• 533 Proposal 533 Roshi Phased Array Feed vs Focal Plane Array for ALMA Frequency Bands

  • Reviewer 3

Grade: 9 (poor)

Phased Array Feed vs. Feed Array for ALMA Frequency Bandss

1. Alignment with NA ALMA Partnership strategic goals; -- OK, in that mapping wide fields is a goal.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents. -- Increasing the mapping speed of the array, or of just the 4 total power antennas, would benefit many observations of molecular clouds and nearby galaxies. However, cramming a PAF or FPA into the footprint of the existing ALMA dewar would boost the mapping speed by only a factor of a few, in a few frequency bands, at a huge cost in development and construction. It is not worth the expense.

3. Quality of the upgrade conceptual design; -- A PAF operating at 3mm wavelength that could process 8 or 16 GHz IF bandwidth, is likely to be extremely complex and expensive. A previous study by Henke et al already computed the improvement in mapping speed for an FPA - how will this study do better?

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development); -- This is a very long term project.

5. Strength of the consortium organization (if applicable); -- OK, although one wonders why some UMass people have not been folded into this study, since they have direct experience with building a 3mm PAF for the GBT.

6. Qualifications of the key personnel of the Study; -- Good. Roshi has played an important role in the development of a 1.4 GHz PAF on the GBT.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study; -- Good.

8. Assessment of the level of risk inherent in the design; -- High risk.

9. Strength of the Scientific Team supporting the Study; -- Not applicable for this engineering study.

10. Level of support guaranteed by the Institutes; -- OK.

11. Budgeted cost of the Study; -- OK.

  • Reviewer 4

Grade: 1

Title: Phased Array Feed vs Feed Array for ALMA Frequency Bands (PI: Roshi)

1. Alignment with NA ALMA Partnership strategic goals;

Comment: This study on multi-beam system for ALMA extends the technical capability and increases the operating efficiency of ALMA in the long term.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents.

Comment: This study aims to address one of the key recommended development paths of increasing the wide field mapping speed. The scope of the study is limited to the performance comparison of phased array feed vs feed array, but this may be a critical study based on the earlier analysis by Henke et al.

Given the relative abundance of available time in the low frequency windows, their focus on Bands 1-3 might not be as urgent as that of a multi-beam system for higher frequency bands. For these lower frequency bands, there are also other options such as using data from existing large single disk telescopes with a large array receivers. This is not a bad start, however.

3. Quality of the upgrade conceptual design;

Comment: A detailed astronomical science case is offered along with a fairly detailed technical description and analysis of the proposed study. It clearly demonstrates the experience and knowledge on the ALMA receiver system (and their limitations) by the proposing team.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

Comment: very good

5. Strength of the consortium organization (if applicable);

Comment: very good

6. Qualifications of the key personnel of the Study;

Comment: highly qualified

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Comment: highly qualified

8. Assessment of the level of risk inherent in the design;

Comment: assessment and mitigation of risks seem reasonable

9. Strength of the Scientific Team supporting the Study;

Comment: good

10. Level of support guaranteed by the Institutes;

Comment: good?

11. Budgeted cost of the Study;

Comment: the budgeted cost seems slightly high compared with other similar proposed studies, but it seems reasonable considering the man power allocated. Is the overhead included in this budget?

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  • Reviewer 12
Grade: 3.0

Title: 533 PHASED ARRAY FEED VS FEED ARRAY FOR ALMA FREQUENCY BANDS

1. Alignment with NA ALMA Partnership strategic goals

The study is aligned.

2. Strength of the scientific case for the proposed ALMA upgrade concept Comment on the relevance to the ‘ALMA 2030’ development documents.

The study is directly relevant to ALMA 2030, item #4. Science case has been presented in the proposal.

3. Quality of the upgrade conceptual design

This is a 1-year study with specific measures of success provided. The measures of success (Section 12.4) clearly state the important questions regarding a PAF implementation. The choice of a comparative study is good and the scope of the study fits the timeline. It’s unclear where the PAF will be placed, but Fig 1a appears to indicate that the PAF will not be placed at the focal plane, since spacing is ~6 times the wavelength (resulting in poor aperture efficiency with that element spacing). The investigators do mention refocusing optics in terms of window truncation and array size, so re-positioning is planned. The proposal mentions that GRASP is not available; perhaps collaboration with another university or institute could provide a useful cross-check. The proposal would benefit from including more details on the type of feed element and refocusing optics that are planned.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development)

The study is aligned with longer-term research.

5. Strength of the consortium organization (if applicable)

6. Qualifications of the key personnel of the Study

Highly qualified

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study

Strong technical experience.

8. Assessment of the level of risk inherent in the design

Risk level is appropriate to study, timeline and scope are realistic.

9. Strength of the Scientific Team supporting the Study

10. Level of support guaranteed by the Institutes

Level of support by institute appears to be directly related to ALMA development study funding

11. Budgeted cost of the Study

Budget is just under $200 k limit.

-- AlWootten - 2017-07-19
Topic revision: r1 - 2017-07-19, AlWootten
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