Gouiran, R

Hanon, J M

Höfert, Manfred

Lambert, K P

Steinbach, C

CERN Document Server

/je EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH SHIELDING OF AN INTERNAL DUMPING FACILITY FOR THE PS: RESULTS OF EXPERIMENTS IN THE SE 62 TEST BEAM AND COMPARISON WITH MONTE CARLO CALCULATIONS R. Gouiran, Ch. Steinbach, MPS J.M. Hanon, M. Hofert, Health Physics K. Lambert, ISR CERN/MPS/OP 74-3 26 April, 1974 1. INTRODUCTION The internal dumping of 101 3 protons per pulse raises the problem of the dose received by the next PS magnet unit and its pole face winding. The estimations are that it would take something like 2000 hours' continuous dumping on a conventional internal dump target before the pole face windings fail and the sheets of the magnet corne apart1 ' 2). This has to be compared with the average 6000 hours of PS acceleration per year, of which approximate-ly 5% will be devoted to internal dumping. 3) A movable shielding arrangement (shower catcher) has been proposed to attenuate the radiation damage due to internal dump targets and its study has been approved4). Other sophisticated dumping systems have been suggested as wellS-?), all aiming to dispose of the beam by fast vertical deflection directly onto a black under or above the closed orbit in a straight section. Monte Carlo programs for hadron cascades 8) allow for the calcula-tion of the energy deposition (dose) in cylindrical geometries approximating to a magnet downstream of a target. The results of such calèulations are given below and are compared with experimental results. An appropriate location for an experimental set-up was the slow extraction test beam in the East Hall junction, as shown in Fig. 1. As a last preliminary remark we have to mention that some of the 1 h . . d b d . h 6, 7, 9, 10) resu ts ave alrea y een quote or used in ot er reports • 2. EXPERIMENTAL STUDIES 2.1 Layout The experimental layout conunon to all three experiments consists of an assembly of iron blocks each measuring 27 x 10 x 10 cm (Fig. 2). The gap - 2 -of this 3.80 m long collimator simulates a magnet with a gap of 7 cm. Slots are provided for insertion of expanded polystyrene plates holding the dosimeters and activation detectors (Fig. 3). The shower catcher in front of this assembly (used in experiments 2 and 3) is built of lead blacks 20 x 10 x 5 cm with, here again, slots for insertion of detector supports (Fig, 2). The gap has been chosen equal to 4 cm, a reasonable valuesimulating the movable shield according to beam size . f . h . . b ll) . h. f f 2 expectat1ons or h1g intens1ty eams wit in a actor o . The dump target finally used in experiments 1 and 2 is simulated by an external target of tungsten in air, 75 mm long and 6.3 mm diameter placed 130 cm in front of the magnet, therefore simulating a short PS straight section. About 70% of the incident protons, measured on the secondary emi.s-sion. chamber SEC 1, interact in the target as the interaction length in tun_g-sten is about 6 cm12). 2.2 Experimental programme Three experiments were carried out: 1. simulation of an internal dump target in a PS short straight section in order to measure the dose* in the next magnet; 2. simulation of an internal dump target followed by a shower catcher in the straight section to estimate the reduction of dose to the next magnet; 3. a direc.t hit of the shower catcher by a proton beam to evaluate doses in the next magnet in a simulation of a vertical deflection dumping system. The beam in this case bits the upper part of the local shield at about 3 cm from the axis, i.e. 1 cm from the edge. 15 mm wide and 8 mm high. It is about * Dose in this context mcans dose to iron. As the magnet is built of laminated iron sheets separated by organic insulation material, the dose to the latter is determined by the dose to the iron resulting from the nuclear cascade. - 3 -2.3 Approximation to the actual situation The simulation of the magnet following the target has two disad-vantages: flat "pole faces" instead of hyperbolic ones, and the absence of a magnetic field in the gap of the magnet. The lead bricks employed in experiments 2 and 3 do not exactly simulate the real absorber proposed in ref. S, since the latter is made up of two collimators, the first one having an aperture of 2.8 cm and the second 5.2 cm. The experiment should however give a good approximation to the radiation situation in the case of the shower catcher. The efficiency of the external tungsten target used in experiments 1 and 2 lies in the samc region as the multi-traversal efficiency of an internal <lump target. All values given in this report have, however, been normalized to one incoming proton for the purpose of comparison with results from Monte Carlo programs. The R.M.S. Coulomb scattering angle in the target 13 ) vertically for 24 GeV/c protons is cr= 2.9 millirqdian~, so less than 2% of the scat-tered primary protons should hit the magnet according to Rossi's model. 3. DOSIMETRY 3.1 Glass dosimeters 3.1.1 g~~i:~E~2~~-1~~~!.!~~~~~~-_{g~~2.-~2~.i~~~~E~ Exposure to ionizing radiation of the glass (LiP03 and Al(P03) 3 in equal parts + 7% Ag(P03)) induces stable luminescent centres which pos-sess discrete allowed energy levels. The absorption of a photon of the appropriate frequency in the UV region produces excitation and radiative transitions between these energy levels, and the intensity of the luminescent emission resulting from optical stimulation is a function of the absorbed radiation dose. The dosimeter dimensions are 6 nun x 1 nun ~ and the dose range is from 1 rad to s.108 rad. - 4 -Ionizing radiation induces optical absorption bands in the glass (by weight % P2o5 (70.5), K20 (12), Al 203 (9), MgO (4), B203 (3) and other components (1.5)), of which the principal one is measured spectrophoto-metrically at 510 nm. The glasses have surface dimensions of 36 mm x 12 nun and are used in two thicknesses, i.e. 5 nun and 1.5 mm to caver the dose range of l.6·104 rad to 2·107 rad. 3.2 Activation detectors Different activation detectors fixed to the polystyrene plates were inserted into the slots of the shower catcher or simulated magnet. During the experiments aluminium foils and sulfur disks were used and the following reactions allowed for the study of fast neutrons (FN) and high energy particle (HEP) flux densities. cross-sections given below are assumed: In the energy ranges quoted the 27Al(n,a) 24Na Neutrons 6 - 25 MeV a = 120 rnb 3.2S(n,p)32P Neutrons 3 - 25 MeV (j = 300 rnb 27Al(spal) 22Na Hadrons above 25 MeV a :::1 20 mb lt bas been shown in the past that estimations for radiation doses in organic material could be made by combining a detector for fast d d f . h . 1 . l' 1 . 15 ) neutrons an a etector or h1g energy partie es into inear re ations . Thus the following equations were used for the determination of absorbed doses 16): D m 5 . 10-B ~ NA22 + 6 . 10-B 0 P32 where D is the dose in rad and ~ are the fluences measured with the different detectors in cm-2 • - 5 -4. EXPERIMENTAL RESULTS The experimental results are presented in Figs. 4 to 7. The dose in rad per incoming proton is plotted over the position of the slots in both shower catcher and simulated magnet. The normalization to absorbed dose per incoming proton allows for the direct comparison of the results of Monte Carlo calculations. Although more positions were covered with detec-tors during the experiment, the following discussion will be limited to the upper (Figs. 4 and 6) and lower (Figs. 5 and 7) central positions, i.e. to detectors positioned in the central axis but in the slots just below and above the air gap. The doses recorded on these detectors turned out to be the highest ones and thus most important for the problem of protecting the following magnet by a shower catcher. As can be seen from Fig. 3 the location of the detectors consider-ed was not exactly the same in all positions. Aluminium foils cover a much greater area than the ·other detectors. For this reason the results of the glass dosimeters and activation detectors cannot be directly compared. It is however possible to correlate the same detector results for the three experiments. S. · MONTE CARLO CALCULATIONS The Monte Carlo program MAGKA makes use of a cylindrical geometry. To simulate both shower catcher and magnet as well as the experimental layout the followi_ng dimensions were used: Magnet Shower catcher Length cm 210 80 Diameter cm 35 20 Ho le cm 7 4 Material cm iron le ad The target is placed at 134 cm in front of the magnet or 12.5 cm in front of the shielding cylinder. - 6 -6. EFFECT OF A SHOWER CATCHER FOLLOWING A DUMP TARGET IN A SHORT STRAIGHT SECTION A comparison is made for the maximum doses at the position of · the pole-face windings, when the beam is incident on a thick dump target located on the beam axis, with the dose at the magnet front face, when the latter is protected by an 80 cm lead shower catcher to be placed in a short straight section. 6.1 Results of glass dosimeters At point No 6 in the lower position on the front face of the magnet (Fig. 5) the dose in experiment 1 without shield or shower catcher is 1.6 · 10-lD rad per incoming proton. By comparing this value with the situation in experiment 2 where the shielding had been placed between tar-get and magnet - the dose determined is 6 • 10-11 rad per proton - an atten-uation factor of 2.6 is calculated. For the upper position (Fig. 4) the comparison is not possible as the glass dosimeter in point No 6 could not be evaluated. It should however be noted that the protection factor of 2.6 for the front face upper position decreases with penetration into the magnet and reaches a zero value after approximately 60 cm. 6.2 Results of activation detectors The results of experiment 1 without shower catcher clearly show a small build-up of the dose with depth in the magnet. Thus the maximum values without shield should be compared with the maximum values in case a shower catcher protects the front face. In the upper position the doses under consideration are thus 1.4 · io-lO rad ~er incoming proton, to be com-pared with 5 · lo-11 r~d/proton. This results in an attenuation factor of 2.8. In the lower position the corresponding figures are 1.2 · lo-lO and 5 · 10~11 rad/proton, which leads to protection in dose for the pole-face winding in the magnet by a factor of 2.4. - 7 -6.3 Results of program MAGKA The result of the Monte Carlo calculation shows a pronounced build-up in dose for the unshielded magnet with a dump target in front. On the front face a dose of 7 · io-10 rad par incoming proton is calculated, in-creasing to a value of 1.4 · 10-9 rad/proton at a depth of 40 cm. This maximum value is to be compared with the dose of 7 • 10-10 rad/proton behind the shower catcher of 80 cm length in a short straight section. This leads to an attenuation of a factor of two. 7. EFFECT OF A BEAM DUMP DIRECTLY HIT BY THE PROTON BEAM AND LOCATED IN A LONG STRAIGHT SECTION The aim is to evaluate the protection given by a dump arrangement proposed in ref. 5. By a vertical deflection the proton beam hits a black of metal installed in a long straight section. To simulate such a dump system the shower catcher was thus hit directly by the proton beam. For an estimation of the protective effect of such a device the dose maximum at the place of the pole-face winding in the unshielded case has to be compared with the position at a distance of .230 cm from the beginning of the shield (position 9 in the experiment). 7.1 Results of glass dosimeters The dose of 1.6 • lo-10 rad per incoming proton in the unshielded case at the front end of the magnet has thus to be compared with a value of 2.4 · io-li ~ad in point No 9 upper position. The attenuation in dose amounts to a factor of 6.7. For the lower position two types of glass dosimeters were used. For the Toshiba radiophoto luminescent dosimeters the corresponding values are 1.6 · io-10 and 2.7 • io-11 rad per incoming proton, thus the attenuation is 5.9. ment 3. - 8 -The CERN optical absorption dosimeters were only used in experi-The value in position 9 is 2.2 · lo-1 1 rad per incoming proton. Previous experience with these glass dosimeters on the front end of a mag-net steel black at the end of a long straight section with a thick dump target has lead to values of 1.4 · lo-10 rad per incoming proton. The protection factor is thus 6.4. 7.2 Results of activation detectors Also for these detectors the maximum dose at the place of the pole-f ace winding of a magnet following a thick dump target in a short straight section will be compared with point No 9. The comparison is only possible for the lower position. The value without shield of 1.2 · 10-10 and the value of 2.3 · 10-11 rad per incoming proton behind a long dump system leads to an attenuation in dose of a factor of 5.2. 8. CONCLUSIONS 8.1 Merit of a shower catcher following a <lump target If one wants to lower the radiation damage caused by an internal <lump target on the next PS magnet, the average protection factor, as calcu-lated in section 6, is 2.5. Taking into account the complexity, the price and maintenance foreseen, it seems questionable whether such a device is warranted. 8.2 Merit of kicking the beam vertically onto a block It bas been shown in section 7 that a protection factor of about 6 could. be expected at the end of a long straight section for a direct bit on a beam dump. One should consider the fact that, in the present situation as described in ref. 5, the beam will not be deflected upwards instantaneously. A finite rise time ranging between 0.7 and 1 µs already cuts this factor by - 9 -nearly a half and consequently only a protection factor of 2 to 4 could be expected from such a configuration. REFERENCES 1. J.H.B. Madsen, On the high intensity running of the PS, MPS/CO Note 70-27 2. R. Gouiran, Taux d'irradiations des unités de l'aimant, MPS/MU NOTE/EP 72-15 3. J.P. Potier, Ch. Steinbach, Dumping the high intensity beam, MPS/CO Note 71-27 4. SIC Meeting, May 1971 5. R. Gouiran, A possibility for internal beam dumping, MPS/SR/Note 73-7 6. Ch. Steinbach, Possibility of vertical dumping on a fixed black in the CPS, MPS/CO Note 73-2 7. Ch. Steinbach, Resonant internal dumping, MPS/OP Note 74-5 8. J, Ranft and J. Routti, FLUKA and MAGKA, CERN/Lab.II-RA/71-4 9. O. Barbalat, Essai de synth~se du séminaire PS du 14.3.73, MPS/DL Note 73-3 10. Machines and Areas Committee, Summary of Meeting No 11, MPS/DL Min. 73-20 11. O. Barbalat, Bearn emittance estimates, MPS/DL Note 73-3 12. G. Belletini et al, Proton-Nuclei cross-sections at 20 GeV, Nuclear Physics ].J_ (1966), pp 609-624 13. E. Segré, Experimental Nuclear Physics, Vol. I 14. K.P. Lambert and M. Van de Voorde, High radiation dose luminescent and optical dosimetry systems, CERN/ISR-MA/73-36 15. M. Hofert, Dosemeter response in the high energy radiation field around the CERN proton synchrotron, DI/HP/162 (1972) 16. J, Routti, M. Van de Voorde, M. Hofert, CERN ISR~MA/71-29 / 1 0 ; / I I , . Ol ·-LL. TV CAMERA ~ TUNGSTEN TARGET .0' 0.63x7.5cm ---.--f----- ~ _.._ 2 r <D N PS SLOW EXTRACTED BEAM ~ -1 16 -0 I'"'? --~~ -~ .:j :' 130 LEAD BRICKS COLLIMATOR 0 - . ~---_, ,_ 0 "' ~· l .~ r--- --- '< 0 P!" mœ-n ="" !!?"'1 ----1 -. "::\">~ ~ ' ~.J IRON BLOCK SllMULATED MAGNET -:~-:~{;:=~.1;~~r~~t;~~~t-t:)~~:,~J.r: .. ;~:\.}~~;~~:::6::;~:~:?:f~~:.f2Ji::~::~:;:~·?:{;;:~~·Y\~~~~~~~~~1~~f5~~jJ~~;,~~~~~~l~;wi,~:;~-:~_7e.,:;:_ ... ~~f;~-i~~:·0V;}~.wt~{~~·~w::~~:;~:(Z?~:~::::-~·~:~~{1{(l~~ .. :/:I/\~(:i Fig. 2: EXPERIMENTAL SET UP POLYSTYRENE PLATE upper position lower position ALUMINIUM SUL FUR CERN GLASS SULFUR TOSHIBA ALUMINIUM a.. ON SCALE FIG. 3 " ns ._ z -9 0 10 ..... 0 0::: a.. ............ UJ (/) 0 0 -10 10 -n 10 -12 j ~Si! ~ upper position • TOSHIBA, EX. 1 e TOS HIBA, EX. 2 o TOSHIBA, EX.3 FIG.4 10 '--~~--L..~~~..L..-~~.l..-~~--'-~~~..1...-~~--'-~~~..1...-~~--'-~~~~~~--1.~~~--~~--1.~~~-.-! 8,75 52,5 96,25 130 1 3 5 6 172,S 7 8 g 10 cm . 11 12 13 14 15 posn. z 0 ..,_ 0 0::: • a.. ............ " LLJ (/) ... 0 c - 10 10 -11 10 -12 ~ \ \ \ \ \ I I I I I lower position ~. 10 1 1 1 8,'JS 5~ 96,25 130 17 2,5 1 3 5 6 7 8 9 10 11 12 et TOSHI BA, EX,1 0 TOSHIBA, EX.2 + TOSHIBA, EX. 3 o CERN GLASS.EX. 3 -----+----... FIG. 5 cm. 13 14 15 posn. c 0 Cf) 0 a. ~c.D ... "' '--~..i-._ ...... ~--0'·----"---~--'--i.-.. ...... ~...i..~~~._~~__.. ...... __ _._~~~~~"--~--.... ~-~o GO 10 -en •O -(Pl!J) NO!O~d/3500 ·-"'O ns L.. -z 0 r-0 ~ a.. ............. w -8 10 (/) -9 0 10 0 -10 10 -11 .. - "",. lower position 10 1 1 8,75 1 52,5 3 ~25 5 130 6 172,.5 7 8 9 10 11 12 13 • NA22 +P32 , EX. 1 • NA22+ P32 , EX. 2 o NA22+ P32, EX. 3 FIG. 7 14 15 cm. posn . 

Shielding of an internal dumping facility for the PS; results of experiments in the SE 62 test beam and comparison with Monte Carlo calculations

Hanon, JM

Höfert, M

Lambert, K

Shielding of an internal dumping facility for the PS:  Results of experiments in the SE 62 test beam and comparison with Monte Carlo calculations

Shielding of an internal dumping facility for the PS; results of experiments in the SE 62 test beam and comparison with Monte Carlo calculations

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