Niels Doble / SL-EA

INSTRUCTIONS FOR USING THE H4 BEAM TO TEST AREA H4A

1. Beam control

The NODAL system only recognises UPPER CASE.
The backspace is CTRL-A.
The control program is invoked by

	SET  INDEX=207
	RUN TREE

Leave the program by hiting the ESC key. To get back, the following options are available:

	RUN TREE     Start at the top of the tree,
	RUN          Go back to where you were,
	BACK         Go back to the previous level in the tree.

2. Access

Access to door 154 is controlled by moving TAX1 (TAXMOT(3)) and TAX2 (TAXMOT(4)) into the beam and switching off Bends 3, 4, 5 via the access programme:


	RUN TREE
	   ACCESS
	   DOOR
	      154
	      OPEN  (for access)  or  BEAM  ON
		     your name, which will be registered

Please check that BEND 3,4 and 5 are powered and that the TAX 3 and 4 are open to -140 mm via


	STATUS -> MAGS
and
	TUNE -> SPECIAL -> TAX -> -140

These elements are in fact used to give access to your own as well as to the upstream zones.

3. Change of energy

The energy of the beam is defined by magnet currents and collimators. Their nominal values for the different energies are defined in beam files. Files are activated by typing


	FILES / LOAD / file-# /ALL

	H4.11 (120 GeV)	H4.14 ( 50 GeV)	H4.17 ( 15 GeV)		
	H4.12 (100 GeV)	H4.15 ( 35 GeV)	H4.18 ( 12 GeV)		

	H4.13 ( 80 GeV)	H4.16 ( 20 GeV)	H4.19 ( 10 GeV)

File H4.4 is like H4.14, but it has been saved with a larger spot.

For low momenta it is recommended rather to use

	H4.J ( 12 GeV)	H4.G  ( 10 GeV)	H4.9  (  8 GeV)

as they have fewer magnets activated (and therefore have a higher current per magnet). It is important in going to or from these files, to load the files including collimators (COLL-6 has to be off-centered).

4. Monitoring of beam

Check status via


	STATUS / CHECK

 and print MAGNET and COLLS settings using 

	STATUS / MAGS 

	STATUS / COLL .

For electron beams it is important that:

The converter is in (TUNE -> SPECIAL -> CONVERTER -> LEAD)

Triggers 1 (with lead) and 2 are out (TUNE -> MEAS -> TRIG -> 1,2 -> OUT)

5. Adjustment of the beam rate

The beam as obtained by loading the file (see Section 2) should give a flux in the range of some 10³ to some 10⁴ electrons for ~ 3 10¹² ppp onto target T2 ( = NORM-2). This should be checked, either your own counters, or on theTRIG 4+5 coincidence:


	TUNE -> MEAS -> COINC -> USE -> Norm: 2 -> Bursts: 3 .

NB: These counters should be set OUT of the beam afterwards!

Normally also TRIG 6 and TRIG 7 should be set out (TUNE -> MEAS -> TRIG) if not needed to trigger the Çerenkov counter. At present neither TRIG 6, 7 nor the Cerenkov are installed.

Also the beam profiles in front of H4A should be checked via


	TUNE -> MEAS -> MWPC -> PROF -> 5 (Horiz), 6 (Vert).

The beam can then be 'steered' as described under Section 5 and the profiles checked again.

The beam rate is adjustable with collimators. COLL 3 governs the beam momentum bite (± 3 mm opening corresponds to ± 1 ‰ Dp/p). The smaller the gap, the smaller the rate. The gap is changed by typing


	TUNE / SET / COLL / 3 / JAWS / new-down / new-up

Other important collimators which may be used are:

	COLL 1	Horizontal acceptance
	COLL 2	Horizontal intermediate focus
	COLL 6	Vertical acceptance
	COLL 8	Vertical intermediate focus, 
	      	defines Dp/p resolution together with COLL 3.

These have been set to obtain a well-defined beam of useful spot size (see SECTION 6).

TO REDUCE THE BEAM RATE it is therefore proposed instead or also to detune progressively QUAD-6 via TUNE -> SET in steps between the file value and an equal current of the opposite sign or further increase the current with this opposite sign.

Please note such changes and the resulting flux in the Logbook!

For an example of tuning of the beam, see H4 beam book E, page 81.

6. Fine steering onto H4A

Fine steering can be done with the following magnets:

	TRIM-5	Horizontal position	(0.009 ^.p  Amps / mm )
	TRIM-6	Vertical position	(0.009^.p  Amps / mm )

where p is the momentum in GeV/c. Positive I in Trim-5 sends the beam towards the Saleve, i.e. negative on MWPC 5. Positive I in Trim-6 sends the beam up, i.e. positive on MWPC 6.

The currents are changed by typing


	TUNE / SET / TRIM / 5 or 6 / new-current

The beam profile at H4A can be seen by


	TUNE / MEAS / MWPC / PROFILE

and then selecting chambers 5 (Hor.) and 6 (Vert.). When you are happy, new settings can be printed out by typing


	STATUS / MAGS / Y
	STATUS / COLL / YES

7. Spot size

The beam spot (i.e. the focussing on our apparatus) is controlled by quadrupole Q16. In fact Q16 affects both the horizontal and vertical spot sizes in a similar way. The beam size can be observed using MWPC 5 and 6. It is suggested to vary the Q16 current in steps between the file value (small spot) and zero current (large spot) by


	TUNE / SET / QUAD / 16 / new-current

For the purpose of the present run, Q16 has been set in all files to obtain a focussed beam at H4A to check the beam before deciding to reduce its current.

8. Muons

A low-intensity muon beam is easily obtained by loading file H4.14 and opening to +/- 40 mm all collimators, except COLL 9 and 10, that should be closed to slits from +40 to +45 mm in order to stop all hadrons and electrons.

Note that for reasons of safety it is recommended to close C9 and C10 first before going to muon beam and to open C9 and C10 only at the end when going back to electrons. Otherwise your apparatus may be exposed to high electron fluxes (of the order of 10 million per burst ! ).

9. Problems

It may well be that after loading a new file the beam rate is lower than normal or that the profiles in MWPC 5 and 6 are funny. In such cases it may be sufficient to change the current in one of the main bends B3 or B4 by just a few tenths of an Amp. Never change the current in B6 and B7, as these are the momentum defining bends!

In case of remaining problems, please contact the CRN operators:

		Phone 75566
		Beeps 13+4190 or 4191

Figure 1: (Postscript file)

The test beam optics for the H4 beam. Also indicated are the magnets, collimators and detectors along the beamline. The drawing is to scale.

Last updated : 3 July 1996 by Niels Doble