This paper presents the project of an industrial accelerator of the modular structure. Accelerating structure consists of the chain of coaxial ILU cavities, connected by the coupling cavities. Two designs of accelerating structure, differing by a version of coupling cavities, are presented. Main parameters of the accelerator are: energy of electrons 5-10 MeV, average beam power up to 150 kW, operating frequency 176 MHz, duty factor 10%

Auslender, V.L.

Bazhenov, O.Yu.

Cheskidov, V.G.

Karliner, M.M.

Kuznetsov, G.I.

Makarov, I.G.

Ostreiko, G.N.

Panfilov, A.D.

Tiunov, M.A.

Tkachenko, V.O.

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

INDUSTRIAL HIGH POWER ELECTRON ACCELERATOR FOR THE ENERGY 5-10 MEVV.L. Auslender, O.Yu. Bazhenov, V.G. Cheskidov, M.M. Karliner, G.I. Kuznetsov,  I.G. Makarov, G.N. Ostreiko, A.D. Panfilov, M.A. Tiunov, V.O. TkachenkoBudker Institute of Nuclear Physics, Novosibirsk, RussiaThis paper presents the project of an industrial accelerator of the modular structure. Accelerating structure consists of the chain of coaxial ILU cavities, connected by the coupling cavities. Two designs of accelerating structure, dif-fering by a version of coupling cavities, are presented. Main parameters of the accelerator are: energy of electrons 5-10 MeV, average beam power up to 150 kW, operating frequency 176 MHz, duty factor 10%.PACS number: 29.17.+w1  INTRODUCTIONExperience  in  development  and  maintenance  of ILU-type accelerators has shown that the single-cavity system  with  one  accelerating  gap  can  be  effectively used for the industrial accelerators with the energy up to 5 MeV and beam power up to 50 kW [1, 2]. Increasing the  electron  energy beyond 5 MeV evidently  requires the system with several accelerating gaps, connected in sequence. ILU-11 with two accelerating gaps was the first accelerator of such a type [3]. Its RF power source, modulator and control system were similar to those of the other ILU-type machines. ILU-11 was designed as a basic unit for the further development of new accelera-tors with a higher energy and power of electron beam. The main parameters of ILU-11:Energy – 2.5-5 MeVAverage beam power – up to 60 kWOperating frequency – 176 MHzShunt impedance of the accelerating structure – 13.4 MOhm/mDuty factor – 2.5%2  ACCELERATING STRUCTUREThere are two possible variants of accelerating struc-ture design. First variant is based on the ILU-11 acceler-ating structure. It is a three-circuit cavity, in which the coaxial line with length  λ/2 plays the role of coupling cavity.  In  the  accelerating  quarter-wave  cavities  with operational mode pi/2, the oscillations with phase shift pi is formed, thus providing the electron acceleration.Fig. 1. ILU-11 accelerating structure unit:  (a) -  coupling cavity, (b) - accelerating cavity.Заголовок:T:\BAZHENOV\RIS2.EPS Создан:AutoCAD PSOUTЭскиз:При сохранении этого рисунка EPSне был включен его эскиз.Заметки:Этот рисунок EPS можно напечатать только на принтере PostScript.Fig. 2. Drawing of the accelerating structure, con-sisted of four ILU-11 units.Fig.  1  shows  the  unit  of  accelerating  structure ILU-11 with electric field lines distribution. At the opti-mal dimensions of the cavities the coupling could reach 15%. Such units,  consisted of  2 quarter-wave cavities and half-wave coupling cavity, could be combined into extensive accelerating structure. Increasing the number of these units we can either increase the energy gain of the accelerator or decrease the RF power, spent on ac-celerating field creation. Fig. 2 presents a drawing of ac-celerating structure,  which consists  of four  units.  The DC voltage for the multipactor suppression can be creat-ed at the isolated inner parts of cavities with alternating polarity. However, such design makes difficulties with the cavity inner parts cooling.Another  variant  of  the  accelerating  structure  as-sumes that  coupling cavity appears on the axis in be-tween the neighboring quarter-wave accelerating cavi-ties. Its resonant frequency is provided by the intrinsic capacity,  while  coupling –  by two slots  in  the  walls. With length of the slots about 80° of circumference, the coupling is about 10%. Fig. 3 presents the accelerating structure unit  with electric  field lines at  the operating mode pi/2.Fig. 3. Accelerating structure unit with an axis situ-ated on the coupling cavity: (a) - coupling cavity,  (b) - accelerating cavity.       ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.Серия: Ядерно-физические исследования (38), с. 18-20.18Fig.4 presents a design of accelerator with structure, combined from four units described above. The advan-tage of this scheme is simplicity of the single-wall de-sign, convenient cooling (through wall tubes), and high resistance to the thermal deformation. The disadvantage is, obviously, the necessity of covering the copper sur-faces  by  titanium nitride  for  the  multipactor  suppres-sion. Nevertheless, due to relative simplicity of the con-struction, we have chosen the variant of the accelerating structure with an axis situated on the coupling cavities. The design, described below is based on this variant.Заголовок:T:\BAZHENOV\RIS4.EPS Создан:AutoCAD PSOUTЭскиз:При сохранении этого рисунка EPSне был включен его эскиз.Заметки:Этот рисунок EPS можно напечатать только на принтере PostScript.Fig. 4. Accelerator design with an axis situated on the coupling cavities.3  OPERATION OF THE ACCELERATORThe  accelerator  operates  in  pulsed  mode  at  a  fre-quency of 176 MHz. In order to create a necessary ac-celerating gradient  for  gaining 5 MeV by electrons at 4-units accelerating structure, we need the RF power of about 0.6 MW. Table 1 presents values of the RF pow-er, dissipated in the accelerating structure in dependence on the electron energy and quantity of units (in paren-theses).Table 1E, MeV 5(4) 7(4) 7(6) 10(8) 10(10)Pc MW 0.625 1.22 0.8 1.25 1.0Limiting the power level for creation of the acceler-ating gradient by 1 MW, with a power supply output of 2.5 MW, we can transfer about 1.5 MW to the beam. Accepting 150 kW as an average beam power we can set the duty factor to 10%. Such a power output could be obtained from the tetrode EIMAC 4CM2500KG or diacrode TH628.4  RF POWER SOURCEFig. 5 presents the design of the generator based on the  EIMAC  4CM2500 KG  tetrode  at  a  frequency  of 176 MHz. Anode and cathode circuits are situated at the opposite sides of the tetrode. High frequency blocking of the shielding grid is performed using a structural ca-pacity. The driving grid is solidly grounded, while the cathode is  under  positive potential  due to  the voltage drop on the bias resistor. The electric length of the an-ode circuit is equal to the wavelength λ [4]. This design allows one to make cooling water input and DC anode voltage supply inlet at the second minimum of voltage in the anode circuit. Moving of external tube bottom of the anode circuit performs fine tuning of the frequency. Diameters of the tubes are 600 and 300 mm correspond-ingly.  Coupling  with  the  anode  circuit  is  inductive. Feeders cross-sections is 160x70 mm. Diameters of the cathode  circuit  tubes  are  280 and 216 mm.  High fre-quency  blocking  is  performed  by  the  ring  capacitor KVK, circuit placed at the minimum of the central con-ductor current. The circuit is tuned by a short-circuiting plunger. The cathode circuit has a conductive coupling. The electric length of the circuit is about 1m.Заголовок:T:\BAZHENOV\RIS5.EPS Создан:AutoCAD PSOUTЭскиз:При сохранении этого рисунка EPSне был включен его эскиз.Заметки:Этот рисунок EPS можно напечатать только на принтере PostScript.Fig. 5. Drawing of the RF power source, based on the 4CM2500KG tetrode.       ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.Серия: Ядерно-физические исследования (38), с. 19-20.19Power from the anode circuit, through the feeder and the  coupling  loop,  goes  to  the  accelerating  structure (there  is  also  a  variant  of  power  supply  through two coupling loops). Our Institute has an experience in the feeding of accelerating structures by the coupling loop (up to 200 kW of continuos power). Couplers are placed on the cowling of the central cavity that gives twice as less frequencies at the dispersion characteristic. There is also  the  feedback  loop,  from  which  the  power  goes through the feeder with a cross-section of 70x30 mm to the cathode circuit, thus creating the feedback. For the appropriate phasing the line has a phase shifter - either mechanical or ferrite. Fig. 6 shows the generator with an accelerating structure.Заголовок:T:\BAZHENOV\RIS6-BW.EPS Создан:AutoCAD PSOUTЭскиз:При сохранении этого рисунка EPSне был включен его эскиз.Заметки:Этот рисунок EPS можно напечатать только на принтере PostScript.Fig. 6. RF power source with the accelerating structure.5  BEAM DYNAMICSAs an electron source, the triode RF gun is used. It is formed by placing the cathode-grid unit directly into the first accelerating gap. The cathode is made from LaB6 and its diameter is 20 mm. A required current magni-tude is obtained by choosing the cathode-grid gap and the penetration factor of the grid. If the higher current is needed or/and we need to compensate transit effects, it is possible to put an additional voltage of either basic or second harmonic with the appropriate phase shift to the cathode-grid gap. Numerical simulation of the beam dy-namics from the grid to the accelerator output was per-formed in a long-wave approximation using the SAM code [5, 6]. The transverse velocity spread of electrons, due to scattering on the microlenses, formed by the grid mesh, was taken into account. This led us to increasing the accelerator aperture in comparison with a single-gap variant. Fig. 7 shows the results of simulation of four-gaps accelerator on the energy 5 MeV. There are trajec-tories of the electrons, started from the cathode edge at different  input  phases.  The  simulations  showed  that there is no need in any magnetic focusing elements for the successful transportation of the beam.Заголовок:T:\BAZHENOV\H55_8P05S_8GH_A70_R10_R20_V1_02.EPS Создан:AutoCAD PSOUTЭскиз:При сохранении этого рисунка EPSне был включен его эскиз.Заметки:Этот рисунок EPS можно напечатать только на принтере PostScript.Fig. 7. Trajectories of electrons in the accelerator.6  CONCLUSIONHere presented is the project of the industrial elec-tron accelerator of a modular design, based on the chain of  coaxial  ILU cavities,  connected  each  other  by  the coupling cavities. We have chosen a variant with axis-situated  coupling  cavities.  Number  of  units  is  deter-mined by the energy of the beam. The supposed energy range is 5-10 MeV, operational frequency is 176 MHz; average beam power is 150 kW at a duty factor of 10%.REFERENCES1. V.L.Auslender.  ILU-type  electron accelerators  for industrial technologies //  Nuclear Instruments and Methods  in  Physical  Research. 1994,  B89, p. 46-48.2. V.L.Auslender,  et  al.  Compact  ILU-type  electron accelerators as a base for industrial 4-sided irradia-tion  systems  for  cable  and  tubes  //  Radiation Physics and Chemistry. 1999, v. 54, p. 609-618.3. V.L.Auslender,  A.D.Panfilov,  V.O.Tkachenko, A.A.Tuvik.  Powerful  high  frequency  electron  ac-celerator ILU-11 for the energy range up to 5 MeV // Proc. of ECAART-99 Conference, Dresden, 1999.4. B.P.Murin  et  al.  Ion  linear  accelerators. Vol.  2. Moscow: Atomizdat, 1978, 157 p. (in Russian).5. B.Fomel,  M.Tiunov, V.Yakovlev. Computer-aided electron gun design // Proc. of the XIII Internation-al  Conference  on  High  Energy  Accelerators, Novosibirsk, 1987, v. 1, p. 353-355.6. B.Fomel, M. Tiunov, V.Yakovlev. SAM – an inter-active code for evaluation of electron guns. Preprint BudkerINP 96-11, 1996.20

Industrial high power electron accelerator for the energy 5-10 MeV

http://dspace.nbuv.gov.ua/bitstream/handle/123456789/79217/06-Auslender.pdf?sequence=1

Industrial high power electron accelerator for the energy 5-10 MeV

Abstract

Similar works

Full text

Available Versions

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