th
column:
Do this with the TM110 cavity off, partially on, 100% on, and greater
in
out
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
z
y
y
x
x
D
D
D
D
D
D
D
0
0
0
0
0
'
'
66
65
64
63
62
61
56
55
54
53
52
51
46
45
44
43
42
41
36
35
34
33
32
31
26
25
24
23
22
21
16
15
14
13
12
11
EEX Beamline: Vertical Spectrometer BPM
For a given TM
110
strength, k, changed beam central momentum by
±
2.15 % in
0.70% increments by varying 9
-
Cell cavity gradient. Repeated for several TM
110
k:
TM
110
cavity
strength, k
o
Intro
p from 9
-
Cell
Vary k
record vertical BPM reading
in
out
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
z
y
y
x
x
D
D
D
D
D
D
D
0
0
0
0
0
'
'
66
65
64
63
62
61
56
55
54
53
52
51
46
45
44
43
42
41
36
35
34
33
32
31
26
25
24
23
22
21
16
15
14
13
12
11
Intro
p from 9
-
Cell
OFF
73%
90%
100%
105%
EEX: Beam Line Horizontal Dispersion
measurement with TM
11O
cavity off
Lines: ideal
Dots : Horizontal
BPM measured
difference data
δ
P =
±
1.05 %
in 0.35 % increments
D1
D2
D3
D4
TM
110
SPECT.
+1.05%
+0.70%
+0.35%
0
-
0.35%
-
0.70%
-
1.05%
EEX: Beam Line
with
TM
110
Cavity
On,
Ideal:
+1.05%
+0.70%
+0.35%
0
-
0.35%
-
0.70%
-
1.05%
Lines: ideal
δ
P =
±
1.05 %
in 0.35 %
increments
D1
D2
D3
D4
TM
110
SPECT.
OFF
20%
40%
60%
80%
100%
120%
EEX: Beam Line with TM
110
Cavity on
Measured:
+1.05%
+0.70%
+0.35%
0
-
0.35%
-
0.70%
-
1.05%
D1
D2
D3
D4
TM
110
SPECT.
Cavity
strength, k
o
OFF
44%
67%
85%
100%
in
out
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
z
y
y
x
x
D
D
D
D
D
D
D
0
0
0
0
0
'
'
66
65
64
63
62
61
56
55
54
53
52
51
46
45
44
43
42
41
36
35
34
33
32
31
26
25
24
23
22
21
16
15
14
13
12
11
Streak Camera TOF measurements
Introduce
p from 9
-
Cell
Streak camera ~
1pSec resolution
y = 8.0444x
-
115.04
R² = 1
y = 18.214x
-
260.38
R² = 0.9968
-1.00E+00
0.00E+00
1.00E+00
2.00E+00
3.00E+00
4.00E+00
5.00E+00
6.00E+00
14.25
14.3
14.35
14.4
14.45
14.5
14.55
14.6
delta
-
z [mm]
Beam energy [MeV]
TM110 k=75%ko
TM110 off
Similar for 2nd Column: vary ∆x
in
’
in
out
x
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
z
y
y
x
x
D
D
D
D
D
D
D
0
0
0
0
'
0
'
'
66
65
64
63
62
61
56
55
54
53
52
51
46
45
44
43
42
41
36
35
34
33
32
31
26
25
24
23
22
21
16
15
14
13
12
11
Impart
D
x
’ by adjusting a
horizontal corrector
magnet
… And
D
x,
D
y,
D
y’… The
D
z can be achieved by adjusting the TM
110
cavity phase
k=62%k
o
D
x’in data from today
Today’s BPM8/30 Dispersion Measurements
BPM8 & 30 Special 4
-
inch housing
Ray’s cald XS4 Vert Disp : 865mm
Tim’s measuremnt 855+/
-
5mm
Ray’s calc of XS3 Horz Disp: 225mm
Tim’s measurement 226mm
Finally nice agreement !
Note non
-
lin > 8 mm
Summary of Today & yesterday
data collection (March 13 thru 14)
TM110 5
-
Cell off
25%
ko
50%
ko
75%
ko
~90%
ko
∆x
X
X
X
X
X
∆x’
X
X
X
X
X
∆y
X
X
X
X
X
∆y’
X
X
X
X
X
∆z(
ф
)
-
X
X
X
X
δ
X
X
X
X
X
δ
energy incriments calibration against BPM8
Now, off to analyze…
in
out
z
y
y
x
x
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
z
y
y
x
x
'
'
'
'
66
65
64
63
62
61
56
55
54
53
52
51
46
45
44
43
42
41
36
35
34
33
32
31
26
25
24
23
22
21
16
15
14
13
12
11
EEX: Next Steps
•
Continue to populate the matrix
•
Measure input and output emittances
•
Graduate !
Many thanks go to:
•
Helen Edwards
-
Advisor
•
Don Edwards
-
Voice of reason
•
Leo Bellantoni
–
[tor]Mentor & CKM
•
Ray Fliller
–
A0 Post Doc
•
Jinhao Ruan
–
Laser, All things optical
•
Jamie Santucci
–
fireman
•
Alex Lumpkin
–
streak camera
•
Uros Mavric
–
Ph.D. Student
•
Artur Paytan
–
Yerevan U. Ph.D. Student
•
Mike Davidsaver
–
UIUC staff, controls guru
•
Grigory Kazakevich
–
Guest Scientist, OTRI
•
Manfred Wendt & Co
–
Instrumentation, BPMs
•
Elvin Harms
–
kindly sharing a klystron
•
Randy Thurman
-
Keup
–
Instrumentation, Interferometer
•
Vic Scarpine
–
Instrumentation, OTR and cameras
•
Ron Rechenmacher
–
CD, controls
•
Lucciano Piccoli
–
CD, controls
•
Brian Chase, Julien Branlard, & Co
–
Low Level RF
•
Gustavo Cancelo
–
CD, Low Level RF
•
Wade Muranyi & Co
–
Mechanical Support
•
Bruce Popper
–
drafter & artist
•
Chris Olsen
-
assistant
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