On 21/02/2018 after beam tuning and pumping down at 18:07 the pressures read Up = 1.2e-5mBar, Down = 3.2e-5mBar. We were happy to power the detectors and try to observe spectra from beam in both the S2 and pin diode.
Whilst waiting for the turbos to spin up the Pin diode was daisy chained with the +ve pulser, +15V, and -15V preamp power cables used with EDI Preamp 2 for the S2.
Channel 3 of the Silena Quad Power Supply was set to -70V ready for the diode.
The S2 bias was ramped to -130.3V, leak current = 1.19uA. The Pin diode bias was ramped to -70V, leak current = 0.01uA.
The preamp power was switched on, +15V read current 0.8A, -15V read current 0.4A, as expected.
The pin diode output was split between an Ortec 571 Amplifier and channel 2 of a Quad TFA.
The unipolar output of the Ortec 571 Amplifier was sent to a Delay Amp 1457. The Delay Amp output was sent to ADC 6 Channel 31.
The Quad TFA output was sent to channel 4 of a Quad CFD. The CFD output was sent to the Lecroy 622 module and setup as an OR with the S2 strips. This OR is sent to the DAQ trigger.
We mounted the preamp box cover. The grounding cable for the ribbon signal cables was attached to the box. We confirmed the grounding of these ribbon cables with a voltmeter.
Now with no beam the DAQ trigger rate ~ 60Hz. This suggests the ~6kHz rate seen before is noise from the previously exposed preamp, note the downstream turbo is very close (a couple centimeters) to this preamp.
To double check the tuning was still ok we sent the 7Li beam to FC-0 = 48pA.
We decided to close the GSI slits located before the quadrupole and slowly open these to their values in eLog entry #14. We closing the left and right slits had no effect on reducing beam current, so we kept these positioned at 5.5mm and 1.5mm respectively. The up slit was already 0.0mm.
Slowly opening the down slit we saw the following:
| GSI Down Slit Position (mm) |
DAQ Trigger Rate (Hz) |
| 0.0 |
60 |
| 0.1 |
110 |
| 0.2 |
180 |
| 0.3 |
250 |
| 0.4 |
250 |
| 0.5 |
380 |
| 0.6 |
450 |
| 0.7 |
550 |
| 0.8 |
675 |
| 0.9 |
750 |
| 1.0 |
850 |
| 1.1 |
925 |
| 1.2 |
850 |
| 1.3 |
1000 |
| 1.4 |
1100 |
| 1.5 |
1100 |
| 1.6 |
1050 |
| 1.7 |
1100 |
| 2.0 |
1300 |
| 2.2 |
1350 |
| 2.5 |
1300 |
| 3.0 |
1300 |
| 3.5 |
1400 |
| 4.0 |
1600 |
| 5.0 |
1600 |
| 5.5 |
1600 |
We saw on the backscattered diode counts at channels 50 -> 400, even when increasing the Ortec 571 Amplifier gain to 1K and the fine gain to maximum.
We checked the faraday cup upstream from the bending magnet, FC-4 = 100pA.
We also checked the faraday cup just upstream from the chamber, FC-0 = 53 pA.
The Ortec 571 Amplifier settings (for pin diode) were:
Fine gain = Max
Course gain = 1K
Shaping time = 0.5us
Input = Neg
BLR AUTO ON
Uni Output taken with Out setting
The Ortec 935 Quad CFD CH4 threshold was = 175mV
At 20:50 we sent 3.0 MeV of 7Li beam onto CH2 930ug/cm2 Target VII. We started the DAQ whilst writing to disk.
The DAQ dead time ~ 3%, Trigger rate ~ 1500 Hz, Event Mult. = 6.2.
The save path and name: /Remote_Objs/RData_1/180221205456
It became apparent within the first 1/2 hour that the trigger rate (1500 Hz) is almost entirely from the pin diode.
At 22:10 we stopped the DAQ data collection, run time = 01:19:46, dead time = 4%, # of Good Events = 7180956.
We checked the current on FC-0 = 53 pA.
The beam voltage ~1.2730 MV.
Checking the detectors: The pin diode voltage = -70V, leak I = 0.00uA. The S2 bias = -130.3V, leak I = 1.46uA. Both detectors were switched off for the night.
At 22:18 the pressures in the chamber are:
TPU1 = 3.4e-6mBar
TPU2 = 7.5e-7mBar
TPD1 = 1.5e-6mBar
TPD2 = 1.8e-6mBar
CHUP = 6.1e-6mBar (also referred to as Up)
CHDW = 1.6e-5mBar (also referred to as Down)
See attached "180221_PinDiode.png" for the pin diode spectrum after the run. In the morning of 22/02/2018 we realised this was just amplified noise.
See attached "180221_S2BackStrip_ADC4CH24.png" for a sample spectrum of one of the S2 back strips
See attached "180221_S2BackStrip_ADC2CH7.png" for a sample spectrum of one of the S2 front strips |