Transcript Phase Adjustments (Ends vs K)

Break Length Tuning and
Phase Adjustment
I. Vasserman
LCLS UNDULATOR SYSTEM MEETING
June 29, 2004
Argonne National Laboratory
Office of Science
U.S. Department of Energy
A U.S. Department of Energy
Office of Science Laboratory
Operated by The University of Chicago
Outline
•
•
Break length correction at regular part:
Phase shims, pole gap change, trajectory
shims, Keff
Phase correction at saturation
Complex amplitude vs. distortions
•
•
One device removed
Summary
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Argonne June 29, 2004
Isaac Vasserman
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U.S. Department
of Energy
Breake length change vs. phase shim number
0.2 mm thick phase shims at one end (magnets from 7 to 2)
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Phase Shims Signature
Phase shims 0.2 mm thick applied to 12 magnets at U/S end
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Complex amplitude and phase
• Complex amplitude of radiation and phase slippage are defined
below
Complex amplitude of radiation
z
L
A   I ( z )e
z


0
0
ik / 2  2 [ z  I ix 2 ( z ' ) dz '  I iy 2 ( z ' ) dz ' ]
1y
dz
0
Phase slippage over the length of one section
k
 2
2
L
 L 2

2
L

I

z

dz

I

z

dz
 1y


 0 1 x

0
Intensity of radiation is defined by |A|2
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Break length definition
•
Lf = nu(1+K2eff /2) -> required length in free space:
• Tolerance for phase error between sections ~10
Supposed tapering required after saturation at last
30 m of undulator to compensate for particle energy
loss 0.4%:
corresponds to 2.5° of phase error for
break section with n=1, or 7.5° with n=3
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|A| vs. arg(A) for two devices in row n=3
90
8
6
4
2
ER1kd
180
0
0
270
ER kd
E
LCLS prototype. Close to 100%
performance. |A| is equal to
length of the vector at plot
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9.09
Argonne June 29, 2004
 0.9991
Isaac Vasserman
Office of Science
U.S. Department
of Energy
Energy changed by 0.4%
90
1.5
1
0.5
ER1kd
180
0
0
Worst case with biggest
energy loss and long
break is chosen
270
ER kd
Performance is close to zero, very sensitive to the
energy change.
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E
9.09
 0.08892
Isaac Vasserman
Office of Science
U.S. Department
of Energy
0.4% Energy change. Keff corrected
90
8
6
4
2
ER1kd
180
0
0
E
9.079
 0.97541
270
ER kd
Performance is 97.5%. Close to requirements with no break
length correction
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Full correction of Keff to compensate for phase
90
8
6
4
2
ER1kd
180
0
0
E
9.079
Performance is 99.2%,
close to perfect. No break
length correction
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 0.9921
270
ER kd
Argonne June 29, 2004
Isaac Vasserman
Office of Science
U.S. Department
of Energy
Discussion
• Recent 3 mrad cant requires ~8mm shift in X to obtain change
•
in Keff for compensation of 0.4% change in energy. A possible
option is to shift devices at saturation area in X to –4 mm in
advance to allow then going full way up to 4 mm to cover all
range of energy change. Additional tuning for such devices
could be necessary to provide proper performance in wide Xrange
Possibility to remove one device during commissioning was
investigated. For recent design with Keff=3.63 Ld/Lf=16.08
Such distorrtion could be corrected by changing the Keff; for
Keff=3.44 (gap 6.9 mm) Ld/Lf=16.54. It means that this option
requires a phase shifter to adjust the phase after removing the
device
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One device removed, Keff corrected
(k=3.636*0.9996)
Trajectory
90
8
6
0.1
4
2
IB2k8
ER1kd
180
0
0
0
0.1
5000
270
ER kd
E
9.09
1 10
4
1.5 10
k8
4
2 10
4
2.5 10
4
 0.99326
0.08 phase distortion compensated by 0.0004
change of K/K (0.8mm shift in X), 99.3%
performance
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3 10
4
Same as before for K=3.44
90
6
4
2
0.4 phase distortion compensated
by 0.0016 change of K/K (3.2 mm
shift in X), 81.6% performance
ER1kd
180
0
270
ER kd
0
E
9.09
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 0.81634
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Summary
Initial tuning
•
•
•
If phase between devices too big:
Phase shims must be applied to correct the
break length;
If phase between devices too small:
gap for end poles must be decreased.
This option is undesirable, and initial break length
should be defined with part of phase shims already
in place to allow tuning of the break length in both
directions without affecting the gap;
Other possibilities could be chosen as well if
necessary (Keff correction, trajectory shims)
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Summary (Cont)
• Main reason for Keff variation desirability is particle energy change
•
•
at saturation stage;
By adjusting the Keff proper performance could be easily restored.
Performance is extremely sensitive to Keff . Even in case of tuning
in advance the devices to the proper Keff , remote control of it is
absolutely necessary during commissioning, taking into account
uncertainty in beam energy loss at saturation;
Another source of concern for Keff stability is temperature
variation. Two possible solutions are: remote X-position control to
compensate for temperature change and/or temperature
stabilization of the whole tunnel. Each section must have at least 2
temperature sensors at U/S and D/S end of the device and this
temperature must be stable within ±0.2°C. Could it be achieved by
tunnel temperature control only remains doubtful.
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Summary (Cont)
•
Main conclusion from here:
no active correction of phase between
devices is necessary
Keff tuning is crucial and remote control
of X-position is necessary
option with Keff =3.44 requires phase
shifter to work with one device removed
Pioneering
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Argonne June 29, 2004
Isaac Vasserman
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U.S. Department
of Energy