RU2206140C1 - Laser ion source - Google Patents

Abstract

FIELD: acceleration engineering, ion implanting technologies and other industries using charged-particle sources. SUBSTANCE: laser ion source has target, laser, transit-time channel in the form of metal tube whose longitudinal central axis is aligned with original direction of hydrodynamic flow of plasma from target, and ion extraction system mounted on central longitudinal axis of transit-time channel; magnets are installed in transit-time channel so that they form in the latter multiple magnetic field inside the latter over entire length between target and ion extraction system; magnetic lines of force of this field are perpendicular to longitudinal axis of transit-time channel and its intensity approaches zero on central longitudinal axis and abruptly rises in vicinity of transit-time channel walls. EFFECT: enhanced efficiency of plasma holding in transit-time channel; reduced difference in speeds and angles of ion beam extracted from such source. 1 cl, 2 dwg

Description

 The invention relates to ion sources and can be used in accelerator technology, in ion implantation technologies and other areas of the economy where charged particles are required.

 Analogs of the invention are: a laser source with inertial ion confinement [1] and a laser source [2].

 The prototype of the invention is a laser ion source [3], consisting of a target, a laser, a passage channel made in the form of a metal pipe, the central longitudinal axis of which coincides with the initial direction of the hydrodynamic movement of the plasma flow from the target, an ion extraction system mounted on the central longitudinal axis of the transit channel, four electromagnetic coils mounted on the passage channel and creating an axially symmetric longitudinal magnetic field in it.

 The disadvantage is the low confinement of the laser-initiated plasma in the magnetic field of the transit channel and the large spread in the velocities and angles of expansion of the ions of the laser plasma, which reduces the ion beam current at the accelerator output.

 The aim of the invention is to increase the efficiency of plasma confinement in the passage channel of a laser ion source and to reduce the spread in the values of velocities and angles of expansion of the ion beam extracted from such a source.

 This goal is achieved by the fact that in the laser ion source, consisting of a target, a laser, a passage channel made in the form of a metal pipe, the central longitudinal axis of which coincides with the initial direction of the hydrodynamic movement of the plasma flow from the target, an ion extraction system mounted on the central longitudinal axis span channel, characterized in that the magnets are mounted on the span channel so that they form inside it along the entire length between the target and the multi-ion extraction system Aulnay magnetic field whose lines of force are perpendicular to the longitudinal axis of the transit channel, and the intensity of this field, approaching zero at a center longitudinal axis, increases sharply in the transit channel walls.

As a result of the proposed structural changes in the invention, new physical properties arise, namely:
- electrons, as the lightest and most mobile particles in a plasma, reflected by a magnetic field, are grouped on the central longitudinal axis of the passage channel, creating a radial electric field, which additionally contributes to the confinement of plasma ions in the region of this axis;
- multidirectional plasma ions, crossing the magnetic field lines, the direction of which in most cases, except for the region of the central longitudinal axis of the channel perpendicular to the ion velocity vector, is reflected from regions with a large magnetic field gradient to the center and are also grouped along the longitudinal axis of the channel. Since the laser plasma flow has an initial hydrodynamic velocity of directed motion, which structurally coincides in direction with the axis of the passage channel [4, 5], ions grouped in the region of the central axis of this channel are accelerated by the self-consistent electric field of the moving plasma [6] only in the extraction direction beam, improving its angular orientation;
- ions having a large transverse velocity component or moving away from the central axis of the passage channel, falling into the region of a stronger magnetic field, increase the length of their trajectories in comparison with ions moving along the central axis and having a small transverse velocity. Experiencing more collisions with the neutral component of the plasma, they transfer more kinetic energy to it than ions with a short trajectory. This energy is carried to the channel walls. This nature of the energy exchange and its dissipation, lowering the temperature of the ionic component of the plasma, contribute to a decrease in the spread of velocities and expansion angles in the ion beam extracted from the source.

 These physical properties contribute to the occurrence of positive effects compared to the prototype. The presence of a magnetic field of a given configuration and the resulting electric field increases the efficiency of confinement of a freely expanding laser plasma in the passage channel. Changing the resulting motion vector of plasma ions in the direction of extraction of a beam of charged particles and reducing the spread of their kinetic energy helps to improve the laminarity (congruence) of the ion beam extracted from the plasma and reduce the disordered component of the velocity of the beam particles. All this allows increasing the capture of ions by the accelerator and increasing the beam current at its output.

 It is known to use a multipole magnetic field to hold the plasma between the anode and cathode in an electric discharge [7], but no such field was used to hold a freely expanding laser plasma and change the direction of the ordered velocity of its ions.

 Analysis of the distinctive essential features and the properties manifested due to them associated with the achievement of a positive effect: the presence of structural changes that caused the appearance of new physical properties that led to a positive effect, allows us to assume that the claimed technical solution meets the criterion of significant differences.

 The laser ion source is shown in FIG. 1. It consists of a solid-state target 1 onto which a laser beam 2, a passage channel 3, magnets 4, and the well-known ion selection system 5 are incident. 5. FIG. 2 shows the placement of magnets 4 on the body of the passage channel 3 and the picture of the magnetic fields 6 and electric 7 in the passage channel, existing during the expansion of the plasma.

 The source works as follows. A laser beam 2, hitting a target 1 through an optically transparent technological window in the metal case of the passage channel 3 (the window is not shown in Fig. 1), evaporates the target material, ionizes it, forming a plasma bunch with characteristic dimensions do ~ 1-2 mm [8 ]. Technologically, the point where the laser beam hits the target is selected so that this bunch, forming on the central longitudinal axis of the passage channel 3, has a direction of the hydrodynamic component of expansion [9], which coincides with the axis. Magnets 4 are placed on the body of the passage channel 3 in such a way that the magnitude of the magnetic field 6, FIG. 2, which is close to zero on the central axis of the channel, increases sharply near its walls.

 It was shown in [7] that a magnetic field of a similar configuration with this kind of gradient reflects charged particles moving in the radial direction to the region of their minimum, holding the plasma in this region. Due to their low mass, plasma electrons will immediately be grouped on the central axis of the passage channel 3, having a free degree of motion only along this axis. As a result of such a redistribution of charged particles of the expanding plasma, a radial electric (E) field 7 is formed in the passage channel, FIG. 2, which, along with a magnetic (B) field 6, prevents the passage of positive ions to the walls of the passage channel. In analogs, plasma freely scatters in the passage channel.

 In the prototype [3], the longitudinal axial magnetic field does not reflect charged particles in the region of the central axis, but “freezes” the electrons on the lines of force over the entire section of the passage channel, as a result of which the plasma has a weak radial component of the electric field. The effect of its retention in such ion sources compared with the invention is significantly reduced.

 Unlike analogues [1, 2] and prototype [3], where the laser plasma has a free expansion zone before entering the magnetic field of the passage channel, and its ions acquire an additional transverse velocity component due to acceleration in self-consistent fields of the expanding plasma [6], in the present invention, the plasma is immediately formed in a magnetic field, which initially prevents its expansion and an additional increase in the speed of ions in all directions, except for the direction of beam emission, which coincides with the central axis of the longitudinal channel. In the proposed laser ion source, plasma whose electron temperature in the initial section of the passage channel does not exceed 50-70 eV should be kept from scattering [8]. We evaluate the possibility of its retention from a technological point of view.

где Те - температура плазмы, то протоны лазерной плазмы с Те= 100 эВ будут иметь скорости разлета на порядок большие. Выберем в качестве критерия удержания плазмы отражающую способность магнитного поля, которую приближенно можно оценивать через циклотронный радиус частицы ρ в этом поле, рассчитываемый в работе [9] по формуле ρ=Mi•ui/q•B, где Mi - масса иона, ui - составляющая скорости его движения перпендикулярно магнитному полю, В - величина магнитного поля, q - заряд иона. Видно, что для того же значения ρ, характеризующего эффективность удерживания ионов магнитным полем, для лазерной плазмы надо использовать большее на порядок магнитное поле. В работе [4] показано, что поперечная скорость ионов Рb²⁰⁷ лазерной плазмы на выходе пролетного канала длиной 75 см составляет величину V_┴~10•10⁵ см/с. Очевидно, что одни только "теплые магниты" (без использования криогенных технологий) не могут обеспечить поле с магнитной индукцией в десятки Тл, способное эффективно удерживать тяжелоионную плазму от разлета.According to [7, 10], a hydrogen plasma with a temperature of ~ 1 eV is effectively held in the region of an electric discharge in the center of a multipole magnetic field with an induction of 1-2 kG, with a tension gradient from the center to the periphery. The proton velocity of such a plasma, calculated according to well-known formulas, has a value of ~ 4 • 10 ⁴ cm / s. Since the transverse velocity of an ion in a plasma

where Te is the plasma temperature, then the protons of the laser plasma with Te = 100 eV will have scattering velocities an order of magnitude greater. Let us choose the reflectivity of the magnetic field as a criterion for plasma confinement, which can be estimated approximately through the cyclotron radius of the particle ρ in this field, calculated in [9] by the formula ρ = Mi • ui / q • B, where Mi is the ion mass, ui is a component of its speed perpendicular to the magnetic field, B is the magnitude of the magnetic field, q is the ion charge. It can be seen that for the same value of ρ, which characterizes the efficiency of ion confinement by a magnetic field, it is necessary to use a magnetic field larger by an order of magnitude for laser plasma. In [4], it was shown that the transverse velocity of Pb ²⁰⁷ ions of the laser plasma at the exit of the passage channel with a length of 75 cm is V _┴ ~ 10 • 10 ⁵ cm / s. Obviously, “warm magnets” alone (without the use of cryogenic technologies) cannot provide a field with a magnetic induction of tens of T, which can effectively keep the heavy-ion plasma from scattering.

где k - постоянная Больцмана, Те - электронная температура плазмы, е - заряд электрона, обеспечит перепад напряжения между электронной компонентой плазмы на центральной оси пролетного канала 3, и его стенками Vo~350-500 В. При движении плазмы вдоль пролетного канала ее плотность и температура будут уменьшаться. Согласно выражению (1) будет уменьшаться и удерживающее ионы электрическое поле Vo. Уменьшение температуры плазмы в процессе ее разлета, оцененное в [8]
VpTe^γ-1 = const (2),
где Vp - объем, занимаемый плазмой, Те - ее температура, γ - показатель адиабаты (для одноатомных газов γ=3/2) с учетом того, что объем плазмы изменяется по закону Vp~L, поскольку плазма от расширения по двум другим перпендикулярным координатам удерживается (Е • В) полями, произойдет в n~ (L/do)² раз. Если выбрать разлет L~4d_o, то n≅16 раз. Характер изменения радиального электрического поля по длине пролетного канала будет происходить, согласуясь с выражениями (1) и (2). В [6] показано, что процесс ускорения ионов, особенно многозарядных, происходит на расстояниях порядка радиуса пятна фокусировки. Образовавшийся при этом плазменный пакет движется далее со скоростями ~(10⁶-10⁷ см/с). Выберем в области с линейными размерами ~4do, учитывая изменение температуры плазмы (2), некоторое усредненное, явно заниженное, значение радиального электрического потенциала ~10 В/см. При диаметре пролетного канала D=10 см, видно, что даже такие тяжелые ионы лазерной плазмы, как Рb⁺¹ (имеющие температуру 30-50 эВ), будут удерживаться скрещенными (Е•В) полями на протяжении всего времени ускорения в области с размерами нескольких пятен фокусировки. Далее эти ионы будут двигаться в направлении системы отбора 5, фиг. 1, со все возрастающей упорядоченной составляющей дрейфовой скорости, а их диффузионная скорость, которая уже после прохождения области с линейными размерами ~4d_o становится в несколько раз меньше упорядоченной продольной скорости, будет постоянно уменьшаться с падением температуры разлетающейся плазмы. Эти факторы будут способствовать пролету ионов через канал дрейфа. Учитывая, что в начальной части пролетного канала (область пятна фокусировки) величина удерживающего радиального электрического поля наибольшая (~1000 В), т.к. Те плазмы наибольшая (~100 эВ), плотность заряженных частиц в плазме наибольшая, а радиус Дебая, характеризующий величину ускоряющего ионы самосогласованного электрического поля, между быстрой электронной и медленной ионной компонентами плазмы наименьший. Можно сделать вывод, что на данном участке происходит наиболее активный прирост горизонтальной составляющей скорости. Этот прирост продолжается и в дальнейшем, по мере прохождения частицами пролетного канала 3 согласно [6] . С учетом быстрого спада величины удерживающего ионы электрического поля, связанного с изменением температуры плазмы (2), видно, что ионы, родившиеся на мишени, свободно пройдут через пролетный канал, получив большее приращение скорости, совпадающей с направлением их экстракции, по сравнению другими направлениями движения.In the present invention, plasma ions will be held by a radial electric field, especially effectively in the initial section of the passage channel. The magnitude of the arising electric field in the passage channel, which, according to [11], depends on the plasma potential Vo

where k is the Boltzmann constant, Te is the electron temperature of the plasma, e is the electron charge, will provide a voltage drop between the plasma electron component on the central axis of the passage channel 3 and its walls Vo ~ 350-500 V. When the plasma moves along the passage channel, its density and temperature will decrease. According to expression (1), the ion-holding electric field Vo will also decrease. The decrease in plasma temperature during its expansion, estimated in [8]
VpTe ^γ-1 = const (2),
where Vp is the volume occupied by the plasma, Te is its temperature, γ is the adiabatic exponent (for monatomic gases γ = 3/2), taking into account that the plasma volume varies according to the law Vp ~ L, since the plasma expands along two other perpendicular coordinates held by (E • B) fields, will occur n ~ (L / do) ² times. If we choose the expansion L ~ 4d _o , then n≅16 times. The nature of the change in the radial electric field along the length of the passage channel will occur in accordance with expressions (1) and (2). It was shown in [6] that the process of acceleration of ions, especially multiply charged ones, occurs at distances of the order of the focus spot radius. The resulting plasma packet moves further with velocities of ~ (10 ⁶ -10 ⁷ cm / s). In the region with linear dimensions ~ 4do, we take into account the change in plasma temperature (2), a certain averaged, clearly underestimated value of the radial electric potential of ~ 10 V / cm. With the diameter of the passage channel D = 10 cm, it is clear that even such heavy laser plasma ions as Pb ⁺¹ (having a temperature of 30-50 eV) will be held by crossed (E • B) fields for the entire acceleration time in the region with dimensions a few spots of focus. Further, these ions will move towards the selection system 5, FIG. 1, with an ever increasing ordered component of the drift velocity, and their diffusion velocity, which after passing through the region with linear dimensions ~ 4d _o, becomes several times smaller than the ordered longitudinal velocity, will constantly decrease with decreasing temperature of the expanding plasma. These factors will contribute to the passage of ions through the drift channel. Considering that in the initial part of the passage channel (the area of the focusing spot), the value of the retaining radial electric field is the largest (~ 1000 V), because Those plasmas are the largest (~ 100 eV), the density of charged particles in the plasma is greatest, and the Debye radius, which characterizes the value of the self-consistent electric field accelerating ions, is the smallest between the fast electron and slow ion components. It can be concluded that the most active increase in the horizontal component of speed occurs in this area. This increase continues in the future, as the particles pass the passage channel 3 according to [6]. Taking into account the rapid decrease in the ion-confining electric field associated with a change in the plasma temperature (2), it can be seen that ions generated on the target pass freely through the passage channel, having received a larger increment in velocity, coinciding with the direction of their extraction, in comparison with other directions of motion .

где ρе, ρi - соответственно электронный и ионный радиусы Лармора, показывает, что в канале пролета с принятыми параметрами (фиг. 1) уход плазмы через магнитные щели даже для свинцовой малозарядной плазмы не превысит 25%.It is known that in a multipole confinement system, plasma can escape to the side walls through magnetic slots at the poles of magnets 4 (Figs. 1, 2). Estimation of plasma losses through magnetic gaps whose width according to [5]

where ρе, ρi are Larmor’s electron and ionic radii, respectively, shows that in the passage channel with the accepted parameters (Fig. 1), the plasma escape through magnetic gaps even for a low-charge lead plasma will not exceed 25%.

It was shown in [2] that ion beams extracted from laser sources have temperature emittances of the order of ^10–2 cm mrad [4]. In an isotropically expanding laser plasma, the average ion energy increases to hundreds of keV during their acceleration by self-consistent plasma fields [4, 6]. It was shown in [8] that a plasma bunch on a target is not a Lambert radiation source. As a result, after the selection of ions in the beam, many current tubes are formed, directed at different angles with large ordered components of the ion velocity. This leads to a distortion of the shape of the absolute (temperature) emittance on the phase coordinate plane and increases the value of the effective emittance of the beam [12]. If an ion beam is characterized by a large effective emittance, then it is difficult to reconcile it with the acceptances of accelerating structures [12]. Since plasma ions, after passing through the passage channel, increase the direction of their motion, which coincides with the direction of extraction of charged particles, the laminarity of the current tubes in the extracted ion stream improves and its effective emittance decreases [14].

Since the plasma can move in only one of three coordinates in the proposed passage channel, the dependence of its density on the span length L will be described by the expression n ~ n ₀ (1 / L), and not n ~ n ₀ (1 / L ³ ), which is typical for plasma free expansion conditions [6, 8]. According to [8], when the initial plasma density in the laser spot is n _о ~ 10 ¹⁹ cm ^-3 after the passage of L ~ 1 m, its density in the ion selection zone decreases to n _L ~ 10 ¹¹ cm ^-3 , which allows one to select the ion current with j <20 mA / cm ² . Given that the maximum current density j, which can be taken from the plasma emitter, is determined in [11]
j = 0.344 n _L e (2kTе / Mi) ^1/2 (4),
it can be estimated that j at the output of the proposed channel, having a length L = 1 m and a higher plasma temperature Te, will be several times larger than in the analogue and prototype. According to [6, 9], the duration of the ion packet increases as the plasma moves in a transverse magnetic field. Since in the present invention the magnetic field lines 6, FIG. 2, in the passage channel 3, FIG. 1, are perpendicular to the main direction of plasma motion everywhere, except for the region of the central longitudinal axis, there will be an increase in the pulse duration of the ion packet compared to the prototype due to the increase in the path traveled by particles in a complex magnetic field. Otherwise, while maintaining the same duration of the ion packet, the span channel of the invention will have a length shorter than the channel of the prototype, which contributes to an increase in the plasma density in the region of formation of the ion beam, allowing an increase in the current of extracted ions (4).

 According to [6, 9], a laser plasma contains a significant neutral component in the form of atoms of the material of the sputtered target and the gases contained in it. The presence of neutrals makes us consider the span channel as a system in which energy dissipation takes place in the form of heat transferred to the side walls of the channel by neutrals after their collision with plasma ions oscillating relative to the central axis of the channel. Such collisions contribute to a decrease in the average temperature of the ion component of the laser plasma in the zone of formation of a beam of charged particles, reducing its emittance.

 It was shown in [2, 4, 8] that an increase in the length of the passage channel leads to a decrease in the yield of highly charged ions.

 It was shown in [13] that, during the expansion of a laser plasma, the plasma heating during triple recombination through excited states has a significant effect on the formation of a charge composition. According to [2, 13], an increase in plasma temperature leads to an increase in the fraction of highly charged ions. In the present invention, the length of the passage channel is reduced and the ion drift path is increased. These factors contribute to an increase in the number of ions with large charges in the extracted beam.

где с - скорость света в вакууме, dVx - разброс радиальных скоростей ионов пучка, do - характерный размер эмиттера, Х - текущая координата. Согласно [7] скорость движения иона в плазме связана со скоростью ионно-звуковых колебаний плазмы соотношением ΔVx=0,5Vc, где скорость ионного звука Vc согласно [8]

Учитывая выражение (5), получим, что зависимость верхнего значения поперечного фазового объема пучка от температуры имеет вид Vf~(Te)^1/2. Согласно (2) температура плазмы в пролетном канале изобретения зависит от базы ее разлета L согласно Te~1/L². В пролетных каналах аналога и эта зависимость имеет вид Te~1/L⁶. Учитывая выражение (6), получим, что изменение фазового объема от разлета плазмы для предложенного пролетного канала имеет вид Vc~ 1/L. Для свободно разлетающейся лазерной плазмы Vc~1/L³. Следовательно, фазовый объем ионного пучка, извлекаемого из предложенного пролетного канала, будет в (L/d_о)² раз больше, чем в прототипе. Но в [12] показано, что с увеличением продольной скорости частиц уменьшается эмиттанс пучка из-за того, что уменьшается разброс наклонов траекторий этих частиц. В предлагаемом изобретении согласно [6] скорость поперечного разлета ионов в пучке будет определяться температурой плазменного пятна на мишени. После подавления изотропной направленности упорядоченной составляющей скорости разлета ионов и ориентации результирующего вектора этой скорости в направлении экстракции пучка заряженных частиц, продольная составляющая скорости ионов возрастет пропорционально корню квадратному из энергии ионов, а поперечная скорость уменьшится ~Te/L. В [4] сообщается, что энергия ионов Рb в плазме составляет Ек~ 100 кэВ, температура плазмы в пятне на мишени 30-50 эВ. Сравнивая эти значения с температурой плазмы в зоне формирования пучка (Te•do/L~50do/L, эВ) и переходя в систему скоростей с учетом (5) видим, что верхнее значение змиттанса экстрагируемого ионного пучка уменьшится в N~[(Ек•L)/(d_о•Те)]^1/2 раз. Для ионов Рb из [4] N~(900-1000) раз. Таким образом, если в лазерный источник ионов, описанный в [4], установить предлагаемый пролетный канал 3, фиг. 1, то пучок ионов свинца на выходе источника будет иметь поперечный фазовый объем V_pb~2-3 см•мрад, что само по себе уже удовлетворяет условиям ввода такого пучка во многие виды ускорителей, но форма эмиттанса и его ориентация на фазовой плоскости будут иными. Пучок ионов, извлеченный из предложенного источника, будет иметь меньший эффективный эмиттанс, чем тот, который можно получить в пролетных каналах со свободно разлетающейся плазмой, а его ориентация в фазовом пространстве обеспечит лучшие условия согласования фазовых характеристик пучка с аксептансом ускоряющей структуры.The above statements show that the plasma temperature in the passage channel 3, FIG. 1 will be greater than in channels with free plasma expansion. Its increase leads to an increase in the emittance of the extracted ion beam [14]. Let us evaluate the influence of this factor on the transverse phase volume of the beams, which can be obtained in the proposed design. Determine the transverse phase volume of the ion beam extracted from the laser plasma according to [8]

where c is the speed of light in vacuum, dVx is the spread of the radial velocities of the beam ions, do is the characteristic size of the emitter, X is the current coordinate. According to [7], the velocity of an ion in a plasma is related to the speed of ion-acoustic oscillations of the plasma with the relation ΔVx = 0.5Vc, where the speed of ionic sound is Vc according to [8]

Taking into account expression (5), we find that the temperature dependence of the upper value of the transverse phase volume of the beam has the form Vf ~ (Te) ^1/2 . According to (2), the plasma temperature in the passage channel of the invention depends on the base of its expansion L according to Te ~ 1 / L ² . In the passage channels of the analog, this dependence also has the form Te ~ 1 / L ⁶ . Taking into account expression (6), we find that the change in the phase volume from the expansion of the plasma for the proposed passage channel has the form Vc ~ 1 / L. For a freely expanding laser plasma, Vc ~ 1 / L ³ . Therefore, the phase volume of the ion beam extracted from the proposed passage channel will be (L / d _о ) ² times greater than in the prototype. But it was shown in [12] that, with an increase in the longitudinal velocity of particles, the emittance of the beam decreases because the spread of the slopes of the trajectories of these particles decreases. In the present invention according to [6], the speed of the transverse expansion of ions in the beam will be determined by the temperature of the plasma spot on the target. After suppressing the isotropic direction of the ordered component of the ion expansion velocity and orienting the resulting vector of this velocity in the direction of extraction of the charged particle beam, the longitudinal component of the ion velocity will increase in proportion to the square root of the ion energy, and the transverse velocity will decrease ~ Te / L. In [4], it was reported that the energy of Pb ions in the plasma is Ek ~ 100 keV, and the plasma temperature in the spot on the target is 30-50 eV. Comparing these values with the plasma temperature in the beam formation zone (Te • do / L ~ 50do / L, eV) and going over to the velocity system with allowance for (5), we see that the upper Zmittance of the extracted ion beam will decrease by N ~ [(Ek • L) / (d _o • Te)] ^1/2 times. For Pb ions from [4] N ~ (900-1000) times. Thus, if the proposed passage channel 3 is installed in the laser ion source described in [4], FIG. 1, the lead ion beam at the source output will have a transverse phase volume V _pb ~ 2-3 cm • mrad, which in itself already satisfies the conditions for introducing such a beam into many types of accelerators, but the shape of the emittance and its orientation on the phase plane will be different . The ion beam extracted from the proposed source will have a lower effective emittance than that which can be obtained in the passage channels with freely expanding plasma, and its orientation in the phase space will provide better conditions for matching the phase characteristics of the beam with the acceptance of the accelerating structure.

 In the proposed invention, reduced energy consumption compared with the prototype due to the exclusion of electromagnetic coils. The dimensions of the source are reduced, and the reliability of its operation is increased.

 The above estimates show the technical feasibility of quickly creating a laser ion source without large additional costs, in which the ion-optical properties of the plasma are improved by transforming, when its thermal energy expands, into a directed component of the ion drift velocity, which helps to reduce the spread in the velocities and angles of expansion of charged particles in ion beam, and creating a source with more efficient confinement of the laser plasma in the passage channel. The use of such a source of charged particles makes it possible to increase the beam current at the output of accelerators.

Sources of information
1. LZ Barabash, DG Koshkarev, Yu. J. Lapitskii et all. Laser and Particle Beams, 2, 49, 1984.

 2. A. A. Golubev, Yu.N. Yerema, B.Yu. Sharkov et al. Measurement of currents and charge state of beams formed from laser plasma. Preprint 134-88. - M.: ITEP, 1988.

 3. L. G. Gray, R.H. Hughes, R.J. Anderson. J. Heavy-ion sourse using a laser-generated plasma transported through an axial magnetic field. Appl. Phys. 53, 6628, 1982.

 4. L. 3. Barabash, Yu.A. Bykovsky, K.I. Gyrfalcon and others. The formation of an intense beam of heavy ions from a laser plasma. Preprint 86-146. - M.: ITEP, 1986.

 5. R.H. Hughes, R.J. Anderson, C.K. Manka et all. Appl. Phys. 51, 4088, 1980.

 6. Yu. P. Kozyrev, B.Yu. Sharkov. Introduction to laser plasma physics. Tutorial. - M .: MEPhI, part 1, p. 22, 1980.

 7. H.H. Semashko. A.H. Vladimirov, S.V. Kuznetsov et al. Injectors of fast hydrogen atoms. - M.: Energoizdat, 1981, p. 84-90.

 8. L. 3. Barabash, Yu.A. Bykovsky, A.A. Golubev et al. Characteristics of a laser plasma as a source of ions for a driver of heavy-ion inertial synthesis. Preprint 12. - M.: ITEP, 1983.

 9. J. Brown, R. Keller, A. Holmes and others. Physics and technology of ion sources. - M.: Mir, 1998, p. 29, 323-339.

 10. M.D. Gabovich, I.I. Pleshivtsev, N.N. Semashko. Beams of ions and atoms for controlled thermonuclear fusion and technological purposes. - M .: Energoatomizdat, 1986, p. 41-65.

 11. A. T. Forrester. Intense ion beams. - M .: Mir, 1992, p. 73,163.

 12. I. M. Kapchinsky. Theory of linear resonant accelerators. - M.: Energoizdat, 1982, p. 42-75.

 13.S.V. Latyshev, I.V. Rudskoy. On some questions of interpretation of the results of time-of-flight mass spectrometry of a laser plasma. Preprint 33. - M.: ITEP, 1985.

 14.S.I. Molokovsky, A.D. Sushkov. Intense electron and ion beams. - M .: Energoatomizdat, 1991, p. 142-190.

Claims (1)

 A laser ion source, consisting of a target, a laser, a passage channel made in the form of a metal tube, the central longitudinal axis of which coincides with the initial direction of the hydrodynamic movement of the plasma stream from the target, an ion extraction system mounted on the central longitudinal axis of the passage channel, characterized in that The magnets are mounted on the passage channel in such a way that they form inside it along the entire length between the target and the ion selection system a multipole magnetic field, field lines are perpendicular to the longitudinal axis of the passage channel, and the intensity of this field, approaching zero on the central longitudinal axis, increases sharply in the region of the walls of the passage channel.

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