Method for controlled collective acceleration of electron-ion bunches

FIELD: physics.

SUBSTANCE: invention relates to acceleration engineering. The method involves forming a high-current tubular beam of rotating electrons in a stationary magnetic field, capturing electrons in a magnetic trap, filling the electron bunch with ions by ionising gas in the vacuum chamber of an accelerator or from a plasma bunch prepared in advance. In the disclosed method, the external effective potential well of the magnetic trap is shifted stepwise and synchronously with the movement of ions and electrons are shifted and held in the direction of acceleration. The shift value of the centre of the well is selected at each step such that ions fall in the acceleration region through the electric field of the electron bunch.

EFFECT: avoiding disruption of the electron and ion components of bunches, disruption of the acceleration of ions over a long length and development of numerous instabilities, achieving high periodicity of operation and compactness of the accelerator and the possibility of accelerating a large number of ions per cycle (about 5 to 10) with short pulse duration and the possibility of accelerating ions over a long length.

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The technical field to which the invention relates.

The invention relates to accelerator technology.

The level of technology

Closest to the claimed invention is similar /1/, in which the magnetic field is of type "CASP" formed a thick ring of electrons rotating at relativistic velocities. Linear velocity of an electron ring along its axis after the "cusp" is non-relativistic, which allows to capture it in a stationary magnetic trap using a braking resistive screen. In the second close analogue of /2/ the ring is formed in the magnetic trap and compressed in the growing time of the magnetic field. Staying the ring is filled with ions, using the ionization of residual gas atoms in the vacuum chamber or gas jet /2/. Conclusion the electron-ion rings of traps is carried out by removing one of the barriers of the magnetic trap, which is accompanied by a decrease in the effective depth of the potential well up to scratch. Then the ring falls into the area falling along the axis of movement of the magnetic field and accelerated. If the electrons and ions are moving with the same velocity in the longitudinal direction, it turns out the winning collective acceleration of ions compared to direct their acceleration in an external electromagnetic field.

The lack of capture of high ELEH the throne of the beam in the stationary magnetic trap in the analog /1/ are large beam losses, due to the large acceleration of electrons own charge beam on the fronts of the current pulse. The second disadvantage is the use /1, 2/, and in other similar work (for example, /3/), the acceleration of the electron-ion rings in the falling magnetic field without external focusing of electrons in the direction of movement of the ring. As the experiments showed /2, 3/, the compactness of the ring is broken at small length of acceleration, the electrons run forward from the ions, and the ions do not acquire considerable energy.

Rupture of the electronic and ionic component is also characteristic of the collective method of ion acceleration in a straight high-current electron beams in the formation of a virtual cathode. So for a straight high-current beams have suggestions and successful experiments on laser control movement of the front of the electron beam in the collective accelerator /3-5/and also offer managed stepped collective accelerator using separate sources of high-current beams at each step /6/.

The disadvantage of ways managed collective acceleration /3-6/ being the use of powerful relativistic electron beams with currents of several tens of kA), large losses of electrons in the acceleration of ions and small frequency repetitions qi is fishing acceleration.

The invention

The basis of the proposed solution to the problem managed collective acceleration of ions is that the set of ion energy at the expense of a large private electric field of the electron bunch, and focusing of the electron bunch in the direction of the acceleration is due to the controlled movement of the magnetic potential well.

Known methods of collective acceleration of ions based on the use of circular or rectilinear high-current electron beams /2-3/. The main difficulties of collective acceleration of ions e-rings associated with the requirements of resistance rings in their formation and preservation of the integrity of the electron-ion rings during acceleration. For example, experiments in Garching (Germany) showed that the joint motion of the electron and ion rings breaks down on the length of a few centimeters. The electrons come out ahead and not accelerate ions. The protons gain energy of about 200 Kev /3/. The technical difficulties of ensuring joint acceleration of electrons and ions due to the need to withstand difficult to realize the relative gradient of the leading magnetic field at the level of 10^-4cm^-1.

In the proposed approach, the problem of the integrity of the electron-ion bunch is that the motion of the electron is about clot is controlled by a system of coils with programmable pulse currents so to ensure that the average simultaneous promotion of clots along the system turns with a set of ion energy at each discrete step one.

Information confirming the possibility of carrying out the invention.

The ability of the proposed method managed collective acceleration of ions electron bunches using picosecond relativistic electron beams /7/ shown in the numerical experiments on the basis of the software package CARAT /8/. Schematic diagram of the setup for controlled acceleration of the ions is shown in figure 1. The picture shows a thin-walled tubular cathode with a radius of 30 mm and two counter enabled solenoid, the radius of the solenoids is 50 mm, the Cathode is in the field of homogeneous longitudinal magnetic field with an induction of 2 kgf. Between the solenoid creates a magnetic field with a predominantly radial lines of force of the magnetic field region "cusp". The distribution of the axial component of the magnetic field near the axis shown in figure 2.

In the numerical experiments, the electrons were injectibles from the edge of the cathode with a thickness of 100 μm to a radius of 3 cm in the axial direction with the energy of accelerated electrons - 2.1 MeV. The duration of the current pulse is 0.8 NS, a current of 1 kA, which corresponds to 5·10¹²the particles in the electron bunch. In the field for the "cusp" prodelin the I speed of the electrons is significantly reduced and formed a clot of electrons, rotating at relativistic velocities. The relativistic rotation of the clot weakens the effect of acceleration of the head part of the clot associated with its large spatial charge /7/.

When you enable current loop located at a distance of ~ 18 cm from the center of the "cusp", is formed a magnetic trap, which is captured electron bunch. Before the injection of electrons in the field, where a captured electron bunch, creates a bunch rarefied hydrogen plasma, is presented for modeling in-plane R-Z in the form of a rectangle 1×15 cm and the average radius is 2.5, see the plasma Density is 1.8·10⁹cm^-3that corresponds to the number of ions ~10% of the number of injected from the cathode electrons. When the grip ring in the magnetic trap plasma electrons leave the plasma clot under their own fields injected from the cathode electrons. Thus, in the magnetic trap remains captured clot rotating relativistic electron and ion component of the plasma, which is captured by its own electric field of space charge of the electrons. To increase the density of the electron bunch with the purpose of increase accelerating ions fields were conducted its longitudinal compression by incorporating adjacent to the barrier turns.

Captured this image of the electronic the electronic clot can move along the axis of symmetry of the system, moving in space magnetic hole in which it is located. Such movement of the magnetic holes is ensured by successive washings of coils forming a magnetic trap. When modeling the coils with a radius of 4.75 cm were placed along the axis of acceleration through a 3 cm from each other. To move a bunch of electrons at one stage removed the shock front in the direction of movement of the clot and turn supplied the following after him round. This current in turn back temporarily doubled to boost e-clot. The characteristic time for thermal turns of ~ 5 NS. E-ring is moved after the pit stops it for a while to accelerate ions. Then the described process is repeated. The duration of each such cycle gradually decreases from ~ 8 NS at the beginning of acceleration up to ~1 NS 40 NS after the start of acceleration. Ions of the plasma during this stretch for electronic stirred, gradually speeding up the tempo set the average energy of ~ 3 MeV/m

The main results of the numerical experiment are illustrated by figures 3, 4. In Fig.3 is shown in dependence on the longitudinal coordinate radii random sample of particles R, energy E, the longitudinal β_zand azimuth β_φparticle velocity (in units of the speed of light). Figure ions corresponds to the color red, electric is Onam - blue. The three lines correspond to three specific points in time - the beginning, middle and end of the acceleration process.

The main conclusion that can be drawn from the analysis of the dynamics of particles on the first column: in the numerical experiments are implemented collective acceleration of ions at large length of acceleration while keeping the electrons moving in an effective external potential well. The loss of ions during acceleration is negligible. The electron-ion clot geometrically is a hollow cylinder with a length of about 10 cm, and the inner and outer radii, respectively, 2-3 see

As the accelerated motion of the external potential well synchronized with the movement of the ions, the ions gain energy with great acceleration rate is the second column of Figure 3. The third column demonstrates the synchronous average motion of ions and electrons. The results of the fourth columns show the relativistic rotation of the electron bunch through which reduces the repulsion of electrons in the longitudinal direction.

Fig.4 gives the opportunity to evaluate the rate of the energy and energy spread collectively accelerated ions.

Thus, the numerical experiment showed that the performance in question managed collective method of ion acceleration electron bunches using picosecond relativistic the x electron beams. In contrast to the known collective methods of acceleration of the proposed method prevents the breakdown of electronic and ionic component of clots and disruption of ion acceleration and development of numerous instabilities, since the duration of the acceleration cycle is in the nanosecond range. Using picosecond pulsed electron beam provides the ability to get more cycles of operation and compactness of the accelerator. Advantages of the new method associated with acceleration a large number of ions in the cycle (~5·10¹¹) with a short pulse duration and the possibility of ion acceleration at great length. This accelerator should be of interest for various applications.

1. Schematic diagram of the setup for managed collective acceleration of ions: 1 - cathode, 2 - foil 3 - the system turns with a pulse washing, 4 - power source diode, 5 - system delays for sequential feeding of coils, 6 - power supply coils, 7 - electron-ion clot, 8 - system solenoids.

The picture shows a thin-walled tubular cathode with a radius of 30 mm and 2 counter is enabled solenoid, the radius of the solenoids is 50 mm, the Cathode is in the field of homogeneous longitudinal magnetic field with induction ≈2 kgf. Between the solenoid creates a magnetic field mainly for lname lines of force of the magnetic field area "cusp". The figure also shows the managed current coils with elements of power and control.

Bibliographic data

1. .D.Striffler, R.A.Meger, J.Grossmann, E.Pappas, M.Reiser, M.J.Rhee, T.F.Wang, Electron Ring Accelerator Research at the University Of Maryland, IEEE Transactions on Nuclear Science, Vol. NS-26, No. 3, June 1979.

2. Wppearances, E.a.perelstein, Collective acceleration of ions e-rings, Atomizdat, M., 1979.

3. G.L.Olson, Schumacher U, Collective Ion Acceleration, Berlin-Heidelberg - New York, Springer - Verlag, 1979.

4. C.L.Olson, C.A.Front, E.L.Patterson, J.P.Anthes and J.W.Poukey, Experimental Demonstration of Controlled Collective Ion Acceleration with the lonization-Front Accelerator, Phys. Rev. Lett. 56, 2260 (1986).

5. R.L.Yao, W.W.Destler, C.D.Striffler, J.Rodgers, Z.Segalov, Measurements and Simulation of Controlled Beam Front Motion in the Laser Controlled Collective Accelerator, RAS 1989, pp.624-626.

6. J.L.Adamski, Multi - Stage Collective Field Charged Particle Accelerator, US Patent 4,296, 327, Oct. 20, 1981, Field of Search 250/423.

7. Gaesar, Mielonen, Picosecond electronics high power, UFA, 175, N 3, 2005, s-246.

8. V.P.Tarakanov, User's Manual for Code KARAT", (ver. 7.09, April, 1999).

The way managed collective acceleration of the electron-ion clots, including the formation of high-current tubular rotating beam of electrons in a stationary magnetic field type "CASP", the capture of electrons in a magnetic trap, the filling of the electron bunch ions, the acceleration of ions own electric field of the electrons, characterized in that the speed and synchronously with the movement of ions displace externalities the objective potential hole of the magnetic trap and provide offset and retention of electrons in the direction of the acceleration, the amount of displacement of the center of the hole is chosen at each step, so that the ions hit the region accelerate their own electric field of the electron bunch.