Changes in the West Area

Please have a look at:

• The West Experimental Area at the CERN SPS version 2000 (PS for printing here)
• The West Experimental Area at the CERN SPS version for 1998-1999 (PS for printing here)
• Note SL-99-019 (EA) about the T1 displacement implications
• A simple description of the T1 displacement project
• The paper on the GIF facility
• Some pictures of TCC6 by P.Pierre
• Detailed planning by P.Pierre in Postscript and PDF format.
• Elements affected by T1 displacement project
• New numbering scheme for beam elements in H3
• Access Matrix (PDF)

Present working files:

• Beatch
• Transport
• Currents (not yet corrected for magnet polarities)

The West Hall as a building was completed in 1968. Since then it has gone through three major phases:

Period	Energy	Characteristics
1971 till 1974	28 GeV/c (PS)	Two beams, one to Omega, one for bubble chambers
1976 till 1982	200 -> 240 GeV/c (SPS)	7 beams for Omega, BEBC and other experiments
1984 till 1996	450 GeV/c (SPS)	Two physics beams: H1 for Omega and H3 Four general purpose test beams: X1, X3, X5 and X7/X9

The Research Board has decided that at the end of 1996 the H1 , H3 , X1 and X3 beams should be stopped. This implies also that there will no more be ion beams to the West Area. The upstream part of the H3 beam will remain in operation to serve as a parent beam for the X5 and X7 beams.

< click for full picture

With the material recovered from the stopped beams, the X5 and X7 beams have been upgraded to 250 GeV/c. Please click here for a PS file with the new X5 optics. The new X7 optics can be found here.

The X7 beam has also been made horizontal (in the past it sloped down towards the old BEBC center at 6 mrad). See the Beams page for more details on the special extensions to the CHORUS experiment (1997 version only - now dismantled).

The polarities of all magnets have been measured in 1998 and can be found here.

From the controls point of view the layout has been simplified according to the new synoptical diagram:

• H3 -> The beam from T1 to the X5 and X7 targets
• X5 -> From the X5 target towards the X5 test facilities
• X7 -> From the X7 target towards the X7 test facilities

which looks indeed much simpler than the corresponding old diagram:

The users in 1997 of the West Area beam lines are indicated in the Layout of the SPS West Experimental Area (situation for 1997).

Concerning the Layout of beam lines, the Beatch files are organised somewhat differently (for historical reasons):

• H3-beatch from T1 to the X5-X7 splitter (MSSB)
• X5-beatch from the splitter to the X5 test facilities (old H35 + new X5)
• X7-beatch from the splitter to the X7 test facilities (H37 + X7).

With all the changes above, it is clear that the access conditions for the different beam zones has to be reconsidered. Please click here for the list of access conditions per zone.

The future injection line from the SPS into the LHC will traverse the present location of the T1 primary target. Therefore the present target will be partly dismantled and a new one has been installed about 1.5 metres to the side and 12 metres downstream. As a consequence some 600 metres of the H3 beam have been rebuilt 1.38 metres to the North. A short description of this operation is described here. Most of this work has been done in the 1999/2000 shutdown.

Modifications to the H3 beam

As stated above, most of the H3 beam will be kept operational as 'injector' to the X5 and X7 test beams.

The H3 beam in its mode of parent for the test beams was limited to 200 GeV/c due to the limited bending power of the splitters. In the upgrade project the following changes were made:

1. The X7 splitter used to be a pair of MSSA septum magnets. These were replaced by a pair of more powerful MSSB septa. This brings the H3 top momentum to well above 250 GeV/c.
2. The previous X5 splitter has no more reason of being. However, at this location both the X5 and X7 branches need to be deflected North towards the X5 and X7 targets, respectively. Therefore the previous MSSB septum magnet was replaced by two large aperture MBPL bending magnets.
3. To better control the relative and absolute intensities of the beams incident on the X5 and X7 targets, two new collimators have been introduced:
   • One just upstream of the splitters (COLL-5). Each jaw controls one of the split beams. In fact the same functionality (though with slightly less precision) can be obtained with collimator 1.
   • One 4-jaw collimator in the branch towards the X5 target should allow to reduce the beam on the X5 target without affecting the X7 intensity at all. A collimator with equivalent function was installed in the branch towards X7 a few years ago.
4. The part of H3 downstream of the old X5 split has been dismantled. A massive beam dump will prevent the beam to enter the West hall in case the splitter or the MBPL magnets would trip or receive a wrong current.

The energy of the H3 beam affects both the X5 and X7 beams and is subject to scheduling by the SPS coordinator after discussion with the EA physicists responsible for the changes. Note that with the suppression of the T1 wobbling station, the dedicated electron mode of H3 (which has never been neded) has disappeared.
The optics drawings (Postscript files) of the H3 beam from the primary target T1 towards the secondary targets for X5 (H35) and X7(H37) are available on the Web.

The operation of the H3 beam is under the control of the SL-EA physicists with the help of the CRN operators.

The upgraded X5 beam

In fact all bends and quadrupoles in the X5 beam have been replaced or reinforced to allow higher energy particles to be transported. A synoptical diagram with beam optics and layout of the X5 beam is available for inspection. The maximum beam momentum is given by the magnetic strength and is now 250 GeV/c. This has important consequences, in particular this allows to run the X5 beam as a secondary beam as well as in tertiary mode.

• In tertiary mode nothing changes fundamentally from before. Flexible use of pion, electron and muon beams is possible at energies below the H3 energy. The user has full control over the particle type and beam momentum, like in the past. The typical RMS of the beam spot is of the order of 1 cm in each plane. The intensities vary strongly with particle type and energy, but are usually in the range between 1E2 and 1E4.
• In secondary mode the X5 momentum is identical to the H3 momentum. The typical RMS of the beam spot is now of the order of 2 to 3 mm in each plane. The flux is strictly limited by radiation levels in the hall. The maximum allowed flux has been determined by radioprotection measurements and is 10⁶. The particle type is the same as in the H3 parent beam, depending on schedule meeting discussions. Pure electron beams can be provided, as well as rather pure pion and proton beams, depending on the energy chosen.

X5A

X5B

Downstream of this final dump an irradiation facility will be installed (sometimes called X5C). Here detectors may be tested with parasitic muons passing through the dump in the presence of background radiation produced by a radioactive source.

In the 1997/1998 shutdown the height of the X5 beam has been increased by about 2 cm to the standard height of 3.66 metres above the West Hall floor. This is a consequence of the changes to the X7 beam (see below). It implied a re-alignment of all elements along the beam. Upstream of the X5A test facility a XTDV mobile dump was added. Access conditions to zone PPE105 will thus be based on this XTDV, while the magnets (used so far to make the zone safe for access) can remain on. This has the advantage that the GIF irradiation facility continues to receive some muon flux during access in X5A, provided that the X5 is operated in the appropriate condition for muons.

A user guide for the upgraded X5 beam is available.

The X7 beam

In the 1997/1998 shutdown the X7 beam was upgraded to 250 GeV/c in a way similar to the X5 beam. A beatch listing is available. Note that the beam is now horizontal and therefore the beam height has been increased considerably compared to the past (more than a metre in the X7B zone). The beam can now be operated both in secondary and tertiary mode, like the X5 beam. The maximum allowed flux in secondary mode has been limited to 10⁶ particles per burst after radiation level measurements by the RadioProtection group. As in the past, two test facilities (X7A and X7B) are available.

X7A

X7B

As a consequence of the X7 upgrade, the extension to CHORUS had to be redesigned for a final in-situ calibration. A description of the design and operation of this extension is available. The nominal trajectory of the so-called 'direct beam' through the CHORUS apparatus remained unchanged. CHORUS has now finished its calibrations and the extension X9 has therefore been dismantled.

Muons accompanying the X7 beam may traverse the BEBC and CHARM-II halls. Some explanations about the flux and spatial distributions as a function of X7 consitions are given here. For the moment this does not cause problems, but it certainly did during the running of CHORUS!

A User Guide for the X7 beam is available.

Instrumentation in X5 and X7 beams

In each of the two remaining test beams the following instrumentation is available:

• In each test facility a delay wire chamber provides horizontal and vertical profiles of the beam. A second signal is available for direct readout by the experiments. The resolution of these chambers is of the order of 200 µm or better. These chambers are good for particle fluxes not exceeding ~ 1E4 particles per spill. A CAMAC readout allows to read them also from the beam control system to allow easy tuning of the beam position.
• Around the second group of bends, the momentum defining bends in tertiary beam mode, four additional delay wire chambers (with readout in the horizontal plane only) will be provided. They can be read by the experiments in a way similar to the profile chambers mentioned above. The readout of the chambers through the beam control system will be upgraded to VME readout. The commisioning of these chambers will be done tentatively in May 2000.
• Two threshold Cerenkov counters are available in each beam line. Their gas volume has a length of about 10 metres. They are filled with either Helium or Nitrogen gas. Direct cables to the experimental barracks allow the experiments to use them for particle by particle identifaction. Readout through the beam control system allows to do pressure scans and optimise the settings.
• Six scintillator counters, called "TRIGGERS" in the beam control system. TRIG-1 is located upstream of the secondary target and monitors the incident rate on the target. TRIG-2 and TRIG-3 are located upstream and downstream of the momentum defining Bends in each beam and their coincidence strobes the readout of the spectrometer chambers. Similarly the coincidence of TRIG-4 and TRIG-5 strobes the readout of the two threshold Cerenkov counters. TRIG-6 (Trig-8 for X7) is located at the entrance of the X5A, resp. X7A area and strobes the readout of the profile chambers in both areas. For TRIG-6(8) the anode signal may be used for direct readout by the experiment.
• One X/Y wire chamber with analogue readout (integrates charge per wire over each SPS cycle) per beam allows to check the impact point and spot size of the beam incident on the secondary target. In the X5 beam analogue chambers will also be provided in the X5A and X5B areas to measure the beam spot at high fluxes.

Some typical running conditions of the West Area

Typical modes of operation of the West Area are described in more detail here.

And all this is now heavily exploited, as can be seen from a picture of one of the test facilility control rooms!