1. The ALMA Front End John C. Webber National Radio Astronomy Observatory, Charlottesville VA 22903, USA

2. URSI Boulder 20082 ALMA Front End Organization Work is done by: –The National Radio Astronomy Observatory (NRAO, USA) –The European Southern Observatory (ESO, Germany) –The National Astronomical Observatory of Japan (NAOJ, Japan) –The Herzberg Institute for Astrophysics (HIA, Canada) –The Institut de Radioastronomie Millimétrique (IRAM, France and Spain) –The Netherlands Research School For Astronomy (NOVA, The Netherlands) –Onsala Space Observatory (OSO, Sweden) –Rutherford Appleton Laboratory (RAL, UK) –The Centro Astronomico de Yebes (CAY, Spain) –The University of Cambridge / Astrophysics (CA, UK) –The Academia Sinica (Taiwan)

3. URSI Boulder 20083 Front End Key Design Goals Noise performance as good as the best mm and sub-mm receivers Single sideband systems when possible, to minimize noise from the image sideband (all except Bands 9 & 10) Beam pointing controlled by mechanical tolerances (except Bands 3 & 4, which have mirrors on top of the cryostat) No moving parts except for cryogenics and amplitude calibration loads Short-term phase stability good enough for >90% coherence at 950 GHz Long-term phase stability good enough to go 30 minutes without instrumental calibration Ambient and heated RF loads for amplitude calibration WVR for atmospheric phase calibration by radiometry Rapid switching between bands for atmospheric phase calibration by position switching on a 10-second time scale

4. URSI Boulder 20084 Front End Key Programmatic Challenges Build 70 complete FE assemblies (66 on antennas plus 4 spares) and 3 more sets of spare subassemblies on time and on budget Distribute the work to multiple groups around the world and have everything play together when integrated

5. URSI Boulder 20085 Typical results for Bands 3, 6, 7, and 9. Bands 4, 8, and 10 are in development (dashed lines). The horizontal lines are the specification which applies over 80% of the band. Above 600 GHz, mixers are DSB.

6. URSI Boulder 20086 Front End Wiring Diagram POWER M&C OFFSET LO REF IF OUT OPTICAL LO REF

7. URSI Boulder 20087 3D Model of Front End Assembly

8. URSI Boulder 20088 Front End Assembly Bottom View

9. URSI Boulder 20089 Cryostats Cryostat is 1 meter in diameter, mass ~450 kg Sumitomo 3-stage refrigerator cools below 4K Internal clamp rings provide thermal contact to cold stages Cryostat and prototype chassis mounted on tilt table

10. URSI Boulder 200810 Optics 1.Optics design concept completed: All ALMA Bands 1-10 and WVR pick off mirror have been designed and incorporated into cartridge designs Detailed designs of all windows and IR filters Widget space containing: amplitude calibration device ¼ wave plate holder for Band 7 Solar filter 2.Design verification: Complete physical optics calculations made for bands 3-10 Prototypes tested warm except for bands 5 & 10 Cold tests: done during testing of assembly Tests on the sky at 5000m elevation to begin before the end of 2008

11. URSI Boulder 200811 Cartridge 7 Block Diagram Cold Cartridge Warm Cartridge

12. URSI Boulder 200812 Cold Cartridges Bands 3 (84-116 GHz), 6 (211-275 GHz), 7 (275-373 GHz), and 9 (602-720 GHz) SIS mixer receivers

13. URSI Boulder 200813 Cold Cartridges Band 4, 125-169 GHz (qualification model) Band 8, 385-500 GHz (4K stage in test dewar)

14. URSI Boulder 200814 Front End Local Oscillators Warm Cartridge Assemblies (WCA) –Contain YIG-Tuned Oscillator, Phase Lock Loop, Active Multiplier Chain, and output Power Amplifiers –Locked to output of photomixer driven by photonic signal from Back End –Phase and amplitude noise meet ALMA specifications –Band 3 WCA drives SIS mixer directly –For other bands, WCAs drive cold frequency multipliers mounted in cold cartridge Frequency Multipliers –Wideband varistor designs from Virginia Diodes, Inc. –Designs final for Bands 4, 6, 7, and 9 –Band 8 and 10 prototypes being tested

15. URSI Boulder 200815 183 GHz Water Vapor Radiometer Development status –Two prototype WVRs (Cambridge and Onsala) were completed and fully tested –Extensive testing was carried out at the SMA –Final design is a single channel, Dicke- switched radiometer –First production unit is under test and will be delivered in mid-2008 Dicke switched WVR RF Front End

16. URSI Boulder 200816 Ambient/Hot Load Amplitude Calibration Device

17. URSI Boulder 200817 Integration of Front End Warm Optics Band 3 Cartridge Band 6 Cartridge Band 9 Cartridge Band 7 Cartridge Cryostat Front end chassis Front end IF FE M&C unit Warm Cartridge Assembly Band 3 (1 st LO, Bias, M&C) Warm Cartridge Assembly Band 6 (1 st LO, Bias, M&C) Warm Cartridge Assembly Band 7 (1 st LO, Bias, M&C) Warm Cartridge Assembly Band 9 (1 st LO, Bias, M&C) FE Assembly

18. URSI Boulder 200818 Assembly and Test The first FE assembly rear view with side panels removed (minus the LO Photonic Receiver)

19. URSI Boulder 200819 Principal Test Requirements Noise temperature Image rejection Beam patterns Amplitude stability Phase stability IF output power Gain flatness Gain compression Polarization alignment Vacuum compatibility Electromagnetic compatibility

20. URSI Boulder 200820 Schedule FE#01 –Assembled and tested at the North American integration center (Charlottesville, Virginia) –Delivered as an engineering model without phase stability measurements (waiting for photonic reference test module) –Installed on a Mitsubishi antenna in November 2008 FE#02 –Assembled and tested at the East Asian integration center (Academica Sinica, Taiwan) –Delivered as an engineering model without phase stability measurements (waiting for photonic reference test module) FE#03 –Assembled and under test at the European integration center (Rutherford Appleton Laboratory, England) –Will be delivered in February 2009 as an engineering model without phase stability measurements (waiting for photonic reference test module)

21. URSI Boulder 200821 Schedule FE#04-06 –One each to be assembled and tested at the three integration centers –Qualification and verification of integration center equipment and procedures –Delivery as fully qualified units June-August 2009 FE #07-70 – To be delivered over the period October 2009-October 2012 – Output rate of each integration center: one every 51 days!