Electron Energy Spectrometer for MIR-THz FEL Light Source at Chiang Mai University
Round 1
Reviewer 1 Report
1. Figure 4 is uninformative. Can you scale the diagrams?
2. Str. 22: Typo "tthe".
3. Str. 146: Figure 3.1 should be Figure 6, I suppose.
4. It can be advised you to increase the literature review to clarify your contribution to the area of electron energy spectrometry.
5. Upper-left Picture in Figure 7 is not clear, the blue diagram blocks the red diagram.
Str. 22: Typo "tthe".
Author Response
Response to Reviewer 1 Comments
Point 1: Figure 4 is uninformative. Can you scale the diagrams?
Response 1: Thank you very much for pointing this out. The scaling of the range on both the x and y axes in Figure 4 has been enhanced in this revise manuscript.
Point 2: Str. 22: Typo "tthe".
Response 2: Thank you very much for pointing this out. We have changed the word from “tthe” to “the”.
Point 3: Str. 146: Figure 3.1 should be Figure 6, I suppose.
Response 3: Thank you very much for pointing this out. We have changed the figure number from “Figure 3.1” to “Figure 6”.
Point 4: It can be advised you to increase the literature review to clarify your contribution to the area of electron energy spectrometry.
Response 4: We greatly appreciate you bringing this to our attention. We have added a literature review on energy spectrometers in the introduction section as can be found in lines 34-60 in this revised manuscript.
Lines 34-60:
To characterize aforementioned electron beam properties, diagnostic devices are employed. An alpha magnet equipped with energy slits and a downstream current transformer is used to measure energy and energy spread of electron beam produced from the RF-gun [ 2,3]. A dipole magnet and a Faraday cup at the end of straight section are employed together as an energy spectrometer for measuring the electron after the linac acceleration. Furthermore, the first dipole magnet in the bunch compressor, as described in [4], along with the view screen station positioned downstream this magnet, serve as an energy spectrometer for the MIR and THz FEL beamlines. The electron beam energy spectrometer employing the dipole magnet and beam current monitor or screen is widely used in several facilities. A dipole magnet and a beam current monitor in a form of Faraday cup are used at KU-FEL to measured the electron beam with energy spread of below 5% when applying a slit with proper width [5]. At the Helmholtz-Zentrum Berlin for Materials and Energy Research (HZB), a dipole magnet and a screen station are employed to measure energy and energy spectrum of the electron beam produced from a superconducting RF photoelectron gun (SRF gun) of the Berlin Energy Recovery Linac (BERLinPro). This spectrometer is expected to provide the measurement with energy resolution of about 0.1% [ 6]. A dipole magnet and a screen station are also utilized at the Photo Injector Test facility at DESY, Zeuthen site, (PITZ) to measure slice momentum spread of electron beam a high resolution down to 1 keV/c [7].
The aforementioned examples clearly demonstrate the effectiveness of applying a dipole magnet and a beam current monitor or a screen with a well-designed setup as an electron beam energy spectrometer, allowing for precise measurements with small energy spread and high energy resolution. In our facility, we employ the first dipole magnet in the magnetic bunch compressor and its downstream screen station for the sake of convenience and cost efficiency. In this paper, we thus focused on physical design and development of energy spectrometer utilizing a dipole magnet and a screen station for measuring electron beam energy and energy spread
Point 5: Upper-left Picture in Figure 7 is not clear; the blue diagram blocks the red diagram.
Response 5: Thank you very much for pointing this out. We have changed the transparency of the blue dot such that the red histogram is visible in this revise manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper is well written in general. Two things should be re-editted. They are with red background. The rest are minor editting.
#7: A Space Charge Tracking Algorithm (ASTRA) instead of ASTRA
#22: In tthe RF-gun
#52: "insights on the electron beam mean energy"
#55: ASTRA instead of A Space Charge Tracking Algorithm (ASTRA)
#57: "when it is passing"
#66: Computation of of electron
#73: simulation, We started
#83: electron beam is hitting the phosphor screen
#85: the screen affects the resolution and accuracy (not affects on)
#137: converges around instead of converges to around
#139: error less instead of error of less
#146: There is no Figure 3.1, it is rather Figure 3.a or b
#149: threshold less than instead of threshold of less than
#168: magnets placed between
#168 - 169: Redo Fig 7, upper left quadrant (Time (ps). The red histogram is shadowed and hidden by the blue.
#206-207: It say for the first time in the text that "... 20 MeV with an energy spread of 0.56% and a maximum peak current of 327 A." You failed to talk about this in the body of the paper. Do that and discuss about it, especially about the 327 A current, which could easily make a hole in your apparatus.
Author Response
Response to Reviewer 2 Comments
Point 1: #7: A Space Charge Tracking Algorithm (ASTRA) instead of ASTRA
Response 1: Thank you very much for pointing this out. We have changed the word from “ASTRA” to “A Space Charge Tracking Algorithm (ASTRA)”.
Point 2: #22: In tthe RF-gun
Response 2: Thank you very much for pointing this out. We have changed the word from “tthe” to “the”.
Point 3: #52: "insights on the electron beam mean energy"
Response 3: Thank you very much for pointing this out. We have changed the sentence from “insights the electron beam mean energy” to “insights on the electron beam mean energy”.
Point 4: #55: ASTRA instead of A Space Charge Tracking Algorithm (ASTRA)
Response 4: Thank you very much for bringing this to our attention. We have changed the word from “A Space Charge Tracking Algorithm (ASTRA)” to “ASTRA”.
Point 5: #57: "when it is passing"
Response 5: Thank you very much for pointing this out. We have changed the word from “when it passing” to “when it is passing”.
Point 6: #66: Computation of of electron
Response 6: Thank you very much for pointing this out. We have changed the word in sub section from “Computation of of electron kinetic energy” to “Computation of electron kinetic energy”.
Point 7: #73: simulation, We started
Response 7: Thank you very much for pointing this out. We have changed the word from “We started” to “we firstly investigate” as suggested by reviewer 3.
Point 8: #83: electron beam is hitting the phosphor screen
Response 8: Thank you very much for pointing this out. We have changed the sentence from “electron beam hitting the phosphor screen” to “electron beam is hitting the phosphor screen”.
Point 9: #85: the screen affects the resolution and accuracy (not affects on)
Response 9: Thank you very much for pointing this out. We have changed the sentence from “the screen affects on the resolution and accuracy” to “the screen affects the resolution and accuracy”.
Point 10: #137: converges around instead of converges to around
Response 10: Thank you very much for pointing this out. We have changed the word from “converges to around” to “converges around”.
Point 11: #139: error less instead of error of less
Response 11: Thank you very much for pointing this out. We have changed the word from “error of less” to “error less”.
Point 12: #146: There is no Figure 3.1, it is rather Figure 3.a or b
Response 12: Thank you very much for pointing this out. We have changed the figure number from “Figure 3.1” to “Figure 6”.
Point 13: #149: threshold less than instead of threshold of less than
Response 13: Thank you very much for pointing this out. We have changed the word from “threshold of less than” to “threshold less than”.
Point 14: #168: magnets placed between
Response 14: Thank you very much for pointing this out. We have changed the word from “placing” to “placed”.
Point 15: #168 - 169: Redo Fig 7, upper left quadrant (Time (ps). The red histogram is shadowed and hidden by the blue.
Response 15: Thank you very much for pointing this out. We have changed the transparency of the blue dot such that the red histogram is visible in this revise manuscript.
Point 16: #206-207 : It say for the first time in the text that "... 20 MeV with an energy spread of 0.56% and a maximum peak current of 327 A." You failed to talk about this in the body of the paper. Do that and discuss about it, especially about the 327 A current, which could easily make a hole in your apparatus.
Response 16: Thank you very much for pointing this out. The text describes the electron beam properties at the experimental station which already been described in section 3.2 (lines 186 in this revised manuscript). A maximum peak current of 327 A is a current of an electron micropulse calculated from a charge of 117.6 pC and an electron bunch length of 0.36 ps. Since it is not the macropulse current, it will not make a hole in our screen. To avoid the confusion, we have changed this sentence to be “The simulation results indicated that, at the experimental station, the electron bunch of a charge of 117.6 pC has an average energy of 20.07 MeV with an energy spread of 0.55%.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript presents a simulation study to design and optimize the electron energy spectrometer of the linear accelerator system of the PBP-CMU Electron Linac Laboratory. The results of this simulation allow to evaluate the systematic error of the beam average and spread energy measurement for different beam conditions, for example the initial beam transverse emittance.
The paper is well written, even if I recommend few minor corrections:
Abstract:
Line 5 importance --> important
Introduction:
Line 22: tthe ---> the
Line 26: within a range ---> within the range
Figure 1: Can you indicate with an arrow or something else where is located the screen and the CCD camera?
Methodology:
Line 73: In the simulation, We started ---> In the simulation we firstly investigate
Line 74: "electron with varying" ---> "electron varying"
Line 75: "The electron injects parallel to the center in the dipole magnet" --> what does it mean? "Electrons are injected into the center of the dipole magnet parallel to its axis"? a trajectory is parallel to an axis not to a point (the center of the magnet).
Results and discussion
Figure 6: Please consider or a log scale or drawing horizontal lines corresponding to 10% and 1 %
Line 146:
Fig. 3.1 ---> Fig. 6
Please correct the few typos I spotted in my comments.
Author Response
Response to Reviewer 3 Comments
Point 1: Line 5 importance --> important
Response 1: Thank you very much for pointing this out. We have changed the word from “importance” to “Important”.
Point 2: Line 22: tthe ---> the
Response 2: Thank you very much for pointing this out. We have changed the word from “tthe” to “the”.
Point 3: Line 26: within a range ---> within the range
Response 3: Thank you very much for pointing this out. We have changed the word from “within a range” to “within the range”.
Point 4: Can you indicate with an arrow or something else where is located the screen and the CCD camera?
Response 4: Thank you very much for pointing this out. We have added the location of the screen and the CCD camera on the diagram in Figure 1 as well as the description in this figure caption.
Point 5: Line 73: In the simulation, We started ---> In the simulation we firstly investigate
Response 5: Thank you very much for pointing this out. We have changed the word from “We started” to “we firstly investigate”.
Point 6: Line 74: "electron with varying" ---> "electron varying"
Response 6: Thank you very much for pointing this out. We have changed the word from “electron with varying” to “electron varying”.
Point 7: Line 75: "The electron injects parallel to the center in the dipole magnet" --> what does it mean? "Electrons are injected into the center of the dipole magnet parallel to its axis"? a trajectory is parallel to an axis not to a point (the center of the magnet).
Response 7: Thank you very much for pointing this out and suggestion. We have changed the sentence from “The electron injects parallel at the center into the dipole magnet”. to “Electrons are injected into the center of the dipole magnet parallel to the beam axis”.
Point 8: Figure 6: Please consider or a log scale or drawing horizontal lines corresponding to 10% and 1%.
Response 8: Thank you very much for pointing this out. We have drawn horizontal and vertical lines in Figure 6 for clearer visible for readers.
Point 9: Line 146: Fig. 3.1 ---> Fig. 6
Response 9: Thanks for your kind reminders. We have changed the figure number from “Figure 3.1” to “Figure 6”.
Author Response File: Author Response.pdf
