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Halo Checklist

Things to keep in mind when optimizing halo

It is impossible to provide a single number of paddle counts/triggers per nA that defines good halo conditions. This is because differences in the beam (energy and beam species) as well as the K600 setup (angle, trigger settings, particular fieldsetting) has the effect that good halo looks very different for different experiments. Consider the following:

  • For a 200 MeV proton beam and the K600 at 0 degrees a very good halo count is 50 Hz/nA. These 50 counts are mostly high energy protons, and some of them are inside the PID gate that defines your good events
  • For a 50 MeV 3He beam, looking at tritons in the focal plane, the K600 at zero degrees and using single paddle trigger mode, a good halo count is closer to  150 Hz for 18nA. This may sound good, but consider that with the experimental target in position the countrate just climbs to 180 Hz for 18 nA.  However, other than the case of the 200 MeV proton beam, none of the particles making up the halo rate are tritons.
  • At higher spectrometer angles, and for high energy particles that allows coincidence trigger, you may want almost no trigger at all for the empty target.

Here are some things to check before you start halo tuning. Some of them may seem obvious, but if you are under pressure or tired you will be surprised how many things you forget. Also, if a different experiment was using the dataroom equipment before your experiment, it is worthwhile to check every relevant connection to be sure you know all is right.

1. Is the empty target selected? Does the target system reports that it is actually in the "in" position?

2. Is the CI-scaler pulser off?

3. Are the detectors on?

4. Is the cable from your detectors patched through to the controlroom?

Once you have beam, look at the following:

1. Start a run and see if your trigger rates agrees with that of the operator's ratemeter.

2. Look at the scaler trigger rates, and see how much dead time your DAQ has.

3. Look at PID specrtra (my favorite is pad1-vs-tof) and see if the halo events are to be found inside the region of interest where your particles will be detected. If they are not, and if the rates of the empty target is not limiting your DAQ, then you may have to live with the fact that you have a high empty target rate.


NOTE:

If you do not know where the hardware (referred to above) is located, please ask Ricky Smit or Retief Neveling

Scattering Chamber vacuum checklist: AG11

Previously, we did not have access to the computer control system inside the vault. This meant that a safe and proper procedure needed 2 people: one in the K600 vault, and one at the vacuum controls in AG11. Under these conditions the procedure was as follows:

How to pump down the scattering chamber


For the PERSON in the K600 VAULT:

1) Put the PLUG IN of the roughing pump the LOCAL power SOCKET. Do not switch it on yet!
2) ENSURE that the TURBO and the ROUGHING PUMP are at ATMOSPHERE by taking off the clamp at the roughing pump needle valve (turbo side). Put it back on.
3) SWITCH scattering chamber VALVE (SV-08) FROM REMOTE TO MANUAL that will also open the valve. To do that use a screwdriver.
4) Make sure that the NEEDLE VALVE (hand valve on the roughing pump) is CLOSE.
5) TURN roughing PUMP ON, OPEN HAND VALVE on the pump very slowly (only keep opening when noise is not too loud).
6) KEEP PUMPING until 5-10 mbar.
7) Someone should be in AGII (vacuum remote control room).
8) SWITCH control of SV-08 back to REMOTE which will also close the valve.
9) CLOSE the HAND VALVE/needle valve of the roughing pump.
10) SWITCH POWER for the roughing PUMP FROM the LOCAL TO REMOTE power SOCKET.
11) PERSON in the RC ROOM must open SV-08.
12) PERSON in LAB must slowly open the HAND VALVE on the roughing pump.
13) PERSON in the RC ROOM must SWITCH the TURBO PUMP ON.


For the PERSON in AG11:
(always be in contact with the person in the K600 vault when doing this)

14) OPEN SV-08.
15) OPEN P-34V.
16) After hand valve is open ( step 10) then SWITCH ON P-34.
17)  CHECK the SPEED of the P-34 PUMP on the pump power supply module on leftside (green lights increase with speed).
18) Scatteing chamber pressure will go down but the penning take sometime to start. Wait for a while and don’t worry.
19)  To allow the opening of SV-02 (valve that connects scattering chamber with beamline) the ratio between the two pressures must  <50.

 

How to vent the scattering chamber


For the PERSON in the AGII room:

1) CLOSE SV-02 valve.
2) CLOSE SV-10 valve.
3) CLOSE SV-08 valve.
4) TURN OFF P-34.
5) TURN OFF P-34V.
6) and OPEN (for 1 second) and CLOSE SV-09 valve.


For the PERSON in the K600 VAULT: (only if you are sure that the pumps are off)

7) ATTACH the ARGON bottle to the VENT valve.
8) OPEN the ARGON bottle. (If there is delicate targets inside the flowrate of the argon must be less than 5 litre/min)
9) LOOSEN the CLAMP on the top of the chamber (to prevent overpressurizing the chmaber)
10) WAIT

 vac-control

 

 

Comments on remote control:

OPEN valve are RED

CLOSED valve are GREEN.

Yellow outline OVERRIDDEN or MANUAL



Tel numbers:        

Vacuum remote control in AGII    1200
K600 vault                                   1210
Data room                                    1202
Control room                               1222

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