Boriskin, V.N.

Gurin, V.A.

Popenko, V.A.

Savchenko, A.N.

Tatanov, V.I.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

MONITORING CHANNEL OF THE TECHNOLOGICAL LINAC BEAM CROSS-SECTIONV.N. Boriskin, V.A. Gurin, V.A. Popenko, A.N. Savchenko, V.I. TatanovNSC, KIPT, Kharkov, UkrainePACS number: 79.20.HxIn recent years at the Science Research Complex “Ac-celerator” of NSC KIPT the power current technological electron  linacs  are  developed  and  put  into  operation. Their energy varies from 8 MeV to 30 MeV [1],  the pulse current does not exceed 1A and the operating fre-quency is 150-300 Hz. One accelerating structure linacs, KUT and LU-10, and two accelerating structure linac EPOS are used primarily  for  technological  aims.  The technological object zone irradiated by accelerated elec-trons is created with a magnet scanning system [2]. Irra-diated samples are situated in the ambient air of a linac bunker. The wide-aperture magneto-induction transduc-er is used for position control of the electron beam [3]. A special secondary emission monitor is developed for the operative control  of  the beam cross-section at  the linac exit. The monitor signals are used by a linac con-trol system.1  CONSTRUCTION OF THE BEAM PRO-FILE MONITORThe beam profile monitor consists of three alumini-um lames of 2 mm width and 0.15 mm thick (Fig. 1). The series-connected lames are locked in the hetenax cadre. The spacing of lames is 50 mm. The lame planes are  parallel  to  one  another  and  perpendicular  to  the beam moving plane. In the high-energy electron passage through the lames, the positive signal with an amplitude no more than 800 mV comes due to the secondary elec-tron emission. The beam profile monitor signal by the RK75 cable 40 m in length is fed to the digitizer entry. Simplicity of the monitor construction is conditioned by a high level of induced activated radiation in the work-ing zone. The employment of  the traditional  collector electrode with an accelerating potential was not neces-sary for electron beams we have used [5, 6]. The beam profile monitor is installed in the air at 60 mm from the plane of the scanner exhaust foil.Fig. 1. The profile monitor structure scheme.In  the  air  a  relationship  between  a  charge  on  the beam profile monitor lames and the primary beam inten-sity can not be linear as a result of deposition of charge atmosphere particles and secondary electrons with a low energy on the lames.A relationship between the total beam profile moni-tor signal and the primary electron beam intensity was investigated  to  the  estimate  characteristic  linearity.  In Figure 2 the channel for measurement of the total moni-tor signal is shown, the measurement results are given in Figures 3 and 4. It is shown that in the vicinity of scan-ner exhaust foil the signal level drops and characteris-tics very depend on the beam current.Fig. 2. Structure schematic of the channel for measure-ment of the total beam profile monitor signal:  R -  matching resistance in the end of the coaxial cable,  RL  - resistance RK75 cable, РС - personal computer,  ADC - digitizer.Fig. 3. Videogram of the total beam profile monitor  signal measurement (pulse train at the top of  videogram).ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 147-149.147(1)33.13.23.30 500 1000Ip(mA)Kem(%)(2)33.13.23.30 500 1000Ip(mA)Kem(%)(3)2.22.73.20 500 1000Ip(mA)Kem(%)Fig. 4. Secondary emission coefficient (in %) versus pulse beam current IP (in mA) and the distance (h)  between the monitor plane and scanner exhaust foil.  (1) h=125 mm, (2) h= 65 mm, (3) h=2 mm. Electron energy is equal to 7-11 МeV.2  MONITORING SECTION AND POSI-TION OF THE ELECTRON BEAMAt our linacs in the plane of the beam profile moni-tor, the cross-section diameter (D) of the electron beams used for process of target irradiation ranges up to about 10-15 mm and the distance between the centers of the beam deflected by the scanner at the extreme positions may be equal to 100-150 mm. As an excitation current of the scanner magnet changes linearly, the average val-ue of beam center movement  (R) within the span of two linac pulses is defined by the relationR = 2 FS S/Fr,where FS is the change frequency of the deflecting scan-ner excitation current,S is the beam center movement swing,Fr is the frequency of linac current pulses.For our case R is equal to 2 – 4 mm. Based on this the lame width of 2 mm was selected. Figure 5 and Fig-ure 6 show the results of monitoring the beam position and the section at the linac EPOS. The signal amplitudes from the middle lame allows to estimate a beam section along the axis of the beam center movement. With the known distance between the first and last lames and the linac pulse value between the first and last signals from these lames, one can determine the beam center move-ment swing.Fig. 5. Videogram of profile monitor signals and signals of magneto-induction transducer of position.05001000150020002500300035001 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101106111 116 121126Fig. 6. The total values of the signals induced by the electron scanning beam into the magneto-induction transducer of position (saw-tooth signal) and into the beam profile monitor. The pulse beam current,  pulse frequency and scanning frequency of the linac “EPOS” were equal to 760 mA, 200 Hz and 3 Hz respectively.The familiar X-shaped construction of the beam pro-file monitor [7] is used for two-dimension beam profile control (Fig. 7).Fig. 7. Structure schematic for two-dimension beam 148profile measurement.The results of two-dimension beam profile control in the linac “EPOS” are presented in Fig. 8.00.020.040.060.080.10.120.140.161 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32n Fig. 8. The plots of two-dimension beam profile  changing in the linac “EPOS”.For the described measuring channel  the measure-ment  error  of  the  beam profile  and position is  deter-mined chiefly by the ratio of D, S and R quantities. For our case the error is no better than 20 %.Summary. The on-line channel for measurement of the beam profile and of the beam position has been in suc-cessful  operation  for  over  two years  as  a  part  of  the linac  “EPOS” control  system. Authors  are  grateful  to M.I. Aizatsky,  A.N.  Dovbnya,  V.A.  Kushnir  and V.L. Uvarov for helpful discussion.REFERENCES1. A.N.Dovbnya et al. Electron Linacs Based Radia-tion Facilities of Ukrainian National Science Center KIPT //  Bulletin of the American Physical Society. May 1997, v. 42, No. 3, p. 1391.2. A.N.Dovbnya  et  al.  The  Output  Beam  Scanning and Forming in the Multipurpose Electron Acceler-ators of KIPT // Voprosy Atomnoj Nauki i Tekhniki.  Seriya: Yadernaya Fizika (28). 1997, v. 1, p. 114-121 (in Russian).3. V.N.Boriskin,  A.N.Savchenko,  V.I.Tatanov  et  al. Monitoring of the Electron Beam Position in Indus-trial Linacs // Proc PAC’99. 1999, v. 2, p. 753-755.4. Yu.I.Akchurin, V.N.Boriskin, N.N.Bahmetev et al. Control System for Technological Linacs //  Prob-lems of Atomic Science and Technology. Issue: Nu-clear-Physics Research (34). 1999, v. 3, p. 55-57.5. E.A.Merker.  Equipment  for  precision  coordinates and form measurement of the released proton beam //  Pribory  i  tekhnika  ehksperimenta.  1975,  v.  6, p. 25-27 (in Russian).6. V.A.Golshteyn, V.G.Vlasenko, S.V.Dementij et al. Research  of  the  secondary  emission  monitors  on  the LAE-2000 electron beam. Preprint KIPT 72-14, Kharkov, 1972, p. 27 (in Russian).7. V.A.Moskalev, G.I.Sergeev, V.G.Shestakov.  Mea-surement  of  charged  particle  beam  parameters. Moscow: Atomizdat, 1980, 156 p (in Russian).ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 149-149.149

Monitoring channel of the technological linac beam cross-section

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Monitoring channel of the technological linac beam cross-section

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Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)