gerardo.moreno@LIGO.ORG - posted 15:47, Friday 08 August 2014 (13292)
Pumping HAM3 Annulus
Start time 11:00 am.
Pressure as of 1:46 pm 2.0 x 10-5 torr at the aux cart.
Start time 11:00 am.
Pressure as of 1:46 pm 2.0 x 10-5 torr at the aux cart.
Start time was 10:30 am.
Current pressure as of 1:45 pm 1.3 x 10-5 torr.
Morning Shift Notes 916 - Nathan beginning work in the OSB laser lab 920 - Rai to EX to work on experimental setup 929 - Gerardo moving pump cart from GV-5 to BSC1 for annulus pumping 945 - Kyle verifying picomotors off at EX, preparing to begin pumping 1004 - Kiwamu, Alexa doing projection work at HAM2 (WP 4782) 1008 - Fil and Manny working on cabling at EX 1129 - Bubba craning pelican case with test mass from West Bay to High Bay 1129 - Fred with small tour in LVEA 1202 - Projection work on IMC complete for now
Found cdswiki to be locked up and dead, console showed no display. Rebooted.
With the closing of most of the chambers recently, we are in a state where we can relieve Alarm Levels on some Dust Monitors (note: HAM6 is still open & we have exposed parts in the West Bay Test Stand area). At any rate, I went through Dust Monitors 1, 2, & 3 & raised their alarm levels (on the order of 10^2 counts for 0.3 & 0.5um). Could do this for other Dust Monitors which are away from clean hardware.
I notified Jeff Bartlett about this. Will chat with Calum about whether we want to establish long term values for these levels when we are all buttoned up.
Took a quick look at the FSS MEDM screen and noticed that the RFPD DC value was fluctuating wildly. Pulled up the filter for this channel and saw that the 2 Hz low-pass filter was not engaged and that the gain value was set to 1.000. The 2 Hz low pass filter is now engaged, as it should be, and the gain value was set to 0.150 which gives readings consistent with those obtained with a digital multimeter plugged into the DC output of the RFPD.
no restarts reported
Alexa, Dan, Koji, Sheila, Stefan, Kiwamu,
Today we spent some more time on alignment of the IMC with the use of the WFSs loops. After some struggling, we eventually could close all the loops stably. However, the ASC loops tend to drift on a time scale of 30 min.
In parallel to it, we made a first attempt of the ring down measurement. The data did not make sense this time. Ongoing.
IMC alignment:
Our original hope was that once the WFSs were centered, they should be able to servo the IMC to a good alignment. However, it turned out that stably engaging the ASC loops were very difficult for some reason. The first issue we noticed was that the MC2 trans QPD did not show a reasonable signal. It looked all noise and indeed changing the whitening settings did not change the shape of the noise. This indicated some issues in the analog circuits. Stefan and Sheila went to the rack and found that a number of cables were unplugged. Also, they found that the whitening electronics were turned off. So they plugged the cables back to the whitening box and powered up the whitening box. This recovered signals on the MC2 trans QPD. This then allowed us to close the 'DOF3' loop which is the centering servo for the MC2 QPD.
However, we were still having a difficulty in closing the rest of two loops in the IMC ASC. They use the signals derived from the WFSs. The symptom is that the error signal looked too big even though the loops are closed. It looked as if the loop is not suppressing the signals. Acutually, keep running the ASC loops made the power buildup and visibility worse on a time scale of 30 sec or so. We made sure that the dark offsets were successfully removed and centering on these WFSs were fine. But, no success.
After people left, I did some more investigation on the ASC loops. Since I did not like the beam shape in the reflection camera, I went to the table and checked out the beam. I found that there was a ghost beam not being dumped and going into the WFSs. I narrowed the aparture of the iris that was infront of the REFL RFPD such that it catches the ghost beam. Then I digitally removed the dark offset from all the WFS segments and tried closing the ASC loops again. The loops stayed stable for approximately 10 min. However then it started degrading. See the attached. I am not sure why, but I am worried about RFAM. I am leaving the ASC loops running for the night to see the long term stability.
Ring down measurements:
We also spent some time trying to measure the cavity decay time (storage time) in order to estimate losses in the cavity. We tried various ways of shutting the control or light off, but ended up with switching the polarity of the fast signal in the IMC board. This is the same technique as Livingston did recently (LLO 13748). We were expecting to see something like 17 usec 1/e decay time, but the measurement tended to give us about 35 usec which is twice bigger than the expectation. At this point, it is unclear why the decay time is such long. The attached is a picture of the raw data displaced on an oscilloscope. The PD is Thorlabs, PDA100A on the IOT2L table. The bandwidh is 2.4 MHz according to the data sheet which should be fast enough for this measurement.
It maybe independent, but we know that this transmitted light is largely clipped (seemingly more than 20% of its total intensity) somewhere in chamber before it comes out to the IOT2L table. So we are interested in repeating this measurement at a different port. Maybe at REFL or IOT2R. The measurement is therefore ongoing.
This is just for record purpose:
The attached is a trend from the last night.
You can see that the alignment degrades on a time scale of ~ 2 hours. Every time it hit the lower threshold of the ASC trigger, the alignment was forced to be back to the starting point due to the 'clear history' operation in the ASC loops.
G. Moreno, K. Ryan, J. Worden, R. Weiss A preliminary report of the procedure is given here, a more thorough report will be made once the post injection charge measurements have made. We introduced both positive and negative ions of N2 into the ETMY chamber. The input gas was boil off from liquid nitrogen which was additionally passed through a liquid nitrogen trap before entering the ionizer. The conditions in the ionizer: pressure on the needles 210 to 303 torr, pressure after the apertures was a maximum 45 torr when the chamber was at 42 torr. We stopped the process after the ionizer had become too cold to be comfortable with a elastomer O ring at the needles. (We should have a second heat exchanger to warm the gas back to room temperature before entering the ionizer to avoid the cooling.) The various times: start to stop of the ion injection 29 minutes, roughing pump down time after the injection to reach 1 torr about 3 hours, pressure now 3.5 x 10^-7 torr after 5 hours of turbo pumping. A disappointment of the procedure was that we were never able to achieve equal injection of positive and negative ions, the sampled ion current was: i+ = 4 x 10^-9 ampere, i- = -1 x 10^-9 amps. The injected currents are about 100 times larger. It requires tuning of the pressure on the needles and the flow rate to achieve equal positive and negative currents. If the total gas flow is too large one cannot get to the proper tuning. This was the case today. RW made a mistake in fully opening the gate valve between the chamber and the ionizer before tuning the system in an auxiliary flow to a pump and then gently transferring the flow between the pump and the chamber. There is a reasonable chance that enough ions did enter the chamber to neutralize the etmy. The success or failure should be known shortly after the morning meeting. If the neutralization has failed we could try again today. The times are shorter than estimated.
J. Kissel, K. Venkateswara After gathering a "first light" performance measurement of the H1 EX Beam Rotation Sensor (see first attachment -- the system is at air, poorly thermal shielded, and auto collimator is not well-secured to structure), we've spent nost of the day characterizing the separation between suspension point and center of mass, or "d". The goal is to have this separation be as small as possible, to maximize the rejection of translation noise. We're running one final 1 [mHz] data point over night to confirm, but we believe the C.o.M. is currently 20+/-4 [um] above the suspension point. We think we should be able to get this down to 2 [um], with an overall mass adjustment, which we'll do tomorrow. The second attachment shows the process -- drive the platform at X [mHz], measure the ASD, and since we do not change the amplitude of excitation, this is a direct map of the Beam Tilt / Ground Tilt transfer function. In reality, we make a fit to a sine wave to gather the amplitude with more precision and to have an uncertainty estimate. The first page shows a single measurement to demonstrate our signal is well above the noise floor, the second shows the collection of measurements in the form of an ASD, and the final page shows the modeled transfer function against our measurement points.
Turned off purge air at X-End station. Metal vent/purge valve is closed.
Rai was able to inject ionized gas into the YEND station chambers today. It took about 15 minutes to reach 42 torr where we ended the experiment.
The chamber is roughing down again and will transition to turbo this afternoon.
Pirani gauge plot attached.
Y-End is now on turbo, CC is ON, pressure is at 1.34x10-06 torr.
Cooling lines open for the turbo.
It actually took 29 minutes to get to 42 torr, faster than I had calculated.
The LVEA pumpdown has stalled at 10^-4 torr. There are many possible suspects with vented annuli on 8 chambers, and many new viewports and electrical feedthroughs. We will be busy restoring these systems in the upcoming weeks and probably spraying helium.
Day's Activities
(Borja)
Several issues has not allowed me to drive the ETMY ESD until late afternoon today. At this point I was able for the first time to test, with real data, the automation code for the ESD charge measurements develped at Livingston. I did have previously adapted it for Hanford's slightly different configuration but this was the first time I was able to test its results. Unfortunately the automation on the injection, data request and analysis is not robust, not allowing for the whole process to finish several times. Also the code does not take into consideration conversion factors on the V BIAS from Voltage to counts and viceversa. I assume this is taken care in Livingston outside of the code but certainly that solution does not make it universal.
Looking at the procedure with Rai I realized that we have to be careful on the level of the driving signal amplitude to be below the minimum V BIAS used in the analysis otherwise linear approximation assumptions in the methodology are no longer valid.
Rai is leaving on Saturday and we need to apply his discharging technique before then (optimally tomorrow). Before this takes place we need to have some ESD charge measurement data so that we can compare with data taken after the discharge and see the effects observed. This time constrains has made me decide to do the measurements manually tonight. I may be able to run the automation code afterwards and compare it tomorrow with the manual measurements but this may not be possible. See manual measurements in the attached document.
We are going to use the manual measurements as a basis for comparison before and after the discharge procedure
which we hope to do today.
I cannot comment on the automation program but urge several things:
1) The absolute value of the bias voltage needs to be greater than the absolute control voltage.
2) The phase and amplitude of the motion needs to be used.
3) The linearization routines should NOT be used.
If these simple considerations are observed the algebra to fit for a charge dependent force
coefficient is straightforward and linear.
Vbias + Vcharge = deflection angle*a where a is an unimportant constant
The feeling of the LLO charging people is "Yes!" to all these points. Regarding the automation scripts, it *should* be a simple matter of setting up the desired biases and measurement parameters and hitting go. The scripts take the measurement in exactly the same way one would if doing the measurement manually, with all the amplitudes and bias offsets user-configurable and the signals are injected directly at the individual ESD quadrants (i.e. not through any linearization).
There is an important point which although I did not mention explicitly in the aLog entry is highlighted in the document attached to it. This is that the excitation driving each of the 4 quadrants provided a good SNR (of between 4 and 15 depending on the BIAS Voltage) of the oplev deflection values at the injection frequency with the exception of the LL quadrant which only showed noise (evidenced by the random values of the measurement points in magnitude and phase and by the low coherence of the between the excitation and the oplev deflection at the injection frequency). This issue, I have found, has a long and complex history which I will deal with in another aLog entry on the 9th August. I have also added to this comment the plots of the measurement results, an updated version of the measurements pdf and a table with final values of slope and Veff for each measured quadrant.
| UL | UR | LR | |
| Veff PITCH [urad] | 122 | 52 | 123 |
| PITCH slope [V] | 2.6e-7 | 1.9e-7 | -2.65e-7 |
| Veff YAW [urad] | 125 | 103 | 144 |
| YAW slope [V] | -2.2e-7 | 2.34e-7 | 2.3e-7 |
