ELOG CIRCE

AIDA GELINA BRIKEN nToF CRIB ISOLDE CIRCE nTOFCapture DESPEC DTAS EDI_PSA 179Ta CARME StellarModelling DCF K40

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Entry time:

Thu Feb 22 18:04:12 2018

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Yesterday (21st) night we saw this low channel, high rate (1500Hz) noise on the diode spectrum - see eLog entry #15.

This morning the S2 bias was ramped to -130.3V, leak I = 1.43uA. Diode bias ramped to -70.0V, leak I = 0.01uA.

Starting the DAQ with no beam, the trigger rate is ~250 Hz, with most triggers coming from the diode. Inspecting with the oscilloscope we find a very high noise of ~300mV. The amplifier course gain = 1K.

Lowering the course gain to 200 we decided to try sending beam on target VII and check the diode output on the oscilloscope. I was able to see some signals at ~3V, with very low rate ~0.1Hz

I checked the rutherford scattering rate using the Nuclear_Reaction-master.xlsx excel file, sheet &quot;Rutherford Scattering&quot; columns BH and BP. See attached.

With the current collimator radius = 0.5mm, at our scattering angle 152 degrees, we find an expected rate 2.72e-3 particles per second.

We decided to remove the diode collimator, for the 10X10mm diode this would give an expected rate 0.272 particles per second. This is still not ideal, and before the next shifts we should optimise the position of the diode to improve the rates. This is for a beam current ~40pA, so we would benefit from higher beam current too. A rate of 5 - 10 particles per second would be nice. For now we stuck with the current situation.

At 10:52 the S2 and diode biases were switched off. The preamp power was also switched off. The turbos were also switched off. By 11:48 I saw the turbos had stopped spinning and started venting the chamber.

Once the chamber was vented we managed to remove the central lid without needing to remove the S2 preamp box on the downstream lid.

The 1mm diameter collimator was removed from the diode, this completely destroyed the 0.9um mylar in the process. Next shifts we will use a metal plate to glue the mylar in place, avoiding this issue. For now we left no mylar in front of the diode, because this will not be useful until running 7Be beam.

We also decided to remount the alpha source, allowing us to check the diode is functioning as expected. The target ladder configuration is as follows:

<table border="1" cellpadding="1" cellspacing="1" style="width:500px">
	<tbody>
		<tr>
			<td>Position</td>
			<td>Target</td>
		</tr>
		<tr>
			<td>1</td>
			<td>Blank 3mm</td>
		</tr>
		<tr>
			<td>2</td>
			<td>No Target</td>
		</tr>
		<tr>
			<td>3</td>
			<td>CH2 VII</td>
		</tr>
		<tr>
			<td>4</td>
			<td>CH2 III</td>
		</tr>
		<tr>
			<td>5</td>
			<td>CH2 VI</td>
		</tr>
		<tr>
			<td>6</td>
			<td>No Target</td>
		</tr>
		<tr>
			<td>7</td>
			<td>Alpha source facing upstream</td>
		</tr>
	</tbody>
</table>

After removing the diode collimator the central lid was remounted and at 12:50 the roughing pumps started. At 13:12 the turbos were started.

By 13:53 the pressures read CHUP = 1.2e-5mBar and CHDW = 3.3e-5mBar.

We switched on the preamp power. The S2 bias was ramped to V = -130.3V, leak I = 1.25uA. The diode bias was ramped to -70.0V, leak I = 0.01uA.

The target ladder was moved to position 7 (5.019mm), centering the alpha source in the beam axis and pointing upstream.

We were able to see the two highest intensity alpha peaks in the pin diode spectrum (ADC6 CH31) - so the diode is certainly working

At 14:06 we started an alpha calibration run for the pin diode.We collected data for a preset time 900 seconds. The trigger rate ~80Hz, Event Mult. = 3.0, dead time = 0%.

The save name is: /Remote_Objs/RData_1/180222141134

See attachment PinDiode_AlphaSpectra.jpg for a sample spectrum

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The Ortec 871 Amplifier Settings were:

Fine gain = Max

Course gain = 50

Shaping time = 0.5us

BLR Auto On

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The Delay Amp 1457 settings were:

Delay: 1us

Range: 10V

Polarity: Pos

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At 14:21 the DAQ stopped, # good events = 61406.

Now we were ready to proceed with a beam measurement.

The target ladder was moved to position 3, 65.000mm, target: CH2 930ug/cm2 VII

We still see some alphas from the source, these are 5.1-&gt;5.5MeV, and from the kinematics we expect the beam scatters to be ~2.9MeV so there should be no overlap in energy.

I disconnected the pulser from the pin diode (it was set to too high an amplitude to appear on the alpha spectrum) and switched it ON for the S2 front strips. The pulser rate was changed from 10Hz to 2Hz. (Set to 10Hz when diagnosing pin diode)

With no beam trigger rate ~85Hz, event mult. ~ 8.0

We checked the beam at FC-E0, just upstream from chamber, = 45pA

We bombarded CH2 VII with 3.0MeV 7Li beam, trigger rate ~700Hz.

The pin diode rate for backscattered beam was very low, but we do see some counts at channel ~1300, which is expected.

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We decided to run for 1 hour and see the rates.

15:00 DAQ started for 3.0MeV 7Li on CH2 930 ug/cm2 target VII

Save file: Remote_Objs/RData_1/180222150540

Trigger rate ~ 550Hz, Event Mult. ~ 6.2, dead time ~4%

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Note: from previous tuning and running yesterday (21st) I estimate beam has already bombarded target VII for ~3 hours before starting this run.

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At run time = 01:01:09 we have the following areas:

ADC 6 CH31 (pin diode) area between channels 1159-&gt;1268 = 285

ADC 4 CH24 (S2 back strip) total area = 7353

ADC 2 CH 3 (front S2 strip) total area = 21647 (2Hz pulser connected)

Ratio of back strip to diode = 76.0

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We decided to collect data until 20:00 giving us ~5 hours of data at 3.0MeV.

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At DAQ runtime = 03:03:09 we have the following areas:

ADC 6 CH31 (pin diode) area between channels 1159-&gt;1268 = 911

ADC 4 CH24 (S2 back strip) total area = 66704

ADC 2 CH 3 (front S2 strip) total area = 22335 (2Hz pulser connected)

ADC 2 CH 7 (front S2 strip) total area = 22734 (2Hz pulser connected) - more statistics than ADC2 channel 3, continued monitoring this channel instead of channel 3

Ratio of back strip to diode = 73.2

Ratio of last ~2 hours runtime = 71.0, so target is degrading

&nbsp;

At 19:25 we decided to go to dinner and leave the setup to collect data.

At this time CHUP = 5.4e-6mBar, CHDW = 1.4e-5mBar. S2 bias = -130.3V, leak I = 1.71uA. Diode bias = -70.1V, leak I = 0.00uA.

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At 20:50 we returned from dinner. The DAQ was manually stopped.

DAQ monitor:

Run time = 05:49:09

Event mult. = 6.2

Dead time =7%

# good events = 34296773