Dear Debbie Please find below our response to the comments by the editors and referee to our submission Measurement of Electron Trapping in the CESR Storage Ring With kind regards, Jim ============================================================ James Crittenden Tel. (607) 255-9424 Wilson Synchrotron Laboratory Fax (607) 255-8062 Cornell University Ithaca, New York 14853-8001 PROBLEMS WITH MANUSCRIPT: You should reduce the file size by using different graphics programs and/or bitmapping of images. A reasonable target size for the pdf file for each separate figure file is 1 MB or less. ** We were able to dramatically reduce the sizes of the graphics files ** used in Fig. 1. ---------------------------------------------------------------------- Report of Referee D -- LJ13863Z/Billing ---------------------------------------------------------------------- Followings are my comments. A. Body of the paper 1. In Abstract, the paper describes as "A witness bunch provides a direct measurement of the trapped cloud density." I think that it is not clear how the trapped cloud density is obtained "directly" from the data with the witness bunch. Though it might be possible to say that, for example, " A witness bunch provides a direct measurement which shows existence of trapped electron cloud.", it might be difficult to get the trapped cloud density directly from the data of the detector. If the trapped electron density is obtained from the data by the witness bunch with the help of a simulation, the procedure needs to be given. ** We agree with the referee. ** We have replaced the sentence with ** ** "The effect of a witness bunch on the measured signal provides ** direct evidence for the existence of trapped electrons." 2. On p. 3 left where the experiment is described, the paper describes as "The decrease in cloud buildup rate following the first 6 bunches indicates that a subset of trapped electrons which can contribute signal has become depleted at that time. .... showing that the additional cloud seeded by the long-term trapping is self-sustaining." On p. 5 left where the simulation is described, almost same statement appears again as "The electrons which remain trapped during the 2.3 μs prior to the train arrival are cleared out during the first 6 of the 20 bunch passages, reabsorbed either in the detector or the vacuum chamber wall ......." Does this mean that the data is explained by the simulation? Fig. 3 in ref. 26 compares the data and the simulation. The simulation results for 4.01mA/bunch to 7.26mA/bunch seem not showing knee structure. The simulation result at 8.26mA/bunch looks fitted by a simple straight line. ** Yes, the simulation explains why trapped electrons are swept out during ** the passage of the first 6 bunches of a 20-bunch train to the extent ** shown in the three slides attached. The first slide shows the ** 4 mA/bunch signal alone to allow a detailed view of the comparison. ** The model shown here is a slight improvement over the one used for Ref. 26. ** Our interpretation is not that the knee structure is missing, but rather ** that its timing is a poor match. ** ** The basis for our interpretation is shown in the second and third slides, ** which show that the model does agree with the ** 6-bunch-clearing mechanism described as the source of the signal knee. ** Most of the "old" macroparticles, i.e. those emitted from the wall at a ** preceding time interval comparable to the revolution time, ** are cleared out early in the train passage, the remainder of the signal ** being sourced primarily by electrons produced during the same train passage. ** ** We have added Fig. 8, which shows that the model also explains the effect of the ** intermediate clearing bunch (see our response to comment 4) below). ** ** The modeling of the signal is largely independent of the modeling of the cloud ** buildup, since it depends on detailed simulation of the detector acceptance in ** incident energy and angle, and since only a very small fraction of the cloud ** contributes to the signal. ** ** Our primary goal for this paper is to demonstrate the electron trapping phenomenon ** using the self-consistency of the measurements. The modeling shows that trapping ** is to be expected for the conditions of the measurement. ** ** We cite quantitative results from the model such as overall cloud densities ** and trapping fractions, which are insensitive to the model parameter variations. ** ** At the present stage of development, the modeled signal is very sensitive to ** small changes in the parameters. We expect to publish more detailed signal modeling ** results after further study. 3. On p. 3 left, the paper describes as "The increase in the trapped signal as the bunch spacing is raised from 14 ns to 16 ns is the signature of the beam-induced multipacting enhancement investigated by Harkay and Rosenberg at the Advanced Photon Source [21]." What is the reason for judging that the increased signal is the signature of the beam induced multipacting (BIM)? Does a simulation suggest the BIM at this bunch spacing or is there an analytic estimate of the resonance condition like that described in ref. 21? ** Our intended use of the term "beam-induced multipacting" was intended ** to be generic, i.e. that the level of trapping depends on the bunch ** configuration. The referee correctly points out that our comparison ** to the Harkay/Rosenberg effect is misleading, since their mechanism has nothing ** to do with electron trapping. ** We have removed this reference and added this sentence to emphasize our ** intended message: ** ** "The decrease with increasing bunch spacing can be understood in terms of an overall ** decrease in cloud buildup. However, the enhancement of the signal at 16-ns spacing ** relative to the signal for 14-ns spacing shows that when electron trapping is of concern, ** care must be taken in the choice of bunch spacing. ** ** We have also altered the caption of Fig. 5 to read ** ** "The increase in signal for the 16-ns spacing relative to the 14-ns spacing ** shows that long-term cloud electron trapping can be enhanced by an ** unfortunate choice of bunch spacing." ** ** We have also removed the reference to "beam-induced multipacting" in the abstract ** and summary. 4. On p. 5, the paper describes as "The clearing effect of an intermediate bunch has been measured and successfully modeled,...". I think that the reason why the authors judged the clearing effect has been modeled "successfully" is not clearly described. ** Our modeling does show the reduction in cloud density provided by a witness ** bunch with the spacing and population used in our measurements. It also shows ** the modeled signal decreasing similarly to the observation. ** We have added Fig. 8 in support of our statements on the reduction of cloud ** density provided by the clearing bunch. 5. In INTRODUCTION, the electron cloud buildup, the trapping of the electrons and the mitigation methods etc. are described. However I feel that the relation between these descriptions and the measurement in this paper is not clearly described. ** We have re-organized the Introduction for clarity and relevance to ** the content of the paper. B. References 1. On p. 1 left, the paper describes as "More recently, heat load in the final-focus quadrupoles of the LHC has been attributed to electron cloud buildup [12]." I could not find this statement in ref. 12. Are there more relevant papers to be referred? ** Yes. After consultation with Giovanni Rumolo, the source of this ** information, we have changed this reference to the PhD thesis of ** Giovanni Iadarola. C. Figures and Tables 1. In Fig. 4, numbers in the figure, which will be bunch population, might be ten times larger than the actual. Also on p. 3, "1.3 × 10^11 to 6.4 × 10^11, as shown in Fig. 4." might be "1.3 × 10^11 to 0.64 × 10^11....". ** Many thanks to the referee for noticing this error. 2. In Fig.1, adding name of parts in the figure as in Fig. 2 might be helpful to readers. ** Done.