Descripción del proceso para la gestión de incidentes propuesto

As mentioned previously, a second set of measurements were made during the 100 keV ejection plateau for an ELENA cycle with a longer repetition rate. The measurements were again made in all four directions, but this time an important distinction must be pointed out: The measurements were made twice at the same cycle time t=28.875 s, with electron cooling on and off. Whilst this approach is somewhat different, it again allows for investigation into the effects of the electron cooler. Electron cooling began at the start of the plateau at t= 24.897 s and so the measurements highlight the effects of 3.888 s of electron cooling compared with a coasting beam subject only to collective effects such as IBS.

6.5.2.1 Vertical Measurements

Analysis of the vertical data using the two scan algorithm gave emittances of 2.55 (± 0.03) mm mrad and 0.53 (± 0.01) mm mrad, without and with cooling respectively. After 3.9 s of electron cooling at 100 keV the vertical beam emittance

Figure 6.21: CDFs compared with simulations for vertical scraper measure- ments along the ejection plateau. Both sets of data are taken at the same time

in the cycle, with and without electron cooling.

is significantly reduced by 79 (± 2) % of that without. The data showed negligible changes in the closed orbit offset with values of -2.08 (±0.03) mm and -2.03 (±0.03) mm calculated without and with electron cooling, respectively.

Similarly to the previous section, Fig. 6.21 shows a comparison of the data with simulations, yet this time more obvious deviations from a Gaussian distri- bution are observed for the beam with no cooling. Another difference is that the beam has a wider core than the Gaussian approximation compared with a thin- ner core after cooling during the intermediate plateau. This distribution could be explained by the fact that the beam has been measured 3.9 seconds after the end of the deceleration ramp with no cooling. The more dense region at the core may have expanded faster than at the tails during this time due to IBS being more significant at higher intensities. After cooling the beam is well approximated by a Gaussian distribution, perhaps due to the cooling being more effective at the core and correcting for more IBS at the core. Also, when the beam size is even- tually smaller so is the deviation in electron velocities interacting with the beam, resulting in more even cooling across the entire beam.

6.5.2.2 Horizontal Measurements

Due to no Schottky data being available for this plateau it was necessary to make an estimate of the longitudinal momentum spread in order to use the two scan algorithm. Preliminary analysis of the data showed that indeed there was a cross- ing of CDFs above zero in this plane. Measurements at this final plateau were not taken on the same day as for the intermediate plateau but current readings for the 3 quadrupole families showed negligible changes in the optical configuration. It is possible that injection conditions were different. This would support the optical mismatch hypothesis when trying to understand the absence of a raised crossing point in the CDFs taken at t = 7.8 s, assuming a more well optically matched beam for these measurements, however as previously stated, further measurements are required.

After confirming that the Gaussian fit algorithm is accurate for determining the emittance for vertical measurements, and combined with its capability to ac- curately estimate momentum spread for simulation results, it was used to make an estimate for the longitudinal momentum spread of the beam. This was done first using the data for an uncooled beam, since vertical measurements along the intermediate plateau suggested the beam becomes less Gaussian with cooling.

The Gaussian fit algorithm was run twice, once for each direction and results were compared. When scraping from the “Ext” direction, the momentum spread estimate had extremely large uncertainty values (based on the goodness of the fit) and so the estimation was discarded. The fit can be seen in Fig. A.10. The estimations from the “Int” direction returned σδ = 9.4 (±0.2) × 10−4. The fit is

displayed in Fig. 6.22, showing an excellent agreement at the tails but some small deviation towards the core, suggesting an underestimation. The error on the value, based on the goodness of the fit, was deemed acceptable for this method to form the basis for the estimate of the momentum spread. The uncertainty of the estimate was increased to 20% (±1.9 × 10−4) to account for the uncertain nature of this method, and was carried through to the error on the reconstructed emittance.

The two scan algorithm was run with this estimation and returned an emittance of 2.5 (±0.2) mm mrad. For the case with cooling present an RMS momentum

Figure 6.22: Application of the single scan Gaussian fit algorithm to a hori- zontal measurement along the ejection plateau in the absence of electron cooling. Data has been mirrored about x = 0 mm to accommodate the fitting algorithm,

this process does not affect the result.

Figure 6.23: Data vs Gaussian simulations for the ejection plateau.

spread of 0 (±2 × 10−4) was estimated, based on the Gaussian only algorithm estimating values of the order 10−7 for both directions. With this input, the two

Figure 6.24: Zoom on beam core region for data vs Gaussian simulations along the ejection plateau.

scan method returned an emittance of 0.55 (±0.04) mm mrad, a change of 78 (±10) % of the emittance at this time without electron cooling. Again, a shift in the closed orbit of −0.24 (±0.08) mm was seen, suggesting that because the mean momentum offset of the beam has changed due to electron cooling, so has the closed orbit through dispersion. Using the same method as for the intermediate plateau (∆x0 = Dx∆¯δ), the change in momentum offset with and without electron cooling

was calculated at ∆¯δ = −1.7 (±0.3) × 10−4. (It was ∆¯δ = −1.2 (±0.3) × 10−4 for the intermediate plateau.)

The data and Gaussian simulations based on the two scan algorithm result are shown in Figs. 6.23 and 6.24. Again there appears to be good agreement with the Gaussian simulations, and this time the crossing height of the CDFs is much closer to the data for the non-cooling case. The Gaussian simulation for the non- cooling case serves well to highlight an asymmetry in the measured distribution. Such asymmetries were observed during the simulation phase (Section 5.7.1) when investigating correlations between momentum offset and emittance and so the correlation coefficient was investigated next.