JLAB-TN-01-038
10 August 2001
IR/UV FEL Upgrade Energy-Recovery Dump
Transport Design
C. Tennant
Abstract
We present a design for beam transport to the 10 MeV IR/UV FEL upgrade energy recovery dump.
Introduction
The IR/UV FEL upgrade dump line must provide loss free transport of 10 mA of beam at 10 MeV. Specifically we require that the acceptance accommodate
● 6% spread in momentum
● 6 sigmas of 60 mm-mrad
● 4 cm of working aperture for diagnostics.
The first two requirements have been padded by a factor of two from the upstream acceptance to allow for beam degradation. In addition, we provide a ~2 m drift prior to the dump for the raster.
In order to satisfy these requirements, we look for a beam line configuration that produces a beam meeting the following criteria,
● Dispersion < 0.5 m
● Beta Functions < 10 m
● Emittance < 60 mm-mrad.
Design Details
The beam line consists of a 20-degree sector dipole, which bends the energy-recovered beam towards the dump, followed by a triplet and then a ~2 m drift to the dump face. A DIMAD model of the beam line is available on JLABH [1]. A sketch of the layout is given in Figure 1 below.
Figure 1: Layout of energy recovery dump
The beam enters the dipole and is deflected towards the beam dump. At an energy of 10 MeV the dipole provides a 60 cm bend radius and in addition provides horizontal focusing.
The beam then enters the triplet. The quads are configured in a “classical” triplet in the sense that the [horizontal] defocusing quad strengths are –1/2 the strength of the single focusing quad. Also, the two drifts between the quads are the same length. These drifts will need to accommodate a viewer and BPM. Traveling through the triplet, the beam is confined and well behaved. Upon exiting the last quadrupole, the beam is strongly defocused horizontally and diverging (bx = ~9 m, ax = -4 radians) while vertically the beam is neither converging nor diverging (by = ~7 m, ay = ~0 radians).
Finally, the beam travels through a 1.85 m drift where the raster will be used to spread the beam over the dump face. A viewer will also be needed at/near the dump face.
The machine layout generated by DIMAD for the beam line is given in Appendix I.
Performance
Using DIMAD, we investigated several properties of the beam more closely. Of most importance was ensuring that the beam was well confined through the beam line - particularly through the triplet - but which was diverging as it approached the dump face. We also investigated the affects of changes in momentum on the Twiss functions b, n, and a, the positions and slopes. Phase space dynamics were investigated as well.
Figure 2 provides plots of the dispersion, rms spot size, beam size and stay clear (which is the beam size with an additional 4 cm provided for a working aperture). Throughout the transport line the beam is well confined except near the dump face where it begins to diverge. As shown on the stay clear plot, the beam exceeds the 10 cm physical aperture, but in reality the aperture expands after the triplet and will therefore accommodate the growing beam.
Figure 2: Dispersion, rms spot size, beam size and stay clear along dump beam line
Figure 3 shows the results of a momentum scan of the beam over a +6% momentum range. Everything is well behaved.
Figure 3: Momentum scan of beam
Figure 4 shows the results of a study of the geometric aberration performance. Individual phase spaces were injected with the design beam envelopes and propagated at 1% momentum intervals over the +3% momentum range. We see no serious phase space distortions due to geometric aberrations.
Figure 4: Geometric aberrations analysis
Figure 5 provides the results of the vertical and horizontal phase spaces after DIMAD has
tracked 1000 particles through the beam line to the dump face.
Figure 5: Horizontal and vertical phase space at the dump
Figure 6 shows the physical phase space of the beam at the dump. The results indicate that the beam at the dump face is approximately 2 cm by 4 cm.
Figure 6: Physical phase space at dump
In summary, we have designed a dump transport line that meets the requirements set forth at the beginning of this paper. The beam is well confined through the transport line and delivered to the dump face with a sufficiently large cross section. Operational constraints have also been met so that there is ample room for the raster in the final drift as well as other diagnostic tools along the transport line.
Acknowledgments
I would like to thank David Douglas for allowing me to work on this project, for his much needed guidance, and for his willingness to teach me to use DIMAD.
Notes and References
[1] DIMAD input file is in
~tennant/BDump/in
and output is in
~tennant/BDump/out
Appendix I: Machine Layout
DIMAD COORDINATES
THE SXYZ COORDINATES,AZIMUTH,ELEVATION AND ROLL ANGLES ARE :
# NAME S X Y Z THETA PHI PSI ALPHA
1 D1 162.4205370 .0000000 .0000000 32.5505243 .00000000 .0000000 .0000000 .0000000 R
2 B1 162.6299765 -.0361844 .0000000 32.7557364 -20.0000000 .0000000 .0000000 .0000000 R
3 D2 162.9799765 -.1558915 .0000000 33.0846288 -20.0000000 .0000000 .0000000 .0000000 R
4 Q1 163.1299765 -.2071945 .0000000 33.2255827 -20.0000000 .0000000 .0000000 .0000000 R
5 Q1 163.2799765 -.2584975 .0000000 33.3665366 -20.0000000 .0000000 .0000000 .0000000 R
6 D3 163.7299765 -.4124066 .0000000 33.7893983 -20.0000000 .0000000 .0000000 .0000000 R
7 Q2 163.8799765 -.4637096 .0000000 33.9303522 -20.0000000 .0000000 .0000000 .0000000 R
8 Q2 164.0299765 -.5150126 .0000000 34.0713061 -20.0000000 .0000000 .0000000 .0000000 R
9 D3 164.4799765 -.6689217 .0000000 34.4941678 -20.0000000 .0000000 .0000000 .0000000 R
10 Q3 164.6299765 -.7202247 .0000000 34.6351217 -20.0000000 .0000000 .0000000 .0000000 R
11 Q3 164.7799765 -.7715277 .0000000 34.7760755 -20.0000000 .0000000 .0000000 .0000000 R
12 D4 166.6299765 -1.4042650 .0000000 36.5145069 -20.0000000 .0000000 .0000000 .0000000 R
“20/80” COORDINATES
THE SXYZ COORDINATES,AZIMUTH,ELEVATION AND ROLL ANGLES ARE :
# NAME S X Y Z THETA PHI PSI ALPHA
1 D1 162.4205370 20.0000000 .0000000 47.4494757 180.0000000 .0000000 180.0000000 .0000000 L
2 B1 162.6299765 19.9638156 .0000000 47.2442636 -160.0000000 .0000000 180.0000000 .0000000 L
3 D2 162.9799765 19.8441085 .0000000 46.9153712 -160.0000000 .0000000 180.0000000 .0000000 L
4 Q1 163.1299765 19.7928055 .0000000 46.7744173 -160.0000000 .0000000 180.0000000 .0000000 L
5 Q1 163.2799765 19.7415025 .0000000 46.6334634 -160.0000000 .0000000 180.0000000 .0000000 L
6 D3 163.7299765 19.5875934 .0000000 46.2106017 -160.0000000 .0000000 180.0000000 .0000000 L
7 Q2 163.8799765 19.5362904 .0000000 46.0696478 -160.0000000 .0000000 180.0000000 .0000000 L
8 Q2 164.0299765 19.4849874 .0000000 45.9286939 -160.0000000 .0000000 180.0000000 .0000000 L
9 D3 164.4799765 19.3310783 .0000000 45.5058322 -160.0000000 .0000000 180.0000000 .0000000 L
10 Q3 164.6299765 19.2797753 .0000000 45.3648783 -160.0000000 .0000000 180.0000000 .0000000 L
11 Q3 164.7799765 19.2284723 .0000000 45.2239245 -160.0000000 .0000000 180.0000000 .0000000 L
12 D4 166.6299765 18.5957350 .0000000 43.4854931 -160.0000000 .0000000 180.0000000 .0000000 L
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