• Study 540 ALMA Central LO Improvements and Upgrades (Strategic)

• Reviewer 1

Grade: 3.8

Title: ALMA Central LO Improvements and Upgrades (Strategic)

1. Alignment with NA ALMA Partnership strategic goals;

Comment.

The program aligns well with the goals of longer baselines through a study of changes necessary to the current LO system to accommodate the longer baselines.

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

Comment.

The science case behind extended baselines is very strong as is the case for improved LO performance. The case is briefly summarized in the proposal.

3. Quality of the upgrade conceptual design; Comment:

The program will be broken down into stages beginning with a requirements review in the initial stage followed by a review of technical solutions. They will identify candidate technologies for additional investigation. In the testing phase they will make a preliminary test of the identified technical solutions with possible iteration. Overall the programs seems well designed.

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

The result of the program will be a recommendation to ALMA on how to achieve the baseline expansion and performance improvement. They will give a time and cost estimate. Over the longer term when ALMA is prepared to move to longer baselines this study will be important for guiding that development.

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

Comment.

6. Qualifications of the key personnel of the Study;

Comment.

The investigators are very strongly qualified for the study as they have played key roles in the design, construction, test and delivery of the Central LO and Fiber Optic Wraps, LO Photonic Receiver and Front End LO. Aside from this they have an impressive history of accomplishments.

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

Comment.

As above, the personnel have significant technical expertise in the areas needed to implement this program.

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

Comment.

The level of risk described for the study is low. The team is well acquainted with the system.

9. Strength of the Scientific Team supporting the Study;

Comment.

10. Level of support guaranteed by the Institutes;

Comment.

No support provided by institutes.

• Reviewer 2

Review of proposal "ALMA Central LO (CLOA) Improvements and Upgrades"

Proposal index number: 540

Principal Investigator: Christophe Jacques

Cost: $399,123

In-kind contributions: none

Review date: 10 July 2017

Overall score: 3.0 (0.1 best to 9.9 worst)

Proposal Summary The main focus of the study is to enable extension of ALMA baselines by providing for precise LO reference transmission at fiber distances beyond 15 km. Longer baselines is one of four major development paths recommended in the ALMA 2030 Road Map. The science case for this is reviewed in the proposal. A second focus is to improve the coherence and stability of the LOs (independent of baseline length). This should increase the fraction of the time that the telescope is environment-limited, rather than instrumentation-limited. The impact of this is primarily at high observing frequencies (bands 8-10). Finally, a limitation of the current line-length-correction (LLC) system is that it can provide continuous delay correction only over a finite range. That range is occasionally exceeded, forcing a reset and astronomical re-calibration. Extending the range could increase the available on-source time. The investigators believe that these objectives can be achieved mainly by modifications to the Central LO (CLO). The proposal is for an open-ended investigation phase, including consultation with vendors and other research groups, followed by implementation of the modifications found to be most promising and finally testing in the CDL's Central LO Test Set (CLOTS). Although the proposal is vague about what modifications will be most effective, since these are intended to be determined in the first phase, some of the ideas to be investigated are mentioned: • Adapt or replace existing master laser for improved coherence • Use newer techniques for laser synthesis of mm-wavelength signals for improved coherence • Add bi-directional fiber amplifiers to increase signal strength at distant antennas • Increase the range of the fiber stretcher in the LLC unit • Eliminate fiber stretcher and use a different bi-directional line length adjustment mechanism (e.g., air gap) • Increase resolution (16b) and sensitivity of the round-trip phase detector • Increase bandwidth of the phase detector (target of 40 MHz) • Eliminating the length adjustment mechanism and relying instead on open-loop correction, either in real-time by feed-forward to the antenna's LO electronics, or in non-real time by software-applied corrections to the visibility data. Improved coherence in the master laser, amplification to overcome fiber loss, and improved speed and accuracy in the LLC are all needed to support longer baselines. The same improvements will also result in better phase stability on all baselines, where the benefit is mainly at bands 8-10.

• Comments on Details of Proposal

Sec 4, Study Scope. The proposal's vagueness about exactly which improvements will be implemented and how effective they will be makes it difficult to evaluate. This is perhaps unavoidable, but in such a situation it would be valuable to have a way to discontinue the study after the investigation phase. See also comments under Risk Management. Some of the ideas proposed for investigation seem questionable to this reviewer. (a) Increasing the phase detector resolution is useful only if it can be shown that the current resolution is somehow limiting. Even then, in a closed-loop servo, increasing the digital resolution ("16b") does not help any more than simply increasing the gain at the same number of bits. (b) There seems to be no point in increasing the phase detector bandwidth to 40 MHz; the loop bandwidth for the correction is limited to something orders of magnitude smaller by the speed of the correction mechanism (10s of kHz?) and the round-trip delay on the fiber (~10 kHz at 15 km, less for longer distances). (c) Abandoning the closed-loop correction in favor of open-loop methods (whether real-time or not) introduces the difficulty of making the phase detector accurate at all phases. Improving its resolution does not improve its accuracy. In the closed-loop servo, the phase detector needs to be accurate only at one phase (the set point, typically 0 or π/2). (d) Some ideas may be expensive and/or time consuming to implement, including improvements to the master laser's performance and creating of a new method of laser synthesis. These may be too much for the budget to support. Sec 9, Staffing. The PI and one other senior engineer plan to devote 20% and 22% of their time to this project over its 24 month duration, and others will devote smaller fractions. It appears that no person will devote a majority of his time, so there will be no one whose main responsibility is this project. That creates a risk that it will get insufficient attention and not be completed on schedule. The total scheduled effort is 1.32 person-years (PY); this seems adequate for the given scope, but if would be more effective with fewer people and/or shorter duration so that someone could make it his main job. Sec 10, Cost Breakdown. The labor cost seems reasonable to cover 1.32 PY, but the $17,250 for materials and services may be insufficient to do an adequate demonstration in the experimental phase of the project, especially if some of the more expensive options (e.g., new master laser) look promising. Sec 12.5, Risk Management. If the results are disappointing, the only mitigation proposed is to "manage shareholder expectations." Another approach would be to discontinue the study as soon as it becomes apparent that finding affordable solutions is unlikely. There are also other risks, such as that the study budget is insufficient to implement and test approaches that otherwise look promising (and that would be affordable in the context of a telescope upgrade rather than a study), or that there is insufficient time to pursue complicated but otherwise promising ideas. (The latter could be due to resource availability, primarily senior personnel. Resource availability is identified as a risk, but only due to funds not being available when expected.)

Scoring The investigators are exceptionally well qualified to carry out this work since they are the same people who implemented the current CLO. The availability of the CLO Test Set at NRAO-CDL is crucial to the project. For these reasons, it is unlikely that this work could be efficiently carried out anywhere else. The ideas suggested for study are mostly good ones. A successful outcome of this study (or one like it, or a successor) is essential for meeting the scientifically important goal of longer baselines, as identified in the ALMA 2030 Road Map.

For these reasons, a very favorable score near 1.0 seems appropriate. But because of the vagueness about which technical approaches will get the most attention, and risk that good solutions will prove elusive, it may be wise to apply the limited ALMA Development funds to projects that are more ripe for exploitation. Therefore I am degrading my final score to 3.0.

• Reviewer 6

Grade: 0.1

Title Study Proposal 540: ALMA Central LO (CLOA) Improvements and Upgrades

1. Alignment with NA ALMA Partnership strategic goals;

Excellent.

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

Improving ALMA's LO system, the subject of this study, is an essential component of ALMA's future development.

3. Quality of the upgrade conceptual design;

Excellent. The proposal gives a clear account of the problem and a plan to explore solutions.

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);

Work here would follow ALMA fabrication and test protocols and could lay excellent groundwork for actual production, which is a long-term rather than immediate goal here.

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

Experience with ALMA LO system.

6. Qualifications of the key personnel of the Study;

Excellent: team incorporates those most knowledgeable about ALMA LO system, its practical problems, and state of the art in associated technologies.

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

Excellent: unique access to experience and test equipment.

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

Low risk study.

9. Strength of the Scientific Team supporting the Study;

Scientific requirements are well documented in proposal; no team is needed.

10. Level of support guaranteed by the Institutes;

Reasonable.

11. Budgeted cost of the Study;

Reasonable effort estimates and hardware costs.

• Reviewer 11

Grade: 5

Title ALMA Central LO (CLOA) Improvements and Upgrades

1. Alignment with NA ALMA Partnership strategic goals; The primary aims of increasing maximum baselines and visibilities/coherence are in line with the strategic goals of increasing the scientific capability and efficiency of the array (goal 1.3).

2. Strength of the scientific case for the proposed ALMA upgrade concept; The science case is not very explicit, but increasing the maximum baseline length and hence resolution of ALMA will clearly impact a wide range of science by increasing the range of spatial scales over which e.g. galaxies, disks, masers, and solar system objects can be studied. Comment on the relevance to the ‘ALMA 2030’ development documents. Increasing the maximum baseline is one of the explicit goals outlined for ALMA 2030.

3. Quality of the upgrade conceptual design; This proposal is more of a design study rather than development of a specific concept. However, the scope of the proposed study is very well reasoned and the constraints well described.

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 proposal seems to precede a specific upgrade proposal, so is in the longer-term category.

5. Strength of the consortium organization (if applicable); The organization and personnel seem to be the most qualified given their experience developing the current ALMA LO system and intimate familiarity with the existing system

6. Qualifications of the key personnel of the Study; See above

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study; See item 5

8. Assessment of the level of risk inherent in the design; The main risk seems to be that the conclusion of this study is that longer baselines and greater coherence are not practical either technically or financially. The proposal gives estimates for these eventualities, but they don’t seem particularly well justified.

9. Strength of the Scientific Team supporting the Study; Not applicable?

10. Level of support guaranteed by the Institutes; Sufficient

11. Budgeted cost of the Study; Seems a bit arbitrary to fit the available funds, but not unrealistic.

• Reviewer 12

Proposal 540:

- Comment: This proposal aims to improve the ALMA LO performance, investigate the LO coherence over long baselines, which is excellent in line with the ideas of 2030 Pathway "larger bandwidth" and "longer baselines"

- Score: 1

-- AlWootten - 2017-07-18