(ALG meeting, March 9^th, Leiden)

Implementation paths for options of

Japanese contributions to "Enhanced ALMA"

1.Introduction

Japanese LMSA project has been proposed with special emphasis on the scientific performance of the array at submillimeter wavelengths with a collecting area and spatial resolution comparable to fifty 10m antennas and 10km maximum baseline, respectively. Large FX correlator system with very high spectral capability has also been considered as a key device in the project.

The ALMA Liaison Group (ALG) had three face-to-face meetings in Grenoble, Tokyo, and Leiden in order to produce and evaluate options for Japanese contributions which would lead to the enhanced Aracama large milllimeter/submillimeter array (hereafter E-ALMA) referred to the Resolution signed in 12 November 1999. The implementation paths and their priorities are proposed for Japanese contributions to the E-ALMA project considering the best compatibility between the baseline ALMA project and the LMSA project.

The Japanese contributions are classified into two parts; 1)participation to the baseline ALMA project, and 2)enhancements to the baseline ALMA project. The ALMA Liaison Group(ALG) has investigated and evaluated their scientific benifit and technical importance in order to prepare a report to the ACC and NAOJ.

In the following, priorities are shown as A: high, B: medium, C: low).

2.Participation to the baseline ALMA project

1.1 One third of 12m antenna elements (priority: A)

Japanese group will accelerate the design and cost estimate of 12 m antenna to be compared with the US/Europe prototype antennas. Japanese antennas will be designed with a special emphasis on the performances in submillimeter wavelengths. The antenna design should not necessarily be the same, but plug-in compatiblity with US/Europe antennas is highly recommended.

European, Japanese and US groups will exchange the necessary information to coordinate the design effort of the production antennas to make their antennas as compatible as possible.

Japanese group will examine the Interface Control Document and will propose necessary modifications and/or additions as soon as possible.

Japanese group will design the antenna transporter to contribute one of three transporters.

The ALG will determine the optimum number of antennas to be shared between Japan and US/European groups.

7.1 10km configuration (priority: A)

Japanese group will estimate the cost for the 10km configuration including antenna pads, electric power transmission, signal transmission, access road.

3.1 SIS junction effort (priority: A)

Japanese contribution to the junction fabrication is absolutely necessary to guarantee a stable supply of junctions in order to achieve a reliable operation of the telescope system. A plan of sharing the frequency range should be determined.

3.1 Fabrication of selected receiver frequency bands (priority: A)

Japanese receiver group has already been participating in the ALMA phase 1 activities by providing a design for the band #8(385-500GHz). The effort could be extended to the band #10(787-950GHz). Japanese group will accelerate the design and cost estimate of the modules for those frequency bands. The ALG has tacit understanding that each group will provide the receiver modules for all antennas.

3.1 Cryogenics effort (priority: B)

Japanese group will develop a reliable cryogenic system under the collaboration with Japanese industries. The reliability of the cyogenics will be evaluated with the actual experiences in the ASTE project.

3.1 Photonic reference system (priority: A)

Japaese group is developing a high frequency photodiodes in collaboration with NTT. The Japaense baseline plan is producing a photonic reference siganal up to 300GHz. All photonic option is also within the scope of the Japanese development and should be recommended.

If a photonic calibration system is proved to be very effective, Japanese group will also participate in the joint develoment.

4.1 High speed sampler (priority: A)

Japaenese group is developing a high speed sampler in collaboration with OKI. These is a possibility of Japan - Europe collaboration in this area.

3.Enhancements to the baseline ALMA project

3.1 Increase the total number of 12m antennas (priority: A)

The total number of antennas in the E-ALMA could be between 64 and 96, possibly around 75. The number should be optimized based on the scientific rationale as well as the impact to the total cost.

The same argument as in 1.1 could be also applied here.

4.1 Ultra Compact Array (UCA) with smaller antennas (priority: B)

European, Japanese and US groups recognize the importance of the small array of smaller antennas to fill the gap in short spacings and will study of the design and cost estimate of UCA jointly.

Considering the higher cost for a small number of antennas, the ALG would give each smaller antennas the same value as a 12m antenna.

Due to the limited man power, Japanese group set a lower priority in supplying the UCA than adding 12m antennas.

5.1 More digital bandwidth (priority: C)

Technology for tera-bit data link is already existing in Japan and there is a possibility of Japanese contribution in this area. Japanese group will estimate the cost of enhanced link system if US/Europe group consider this valuable contribution.

3.1 Next generation correlator (priority: A)

Europe and Japanese groups will try to find a scheme of joint effort in the development of the next generation correlator system.

In order to define the joint development program, the basic correlator architecture (i.e. FX vs XF) should be agreed.

The reliability of a large scale digital system is also very important for the stable operation at the very high site. The expertise of Japanese correlator designer could be integrated in the design and development efforts.

5.1 Large computer system for data archiving and mining (priority: C)

Although the shortage in Japanese man power will limit the software development, there will be a possibility of Japanese contribution in introducing a large computer system.

(Masato Ishiguro)