Introduction to the use of the H4 beam

Last update (19/05/2010)

 

 The control of your beam line  is done with the graphical user interface CESAR . And for that it's essential to know its basic commands

 

 

 

Summary:

• The Main Parameters
• The Layout of the H4 beam
• Different optic modes of H4
• Experimental areas in H4
• Beam File Actions
• Monitoring of beam
• Fine Steering and Focussing of the Beam
• Beam Intensity and Momentum Spread
• The type of particles in your beam
• Access to your zone
• Using detectors in your beam

   

 

The H4 beam is a secondary particle beam that provides hadrons, electrons or muons of energies between 10 and 360 GeV/c, as well as 400 GeV/c (primary) protons . The H4 beam is a part of the SPS North Area (EHN1, building 887). This note gives a short introduction to the basic elements of the H4 beam. For more detailed information the users are referred to one of the Experimental Area liaison physicists.

 

1.    The Layout of the H4 beam

 (See also the North Area layout)

 A 400 (450) GeV/c primary proton beam is extracted from the SPS towards the North Areas, split into three beams of which one is directed onto the T2 primary target . The proton intensity incident on this target is decided by the SPS coordinator and typical intensities of this primary beam are a few 10¹² protons per burst.

For proper operation of the beams the symmetry on the T2 target should be at least 80%, with a small "a" indicating that the angular asymmetry is included in the value displayed. This number as well as the T2 intensity can be read from the so-called 'PAGE-1' TV screens in the electronics huts and control rooms (explanations are available here).

 

From the T2 target and thanks to the T2 Wobbling station, two secondary beams are derived: the H2 and H4 beams to EHN1. The momentum, production angles and polarities of the two beams are strongly correlated.

For example:

o       The "democratic" wobbling or standard condition centres the beam between H2 and H4 on the TAX and the two beam lines get the same momentum 150 GeV/c with opposite sign at a production angle of 0 mrad.

o       Alternatively, both beams can run with tertiary particles derived from neutral secondary of any low to medium momentum (e.g. e+ or e- from γ conversion or π- from Λ and Ks_o decay at a difference of production angles = 9.04 mrad

e.g. H2 at +4.52 mrad, H4 at -4.52 mrad (see The "Multipurpose" wobbling - Electrons ).

o       Another very often used wobble scheme is to turn B1T and B2T off, such that the 0 mrad production angle is pointing towards H4, which allows providing high electron intensity there. H4 is delivered with charged particles by using B3T.

Any of these "front-end" changes of the beams should be done by an Experimental Area liaison physicist or a CCC operator and only during working hours.  

2. Different optic modes of H4

There are four distinct modes of operating the H4 beam:

            1) The high resolution mode

            2) The high transmission mode

            3) The "filter" mode optics (test beam mode the most often used )

            4) As a heavy ion beam (not discussed in this note)

 

3. Experimental areas in H4

Like in all other beams in EHN1, we distinguish experimental areas and test zones. For the moment we have only test activities which takes place in the test zones:

• H4A (H4-134) using  barracks (HNA343 & HNA348)
• H4B (H4-154) using barrack (HNA???)
• H4C (H4-164) using barracks (HNA903 & HNA909)

in all of these zones the beam height from the ground is: 2060mm

 

4. Beam File Actions

see detailed explanations given in the Cesar manual

5. Monitoring of beam

It is wise to check that the equipment has responded correctly to the requested changes or are still in a good state:

• by verifying on the Status/Magnet & Collimator Status Panel that the currents (positions) Read correspond within tolerances to the currents (positions) in BeamRef. An equipment out of tolerance is displayed in red, otherwise in black. Tolerable deviations are usually 0.3 Amps for magnets and 0.2 mm for collimators.
• In case of few problems, try to re do individually  the setting
• In case of many problems, try once more to load the file.
• If the problem still persists, call the CCC operator (over the intercom - or by phone 77500. The liaison physicist can do nothing for you in this case!

For electron beams it is important that:

• The Gamma to Electron lead CONVERTER01 is IN and the lead absorber OUT. Two ways to do it:
  • Status/Mode Analysis and check on the  Actual Values line
  • Status/General Status

6. Fine Steering and Focussing of the Beam

 

BENDs Steering of a beam is done by BENDing magnets (dipoles). Normally the currents in the dipole magnets are defined correctly in the beam files and the user should not modify them without discussing with the EA physicists.

QUADs Quadrupoles are like lenses in conventional optics, they are used to (de-)focus the beam and thus change the spot size of the beam. The spot size of the beam is controlled by the last QUADs in front of each experiment. Which quad controls what projection depends on the beam file used. In the beam files these quads are usually defined to minimise the spot size at the main experiment locations.

TRIMs Trim magnet are correction dipoles, used for fine steering of the beam. Normally the last TRIMs upstream of each experiment should only be used for steering. Typical values for

    - TRIM5 Horizontal position (0.009 ^. p Amps / mm )

        Positive current in Trim-5 sends the beam towards the Saleve, i.e. negative on MWPC 5.

    - TRIM6 Vertical position (0.009 ^. p Amps / mm )  

        Positive current in Trim-6 sends the beam up, i.e. positive on MWPC 6.

    where p is the momentum in GeV/c. 

The currents in these magnets can be set via the Status/Magnet Status panel.

Reminder: These changes are not saved in the file (except the BeamRefs file for the present status)!  See Cesar manual/BeamRefs-->SelectedFile

7. Beam Intensity and Momentum Spread

 

The beam intensity is normally controlled by three collimators, namely:

• C1  (filter mode)                 Horizantal Acceptance
• or C2 (HR and HT mode)               - " -
• C3                                        Momentum defining (vertical),
• C6                                        Vertical Acceptance .

The collimator C3 defines the momentum bite of the particles transported to your detector. The momentum bite delta p/p is proportional to the opening of the collimator. A gap of 3 mm gives a delta p/p of approximately 0.1%.

Decreasing the opening of C1 or C2 and C6 results in a (non-linear) reduction of rate. It is not related to the momentum band of the beam. The collimators are controlled by:

Note that depending on momentum bite requirements it may be more advantageous to close C3 than C1/2, 6, or conversely, to open C1/2, 6 rather than C3.

8. The type of particles in your beam

 

Electrons from converted gammas produced at xx mrad (depending on T2 Wobbling):

• Load relevant file (adapted to the correct production angle but independently of the selected momentum)

• Move the Electron lead CONVERTER01 to the IN position

• Move the ABSORBER01 to the EMPTY position

• Remove all the scintillators from the beam

Hadrons from decay of lambdas and kaons produced at xx mrad (depending on T2 Wobbling):

• These can be obtained with the same target station 'wobbling' as for electrons from photon conversion and are mainly pi- from Lambda and Ks^o decay.

• Move the Electron lead CONVERTER01 to the OUT position

• Load relevant file (adapted to the correct production angle but independently of the selected momentum)

• Move the ABSORBER02 to the 5mm position. It will absorbs electrons in the beam

• Open up collimators to get enough rate and specially if you used the same files than the electrons files

Secondary pions and protons

• Load relevant file (adapted to the correct production angle, which is different for each momentum)

• Move the Electron lead CONVERTER01 to the OUT position

• You can kill the electrons with the ABSORBER01 (8mm of lead)  if necessary....?

Muons

• Displace C8 & C9 out of axis (e.g. 38mm, 40mm) and asymmetrically to get rid of everything else except the muons. In this case the muon momentum  is only selected in the horizontal with B8 & B9. If the momentum selection is not sufficient, one can close the C6 and open collimators upstream to get higher flux.

9. Access to your zone

 

Frequently you will need access to your zone in order to modify, adjust, move or repair your apparatus. This is done through the command Access/Access Command. see detailed explanations given in the Cesar manual

10. Using detectors in your beam

 

The H4 beam is equipped with various detectors:

SCINT Scintillation counters with a sensitive area of 100mm diameter. SCINT01 counts the rate between the two main BENDs, and see many 'parasitic' particles of H4 & H2. SCINT04 or SCINT05 are used  to monitor the total intensity of the beam upstream end of the zone PPE134 (H4A)

 

XWCA (MWPC) Multi Wire Proportional Chambers that allow to make beam profiles in two planes. They only perform reasonably for beam rates above few 10^3 particles per burst. These profiles are made by selecting Tune/Measure/Analog Wire Chambers Profile or directly with the icon tool bar.

 

XDWC Delay Wire chambers that allow to make beam profiles in two planes and in this sense work like the MWPC. But they perform reasonably for lower beam rates -  ~few 10^2 particles per burst. These profiles are made by selecting Tune/Measure/Delay Wire Chambers Profile or directly with the icon tool bar .

 

FISC Scintillation counter filaments of e.g 0.2 mm widths, moving through the beam at 1 step per burst in slow mode or through all the beam per one burst in fast mode, which provide horizontal and vertical profiles. To use a FISC, select Tune/Measure/Fisc Profile and accordingly to your request set the different parameters on the scan panel. To get a reasonable profile in fast mode you need at minimum a rate of 10^5 particles per burst. In slow mode you are more sensitive, but you need more time .....

 

EXPT Experimental scalers do not count any of our detectors but rather yours. In your barrack there is a panel with four (or more) plugs marked. In each of the four you can provide a standard NIM-signal that is counted over each burst and read into the SPS computer system. The scaler name depends on the barrack + the channel number These counts are displayed by Detectors/Experimental Scaler Status