Characterizing Low-Energy Charged Particles in the Magnetosphere with the LEM CubeSat Spectrometer Project: Detector Concept and Hardware Characterisation^†

Round 1

Reviewer 1 Report

This article presents the concept and characterization of an energetic particle detector, Low-Energy Module (LEM), which is under development for accurate flux measurement of low-energy charged particles in the Earth’s magnetosphere. It is also capable of detecting X-rays and gamma-rays. Identification of particles is based on the well-known dE-E technique used in many telescopes of energetic particles in space. A feature of this instrument is the use of an active anticoincidence shielding, which allows to measure the arrival direction of particles (within the field of view 60 x 60 deg), identify different types of particles, electrons (0.1-10 MeV), protons (3-30 MeV) and alphas (10 -100 MeV). At the same time, the detector has a compact size (10x10x10 cm3) and is suitable for installation on CubeSats.

The article presents a detailed description of the concept of the detector, the results of simulations of the passage of particles in the detector materials using Geant4, some laboratory tests of a silicon detector considered as a possible candidate for use in this device.

The article is well prepared, the description is in understandable English. I can recommend the article for acceptance for publication after a minor revision. The list of comments and remarks is below.

 

1)   The scheme of the instrument is rather complicated. It contains more than 30 detector elements (16 silicon detectors, 16 CZT detectors, several elements of the active scintillator shielding). The questions arise: can such a complicated device be implemented within CubeSats from the point of view of providing power and telemetry, maintaining the necessary thermal modes of operation of semiconductor detectors? It would be desirable to discuss these issues at least briefly. It is also desirable to explain what kind of data is planned to be transmitted to the ground. Will particle identification be carried out automatically on board the spacecraft or on Earth?

 

2)   Geant4 simulations are shown only for electrons, protons, alpha particles, and gamma quanta, but not for heavier ions. What other ions can the detector identify?

 

3)   Based on the scheme presented in Fig. 2, most likely, some number of energetic particles will also arrive at the detectors, having passed through the edges of the upper passive aluminum shield and lost part of the energy there, without interacting with the active scintillation shield. Have any calculations been made for such particles and how much will they "contaminate" the normal operation of the device?

 

4)   The paper discusses the characteristics of the PIPS detector AP-CAM25 (500 mkm) manufactured by Mirion. Why did you choose this detector model? Please, explain briefly what advantages it has over other similar silicon detectors?

For the dE-E scheme, in particular, it is necessary that a particle fly through the first (upper) detector, without energy loss outside the depletion region. Is this condition provided by this detector (for example, is front-end electronics or detector housing blocking the way for particles)?

 

 5)   In section 5.2 it is possibly worth mentioning terrestrial gamma-ray flashes (TGFs) as another potential object for detection by the LEM instrument.

 

A few other minor comments:

1) Figure 1. I’m not sure whether this figure is needed in the article, since these types of motion of trapped charged particles in the dipolar magnetic field is known and it is not directly related to the topic of the article. Nevertheless, if the authors will decide to remain this figure, I would suggest to add the colorbar with notation of colors in physical units or, at least, to mention the durations of a particle’s full drift orbit around the Earth and the bouncing time  in the figure’s caption.

2) Lines 61-63. It seems “is shown” is forgotten in the sentence starting from “In Figure 1,…”

3) The information in column “Size, Weight” in Table 1 is not full. In some lines only weight is given, in some line - only sizes. Please, add the information.  Also, there is no information (separate line) about HEPP-H on CSES which is mentioned in the text (line 98).

4) Line 104 “By comparing the six detectors studied…” Which six detectors? There are only four detectors in Table 1.

5) In Fig.2 the width of the silicon detectors is 300 mkm, although in the text (line 145) the 100 mkm detector is discussed. Please, make it consistent.  

6) The last paragraph of section 5.1. Please, explain how you defined the angular resolution from Fig.5

7) In Fig.7 (left), X-axis title should be in keV, not in MeV (I guess).

8) Lines 237 and 259, repetition “detector detector”

9) Lines 266-267. “On the left-hand side of the plot is reported the detector’s resolution estimation.” It seems that the detector’s resolution is shown on the right panel.

10) Line 295. “LeCCroy” -> “LeCroy”

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Page 13, raw 362:

(11.1 ± 0.4stat ± 1.2syst)

should be

(11.1 ± 0.4stat ± 1.2syst)

 

 

 

Comments for author File: Comments.pdf

Author Response

Dear Referee,

Thank you for your review. I corrected the typo indicated. 

We appreciate your time and consideration.

Best regards,

Riccardo Nicolaidis

 

Reviewer 3 Report

I have no special comments for authors

Author Response

Dear Referee,

Thank you for your review.  We appreciate your time and consideration.

Best regards,

Riccardo Nicolaidis