The ring heater was turned on today to check whether running the ring heater had an effect on the vacuum pressure. 15W of power was put through each segment of the ring heater at 19:07:30 UTC until 19:37:08 UTC (by adding an offset of 25,000 counts to H2TCSETMY _EMTY_RING_HTR_SEG1_DC_I_SET and H2TCSETMY_ETMY_RING_HTR_SEG2_DC_I_SET), which is close to the maximum ouput of the ring heater. The vacuum in BSC6 was not affected by running the ring heater, which is good.
I added in gains to the ring heater input and readout channels so that the we can input the current in amps and readout the voltage and ring current on volts and amps instead of counts (reffering to D1002529 for the required conversion factors).
Just a note, the temperature sensors are in fact broken on these ring heater segments, the attached image shows the signals railed for the sensors.
I measured the TMS ISC table angular and lateral stability when the end station VEA was quiet last night.
I found the table displacement to be around 5-10 um rms laterally and 1-3 urad rms in angle over 100s. The motion thus appears to be within the requirements: 100 um and 1 urad, respectively.
These are the close loop plots of the same measurements.
As Keita noted, the HEPA-off curves show a large bump at around 100mHz which which goes above spectra with the HEPA on. It's not clear why.
I've aligned the Hartmann plate onto the conjugate image plane of the ETM. This was done by yawing the ETM periodically (excitation of H2:SUS-ETMY_M0_TEST_Y_EXC at 0.25Hz and 200 counts) and measuring the amount of motion of the beam spot on the CCD with the Hartmann plate removed. Using DTT I obtained a transfer function of spot movement on the CCD over the yaw in the ETM (H2:TCS-HWS_ETMY_ITMM_CENTER_X/H2:SUS-ETMY_L1_WIT_YMON). I moved the lens F1 along the beam path to find the position where the transfer function was zero, at which point the HWS CCD is at the image plane of the ETM. Attached is a graph of the transfer function versus the position of F1.
The HWS was then moved back 11mm (see second attachment) so that the Hartmann plate rather than the CCD is located at the ETM image plane. The Hartmann plate has been reattached. The next step is to look at the quiescent prism and defocus of the beam on the HWS.
Starting last thursday, 5th July, the backups of h2boot by the disk-to-disk backup server cdsfs1 causes a significant slowdown of all H2 front end EPICS systems. It is most noticable on MEDM screens, where the refresh rate drops to several seconds. Once the backup is completed (after about 15 minutes) the systems immediately recover. I am unable to reproduce the error on H1 or on the DTS test stand. I'll reboot h2boot at the next opportunity as part of the investigation. No significant change to the h2boot file system occured late last week (most of us were on vacation).
For now the backup of h2boot's perioicity has been reduced from every 4 hours to daily at 05:41 until the problem can be resolved.
35W beam. The ISS gain was changed from -2.1 to 7dB which seemed to quiet the noise at high frequencies.
Thomas V. Mark D.(Apollo) John W. Gerardo M. We have finished installing the enclosures for ITMY and ETMY. During installation, ETMY was misaligned and I mistakenly re-aligned to the reaction mass ghost beam, will fix to reflect off the ETM. ITMY is fully operational, some internal focusing of the telescope may need to take place since the beam diameter is approximately 8 mm, spec calls for 2-3 mm. However, it is up to the commissioners of the OAT whether or not this adjustment is worth doing. Deviations from design: 1) Due to the tightness between the ITMY transmitter pier and the viewport, we were only able to get the viewport protector in between them and couple the enclosure to the protector via sheet metal and tape. 2) It was also pretty tight between the viewport protector and the enclosure on the ETMY receiver pier, we were not able to fit a full sized bellow to couple the connection between the two. We ended up cutting the bellow to a smaller size and using that. Also, we adjusted the level of the receiver pier in order to not have the enclosure touch the beam tube (the corner of the enclosure was butting up against the side before).
Editorial note:
I assume this entry refers to the enclosures around the optical lever beams for ITMY and ETMY, though nowhere in the entry is the term 'optical lever' (or any of its derivatives) found. This makes the entry rather abstruse, and it also means that if one searched the log for optical levers, oplevs, optlevs, etc, one would not find this record.
Technical note:
If the design calls for the beam size to be adjusted to be 2-3 mm (radius? diameter?) on the detector, it should be adjusted to that. The optical lever isn't really considered to be installed until that is true.
For the evening shift, we set out to check the VCO calibration, and get some new calibrated spectra. This work starts where entry 3400 left off...
After relocking the cavity we found that he SR560 path (which was described in 3400 as having a gain of 10 at the SR560, and another gain of 10 at the TTIF) saturated due to low frequency motion (below 1Hz). With a gain of 1 on the SR560 it worked, and the 2 signal paths (SR560 and FMON) showed essentially perfect coherence. This also showed that the FMON calibration is not -20dB at DC and 20dB at HF, but rather 0dB at DC and 40dB at HF (see comment to 3400). With this direct measurement of FMON in hand, we removed the SR560 path.
Discussions with Bram brought out a missing factor of 2 in my previous calculation: since the PLL is in the 1064nm output of the laser, and we are using the 532 for locking, we get twice as much frequency change in the light seen by the cavity as the light seen by the PLL. (The same result can be achieved by ignoring the fact that green light is used at all, such that the conversion from frequency to length becomes L_cavity / f_laser = 3995m 1064e-9m / 3e8m/s = 14.2pm/Hz.)
In summary:
614pm/count using VCO, which is awesome. 0.8nm/count using OSEM, which is 30% off of the above.
Yet people keep saying that OSEM calibration should be fine at 20% level.
For people outside of the ISC:
1. Frequency offset between the refcav in the corner station lab and the EY ALS red beam is kept at the VCO frequency by a PLL loop.
2. Transfer function from VCO frequency to the red laser frequency is equal to G_PLL/(1+G_PLL) where G_PLL is the OLTF of PLL. Since UGF of G_PLL is about 20kHz, this is almost equal to 1 for f<1 kHz or so.
3. Electronics transfer function from VCO tuning input to the frequency of the VCO was measured to be H_VCO=139kHz/Volt *pole(1.6Hz)*zero(40Hz).
4. The green laser is the second harmonic of the red, therefore the transfer function from VCO tuning input to the green frequency is 2*H_VCO.
5. To lock the laser to the arm, we control the frequency of the green laser by feeding PDH signal via CM board back to VCO tuning input.
6. When the laser is locked to the arm, VCO input is equal to
v= (1+G_PDH)/G_PDH / (2*H_VCO) * df
where G_PDH is the OLTF of PDH loop and df is the equivalent frequency fluctuatoin of the cavity length, refcav and pll loop noise combined.
Since UGF of G_PDH UGF is 8kHz or so, again (1+G_PDH)/G_PDH is almost 1 for f<1kHz or so, therefore
v ~ df/(2*V_VCO)
7. Frequency to length conversion is 4000m/ 563.5THz (green light).
8. PDH CM board output is connected to PDH FMON channel, which has the transfer function of 2^15 counts/10 volt * zero(10, 10)*pole(100, 100).
Therefore, all in all, VCO input measured by FMON is calibrated back to length using
dL = FMON / (2^15 cts/10 V) *pole(10;10) * zero(100, 100) * 2*H_VCO * 4000m/563.5THz
= 602 pm/cts * FMON *pole(1.6;10;10) * zero(40;100;100).
Small difference in number (Matt's is 614 pm/V) came from the fact that I used 2^15/10 cts/Volt for ADC while Matt used the ADC calibration he did with his table top diode box as an amplifier.
Attached are plots of dust counts > .5 microns in particles per cubic foot.
The H1 workstations in the control room now have a controls account. Use caution, the controls account is the same home directory for H1 and H2, but the environment will be set up for H1 on the H1 workstations and H2 for the H2 workstations. So, even though the controls account looks the same on H2 and H1 workstations, you cannot do H2 work on an H1 workstation, or H1 work on an H2 workstation. Confused? The H1 workstations are labeled as such with a tag on the upper left corner of the display. The background of the controls account screen will no longer indicate it is "H2".
HSTS MC1 has been moved to the testing bench and cabled to the test stand. The offsets and gains have been entered into the MEDM screens and the OSEMs have been positioned to 50% light. We will recheck and adjust the 50% light positions in the morning, if necessary. This suspension should be ready for Phase 1 testing. M1 BOSEMs T1 S/N 578 OL = 25960.0 Offset = -12980 Gain = 1.156 T2 S/N 436 OL = 29277.9 Offset = -14639 Gain = 1.025 T3 S/N 440 OL = 27858.1 Offset = -13929 Gain = 1.077 LF S/N 433 OL = 27758.7 Offset = -13879 Gain = 1.081 RT S/N 424 OL = 24529.4 Offset = -12265 Gain = 1.223 SD S/N 658 OL = 25139.5 Offset = -12570 Gain = 1.193 M2 AOSEM UL S/N 453 OL = 27359.6 Offset = -13680 Gain = 1.097 LL S/N 320 OL = 24780.7 Offset = -12390 Gain = 1.211 UR S/N 228 OL = 25117.9 Offset = -12559 Gain = 1.194 LR S/N 438 OL = 25521.6 Offset = -12761 Gain = 1.175 M3 AOSEM UL S/N 227 OL = 28354.2 Offset = -14177 Gain = 1.058 LL S/N 353 OL = 26509.5 Offset = -13255 Gain = 1.132 UR S/N 276 OL = 27920.9 Offset = -13960 Gain = 1.074 LR S/N 299 OL = 28435.2 Offset = -14218 Gain = 1.055
The login scripts have been modified for the controls account to allow use of the account for either H1 or H2. This should have minimal impact on H2 users. Let me know if there are problems with the environment for controls.
Jim & Greg adjusted the level of the HAM3 ISI Table using HEPI Springs. It was a little slower than expected. We are ready for IAS to take another look before we continue with the HEPI Actuator installation.
As of around 4pm, sounds like the Gate Valve (GV18) will be opened tonight for OAT work.
I started the evening shift with calibration of the VCO + Frequency divider used for the ALS PLL (S1200570 and S1000748). The objective was to measure the response of the VCO output to its Tune input, which is used for locking the arm cavity and thus provides a good calibration point for the arm cavity signal.
I set up the DC calibration measurement with a signal generator (output displayed on a scope to be sure), and a frequency counter. I took 6 samples between -1V and 1V, which resulted in an excellent linear relationship: f = 39.6MHz + 139 kHz/V * V_tune. For example, at V_tune = 1V, I measured f = 39.739 MHz. This is not the expected result of 50kHz/V given the nominal 100kHz/V from the VCO and the division by 2 which takes us from 80MHz to 40MHz.
From there I moved on to measure the AC response. I did this by rigging up a frequency to voltage converter with some bubble gum and duct tape I found nearby. The output of the converter was 725mV / V_tune. With the help of an SR785 and a lot of patience I turned this into a response measurment between 0.5Hz and 10kHz. I saved the curves on the SR785 floppy, which is a lot like throwing them into a black hole, so I also wrote down a few points: {-30.7dB, 178dg} at high frequency, {-27.7dB, 138dg} at 40Hz, {-16.8dB 112dg} at 8Hz, {-5.8dB, 136dg} at 1.6Hz and {-3.26dB, 136dg} at 5.62Hz. These are well fit by the measured DC response and the expected 1.6Hz pole and 40Hz zero.
Lastly, in preparation for using this calibration for the arm cavity, I cabled up an SR560 to the IR_PWR_MON channel. The SR560 is AC coupled with a gain of 10, and the tabletop interface gain is set to 10. From the output of the SR560 to counts of IR_PWR_MON, I measured 32060 counts/V. Just to be sure, I checked the gain of the SR560 and appears to be very close to the stated value of 10, so we should expect 320.6 counts/mV refered to the SR560 input, which is attached to V_tune. Assuming the above VCO calibration is correct, this converts to 0.434Hz/count as seen at IR_PWR_MON. The cavity should lock should convert length to frequency as L_cavity / f_laser = 3995m / 5.635e14Hz = 7.09 pm/Hz, so we will be left with 3.07pm/count as our length calibration. (To relate this to the number found with the OSEMS in 3363, we should remove the gain of the SR560, the TTIF box, and another factor of 10 for the FMON signal filtering. This would give 3nm/count instead of the 1nm/count found with the BOSEMS, so somewhere we're missing a factor of 3, not unlike the 139kHz/V vs. 50kHz/V discrepence... to be investigated tomorrow in the light of day.)
On a side note: I found the PLL unlocked and no beatnote evident. On closer inspection there was no light coming from the fiber, so I went to the optics lab and found the laser in Standby. I have no idea why it would be left in this state, since this clearly makes cavity work impossible. That should have been enough to make me leave it as I found it, but instead I turned it back on and relocked the reference cavity. From the trend data, it looks like it unlocked about 15 hours ago (at 16:20 UTC, see figure).
A harder look at the VCO schematic lead Keita and I to believe that 139kHz/V is plausible. Also, the FMON path has a DC gain of 0dB and gain at HF of 40dB (2 zeros at 10s, 2 poles at 100Hz), so the relation to the OSEM calibration in entry 3363 is 0.3nm/count from the VCO calibration (above) vs. 0.8nm/count from from OSEMs. Still a factor of ~3 is missing.
