The Green Team has been been complaining of excess ~0.5 [Hz] pitch motion of the QUADs for the past few days. We had first chalked this up to the fact that the ISI were not yet at full performance. However, after Sebastien and company got both chambers up to a reasonable performance, and even going so far as to tailor the blend filters to get as much performance at 0.4-0.5 [Hz], the cavity pitch motion was deemed still too high. 

I finally just took a comparison ASD of both chambers and their optics' optical levers, and discovered a giant spike in ISI ITMX at 0.5 [Hz], and a subsequent comb cascading up to higher frequency. The 0.5 [Hz] (and its harmonics -- note that 0.5 [Hz] is *not* the fundamental) spike appears obviously in both the ISI ITMX ST2 GS-13s. Only the 0.5 [Hz] harmomic shows up in the SUS ITMX optical levers -- but it happens to perfectly coincide with the QUAD's first "pitch" mode at 0.5 [Hz]. Awesome.

Given that we've seen similar combs at LLO (and I believe DetChar has confirmed their presence at LHO), which were confirmed to be a result of the BSC-ISI's capacitive position sensor master oscillators beating against each other, I immediately suspect that this is our problem.

In order to confirm, we're going to run the corner BSCs in various configurations of OFF to assess whether the comb disappears, if not at least changes. 

Note: since this is systematic problem seen at both sites, a permanent fix to the problem is in the works (i.e. syncing all chambers to a single, GPS synced, master oscillator). It's just not ready yet.

With the recent cabling work at EY, wanted to record notes of where we're at and inventory. 

Problem Cable

Performed elec short tests on in-vac cables, and found an issue with one:  D1000223 S1104078's pin #1 & #23 (may be able to use a D1000225 in its place)

Screws On Cable Feedthru Connectors Confirmed To Be "Screwed In" All The Way

It has been brought up that a possible source of grounding are the sets of screws on the connector which attaches to a Chamber feedthru.  Through handling sometimes these screws can unscrew, and even a little bit will have them protrude out and short to the Chamber.  I went ahead and applied a torque to all of these connectors for TMS cables.  (attaching a photo of these screws on our 25-pin connetors....with head on shot and profile)

Missing Screws For Attaching To Feedthru

In the table below there is a note of cables which are missing screws which attach cables to the in-vac side of the feed-thru.

Cables Screwed Together & Unfortunate Cable Bracket Attachement

Since we've tested all these cables, I went ahead and screwed all cables together (noting we'll have to unscrew the bad D1000223 at some point).  In our Cable Layout drawing (D1200111), the D1000921 cables for the Picomotor & Beam Diverter are said to be OK with connectors "with or w/o metal ears".  If you do not have metal ears, you sort of make life hard for you in that if you have to look at a cable you can't simply unscrew it from the cable bracket.  You remove access to the Cable set screw, so you have to remove both cables and then disconnect cables---which is a pain.

ICS & Inventory Of Cables

I have made an Assembly Load for the TMS EY Cables (ASSY-D1200111).

Daniel, Alexa, Sheila

We have tried to measure the green modulation depth of the X arm by moving the modulation frequency (24.410610MHz) so that the sidebands are antiresonant in the cavity, and then locking the cavity on the carrier (+polarity on servo board) then the sidebands.  We used H1:ALS-C_COMM_A_LF_OUTPUT to measure the transmitted power.

I have changed the offset to -66 counts, so that with no light on the PD we get zero counts (-0.26 counts)  (someone had changed this from the -61 I originally set to -100 sometime last week, I am not sure why).  With the single shot beam we get 46.06 counts.

Below are plots ot the transmitted powers (normalized) when locked on the carrier and sideband, and the second plot is their ratio.  I used the ratio to do a simple fit for the modulation depth that we started with, and got 0.80  Now the modulation frequency is restored to the nominal 24.407079MHz and the 12dB attenuator is in place so our modulation depth should be 0.2.

Also, the ratio of the transmitted power on resonance/ single shot beam should be:

1/(1-sqrt(R1*R2))^2=22.6 for a perfectly mode matched carrier with R1=0.63, R2=0.99, taking into account the 0.2 modulation depth we would expect 22.17.  Since we curently measure a ratio of 14.4 between the single shot and locked trans power, which is 65% of what we would expect.  This means we have about 45% of our power in higher order modes. 

Daneil's alog about the RF powers is 9484

Writing of 64 second full frames has started on h1fw0.

We were measuring the green modulation depth in EX by looking at the transmitted power when locking the cavity on carrier or sidebands. To make the interpretation easier we first used the ifr to move the sidebands to exactly mid-fringe. With a length of 3994.472 m and a multiple of 650.5 we get a frequency of 24.410610 MHz. The ifr was set to +11 dBm for the measurement.

Here we report the measured RF levels. We used an Agilent N1914A with probe E4412A (S/N MY50270005). A zero check and calibration was performed before the measurement. An attenuator was added at the RF patch panel in the field rack between the balun and the cable driving the Pockels cell. As a comparison we list the attenuation values measured with the RF source at a frequency of 24.407079 MHz as well. We left the 12 dB attenuator installed and switched back to the RF source.

The h1nds0 daqd will be shut down for up to 10 minutes to build RCG 2.8.2 versions of daqd to support longer frames.  Longer frame collection should be implemented about 11:00 PST for h1fw0.  Following about an hour of testing, and assuming testing is successful, longer frame writing will be implemented on h1fw1 about 12:00 PST.  

HAM4 and HAM5 are different compared to HAM236, because of the ST0-L4Cs. Consequently, we need to use the proper blocks for the BIO cards.

The changes have been made (see pic attached), the models recompiled and restarted. Everything went fine.