Presented are the results of studies concerning the multybeams systems and considering the possibility to increase the output current amplitudes by changing the geometrical dimensions of guns

Fernandez, Diana

Geiger, Jean-Paul

Ouinten, Mohamed

Tantaoui, A.

The genetic diversity of the date palm wilt pathogen #Fusarium oxysporum$ f. sp. #albedinis$ in Algeria was assessed using vegetative compatibility, restriction fragment length polymorphism (RFLP) of mitochondrial DNA (mtDNA), and random amplified polymorphic DNA (RAPD). Ninety-eight isolates were collected from the main infested regions, Touat, Gourara and Mzab, and 6 isolates from Morocco were added for comparison. All isolates were vegetatively compatible and belonged to VCG 0170. No variation was detected in the mtDNA of a subset of 73 isolates and the RAPD analysis indicated that they were genetically very closely related. However, some geographic substructuring was apparent, suggesting that local diversification of the pathogen might have occurred. These results provide evidence that the Algerian isolates of #F. oxysporum$ s. sp. #albedinis$ belong to a same clonal lineage and support the hypothesis that they were probably founded by a single virulent clone that originated from the Moroccan oases where the date palm wilt (Bayoud disease) was first detected. Based on similarity of RAPD patterns occurring in different oases, and on historical records of the Bayoud disease in Algeria, spread of the pathogen in the different regions is discussed. (Résumé d'auteur

Name not available

Molecular records of micro-evolution within the Algerian population of Fusarium oxysporum f. sp. albedinis during its spread to new cases

Dovbnya, A.N.

Reshetn’yak, N.G.

Zakutin, V.V.

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

STUDYING THE ELECTRON FLOW FORMATION IN MAGNETRON GUNS WITH A SECONDARY EMISSION METALLIC CATHODEA.N. Dovbnya, N.G. Reshetn’yak, V.V. Zakutin National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine Presented are the results of studies concerning the multybeams systems and considering the possibility to increase the output current amplitudes by changing the geometrical dimensions of guns.PACS: 84.40.Cb.INTRODUCTIONThe  problem  of  extending  the  life-time  and increasing of the pulse and average power of many RF-sources is closely related to the design of their electron guns. As it is known, the magnetron injecting guns with secondary  emission  metallic  cathodes  (SEMI)  are specified by the high current emission density and long life-time.  The  main  goal  of  these  investigations  is  to determine  the  advantages  and  limitations  of  using SEMIGs  as  the  electron  source  in  high-power  RF devices and accelerator injector systems. At this stage we  have  studied  some  questions  concerning  the operational  beam  stability,  voltage  and  current increasing.  The  experiments  have  been  performed  by using  the  experimental  setup  to  investigate  SEMIG linear  electron  beam  parameters  from  single  and multiple beams gun assemblies with the anode voltage up to 100 kV, pulse duration up to 10 µs, repetition rate 50 Hz and 0.1-0.2 T magnetic field strength.  Pulse-to-pulse long-term stability of the annular electron beams (internal diameter nearly equal to the cathode diameter, wide  of  ring  1-2 mm  (wavelength  of  cyclotron oscillations)) with beam density up to 70 A/cm2 (1010-1011 e-/cm3)  has  been  achieved.  It  is  shown,  that  the cathode  diameter  extension  provides  a  proportionate increasing  of  the  beam  current,  and  in  the  case  of multiple  beam  gun  assemblies  we  have  separate identical electron beams with the similar parameters of single-beam gun.A  task  of  creating  the  long-lived  high-energy electron  sources  is  one  of  the  main  problems  in  the acceleration engineering. As it was shown earlier [1, 2] the  so-called  secondary-emission  magnetron  guns (SEMIG) with cold metal cathodes are specified by a high  beam  density,  high  lifetime  and  instantaneous operation readiness. On our opinion the guns of such a type are highly promising for the use in RF-sources and accelerators,  in  particular,  in  multybeam  and  cluster klystrons  [3,  4]  as  well  as  in  high-current  injector systems,  for  example,  in  the  installation  such  as  RK TBA  [5],  CESTA  TEST  FACILITY  [6]  and  ion accelerators driving ring electron beams [7].The present paper continues the experimental study of characteristics of such guns. We studied the current-voltage and spatial  characteristics,  conditions of beam generation and stability.  The amplitude modulation of the emission current in the variable electric fields was investigated.  Presented  are  the  results  of  studies concerning the multybeams systems and considering the possibility to increase the output current amplitudes by changing the geometrical dimensions of guns.FACILITY DESCRIPTIONInvestigations on the beam generation in magnetron guns with secondary-emission cathodes were conducted at  the  facility  the  layout  of  which  is  represented  in Fig. 1.  In  these  experiments  the  pulse  of  a  negative polarity  from modulator  1  forming  the  voltage  pulse (amplitude  4  to  100  kV,  duration  4  to  10  µm  and repetition rate 50 Hz) is fed to cathode 5 of the gun and its anode 6 is grounded via resistor R3 and connected to generator 2. The process of secondary-emission electron multiplication took place at the fall of the voltage pulse being formed with modulator 1 or generator 2. The  magnetic  field  for  the  beam  generation  and transport  was created with solenoid 4 consisting of  4 sections having 550 mm length and being supplied from independent current sources that allowed one to change the  spatial  distribution  of  the  magnetic  field  and  its amplitude.  The  beam  transport  was  performed  at  a distance  80  to  160  mm  from  the  anode  cut  to  the Faraday cup.Measurement  of  the  beam  current  was  conducted with applying Faraday cup 7 made as a section of the coaxial line and resistor R4=12 Ohm equal to the wave resistance of the line; the cathode voltage was measured with  the  use  of  divider  R1R2;  the  beam dimensions - with the  use  of  a  dent  on the X-ray film and on the molybdenum foil disposed at the coaxial line end. The magnetron  gun  with  a  copper  cathode  and  an  anode made from the stainless-steel or copper having 120 mm length was placed inside vacuum chamber 3 evacuated to a pressure of ≤ 10-6 Torr. EXPERIMENTAL RESULTS AND DISCUSSIONThe electric field in the anode-cathode gap, which is required for the beam generation in the magnetron gun, should have two time intervals: the first is the section with  the  field  fall  where  the  secondary-emission multiplication  and the  formation  of  an electron cloud around the cathode occur, and the second is the section with a constant field providing the steady-state stage of the  secondary-emission  process  and  beam  generation [8,9].  The  fall  sharpness  and  duration  determine  the PROBLEMS OF ATOMIC ENERGY AND TECHNOLOGY. 2001, № 1.Series: Nuclear Physics Investigations (37), p. 109-111.109stability of beam generation and temporary instability of beam current pulse front generation. A non-uniformity at the flat - top part of the pulse can lead to the beam current pulse modulation or to the current pulse blowout as well as to generation of several electron clusters in the  single  voltage  pulse  [8]  and  determines  also  the permissible spread of the electron beam energy.Fig. 1The  given  time  dependency  of  the  electrical  field between the cathode and the anode is gained by forming the voltage pulse of a special form with the burst at the top having a short fall and long flat part at the cathode or with simultaneous feeding of two voltage pulses towards the cathode and anode forming the given electric field.The first method was based on forming a cathode voltage pulse of a special form with the blowout at the top. In the modulator with a complete discharge of the forming line a voltage pulse with the blowout and flat part  can  be  obtained  using  a  correcting  capacity  C (Fig. 1) connected in parallel to the forming line [10]. Changing  the  C  value  one  can  regulate  the  burst amplitude. A feasibility of forming the burst at the cathode voltage pulse was checked experimentally. The forming line had the wave resistance of 40 Ohm, pulse duration at a half-height  of  4.5 µm.  The  voltage  pulse  of  a  modulator being “on no load” at C=0 had the burst of 25% of the voltage pulse amplitude (Fig. 2). When connecting the capacity C =15 nF the burst amplitude was 50% (curve 1)  of  the  voltage  pulse  amplitude.  In  one  of  the operating modes when generating the 9A electron beam the burst amplitude was ~ 60 kV, the amplitude of the flat part during “on no load” operation was 37 kV and “with the beam” ~ 30 kV.             U (kV)t (µs)Fig. 2The second method (Fig. 2) consists in summation (with a total load - cathode, two voltage pulses) of the long pulse with a  flat  top and the  short  pulse with a sharp fall, and formation of the voltage pulse having the form close to that of above mentioned one.Experimental study of this scheme for forming the pulse was conducted at a wave resistance of the forming line ρ=15 Ohm. The burst amplitude was ~ 15 kV, flat-topped pulse amplitude at a beam current of 23 A was ~ 13 kV (Fig. 3). The burst amplitude and the amplitude of a main part of the pulse during beam generation are almost equal. The fall duration in this scheme, like to the first method, equals to hundreds of nanoseconds that is connected with the influence of stray parameters of the modulator output circuit.Fig. 3             U (kV)                                         J(A)t (µs)Fig. 4The  third  method is  the  summation  in  the  anode-cathode gap of the electrical fields of two pulses: long flat - topped pulse being fed towards the cathode, and short pulse with a sharp fall being fed towards the gun anode in order to obtain the given time dependence of the summated electrical field [8]. The electrical fields of these pulses are summed in the anode-cathode gap. In this scheme the sharing of pulse feeding circuits permits to use a  wide-band transmission line.  Duration of  the fall pulse at the anode providing a process of secondary-emission multiplication and beam current pulse timing can achieve several nanoseconds (Fig. 4).Investigations of beam parameters were carried out with  the  use  of  all  the  described  above  methods  of forming a voltage pulse. The experiments have shown that the beam current amplitude at the Faraday cup has a threshold dependence on the fall sharpness and does not 110depend on the  scheme of  secondary-emission  process excitation.  The  minimum fall  sharpness  at  which one observes  beginning  of  the  process  of  secondary-emission multiplication and beam generation equals 20 to 30 kV/µs. In Fig. 5 represented is the dependence of the  current  towards  the  Faraday  cup  on  the  voltage amplitude at the cathode with a diameter of d=2 mm and anode diameters D=10 mm; D=22 mm and D=50 mm. The figure shows that  the measurement results  are in accordance with the calculation by the “3/2”law. In the process of measuring, in each of points, the magnetic field value was set respectively to the maximum beam current value. In this figure given are the magnetic field values at which the beam generation takes place. In the gun  with  a  cathode  diameter  of  2 mm and  an  anode diameter  of  50  mm  with  a  voltage  amplitude  at  the cathode of 50 kV a beam current  of 7 A was gained. The magnetic field strength was 2550 Oe.U (kV)Fig. 5We have carry out research on generation of electron beams in the magnetron guns of a large aspect ratio with a cathode diameter of 2 mm and an anode diameter of 50  mm and 78  mm depending  on  the  magnetic  field value.  It  is  shown  that  for  the  voltage  amplitude  of flatted-top pulse 40 to 50 kV and low magnetic fields (700  to  1200  Oe)  one  observes  the  generation  of electron beams with a current of 0.5 to 1.5 A (the Hall cutoff field was ~ 600 Oe and ~ 400 Oe, respectively). Here the outside beam diameter was ~ 15 mm. In this case the beam from the magnetron gun with a cathode diameter of 2 mm and an anode diameter of 50 mm at a distance of 130 mm from the anode cut had an outside diameter  of 4  mm and inside diameter  of 2 mm. The measurement results are given in the table.d mmD mmU  kV I  A H   Oe2 50 40…55 0,8 800…12002 50 40…55 7 25002 78 40…55 1,0 700…1200REFERENCES1. F. Skrowron.  The  Continuous-Cathode  (Emitting-Sole) Crossed Field Amplifier // Proc. of the IEEE, 1973, v. 61, № 3, p. 330-356.2. A.N. Dovbnya et al. Secondary Emission Magnetron Injection  Gun  as  High  Current  Durable  Electron  Source. Proc. of 1994 Pulsed RF Source for Linear Colliders  Workshop  (RF’94),  October  1994, Montauk, Long Island, New York. AIP Conference proceeding, 1995, p. 350-359.3. R.B. Palmer  et  al.  An  Immersed  Field  Cluster Klystron  //  Particle  Accelerators. 1990,  v. 30, p. 197-209.4. R.B. Palmer et al.  Status of the BNI - MIT - SLAC Cluster Klystron Project - Proc. of 1994 Pulsed RF  Source  for  Linear  Colliders.  Workshop  (RF’94), October  1994,  Montauk,  Long  Island,  New York. AIP Conference Proceeding. 1995, p. 12.5. G.A. Westenskow et al. Relativistic Klystron Two-Beam  Accelerator.  Special  Issue  on  High  Power Microwave  Generation  //  IEEE  Transaction  on Plasma Science. 1994, v. 22, N 5, p. 750-755.6. I. Wilson.  CLIC  Test  Beam  Facilities-Status  and Results  -  Proc.  of  the  XVIII  Jnt.  Linear  Accel. Conference, Geneva, 1996, v. 1, p. 552-557.7. V.P. Sarantsev  et  al.  Kollektivnoe  uskorenie  ionov  elektronnymi  koltsa, M.,  Atomizdat,  1979  (in Russion). 8. A.N. Dovbnya  et  al.  Obtaining  of  high-power electron beams on magnetron guns with secondary-emission cathodes // Journ/ of Tekhn. Phys. 2001, v. 46, №2, p.98-104 (in Russian).9. S.A. Tsherenshikov.  On  switsh  magnetron  wlth secondary-emission  cathode  //  Elektronnaya tekhnika, ser. 1. 1973, №6, p. 20-28 (in Russian).10. G.A. Mesyats.  Generirovanie  moshnikh  na-nosekundnikh impulsov. М: “Sov. radio”. 1974, 256 p.111

Studying the electron flow formation in magnetron guns with a secondary emission metallic cathode

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Studying the electron flow formation in magnetron guns with a secondary emission metallic cathode

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