Energy Enhancement and Energy Spread Compression of Electron Beams in a Hybrid Laser-Plasma Wakefield Accelerator
, Changhai Yu 1,3,*, Zhiyong Qin 1,3, Wentao Wang 1,*, Zhijun Zhang 1, Rong Qi 1, Ke Feng 1,2, Lintong Ke 1,2, Yu Chen 1,2, Cheng Wang 1, Xiaojun Yang 1, Yuxin Leng 1, Jiansheng Liu 1,3,4,*, Ruxin Li 1,2,5 and Zhizhan Xu 1,2,5Round 1
Reviewer 1 Report
Good paper. Interesting results which should be published. Some English errors could be changed.
Author Response
We greatly appreciate the referee1 for his or her valuable recommendation.
Reviewer 2 Report
Dear authors,
Attached is my review.
Respectfully,
Comments for author File: 
Comments.pdf
Author Response
Thanks a lot for the comments of the referee. The response letter is attached to this reply and can be found below.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript reports on experimental results showing, according to the main statements by the authors, a laser-driven electron acceleration regime in which a first LWFA producing a 2 components e- bunch (the authors call it "two color", although the energy is not that different, according to figure 1d) evolves into a PWFA stage. The major outcome of this hybrid LWFA-PWFA scheme, with respect to previous studies, is an enhanced quality (mainly in terms of energy spread) of the witness bunch, due to both an increase of its energy, driven by the PWFA beyond the laser depletion distance, and an energy chirp compensation in the plasma wakefield.
The work is, in my opinion, interesting and, with some respect, might contain novel findings. Nevertheless, it misses, at the present stage, the presentation and discussion of the main point which could make it worth publishing with respect to the current literature on hybrid LWFA-PWFA. I refer to the generation of the two separated electron components in the LWFA stage. I can guess that such a presentation could have been provided in reference [21], but, since this refers to a submitted manuscript, this cannot be accessed at the moment. This is, in my opinion, a quite critical point of the manuscript, which makes it unsuitable for the publication as it is. I would thus suggest to the authors a major revision aimed at including all the necessary informations on this crucial point. In particular, the authors should, in my opinion, include a brand new section focusing on the following issues:
LWFA regime leading to the acceleration of two well separated bunches. I suspect that the particular plasma density profile (described in ref. [7], as correctly reported by the authors) could be playing a crucial role, but no discussion (supported by PIC simulations) has been currently provided.
Stability analysis of the whole scheme. This both applies to the LWFA (resulting in the 2 component bunch) and to the PWFA (to what extent, for instance, the energy chirp compensation of the witness depends on the 2 components energy and/or space separation?)
Author Response
Thanks a lot for the comments of the referee. The response letter is attched to this reply and can be found below.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
I think the authors have fully addressed my initial concerns in a satisfactory manner. Provided that reference [21] has been accepted for publication - as claimed by the authors in their response - I would only modify its reference to something like "accepted for the publication", so as to allow the reader to access it once published; as I said in my previous report, I believe this is an important point.
Overall, I would thus recommend the publication of this revised version.
