SCUBA noise stability
SCUBA noise stability |
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We recently ran tests to see how long SCUBA takes to settle down after a
liquid nitrogen (LN) fill. During these tests, we noticed that walking on the
Nasmyth platform caused the noise on the SCUBA arrays to increase
significantly (albeit for a short period of time). We thus carried out a
controlled experiment to determine:
- How long it takes for SCUBA to settle after an LN fill.
- Where in the dome are you likely to affect the SCUBA array noise by
walking around.
Figures 1 and 2 show the LW and SW array noise respectively (sampled every 5
minutes) for November 4, 2000. The bottom plot in each figure is simply a
zoom in of the top plot. The orange data points represent the mean array
noise, with a 1-sigma error bar. The green circles give the median noise
level. The blue arrows denote the noisiest and least noisy bolometers for
that measurement. The horizontal lines indicate events that occurred, such as:
- fill: LN fill.
- n_s: 2 people walking on the SCUBA Nasmyth platform.
- mez: 2 people walking on the mezzanine on the way up to the SCUBA Nasmyth platform.
- n_o: 2 people walking on the other Nasmyth platform.
- f_t: 2 people walking on floor the telescope is attached to.
- f_t: 2 people walking on floor the main building is attached to.
- n_s: 2 people walking up and down the stairs up to the SCUBA Nasmyth platform.
- ctrap: 1 person walking gently up to SCUBA and filling the cold trap.
Figure 1: LW array noise measured continually for 3.5
hours after the start of the LN fill on Nov.4,2000.
Figure 2: SW array noise measured continually for 3.5
hours after the start of the LN fill on Nov.4,2000.
There are several things we can conclude about the noise stability of SCUBA
from these data:
- It takes SCUBA up to 20 minutes to recover from an LN fill.
- Walking on the stairs/mezzanine/SCUBA platform can seriously affect the
noise for a short period of time.
- However, one person walking very gently can make it to the SCUBA platform
without the noise level increasing.
- It is thus recommended that people avoid walking on the SCUBA platform
during observing unless absolutely necessary. If someone does need to go to
the platform, only one person should go at a time they should take care to
walk as gently as possible.
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