Transverse-to-Longitudinal Emittance Exchange to Improve Performance of High-Gain Free-Electron Lasers Page: 4 of 15
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
LCLS, i.e., yx= 1 pm and a peak current If= 3.5 kA after bunch compression, while the electron
beam in case (b) is the manipulated one as discussed above, i.e., yx = 0.1 pm and a peak current
= 1.0 kA. Both beams have the same uncorrelated relative energy spread at 1x 10-4. Figure 1
shows the power gain length computed from Xie's fitting formula [6] versus the undulator
parameter K for both cases. The gain length for the case (b) is smaller by a factor of 2 or more.
The length of the undulator will be reduced by a similar factor, reducing the construction cost as
well as the operational complexity.
Note also that the gain length for case (b) changes little as K increases from 1.5 to 4, while it
decreases significantly for case (a). Therefore, the K value may be chosen to be small, K ~ 1.5,
for the latter case while it needs to be large, K ~ 4, for the former case in order to limit the length
of the undulator. The smaller emittance therefore has additional advantages: the undulator
requires less magnetic material, and the electron energy required for 0.4-A radiation is smaller.15
E 10
c5
52
3
4
K
Figure 1. Power gain length LG of an x-ray FEL at 0.4 A versus the undulator parameter K for (a)
a beam with a normalized transverse emittance of 1 pm and a peak current of 3.5 kA, and (b) a
beam with a normalized transverse emittance of 0.1 pm and a peak current of 1.0 kA. The
electron beam energy in both cases is adjusted according to the FEL resonant condition, with the
relative rms energy spread at 1x 10-4.
2.3. Space-Charge Effects on the Gun Emittances
Let us now consider in more detail some of the processes in the above manipulation of the phase-
space distribution. Is the small longitudinal emittance, Eq. (8), consistent with the space-charge
force? The emittance arising from the space charge effect in the rf photocathode gun can be
written as [7]4
- (a) -
- (b) -
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Emma, P.; Huang, Z.; Kim, K. J. & Piot, P. Transverse-to-Longitudinal Emittance Exchange to Improve Performance of High-Gain Free-Electron Lasers, article, September 21, 2006; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc889121/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.