MESON AREA 1000 GeV STUDY. C. N. Brown, A. L. Read, A. A. Wehmann Fermi National Accelerator Laboratory

Transcription

1 -375 MESON AREA 1000 GeV STUDY C. N. Brown, A. L. Read, A. A. Wehmann Fermi National Accelerator Laboratory This report attempts to collect together preliminary thoughts on how protons from the Energy Doubler/Saver might be used in the Meson Area. In the report we discuss the research potential of the Meson Area at 1000 GeV, also we list a number of technical problems which require further thought, together with a brief discussion of these technical matters. We divide the report into two sections. In the first, we examine the consequences of targetting 1000 GeV protons on the Meson Area Production Target. The second half discusses increases in the secondary beam momenta which would be achievable with superconducting magnets. A GeV on Target Table 1 lists the current operating parameters of the major elements of the External Proton Beam line to the Meson Area. Jeff Appel has submitted a memo to this summer study outlining a scheme for converting the switchyard to Doubler Energies. The main assumption, of course, is that superconducting magnets will be used wherever needed. A simple scenario for the three largest items in the Meson Area proton beam is shown in the following table.

2 -376 Element Today at 400 GeV/c possible 1000 GeV/c Left Bend 12.0 kg 40 kg Vertical Bend 10.~ kg 40 kg Meson Targetting Quads 4.5 kg 16 kg/in With the additional space that would be made available, it would be possible to accomplish the beam splitting with normal septum magnets and electrostatic septa by adding more such elements. It is also important that normal quads can be used in the Fl, F2, and F3 manholes; the Switchyard staff believe that a 1000 beam line can be designed with only conventional quads in the manholes. The cooling of the target load must studied to estimate what level of intensity the current target configuration could stand at 1000 GeV. It is assumed that the deposition of energy would be approximately unchanged (shower maximum actually increases logarithmically but this still leaves the major energy deposition in the water-cooled C2 collimator), The present target load has been run with d GeV protons per spill; hence, we conclude that 3 x protons at 1000 GeV would be manageable. Current experience, coupled with secondary beam intensity estimates below, lead one to believe that this would be a quite satisfactory intensity. It is indeed possible that downstream muon problems, not target heating, will limit the usable intensity at 1000 GeV/c.

3 -377 The muon problem will certainly be severe and will have to be addressed in detail by all three operating areas in order to plan for doubler energies. A number of thoughts come to mind: 1. There is 6 m of steel collimator on the train which could perhaps be magnetized m of magnetized steel muon spoiler could be fit into the Meson Front End Hall. 3. There is some room for more collimation and muon spoiling in the current M2/M3 line. We believe many of the present muons seen far downstream arise from this beam line. 4. Most muons are found in a horizontal plane due to the large amount of horizontal bending 'in all the Meson beam lines and muon' spoilers. One could limit the access to selected areas of th~ Meson Detector Building ground floor and not significantly decrease the usefulness of the area. 5. The flattop and spill will be longer at Doubler energies; this fact, coupled with the better time resolution of modern detectors will allow experiments to operate in high muon backgrounds (for example, Experiment 87 in P-East).

4 Additional shielding may still be needed in the M3 beam line at high proton beam intensity. This might be achieved with the use of (local) steel shielding, of appropriate cross section, placed immediately upstream of the experimental apparatus it is intended to protect. What would be the advantage of targetting 1000 GeV/c on the production target? One can consider each of the present beams as they will likely exist when the doubler is first operational: 1. M1 350 GeV/c 3 mrad beam. Figure 1 shows the increase in flux of 300 GeV/csecondary particles at 3 mrad as the incident energy is increased. Clearly, the M1 line becomes a high flux 350 GeV/c pion beam with good minority particle fluxes with 1000 GeV protons incident. 2. M2 400 GeV/c 1 mrad beam. The diffracted protons would no longer be available in the line but instead a very intense 400 GeV/c pion beam would result as shown in Figure M3 1 mrad neutral beam- Currently the neutron spectrum peaks at 300 GeV with

5 GeV protons on target. With 1000 GeV protons the spectrum would peak at about 700 GeV. 4. M4 7 mrad neutral or charged beam. The K L flux in this beam currently tapers off at about 100 GeV, at doubler energies this would be a 200 GeV neutral K L beam or with the currently envisioned 200 GeV charged configuration it would easily yield GeV!c negative particles per pulse including about 105 antiprotons per pulse. 5. M5 test beam. Even the M5 beam would benefit by an increased flux of electrons which seem to be its most popular use 6. M6 20~ GeV!c 3 mrad beam. The percentages of K- and antiprotons in this beam would be improved with the higher energi~s incident. Increased minority particle fluxes and the increased duty cycle of the doubler would certainly be highly beneficial to the current types of experiments installed in this high resolution beam line. B. Upgrade of Secondary Beam Lines We have argued that targetting 1000 GeV protons on the

6 -380 Meson target leads to a definite increase in the potential of the secondary beams. Of course, it is realized that shortly after high energy protons were targetted experimentalists will want also to upgrade the energies of the secondary beams. Upgrading the beam lines in any significant way implies the use of superconducting magnets. All major bend strings in the secondary beams currently consist of main ring B2 magnets run at a maximum =ield of 18.5 kg. Using superconducting dipoles (possibly the magnet developed for the long bend strings in the switchyard) run at 40 kg allows a doubling of current beam momenta. Superconducting quads are expected to have considerably.more than double the strength of 3Q120 quads; hence, space will not be a problem. Thus, one could conceive of a 70~ GeV Ml line, a 1000 GeV M2 line capable of transporting diffracted protons and a 400 GeV M6 line. Similarly the Single Arm Spectrometer might also be upgraded to 400 GeV using superconducting elements. About 500' of 40 kg magnet is required for the upgrade of Ml, M2, and M6. This length of magnet is comparable to the swit~hyard meson left bend and could conceivably be the same type of magnet. The assumption is that the up~raded beams would fit into the present galleries and berm pipes. It should be noted that bend points c::luster together in the.

7 galleries in a reasonable way such that cryogenics would not be overly complicated. One question which must be answered concerns the angles of the beams and the first 150' of the Meson Front End Hall. If one were convinced that pion beams Ml and M6 should be at a smaller angle than 3 mrad at Doubler energies, then the target would need to be redesigned and a scheme would have to be invented to allow the separation of these beams in the first 150'. If one embarks on a redesign of the target collimators involving new secondary production angles, one should include magnetized muon spoilers in the design. It may be wise to reopen the question of the use of magnets at the target, to bend the required particles toward the beam in question: Any upgrading of the beams will involve the sept~ magnets in the front end hall, even if the beam production an~les are not changed. At 50', the end of the target box, 3 mrad beams are separated by only 1.8" from the central M2/M3 beam. Present septum magnets run at about 10 kg and are severely limited by cooling problems. A possible cold, steel dual superconducting septum magnet is sketched in Figure 12. It may be possible by changing the beam optics and using conventional septa to invent a viable solution. Clearly, the layout

8 of the Front End Hall will be a determining factor in any attempt to change the present configuration of secondary beams. Another severe limitation to doubling the present beam energies in the present tunnels involves particle identification. At first blush all Cerenkov counters should be four times longer at double the energy. Table 2 gives the properties of the Cerenkov counters in the three major beam lines. It appears that these counters may be usable for ~/k separation up to 300 to 400 GeV and for ~/p separation up to 800 GeV. Some thought should be given to alternate schemes, possibly involving transition radiation detectors at the highest ener9ies. The optics of the beams mi9ht need to be altered to accommodate different detectors or longer Cerenkov counters. Another ~uestion in this whole examination of higher energies needs to be asked. Is there enough room to do experiments at > 500 GeV energies in the Meson Laboratory? This question is answered simply, yes; we currently have room for three experiments in each beam line. At double the energy we may only have room for one or two. The advent of the high intensity pion beam in P-west and possibly other new facilities should help miti9ate this decrease in total experiments. If not, the extension of the downstream beam lines tunnels is inexpensive and plenty of space exists north of the Meson Laboratory to flexibly accommodate new ideas.

9 -383 Lastly, we feel that most of the changes proposed could be done adiabatically. Clearly, the changing of the switchyard to superconducting magnets will be a major upheaval. After that the upgrading of the Meson beam lines can be done during two-week maintenance and development periods as funds and opportunities arise. It is fair to say that the beam lines can be modified between any two foci without affecting the rest of the beam disastrously. We have not discussed the most vital question of all are there compelling experiments that warrant spending the money to upgrade the Meson Area? We leave the answer as an exercise for the reader.

10 -384 TABLE I SWITCHYARD PARAMETERS AT 400 GeV/c Element Length (ft) Excitation Location Electrostatic Septa Magnetic Septa (Lambertsons) Left Bend Dipoles Left Bend Quads Lower Vertical Bend Vertical Run Quads Upper Vertical Bend Meson Targetting Quads kv 50 7 kg kg 60 4 kg/in kg 60 4 kg/in kg kg/in B Enclosure C Enclosure C Enclosure C Enclosure C Enclosure Fl-3 Manholes Meshall Mesha1l

11 -385 TABLE II MESON AREA CERENKOV COUNTERS Max Momentum for Beam Line Type of Counter Name Length KTr Separation Ml Simple Threshold "Pruss" 28 m >150 GeV/c Ml Differential, with veto "Kycia" 15 m >250 GeV/c M2 Simple Threshold "Caltech" 30 m >200 GeV/c M6 Differential, with veto "SLAC" 13 m >100 GeV/c M6 DISC "Meunier" 5 m >300 GeV/c

12 -386 Incident Energy Dependence of M1 Flux

13 -387 Incident Energy Dependence of M2 Flux

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