Some specific design features of the accelerating units for LINACs model UELR-10-10S designed for radiation

sterilization and the electron beam characteristics obtained experimentally are considered.Описываются некоторые особенности конструкции ускорителей модели УЭЛР-10-10С, приводятся и обсуждаются характеристики электронного пучка, полученные экспериментально.Описуються деякі особливості конструкції прискорювачів моделі УЕЛР-10-10С, приводяться і

обговорюються характеристики електронного пучка, отримані експериментально

Alexeev, V.A.

Baranovsky, A.E.

Belousov, A.V.

Davydov, V.N.

Demsky, M.I.

Denisov, K.A.

Fialkovsky, A.M.

Fomin, L.P.

Gavrish, Yu.N.

Kochin, S.N.

Larionovsky, V.A.

Maslov, K.N.

Nikolaev, V.M.

Obodinsky, D.A.

Orlov, A.V.

Ryabov, V.V.

Ryabtsov, A.V.

Shchepin, Yu.P.

Terentjev, V.V.

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

ACCELERATING UNITS FOR COMMERCIAL RESONATOR LINACS MODEL UELR-10-10S DESIGNED FOR RADIATION STERILIZATION DEVELOPMENT AND RESULTS OF TESTINGV.A. Alexeev, A.E. Baranovsky, A.V. Belousov, V.N. Davydov, M.I. Demsky, K.A. Denisov,  A.M. Fialkovsky, L.P. Fomin, Yu.N. Gavrish, S.N. Kochin, V.A. Larionovsky, K.N. Maslov,  V.M. Nikolaev, D.A. Obodinsky, A.V. Orlov, A.V. Ryabtsov, V.V. Ryabov, Yu.P. Shchepin,  V.V. TerentjevFSUE “D.V. Efremov Scientific Research Institute of Electrophysical Apparatus”St. Petersburg, RussiaE-mail: npkluts@niiefa.spb.su, fax/phone: 812-4646220Some specific design features of the accelerating units for LINACs model UELR-10-10S designed for radiation sterilization and the electron beam characteristics obtained experimentally are considered.PACS: 29.17.+wThe linear electron accelerator model UELR-10-10S is  intended  for  the  commercial  radiation  sterilization and pasteurization of foodstuffs. The radiation parame-ters of this machine are shown in Table 1.Table 1. The radiation parameters of the electron accelerator model UELR-10-10SEnergy of accelerated electrons in the nominal mode, MeV 10Average electron beam power in the nominal mode, kW 10Range of energy variation, MeV 8…10Average electron beam power in the 8 MeV mode, kW 9.5Pulse repetition rate, l/s 300, 150, 100, 50Scanning line size 100 mm from the foil of extraction window, mm up to 800×20Radiation field flatness over scanning length, %. ± 5%Scanning frequency of electron beam, Hz 1…5The  KUY-147А klystrons  produced  by  FSUE “Toriy” are used as a source of RF energy. At the con-sumer’s  request,  it  is  possible  to  use  other  types  of klystrons produced by foreign firms and generating a pulse power of 6 MW at a frequency of 2856 MHz with an average beam power up to 30 kW.The standing wave accelerating structure contains a five-stage buncher, which ensures narrow energy spec-trum and RF focusing of the beam of accelerated elec-trons. The main operating mode is the mode without an external solenoidal focusing magnetic field, which en-sures the production of  the beam of accelerated elec-trons  with  an  energy  of  10 MeV  and  small  energy spread.In the first machine of this model, a double-electrode gun IED-50-0.4 with BaNi cathode of 5 mm diameter was used. In the second such a machine, we applied a gun with a cathode of 14 mm diameter.The main experiments were carried out to measure the kinetic energy of accelerated electrons, the range of energy variation, energy spectrum and current of accel-erated  electrons.  The  energy  of  accelerated  electrons was mainly varied by varying the beam current, which ensured high electron efficiency. A so-called injector device, a beam current regula-tor, was the main means used to vary current magnitude. It is positioned between the electron source and acceler-ating structure and consists of a focusing lens,  a drift tube and a collimator. By changing the lens current, we changed the losses of the beam passing through collima-tor, the current injected and the beam losses in acceler-ating structure.In some cases when measuring load characteristics, the beam current was changed by varying the filament of electron gun. In standard version of the accelerator, two Al plates located in the atmosphere beyond the vac-uum  window  of  the  scanning  magnet  chamber  were used to control the kinetic energy of beam current. The energy of accelerated electrons was estimated from the absorption of the beam current in the first Al plate. To measure energy spectrum in our studies, we used a mag-netic energy analyzer. The effective energy of the beam extracted to  the atmosphere was measured in  compli-ance with the ASTME 1649-94 standard by using a set of Al plates of 2 mm thickness. Film dosimeters of the SPDF-5/50 model were placed between Al plates.In the beginning of the experiments with the first ac-celerating unit, some difficulties emerged in the use of current  regulator.  The  reason  was  parasitic  magnetic fields in the area of electron gun produced by an annular magnet, a component of an ionization lamp used to con-trol vacuum. These fields distorted the trajectories of the electrons injected to accelerating structure.  To correct the  position  of  the  beam  at  the  inlet  to  accelerating structure, we were forced to use the magnetic fields pro-duced by the solenoid coils encircling this accelerating structure. To produce these fields, a current of 16 A was applied to the coils of solenoid. By varying the current in current regulator from 230 up to 300 mA, we man-aged to control the current at accelerator outlet and to ___________________________________________________________PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.Series: Nuclear Physics Investigations (46), p.91-93. 91obtain  the  load  characteristics  shown in  Fig.1.  These characteristics were measured in different ranges of lens current variation. At lower magnetization current, one load characteristic was less steep, which evidently can be explained by higher beam losses on the walls of ac-celerating structure. At low current in the lens, the ac-celerating  structure  was  loaded  with  a  current  higher than the current recorded by the beam absorber located at the outlet of accelerator.Fig.1. The load characteristic of the first accelerating structure with current varying in current regulator.  Ibeam = 230-280 mAThe 10 МeV kinetic energy of electrons was attained at  a  beam pulse  current  of  0.21 А.  When  a  standard pulse klystron modulator with a duty cycle of QRF = 240 was used, the duty cycle of the current of accelerated electrons  was  QI = 270,  taking  into  account  the  time necessary for the onset of oscillations in the accelerating structure. The 210 mА pulse current corresponded to an aver-age beam current of 0.78 mА, which in turn would cor-respond to an average beam power of 7.8 кW and did not ensure specified average beam power.In the course of studies of the first accelerator car-ried out without current regulator, it was experimentally confirmed that  an average power of 7.8 (8.2) kW was obtained at a kinetic power of 10 MeV (see Fig.2). In this case,  to change beam current,  we varied the fila-ment current of electron gun. We succeeded in obtain-ing high current of accelerated electrons by increasing the current in the coils of solenoid up to 50 A (Fig.2). Fig.2. Load characteristics of the first accelerating structure without current varying in current regulatorThe average kinetic energy of accelerated electrons in both the cases considered above was estimated from the absorption of current  in Al plate of  10 mm thick-ness.  It  should  be  noted  that  the  total  current  values shown in Figs.1 and 2 were determined as a sum of cur-rents in these two plates. Due to leakage, these values were less by 6% than the current measured by beam ab-sorber. In this connection, the average beam power at-tained at a kinetic energy of electrons of 10 MeV could be considered equal to 8.2 kW instead of 7.8 kW, and the pulse power generated by the klystron was estimated to be 4.5…5 MW. With the magnetic energy analyzer used, the spectral energy characteristics  in  the  first  accelerating structure were measured at a current of 58 А in the first focusing coil and 35.5 A in the second and third coils. The depen-dencies of the kinetic energy of accelerated electrons at the maximum spectrum and maximum FWHM on the frequency of RF oscillations were measured at the same current (see Fig.3). The minimum width of energy spec-trum obtained FWHM of spectral curve was 2.8% and the kinetic  energy  at  the  maximum energy  spectrum  was 9.7 МeV at a beam pulse current of 253 mА.Spectral characteristics were also measured without focusing field. In this case, pulse current was reduced by  13…17%,  and  the  kinetic  energy  at  the  spectrum maximum and optimal frequency of RF oscillations in-creased up to 10 MeV, which evidently can be attributed to  a  decrease  in  the  current  of  accelerated  electrons (“unloading” of accelerating structure). Fig.4 shows the beam energy and energy spread as a function of the fre-quency of RF oscillations. It  is important that without solenoid  coils,  the  energy  spectrum width  FWHM of spectral curve was reduced to 2%.It should be also noted that with RF focusing only, we managed to attain a beam of accelerated electrons with smaller diameter.When testing the second accelerating unit, we used the KUY-147А klystron with a pulse power of 6 MW, approximately, (duty cycle was QRF = 240).We used the methods of  the ASTM 1649-94 stan-dard to measure the effective energy of the beam; it was 10.9 MeV at a pulse current of accelerated electrons of 270 mA.  With  a  standard  duty  cycle  of  the  beam of QRF = 270, this pulse current corresponds to an average beam current of 1 mA, i.e. an average beam power of 10.9 kW is attained. At reduced kinetic energy, higher beam power can be obtained, for example, by increasing the beam current by feeding currents to the coils of fo-cusing system without changing the filament of electron source. As was mentioned above, when testing the second accelerating unit, we used the double-electrode gun with the cathode of 14 mm diameter. In this case we obtained lower density of the current removed from the cathode, however,  wider energy spectrum was observed (up to 10% HWFM spectral line), and higher beam losses oc-curred  when  passing  through  accelerating  structure. Probably, the use of this electron gun with new optical elements contributed to larger diameter of the beam on extraction  foil,  which  was  placed  1300 mm from the outlet of accelerating structure. Besides, to increase the cross-section size of the beam, we used the current of the lens of current regulator and the currents of focusing coils (Table 2).The  beam  diameter  was  measured  with  a  film dosimeter of the SPDF-5/50 model, and the method of photometry was used. 82The radiation field flatness over the scanning length not worse than ±5% was obtained due to programmed shape of the current in the coils of scanning magnets.Fig.3. Kinetic energy of accelerated electrons at the maximum spectrum (curve1) and maximum FWHM (curve2) as a function of operating frequency Fig.4. Kinetic energy of accelerated electrons at the maximum spectrum (curve1) and maximum FWHM (curve2) as a function of operating frequency Table 2.The current of the lens of current regulator and the currents of focusing coilsLens current, mА Current of the 1st focusing coil, mАCurrent of the 2nd and 3rd focusing coils, mАBeam diameter,half-height, mА275 0 0 2,1260 26 6 4,4255 26 12 4,4245 26 18 4,1A 30-minute test of accelerating unit was performed under  rated  operating  conditions.  In  so  doing,  the steady-state thermal mode of the equipment of acceler-ating unit was attained. The instability of the energy and current  of  the beam of accelerated electrons was less than 2%, even without stabilization systems with feed-back circuits. This test was performed for a short period of time to limit the radiation impact on the ionizing radi-ation-sensitive units, which were located in the area of radiation danger because of the layout possibilities on test stand. When experimentally studying the accelerating units of UELR-10-10S LINACs, we obtained convincing evi-dences that the klystrons with a pulse power of 6 MW and an average power of 25…30 kW allowed the ob-taining of the beam performances necessary for effec-tive application of these linear electron accelerators to commercial systems for radiation processing.РАЗРАБОТКА И РЕЗУЛЬТАТЫ ИСПЫТАНИЙ УСКОРЯЮЩИХ УСТРОЙСТВ КОММЕРЧЕСКИХ РЕЗОНАТОРНЫХ ЛУЭ МОДЕЛИ УЭЛР-10-10С ДЛЯ РАДИАЦИОННОЙ СТЕРИЛИЗАЦИИВ.А. Алексеев, А.Е. Барановский, А.В. Белоусов, В.Н. Давыдов, М.И. Демский, К.А. Денисов, А.М. Фиал-ковский, Л.П. Фомин, Ю.Н. Гавриш, С.Н. Кочин, В.А. Ларионовский, К.Н. Маслов, В.М. Николаев, Д.А. Ободинский, А.В. Орлов, А.В. Рябцов, В.В. Рябов, Ю.П. Щепин, В.В. ТерентьевОписываются некоторые особенности конструкции ускорителей модели УЭЛР-10-10С, приводятся и об-суждаются характеристики электронного пучка, полученные экспериментально.___________________________________________________________PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.Series: Nuclear Physics Investigations (46), p.91-93. 91РОЗРОБКА І РЕЗУЛЬТАТИ ВИПРОБУВАНЬ ПРИСКОРЮВАЛЬНИХ ПРИСТРОЇВ КОМЕРЦІЙНИХ РЕЗОНАТОРНИХ ЛПЕ МОДЕЛІ УЕЛР-10-10С ДЛЯ РАДІАЦІЙНОЇ СТЕРИЛІЗАЦІЇВ.А.Олексієв, А.Е. Барановський, А.В. Белоусов, В.Н. Давидов, М.І. Демський, К.А. Денисов,  А.М. Фіалковський, Л.П. Фомін, Ю.М. Гавриш, С.Н. Кочин, В.А. Ларіоновський, К.Н. Маслов,  В.М. Ніколаєв, Д.А. Ободинський, А.В. Орлов, А.В. Рябцов, В.В. Рябов, Ю.П. Щепін, В.В. Терентьєв Описуються  деякі  особливості  конструкції  прискорювачів  моделі  УЕЛР-10-10С,  приводяться  і обговорюються характеристики електронного пучка, отримані експериментально.84

Accelerating units for commercial resonator LINACs model UELR-10-10S designed for radiation sterilization development and results of testing

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Accelerating units for commercial resonator LINACs model UELR-10-10S designed for radiation sterilization development and results of testing

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