STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
ting the data is difficult. Without the ability to extract beam sizes in real time,<br />
this was only revealed after the fact. As with the previous measurement, fitting<br />
the complete data set results in an unphysical emittance. Since a unique beam<br />
size is expected for each value of the quadrupole strength, points were omitted that<br />
violated this condition. The result is a physically acceptable emittance.<br />
Horizontal Emittance: Einj = 20 MeV<br />
This data set represents an ideal measurement - a large number of data points<br />
with the beta function sweeping through a minimum. The two points that were<br />
omitted were outliers.<br />
Vertical Emittance: Einj = 20 MeV<br />
This measurement shows once again that the quadrupole strength was not suf-<br />
ficiently scanned and the fitting must be applied to half of a parabola. The points<br />
omitted were done so for obvious reasons; the rightmost point was omitted due to<br />
an excessively noisy wire scan (note the large error bar), while the other omitted<br />
point is an outlier.<br />
When scanning the quadrupole, not only is the energy recovered beam affected,<br />
but perhaps more importantly, so is the accelerated or first pass beam. The impor-<br />
tance results from the implicit assumption that the Twiss parameters at the entrance<br />
of the scanning quadrupole remain the same. In order to meet that requirement, a<br />
family of quadrupoles (downstream of the reinjection chicane) was used to produce<br />
compensating optics to counter the effects produced by the scanning quadrupole.<br />
Prior to the CEBAF-ER experiment, the emittance measurements were simu-<br />
lated in Optim [41], including producing appropriate compensatory optics. During<br />
the CEBAF-ER experiment however, the machine optics used for the Einj = 20 MeV<br />
configuration were not those used in the simulations. Hence, compensating op-<br />
46