[[Continuum/NIKA2/Main|Back to the NIKA2 main page]] = Cryostat intervention (June 2-4, 2025) = According to the decisions taken during the April 11th meeting (see the minutes [[https://publicwiki.iram.es/NextIntervention202506|here]]), the next intervention aims to replace the array 2/box C LNA. It is provided to do that on June 3rd. == Participants == Alessandro, Martino, Dave == Overall schedule == * '''End of May: NIKA2 warm-up''' OK, done. * '''June 2nd''': Alessandro, Martino & Dave arrive to the telescope. OK, done. * '''June 3rd''': Start working Opened the cryostat from the back without moving it. A bit tight but feasible. Replaced the amplifier YL022 (probably faulty) with the official spare YL026 that was already at the telescope. After checking the connector we conclude it is pretty robust, well done and pity to cut the wire so we decide to bet on the fact that the problem was INSIDE the amplifier. Also our theory is based on the behaviour of the YL022 in past cooldowns. Not just OPEN/CLOSE, also doing strange things (high current) at intermediate temperature. In any case we have replaced, then verified that it was working (using Dave's portable VNA). We then close the cryostat but have a leak on the OR, open/close again and the leak is gone after tightening the screws in the back. The cooldown started at 18h. Goal of this cooldown is to check if the problem was really in the amplifier of the C box. Left: 4K BEFORE the change (YL022 ampli). Right: 4K AFTER the change. PLEASE NOTE THAT THE SECOND PICTURE WAS TAKEN BEFORE CONNECTING THE IN/OUT. THIS IS THE REASON OF THE HANGING CABLES. THEY HAVE THEN BE CONNECTED BEFORE CLOSING DOWN BUT WE DID NOT TAKE THE PICTURE. [[attachment:IMG_6926.jpg|{{attachment:IMG_6926.jpg|BEFORE the change|height=600}}|target="_blank"]] [[attachment:IMG_6939.jpg|{{attachment:IMG_6939.jpg|AFTER the change|height=600}}|target="_blank"]] VNA Scan with -40dB attenuation on input after replacement. [[attachment:IMG_6931.jpg|{{attachment:IMG_6931.jpg|VNA scan with -40dB attenuation on input|height=600}}|target="_blank"]] * '''June 4th (daytime)''': Reserved as a backup. Martino goes TWICE to Pico Veleta in one afternoon. * '''Monday 9th (daytime)''': Cryostat COLD, first tests. The amplifier seems to be working but not well with the parameters suggested by Yebes. When I started I had a noise of 10Hz/sqrt5Hz) on box C that was pretty scary. But then I play a bit with the parameters to find a reasonable configuration. The gain is in any case lower than all the others. For example compared to box B the ADC level, for the same parameters, is 45% versus 67% of the box B. It is no more than 3dB difference but still it's the lowest. There was a reason why I had chosen these four amplifiers, probably they were the best. [[attachment:boxCampli.jpg|{{attachment:boxCampli.jpg|Parameters amplifiers for box C|height=150}}|target="_blank"]] FIGURE. A reasonable set of parameters for the amplifier of box C (not necessarily the best, enough to have a noise comparable to other lines). [[attachment:boxBpower.jpg|{{attachment:boxBpower.jpg|Power ADC box B|height=150}}|target="_blank"]] [[attachment:boxCpower.jpg|{{attachment:boxCpower.jpg|Power ADC box C|height=150}}|target="_blank"]] FIGURE. Comparison of powers on ADC for the same excitation parameters. The difference can be nulled by reducing by 3-4dB the attenuation on output, meaning that the gain difference of the amplifiers is around 3-4dB. [[attachment:boxB.jpg|{{attachment:boxB.jpg|Noise box B|height=400}}|target="_blank"]] [[attachment:boxC.jpg|{{attachment:boxC.jpg|Noise box C|height=400}}|target="_blank"]] FIGURE. Noise measured on box B versus box C. I don't see a huge difference, but this will have to be confirmed on the maps. [[attachment:Reso2mm.jpg|{{attachment:Reso2mm.jpg|Resonances array 2 balayage|height=400}}|target="_blank"]] FIGURE. Balayage resonances array 2. The four lines look OK. Number of bad pixels in monitor is 6/578. It is around 10/950 for Array 1 and 20/1000 for Array 3. [[attachment:Array1.jpg|{{attachment:Array1.jpg|Noise Array 1|height=400}}|target="_blank"]] [[attachment:Array3.jpg|{{attachment:Array3.jpg|Noise Array 3|height=400}}|target="_blank"]] FIGURE. Noise on Arrays 1 & 3. Bad pixels around 10/950 on A1 and around 20/1000 on A3. Very good for the tuning etc. '''CONCLUSIONS: the most important thing is that WE CONFIRM THE PROBLEM WAS IN THE AMPLIFIER OF BOX C. Then, very important we confirm that NIKA2+ is FULLY FUNCTIONAL. But the spare amplifier is a bit less good and the real noise in the maps will have to checked.'''