RU2009526C1 - Device for diagnosing parameters of electron flux - Google Patents

Abstract

FIELD: amplification engineering. SUBSTANCE: device has electron current converter made in form of conducting flux absorber and conductivity current meter. Absorber is made in form of two galvanically coupled bodies for simultaneous movement with the same speed in the opposite direction to be disposed in perpendicular and symmetrically to beam axis in different sides of common surface of sliding. Forward parts of the bodies have shapes of wedges. EFFECT: improved efficiency. 4 dwg

Description

 The invention relates to converters of parameters of low-energy electronic radiation (≈ 10 MeV) and can be used in accelerator technology, radiation technology, metrology of electronic radiation.

 A device for measuring the energy spectrum of an electron stream with the possibility of simultaneously measuring their spectral density, containing an electromagnet with a collimator and a Faraday cylinder at the output of the magnet [1].

 The disadvantages of the device are the complexity of implementation associated with the need to manufacture a magnet and its power source, as well as low accuracy of measuring the electron flux due to losses during its transportation to the transducer (Faraday cylinder - CF).

 A device is known - a transducer of flux and electron flux density, containing a collimator and a DF located behind it, with the possibility of two-coordinate movement of the device in the radiation field [2].

 Its disadvantages are the relative complexity of the implementation, associated with the need for two nodes to move the device in two coordinates, the low efficiency of measurements of the beam density profile, and the impossibility of measuring electron energy.

 The prototype of the invention is a device that converts the energy spectrum and electron flow, containing a set of flat conductive absorbers of the beam (foils), with the ability to measure the charge received by each foil as a result of the influence of the electron flow [3].

 The disadvantages of the device are the relative complexity of carrying out measurements with it, associated with the need for separate storage and measurement of the charge of each foil, the limitation on the energy resolution due to the use of a finite number of foils with a fixed thickness, and the inability to measure the density profile of the studied electron flux using the prototype device .

 The aim of the invention is to simplify the design and expand the functionality.

, (1) где R - максимальный пробег электронов в материале;

- энергетическое разрешение преобразователя; Δ х - пространственное разрешение преобразователя, а ширина основания каждого клина составляет R, причем у ближнего к источнику электронов тела клин у основания переходит в плоскопараллельную пластину, имеющую в верхней части под углом 45^о к оси перемещения тел прямоугольный вырез глубиной
a =

(h+d

) , (2) где h - поперечный размер поглотителя; d - максимальный размер сечения пучка.The goal is achieved in a device containing an electron beam absorber made in the form of two galvanically coupled bodies with the possibility of their simultaneous movement at the same speed towards each other normally and symmetrically to the beam axis on different sides of the common sliding plane, and the front parts of the bodies along the course of their movement have the form of a wedge , one surface of which is in contact with the slip plane, the other forms an angle with it
α = arctg

, (1) where R is the maximum range of electrons in the material;

- energy resolution of the converter; Δ x - the spatial resolution of the transducer, and the width of the base of each wedge is R, wherein neighbor to source wedge at the base body of electrons transferred in a plane-parallel plate having a top portion at an angle of 45 to the axis ^of movement of the bodies rectangular cutout depth
a =

(h + d

), (2) where h is the transverse size of the absorber; d is the maximum size of the beam section.

 Not found in other technical solutions features similar to those that distinguish the claimed solution from the prototype. Therefore, we can conclude that the proposed solution has significant differences. The proposed solution also allows you to get a positive effect, which consists in simplifying the device and expanding functionality.

 The invention is illustrated in FIG. 1-4.

 In FIG. 1 shows an example of a specific implementation of the device.

 The parts of the absorber (body) 1.2 are mounted on carriages 3.4, which can be moved along the guide 6 with the lead screw 5. The screw 5 is supported by the ends in bearings 7, pressed into the cheeks 8.9 of the support, to which the ends of the guide 6 are also attached A motor 10 is attached to the cheek 9, the shaft of which is connected to a screw 5, divided into two parts with left and right threads symmetrical with respect to the axis of the beam. Corresponding threads have nuts of the screw of carriages 3, 4 (not shown in the diagram). The whole structure is mounted on insulators 11 and grounded through a conductivity current meter (ammeter) 12.

)F(x′, E)dx′, (3) где I(E) - поток частиц, имеющих энергию в единичном интервале вблизи значения Е, F(Х, Е) - функция чувствительности преобразователя, зависящая от величины угла клина и материала поглотителя. Она может быть определена расчетным методом [4] , либо измерена экспериментально, например, с использованием магнитного анализатора энергии.The principle of operation of the device is illustrated in FIG. 2 and 3. At the initial moment (before the start of measurements), both parts of the absorber are separated and the beam passes completely between them to the irradiated object (Fig. 2). For measurements, the absorbers begin to move towards each other normally and symmetrically to the beam axis with an average speed V by transmitting voltage to the motor 10 (for example, the stepper motor SDR 721). When parts of the absorber of the beam overlap (Fig. 3, a), device A begins to register the current I (x), the value of which increases with increasing total thickness of the absorbing bodies with increasing coordinate X of the wedge top relative to the axis of the beam, and, starting from x = d / 2, for all particles of the beam, the wedge-shaped geometry of the parts of the absorber provides an equal thickness of the absorbing layer (Fig. 3, b). Since the electron absorption coefficient in a flat layer is determined by its thickness, the angle of inclination of the absorber to the beam axis and the electron energy [4], the dependence I (x) allows us to determine the energy spectrum of the beam by the formula
I (E) =

) F (x, E) dx, (3) where I (E) is the flux of particles having energy in a unit interval near the value of E, F (X, E) is the sensitivity function of the transducer, depending on the value of the wedge angle and material absorber. It can be determined by the calculation method [4], or measured experimentally, for example, using a magnetic energy analyzer.

необходимо выполнить условие

=

, (4) откуда
α = arctg

, (5)
При величине смещения ХX′ ≥

весь пучок за исключением рассеянных электронов поглощается. Отсюда величину протока электронов можно определить по формуле
Φ =

, (6) где I_м - величина максимума тока, измеренная прибором А, е - заряд электрона, К₂(Е) - поправочный коэффициент, зависящий от эффективного атомного номера Z_эф. материала поглотителя и эффективной энергии электронов Е. Его значение можно установить расчетным путем [5] либо провести калибровку преобразователя по потоку электронов методом прямого сличения с образцовым прибором (например, цилиндром Фарадея из состава государственного эталона ГЭТ 72-90). В частности, для снижения коэффициента рассеяния электронов поглотитель целесообразно изготовлять из материала с малым Z_эф. (графит, Al и т. д. ).Moving in the formula (3) from integration to summation over Δ x, where Δ x is the step of moving the absorber, it is easy to verify that to ensure the energy resolution ≃

it is necessary to fulfill the condition

=

, (4) where
α = arctg

, (5)
With the displacement value XX ′ ≥

the entire beam with the exception of scattered electrons is absorbed. Hence the magnitude of the electron flow can be determined by the formula
Φ =

, (6) where I _m is the maximum current measured by the device A, e is the electron charge, K ₂ (E) is the correction coefficient, depending on the effective atomic number Z _eff . the absorber material and the effective electron energy E. Its value can be determined by calculation [5] or the converter can be calibrated by the electron flow by direct comparison with a standard device (for example, the Faraday cup from the state standard GET 72-90). In particular, to reduce the electron scattering coefficient, the absorber is expediently made from a material with a small Z _eff. (graphite, Al, etc.).

= -

j(x₁y)dy , (7) где j(x, y) - распределение плотности потока электронов в системе координат X, Y, совпадающей с направлениями сторон выреза. Иначе говоря, производя перемещение поглотителя с шагом Δ хмы тем самым обеспечиваем зондирование потока электронов в направлении оси Х с величиной шага (пространственным разрешением)
Δx =

. (8)
Аналогичная процедура имеет место при перекрытии пучка левой стороной выреза (фиг. 4, б) с той лишь разницей, что в этом случае

= -

j(x₁y)dx , (9) т. е. I(х) возрастает, причем зондирование пучка производится вдоль оси Y с шагом
Δy =

. (10)
Таким образом, с учетом (8), (10) формула (5) приводится к окончательному виду (1).In FIG. 4 shows the principle of operation of the Converter in the mode of measuring the profile of the electron flux density. So, in the process of moving the absorbing bodies, there comes a moment when the cutout of the front of them with the right side opens part of the beam (Fig. 4a), as a result of which the current I (x) detected by the device begins to decrease so that

= -

j (x ₁ y) dy, (7) where j (x, y) is the distribution of the electron flux density in the coordinate system X, Y, which coincides with the directions of the sides of the cut. In other words, by moving the absorber with a pitch Δ step, we thereby provide sounding of the electron flow in the direction of the X axis with a step size (spatial resolution)
Δx =

. (8)
A similar procedure takes place when the beam is blocked by the left side of the cut (Fig. 4, b) with the only difference that in this case

= -

j (x ₁ y) dx, (9) i.e., I (x) increases, and the beam is probed along the Y axis with a step
Δy =

. (10)
Thus, taking into account (8), (10), formula (5) is reduced to the final form (1).

y
Решая систему уравнения (10, 11) с учетом

j(x₁y)dx dy = eΦ , (14) получаем
j(x₁y) = -

, (15) где

и

- производные тока поглотителя по координате хпри его перемещении левой и правой сторонами выреза соответственно.The distribution of j (x, y) from the experimental dependence I [x, j (x, y)] is reconstructed as follows. Since the distribution of the flux density over both coordinates is mutually independent, we can write
j (x, y) = A (x) ^. B (y) (11) whence

y
Solving the system of equation (10, 11) taking into account

j (x ₁ y) dx dy = eΦ, (14) we obtain
j (x ₁ y) = -

, (15) where

and

- derivatives of the absorber current along the coordinate x when it is moved by the left and right sides of the cutout, respectively.

(h+d

существует интервал времени перемещения поглотителя, когда пучок одновременно взаимодействует с обеими сторонами выреза, что не позволяет разделить во времени зондирование потока по каждой из осей Х; Y (формула (15) не работает); при a >

(h+d

пучок свободно проходит между сторонами среза, не взаимодействуя с поглотителем, что снижает эффективность работы преобразователя (оперативность проведения измерений). Указанные обстоятельства определяют соотношение (2) в формуле предполагаемого изобретения.From the principle of operation of the proposed meter of the electron flux density profile considered above, the requirement for the cutout depth follows: in the case a <

(h + d

there is a time interval for the movement of the absorber when the beam simultaneously interacts with both sides of the cutout, which does not allow time separation of the sounding of the flow along each of the X axes; Y (formula (15) does not work); for a>

(h + d

the beam passes freely between the sides of the cut, without interacting with the absorber, which reduces the efficiency of the transducer (the efficiency of measurements). These circumstances determine the ratio (2) in the claims.

tgα выпадает из рассмотрения. Это обстоятельство становится несущественным, если выполнить условие

tgα<<R, (16) или, с учетом (1),

<<

, (17) что определяет соотношение между энергетическим и пространственным разрешением преобразователя, и является вполне приемлемым условием. Так, например, в случае характерных параметров пучка технологического ускорителя электронов [6] : Е = 10 МэВ, d ≃ 20 мм, частоте следования импульсов f_у = 300 Гц, задав Δ х = 1 мм,

= 3·10^-2 для преобразователя поперечным размером h = 60 мм из графита (R ≃ 27 мм - [7] ) с учетом (1) получаем α = 16^о. При этом минимальное время, необходимое для проведения измерений, можно оценить по формуле
Δt ≃

, (18)
или в нашем случае Δ t

0,5 с.From (3), in particular, it follows that in the proposed design of the converter, the low-energy part of the range of electrons with mileage

tgα is out of consideration. This circumstance becomes insignificant if the condition

tgα << R, (16) or, taking into account (1),

<<

, (17) which determines the relationship between the energy and spatial resolution of the converter, and is a completely acceptable condition. So, for example, in the case of characteristic parameters of a beam of a technological electron accelerator [6]: E = 10 MeV, d ≃ 20 mm, pulse repetition rate f _y = 300 Hz, setting Δ x = 1 mm,

= 3 · 10 ^-2 for a transducer with a transverse dimension h = 60 mm from graphite (R ≃ 27 mm - [7]) taking into account (1) we obtain α = 16 ^о . In this case, the minimum time required for measurements can be estimated by the formula
Δt ≃

, (eighteen)
or in our case Δ t

0.5 s

It should be noted that to increase the accuracy of measurements of the flux density profile by reducing the number of electrons scattered through the cutout surface, by increasing their reflection coefficient from this surface, it can be covered with a thin (<< Δ x) layer of material with a large Z _eff (Рф, Та , W, etc.).

 Thus, the proposed design of the transducer is notable for its simplicity of manufacture and allows one to determine the main characteristics of the electron beam — the energy spectrum, the magnitude of the flux, and its density distribution — by one-dimensional movement of it in one measurement cycle. A cycle requires only two channels (controlling the drive motor of the transducer and measuring the dependence I (x), which greatly facilitates the possibility of using the transducer in an automated accelerator control system. The listed advantages along with high radiation resistance make it possible to widely use the converter of the proposed design in radiation accelerator complexes . (56) 1. BL Cohen, Rev. Scient. Instrum., 1962, v. 33, p. 85.

 2. V. A. Moskalev, V. G. Shestakov. Control and measurement of parameters of charged particle beams. M.: Atomizdat, 1973.

 3. V.I. Dronin, O.S. Milovanov, V.A. Shabrov. Reports of the IV All-Union meeting on the use of charged particle accelerators in the national economy. L., 1982, T. 2., p. 170-172.

 4. E. I. Kobetich, R. Katz. Phys. Rev. , 1968, v. 170, p. 391.

 5. T. Tabata etal. Ann. Rep. Rad. Center Osaka Pref. 1979, v. 20, p. 87.

 6. V.I. Beloglazov, E.Z. Biller, V.A. Vishnyakov, etc.

 Questions of atomic science and technology. Series: Physics of Radiation Damage and Radiation Materials Science. M., 1986, no. 1 (38), p. 89-91.

 7. L. Pages et al. Atomic data, March 1972, v. 4, N 1.

Claims (1)

DEVICE FOR DIAGNOSTIC OF ELECTRON FLOW PARAMETERS, including an electron current transducer in the form of a conductive flow absorber and a conductivity current meter, characterized in that, in order to simplify the design and expand the functionality, the absorber is made in the form of two galvanic coupled bodies with the possibility of their simultaneous movement from the same speed towards each other normally and symmetrically to the axis of the beam on different sides of the common sliding plane, with the front parts in the direction of travel spruce have a wedge shape, one surface of which is in contact with the slip plane, the other forms an angle with it
α = arctg

where R is the maximum range of electrons in the material of the absorber;

- the required energy resolution of the converter;
Δx is the required spatial resolution of the Converter,
and the width of the base of each wedge is R, and at the base nearest to the electron source the wedge at the base passes into a plane-parallel plate having a rectangular cutout in the upper part at an angle of 45 ^o to the axis of movement of the bodies
d =

(h + d

) /
where h is the transverse size of the absorbers;
d is the maximum size of the beam section.

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