Lena/Dec 2016
December 2016
BACK/NEXT
12/07/2016
The signal amplitude from the OTS cell seems to be smaller than from the buffer gas cells. I talked to Mike and we are concerned that this might be because of the large field gradients due to the small shell coils. It might be possible that the field is not zero in all parts of the cell.
For this reason I've made a larger Helmholtz coil system. Here is the calibration of the coil system. There is also an anti-helmholtz coil in the Y direction, but it's not connected and not calibrated.
Calibration data
| Direction | B at Imax (240 mA), nT | B at -Imax (-240 mA), nT |
|---|---|---|
| X | 11380 | -10250 |
| Y | 13180 | -11600 |
| Z | 8140 | -9760 |
Coil calibration
| Direction | nT/mA |
|---|---|
| X | 45.06 |
| Y | 51.95 |
| Z | 37.29 |
Shell pinout (left to right)
- orange, yellow = X coil
- green, blue = Y coil
- purple, gray = Z coil
- black, white = thermoresistor
12/09/2016
Tested the polarimeter boards assembled by Alec. Most boards work, there are a few connectivity issues with the ones that don't work. Realigned the magnetometer and verified it works with the new Helmholtz system.
12/12/2016
Found a bug in the FPGA firmware that affected the single channel magnetometer setup in Chamberlain. It prevented chrips from coming out due to a race condition. Making a measurement with the buffer gas cell to verify the new coils work correctly.
Resistor values in the current source in Chamberlain and WIMR are: 50 Ω, 50o Ω, 1 kΩ, 5 kΩ. The values in the chamberlain magnetometer VI have to be multiplied by 2 because of how the circuit is designed.
Buffer gas cell runs
- Run 09
- Noise 0 - magnetic field noise (other two didn't work)
- Run 14 (Rcell = 153 Ω)
- Noise 0 - magnetic field noise (5-10 fT/sqrt(Hz))
- Noise 1 - probe noise (2 fT/sqrt(Hz))
- Noise 2 - technical noise
The data is consistent with the previous measurements in Chamberlain
OTS cell runs
- Run 15 (Rcell = 146.5 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Noise 0 - magnetic field noise
- Noise 1 - probe noise
- Noise 2 - technical noise
The performance is similar to Run 14, the OTS cell seems to have higher bandwidth? This is opposite to what I expected from this cell.
- Run 16 (Rcell = 146.5 Ω, Iprobe = 50 uA/V * 2V * 2ch)
Probe noise is 5 fT/sqrt(Hz)
- Run 17 (Rcell = 146.9 Ω, Iprobe = 50 uA/V * 4V * 2ch), doubled probe power
- Noise 0 - magnetic field noise
- Noise 1 - probe noise
(noise floor increased)
- Run 18 (Rcell = 147.1 Ω, Iprobe = 50 uA/V * 1V * 2ch)
- Noise 0 - magnetic field noise
- Noise 1 - magnetic field noise
- Noise 2 - probe noise (5 fT/sqrt(Hz))
- Noise 3 - technical noise (0.5 fT/sqrt(Hz))
- Run 19 (Rcell = 142.4 Ω - 140.6 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 20 (Rcell = 139.4 Ω - 138.5 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 21 (Rcell = 137.9 Ω - 137.3 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 22 (Rcell = 136.7 Ω - 136.0 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 23 (Rcell = 134.3 Ω - 133.8 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 24 (Rcell = 132.9 Ω - 131.4 Ω, Iprobe = 50 uA/V * 2V * 2ch), disabled FPGA lowpass filter in this and the following runs
- Run 25 (Rcell = 130.5 Ω - 129.7 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 26 (Rcell = 129.0 Ω - 128.2 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 27 (Rcell = 127.7 Ω - 126.9 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 28 (Rcell = 125.6 Ω - 125.1 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 29 (Rcell = 124.5 Ω - 124.0 Ω, Iprobe = 50 uA/V * 2V * 2ch)
- Run 30 (Rcell = 122.6 Ω - 122.0 Ω, Iprobe = 50 uA/V * 2V * 2ch)