MANUAL

1. THE SETUP OF THE DETECTOR AND THE RELATED MODULES

The SEETRAM measures the secondary-electron emission induced by a relativistic heavy-ion beam passing through a thin aluminum foil. It is composed of three foils that are mounted on rings. The outer foils and their supporting aluminum rings form the detector housing. The inner foil is supported by a teflon ring and insulated against other parts of the detector. The detector housing has holes drilled in, so that the detector is evacuated to the same degree than the chamber (chamber name: TS1DK5). The outer foils are kept on +80Volts so that the electrons leaving the middle foil are driven there. The corresponding current is measured with a very sensitive charge integrator that is directly connected to the middle foil. The detectors device name in the beam diagnostics software (SD-Anwahlprogramm) is "T S1 DI 4SP".

The Bias Supply and the charge integrator (called Current Digitizer CD1010) are both placed in a NIM frame near to the detector at the FRS target. The CD1010 is composed of different stages, see Figure 1. First the current is converted to a voltage (I/U converter input stage). This analogue voltage signal can be seen at the "monitor output" of the CD1010 and it is transferred to the FRS control room. The next stage of the CD1010 is a filter and then follows a voltage to frequency converter (U/F converter stage), which produces the "digitized output" signal. This signal is also transferred to the FRS control room. The sensitivity of the CD1010 is remote-controlled from the FRS control room. It ranges from e = 10^-4 to 10^-10Ampere full scale. The full scale current produces 1V at the monitor output and 10KHz at the digitized output, that means: 1 count corresponds to a charge of q = e /10⁴ Coulomb.

In the FRS control room, the monitor signal from the CD1010 can be put on an oscilloscope (1MW input). The digitized output (+2.5V at 50W ) is sent to the Level adapter LA8000. The NIM output of LA8000 is distributed to Scaler CS4800, QUAD counter and to HKR.

Figure 1. A schematic view of the current digitiser. It consists of several stages: Firstly, the input current is transformed into a voltage. The fast analogue output of this signal can be used as a monitor for measuring the extraction profile. In the second stage, the signal passes two filters with time constants of 0.1 s and 1 s. The analogue output of the filtered signal is also available. Finally, the signal is digitised.

2. HOW TO MEASURE THE BEAM CURRENT

First, switch the sensitivity e at the remote control to a value e = 10^-5 or so. This prevents the electronics from overloads during the moving of the feedthrough. Remember: SEETRAM is a huge condenser microphone coupled to a sensitive current integrator! Then use the SD-Anwahlprogramm to move the detector in the measure position. Switch the remote control to the desired sensitivity. To change the SEETRAM sensitivity you have to use the NODAL programme:

1) load the programme NODAL (from the terminal XWNCI, go to DIENST and there choose NODAL)
2) on terminal 3 will appear prompt, type "run INTMON"
3) choose the detector type (3)
4) choose the SEETRAM name (3)
5) choose the virtual accelerator (8 or 9)
6) choose 20 to check
7) choose 22 to change the SEETRAM sensitivity. You will see a change in the SEETRAM sensitivity only after asking for the beam.

SEETRAM sensitivity should be changed when number of counts in the SEETRAM are above 10 kHz.

FAST EXTRACTION:
The SEETRAM detector can only be calibrated in slow extraction. However, it can also be applied in fast extraction to determine the beam intensity. In this case, a filter with a time constant in the order of 1 s has to be inserted between the detector and the input of the current digitizer in order to prevent that the first stage of the current digitizer saturates.
The time structure cannot be seen, but the integration of the secondary electron charge should work.

SLOW EXTRACTION:
You can see the time structure of the extracted beam when you look at the monitor signal. You get the integral of the corresponding current on the scaler which is fed with the digitized output.

Before moving the detector out of the beam, protect the electronics by switching the remote control to a sensitivity e = 10^-5.

3. HOW TO CALIBRATE THE SEETRAM

The SEETRAM calibration factor can be obtained from theory with the use of the Brohm’s programme SEETRAM. In order to obtain accurate calibration factor one should perform the calibration measurement of SEETRAM during the experiment, as described below. In the case of the heaviest projectiles, the operational ranges of SEETRAM and the scintillator SC01 overlaps, and the calibration can be performed with the use of scintillator only. For lighter projectiles, the ionisation chamber IC01 should be also used.

The experimental set-up is shown in Figure 2.

Figure 2. Experimental set-up at S0 for the SEETRAM calibration. The detailed overview of electronics between the digital output of the CD1010 and scaler, and CFD and scaler is shown in Figures 2a and 2b.

The calibration procedure is the following:

Put the beam dump at S2 in.

Switch the SEETRAM sensitivity to a value of 10^-5 or so in order to prevent the electronics from overloads during the moving of the feed through.

Put the SEETRAM in the measuring position and switch to the sensitivity corresponding to the beam intensity.

Centre the beam using the current grids.

Reduce the intensity of the beam until you see no spill structure in the SEETRAM monitor.

Put the HV on scintillator SC01 and ionisation chamber IC01 at S0.

Put the SC01 and IC01 in the beam line:

Position of Stroke (TS2DI1_P) ----> IN

Position of SC01 (TS2DI1_S) ---> 0.0 mm

7. Put the lowest SEETRAM sensitivity 10^-10.

8. Put the clock at 10 Hz.

9. Check the threshold of the SC01's CFD:

-Check with the oscilloscope the analog signal of SC01 that has to be of the order of 1V. If this is not the case you can increase/decrease the HV of the PM by steps of 100 V until the amplitude is of 1 V. Also check for damages of the scintillator SC01 by changing the position of the SC01 and checking the shape of the analog signals on the oscilloscope.

-Connect the output of the CFD to an oscilloscope. Increase the threshold of the CFD until the signal in the oscilloscope disappears completely. Check the value of this maximum threshold with a voltmeter. This value of the threshold corresponds to the full amplitude of the signal. The optimum threshold for our purpose is a threshold situated at 1/3 of the analog signal, that is, 1/3 of the maximum threshold.

10. Check with the oscilloscope:

- If the current branches from SEETRAM and IC01 are giving the signals.

- If the particle branch from IC01 is giving signals in the ADC and in the counter. (Amplification of the main amplifier and threshold of the TSCA should be carefully set. TSCA should see all particles).

11. Send TSCA to trigger, and put the gate on ADC for IC01 particle counting.

12. Check that the signals can be displayed by the online analysis.

13. Check that there is a positive offset in the SEETRAM.

14. Go to the Main Control Room (HKR) and ask to the operators for different intensities. Start with the intensity of around 10⁶ particles/spill and decrease it in steps of 30 %. In order not to overload the Current Digitiser of the SEETRAM, when the counting rate in SEETRAM is of the order of 10⁴ particles/s change the sensitivity of Current Digitiser (the same is for the IC01). In the HKR you can see only the number of SEETRAM counts per spill at the target area of the FRS so you need someone in the FRS that tells you the number of counts per spill in SC01 and/or IC01 that can be seen in the scaler. As example, for 1 A GeV ²⁰⁸Pb beam around 10000 ions per Spill in the SC01 correspond to approximately 30 counts in the SEETRAM.

How to obtain the SEETRAM calibration factors from the above described measurement is explained here.

	Figure 2a. Electronics between the digital output of Current Digitiser CD1010 and the Scaler CS4800.
	Figure 2b. Electronics between the CFD and the Scaler CS4800.

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