• Proposal 538 A Quantitative Analysis of Expanded ALMA Long Baseline Capabilities

• Reviewer 6

Grade: 9

Title: A Quantitative Analysis of Expanded ALMA Long Baseline Capabilities

1. Alignment with NA ALMA Partnership strategic goals;

Investigating aspects of long-baseline expansion is within ALMA strategic goals.

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

Expanding ALMA baseline lengths is within the ALMA 2030 recommendations for study.

3. Quality of the upgrade conceptual design;

The quality of the proposed study is low. Extensive numerical simulations are not the first step here, as many questions the study poses can be answered with far simpler calculations that establish whether detailed calculations are even warranted. Realistic array layout calculations would need to incorporate topographical information, but the proposal does not adequately discuss how this information might be obtained, what infrastructure and other considerations would play into antenna location, or other material that might determine actual station locations.

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 types of calculations proposed would be important in a detailed design study of an ALMA with extended baselines, but it it premature at this stage. A much simpler and less costly study to determine basic limits and constraints is a necessary precursor to the proposed study.

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

Fine.

6. Qualifications of the key personnel of the Study;

Fine.

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

Ok.

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

The risk is high that the project will either conclude quickly with simple results, or that the project if carried out will not result in information that is only of general, but not detailed design, use for an ALMA expansion. Both of these carry high cost/benefit risks that are not properly discussed in the proposal.

9. Strength of the Scientific Team supporting the Study;

Ok.

10. Level of support guaranteed by the Institutes;

Limited. The proposal is for > 1 FTE total to make the study.

11. Budgeted cost of the Study;

Effort is not adequately supported by the plan of work. 0.5+ FTE per year must be justified. Proposed cloud computing services is a major cost, but it appears to be ballpark estimate rather than a firm cost.

• Reviewer 8

Proposal # 538: A Quantitative Analysis of Expanded ALMA Long Baseline Capabilities

PI: Nyland

This proposal concerns a study of the scientific and technical expectations of an expanded ALMA array. The improvements would increase the baseline coverage by a factor of 2-3. The proposed work would involve conducting simulations involving antenna number and location to probe the best configuration(s) for scientific results. Image fidelity and sensitivity will be examined on a quantitative level. The science drivers are investigations of massive black holes, protoplanetary disks, solar system objects, and evolved stars. A factor of 2-3 in spatial resolution would be useful for studies of protoplanetary disks, Kuiper belt objects, and evolved stars. It’s not clear that the expansion would be that important for investigating black holes, where extremely high spatial resolution (micro arcseconds) is required to examine GR effects. However, the expected increase in angular resolution is only a small factor relative to the current capabilities of ALMA. The data that is emerging from ALMA currently is clearly insightful and in some cases overwhelming. It would seem more prudent to spend time and effort at this stage to exploit the current facility, especially as more receiver bands become available, than to put energy into a future upgrade that is going to be costly with only a modest gain in scientific output.

Grade: 8

• Reviewer 9

Grade: 7

Title: A Quantitative Analysis of Expanded ALMA Long Baseline Capabilities

1. Alignment with NA ALMA Partnership strategic goals;

This proposal addresses the quantification of the far-future benefit of increased baseline length, thereby improving the capability for ALMA (strategic goal 1).

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

The proposal is well aligned with the ALMA 2030 goal of longer baselines.

Several good science examples are provided where a factor of 2-3 in angular resolution would make an improvement. However, the ALMA 2030 goal of “enabling qualitatively new science” is not clearly made for any of them. For instance, in how many systems can ALMA currently resolve a 5AU-radius protoplanetary disk (i.e., angular resolution of ~2.5AU), as compared to the number with 2x or 3x the baseline length?

3. Quality of the upgrade conceptual design;

In this case, the upgrade is a study of the scientific potential of longer baselines. Specifically, the investigation would use existing simulation tools suitable for ALMA and make multiple simulated images using high performance computing systems. The key image metrics to be compares are image fidelity (which was not defined numerically but certainly could be), sensitivity (both with and without the addition of 6 new long baseline ALMA antennas), and dynamic range.

The study is worthwhile for understanding ALMA’s potential with longer baselines, but the proposal does not make a good case for the maturity of the work to be done. The proposal did not make clear whether the outcome would include definitive siting recommendations or merely explore some candidates; it did not make clear how the metrics would be used to advance one particular implementation, nor how the science cases would be used to change the relative influence of the metrics.

The proposal did not address atmospheric phase correction. Over the longest baselines, this may be the greatest challenge, requiring real-time in-situ water vapor radiometry. The proposal did not present that the sensitivity can be adequately addressed without including this as a variable.

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 effort requires only extant tools and computer time, and hence could be fully carried out now; the actual implementation is a very long-term effort.

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

Being from NRAO, the applications should be well connected with ALMA’s long-term needs.

6. Qualifications of the key personnel of the Study;

The individuals involved are expert in the development of such simulations.

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

None.

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

The only risk, that compute costs might grow but that they have already been factored in, is therefore not a risk. How about the risk that the job takes too long for

9. Strength of the Scientific Team supporting the Study;

The proposal does not adequately address how to weigh various science projects against others in the context of their metric assessment, not whether the science projects are the right set. The proposal does not convincingly show that the science team is the right one for this job.

10. Level of support guaranteed by the Institutes;

Modest.

11. Budgeted cost of the Study;

No comment.

• Reviewer 12

Proposal 538:

- Comment: This proposal aims to provide a quantitative study of the expanded ALMA long baseline capabilities. High spatial resolution mapping is the main driver of the ALMA science. Investigating the capabilities of expansion of the long baselines by a factor of 2-3 could bring out new science possibilities.

- Score: 2

-- AlWootten - 2017-07-18