System

The ALMA system deals with many aspects of ALMA. We expect to revisit many of these areas in the future. We summarize below our recommendations on the issues addressed at this meeting.

1.

The main array should consist of a number of 4 to 6 sub-arrays, but the number of frequencies operating simultaneously will not exceed 3 or 4. At present we could envision 4+1 subarrays. Namely:

(a)

The main interferometric subarray

(b)

Antennas for reconfiguration and baseline determination

(c)

Two subarrays to simultaneously carry out two of the following functions:

• Secondary subarray at second frequency band
• Transient event monitoring
• mm-wave VLBI
• Testing, repair, receiver warm-up or cool-down, etc.

(d)

The single-dish subarray or an ultra-compact array (if included in the final project).

2.

The prototype antennas should be equipped with nutators and stable receivers. The number of ALMA antennas equipped for total power measurements (nutators) should be 4, but this number will be reconsidered after the tests with the prototype antennas. If feasible, the rest of the array antennas should be equipped with receivers of good gain stability ( $\Delta G/G = 10^{-4}$ in 1 second). (See also section 3 and 6).

3.

Due to its scientific interest (Appendix G), the option of the Band 1 receivers has to be kept. The costs of including this band need more detailed evaluation (See also section 3).

4.

A detailed calibration plan, including polarization issues and phase calibration, needs to be elaborated.

5.

Doppler tracking will be needed to provide accurate frequency calibrated data.

6.

Polarization observations in total power mode with ALMA will impose requirements on the system that deserve a detailed study.