=Paper=
{{Paper
|id=Vol-2212/paper22
|storemode=property
|title=Simulation of the control system of the electrodynamic accelerator of dust particles
|pdfUrl=https://ceur-ws.org/Vol-2212/paper22.pdf
|volume=Vol-2212
|authors=Alexey Piyakov,Dmitry Rodin,Marina Rodina,Alexey Telegin,Sergey Kondratev
}}
==Simulation of the control system of the electrodynamic accelerator of dust particles ==
https://ceur-ws.org/Vol-2212/paper22.pdf
Simulation of the control system of the electrodynamic
accelerator of dust particles
A V Piyakov1, D V Rodin1, M A Rodina1, A M Telegin1 and S N Kondratev1
1
Samara National Research University, Moskovskoe Shosse 34А, Samara, Russia, 443086
Abstract. The device and control system of the accelerator of charged micron particles for
simulation of micrometeorites and technogenic particles in laboratory conditions are
considered. The model of the accelerator control system operation is described, the results of
the accelerator control system functioning simulation for various operating modes are given.
The results of comparison of mathematical simulation with experimental data are presented.
1. Introduction
Recently, there has been a trend of increasing concentrations of high-speed technogenic dust particles
in near-Earth orbits. According to different sources, the concentration of technogenic dust particles
already is three times higher than the concentration of natural origin micrometeorites. Considering the
increasing demand for the reliability and durability of spacecrafts(SCs), and as well as new materials
production, there is a demand for further research on the interaction of high-speed dust particles with
materials of spacecrafts elements [1-3].
Currently new materials have been produced and applied in the space industry, which makes it
necessary to conduct impact experiments. Conferences are regularly held on the problem of protecting
spacecraft construction materials from micrometeorites. The technique of high-speed throwing is of
interest not only from the point of view of modeling the factors of the space environment on the
materials of spacecraft structure, but also from the point of view of feeding the thermonuclear reactors
with fuel. Thus, there is an obvious need is to construct various accelerators that cover the entire range
of masses of the required particles.
There are various ways to accelerate dust particles in the laboratory to simulate the interaction of
micrometeorites and technogenic particles with the materials of SC construction, and to create and
calibrate new micrometeorite sensors. The type and construction of the accelerator is determined by
the problem posed and depends on the range of the analyzed masses and the velocities of the
accelerated particles.
The main element of the dust particle accelerator is the control system, which forms accelerating
voltages on the drift tubes. To solve the problem of the voltages formation accuracy, different
measures can be taken: for example, in [4], the authors use the modification of a linear electrostatic
accelerator, which exclude all particles with a specific charge different from 30 coulomb per kilogram
from the acceleration process. Other research teams [5] use accelerators based on Van de Graaf high-
voltage sources, which do not require complex control schemes, but are too complicated.
Thus, the development of high-precision control systems is essential for the construction of
compact accelerators for applied research. This article concerns the operation of the electrodynamic
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A V Piyakov, D V Rodin, M A Rodina, A M Telegin and S N Kondratev
accelerator of dust particles control system in nonstandard operation modes, caused by the dust
contamination of the accelerator internal path.
2. The structure of the particle accelerator
We developed and constructed an accelerator [3, 6-8] of high speed particles, which allows to simulate
impacts of micrometeorites with a size of 1 ÷ 10 um and speeds of 1-15 km / s with materials of
spacecraft structures under laboratory conditions.
Figure 1 shows a block diagram of a linear accelerator for simulation of micrometeorites, the path
of which consists of an injector, linear electrostatic accelerator (LESA), linear electrodynamic
accelerator (LEDA), three measuring lines and an experiment chamber. Vacuum in the system is
provided by two pumping systems consisting of a vacuum diffusion pump AVMD -250, a forvacuum
pump NVPR-16 and the necessary valves (KVE-63). The limiting residual pressure in the system is
10-5 mm Hg.
Figure 1. Structural diagram of the linear accelerator of micrometeorites. A – amplifier; C –
comparator; LE – laser emitter; VPS1, VPS2 – vacuum pumping system 1 and 2;
IPS– power supply of the injector.
The accelerator works as follows. The injector generates charged particles in a given mass range
with the frequency of the order of 1 Hz. The charged particle sequentially passes the first measuring
line, a linear accelerator, a second measuring line, cylindrical electrodes, the third measuring line and
hits the target. The first pair of measuring lines and the linear accelerator are used to determine the
particle parameters (specific charge Q / m and initial speed V0). Flying through the measuring line, the
particle induces potential to two tubes working as induction sensors.The potentioa sign is opposite to
the charge of the particle. Since the tubes are made of metal, their surface is equipotential, which
means it does not matter in which part to measure the voltage. According to incoming signals from the
measuring line, the speed selector and the selector of specific charges form a digital code of the initial
velocity of the particle at their outputs as well as the specific charge code. In the velocity selector, the
time intervals of a particle path between two sensor centers for the first and second induction sensors
are measured. The measured time intervals are directly proportional to the velocity of the particle.
After passing through the linear accelerator, the particle receives a velocity increment. The second
measuring line works similarly to the first one. According to the initial velocity and specific charge
codes supplied to the variable frequency and duration pulse generator, the burst of voltage impulses is
formed on its output which creates accelerating field between each pair of electrodes. This field varies
in time according to the position of the particle in the accelerating path. Parameters of the burst are
selected from a series of pulse-forming data loaded from a PC into the variable frequency and duration
pulse generator. The variable pulse duration amplifier transmits the pulses generated in the variable
frequency and duration pulse generator. The amplified pulses are applied to cylindrical electrodes. The
third measuring line is connected to the interface unit and serves to obtain the output data. Then the
accelerated particle hits the target and the whole process repeats. The computer produces experimental
statistics and controls the accelerator dynamically.
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3. Description of the electrodynamic accelerator control system
To ensure the functioning of the electrodynamic part of the accelerator of micrometeorites, a control
system has been developed, the functional diagram of which is shown in Figure 2.
Figure 2. Functional diagram of the electrodynamic accelerator control system.
The control system works as follows. FLASH memory stores the time intervals between voltage
changes on the drift tubes of a linear electrodynamic accelerator. The incoming signals from optical
receivers to the CPLD MAXII 1270 contain the particle velocity before and after the linear
electrostatic accelerator. The speed codes are sent to the address bus of the FLASH memory to select
the desired burst of pulses corresponding to the accelerated particle. The counter implemented in
CPLD starts counting clock pulses of the DDS generator. When the number of pulses on the counter
coincides with the number in the FLASH memory, pulses are formed on the optical transmitters. The
microcontroller serves for transferring the data about the system operation to the computer. A high-
speed USB interface is used for reprogramming the memory, however, due to interference signals, this
interface is not suitable for data transfer during the operation of the accelerator. Therefore, in the
control system, a more noise-protected optically isolated RS-232 interface was used.
When the internal path is contaminated with metallic dust particles, the maximum accelerating
voltage of the linear electrostatic accelerator is reduced. Thus, the cleaning of the accelerator path is
required (Figure 3) [7].
Figure 3. Disassembled accelerator path (valve
in a vacuum chamber). 1 – area of
microparticle dispersion in the accelerator
internal path.
This time-consuming process requires disassembling the vacuum system making it necessary to
provide the accelerator operation mode with a reduced accelerating voltage. This operation mode is
possible when frequency of the clock generator aimed for generating pulses on the drift tubes of the
electrodynamic accelerator is adjustable. For example, when operating at a voltage of 80 kV instead of
the calculated 100 kV, frequency tuning from the calculated 10 MHz to 12.403 MHz is required. Let
us consider the results of an experiment conducted with the reduced voltage.
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Figure 4 shows the time dependence of the detection of particles on the fifth induction sensor on
the specific charge of the particles. The dots represent the experimentally measured data, the solid line
represents pre-calculated times embedded in the FLASH memory of the generator.
20000
T, [us]
15000
10000
5000
0
0 10 20 30 40 50 [C/kg]
Q/m, 60
Figure 4. Dependence of the registration time of a particle on the fifth induction sensor on the specific
charge.
Figure 5 shows the dependence of the particle velocity on the specific charge. Points stand for
experimental data, solid line represents the calculated speed. The points that much higher or lower
than the calculated curve represent the particles for which the synchronization of the accelerating
pulses is lost.
7000
V, [m/s]
6000
5000
4000
3000
2000
1000
0
0 10 20 30 40 50 60
Q/m, [C/kg]
Figure 5. Dependence of the particle registration rate on the third measuring line on the specific
charge.
Figures 4 and 5 show that the frequency correction with a reduced voltage of the electrostatic
accelerator ensures the normal electrodynamic accelerator operation. Most of the particles pass
through the internal path of the dynamic part.
4. Results of simulation
In order to verify the obtained experimental data, the authors modified the software described in [8],
which includes:
– a class describing the state of each particle (its velocity components, coordinates, time of flight,
mass-to-charge ratio values calculated for 80 kV and 100 kV acceleration modes);
– an array containing a two-dimensional distribution of the field in the drift tubes, calculated on the
assumption that the problem is axisymmetric. The grid has a step of 9.775 10-5 m, which corresponds
to a division of 10 cm of the path into 1023 intervals or 1024 nodes;
– an iterative method for calculating the trajectory of a particle, based on the Runge-Kutta
algorithm. Synchronization check of the particle time of flight with the required switching times on the
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drift tubes is added, in case of inconsistency in the calculation of the current step, all field values are
inverted, which results in the deceleration of the unsynchronized particles;
– the method of calculating the array with the required switching times of the voltages on the drift
tubes, based on the assumption that the moment the particle is in the middle of the drift tube is the
moment of commutation, taking into account the difference between the real and the measured ratio of
mass to charge;
– a method for generating model packets with the Maxwellian velocity distribution corresponding
to the distribution of the flux obtained in the particle injector. This method is implemented using the
Box-Muller algorithm with subsequent summation of the velocity vector components and
normalization for the most probable energy;
– methods for writing and reading files with particle parameters, trajectory points, and generation
of header files for parallel implementation of the algorithm.
The parallel implementation of the algorithm differs singlethreaded one by storing the original
matrices with particle parameters and field grid values in the form of external header files, written in
plain C. The algorithm implements only the modules required directly for calculating trajectories.
Multithreading was provided by connecting the MPI library. The calculation was carried out for
mutually independent particles, so each involved node was used to calculate only a certain part of the
trajectories.
At the initial stage, we simulated the trajectories of the real particles with the known parameters of
input and output velocities and the mass to charge ratio. For each particle, the switching times were
calculated, all the particles started from the center of the first drift tube with the given velocities. The
particle trajectories were calculated by an iterative method, the field interpolation was carried out on
the assumption that the particles have only a positive coordinate along the radial axis. For this reason,
the operation of taking the module from the radial coordinate of the particle is added to the
interpolator function. Interpolation was carried out for a field section of 1 cm x 10 cm, respectively,
the x coordinate within the interpolator function should always lie in the range 0 ÷ 0.1 m. The field
interpolation operation for particles having a negative radial coordinate returned an inverted radial
field component, flag of negative radial coordinate was used. The synchronous motion of the particle
in the path was checked by comparing the current time of flight of the particle with the switching
times from the array for the current drift tube number. The inversion of the field components in this
case occurred if the time of flight was less than the smaller value or larger than the larger neighboring
switching time. The intermediate points of the trajectories were stored during the transition of the
centers of the drift tubes. The calculation was terminated either by a surpassing the inner radius of the
tube, equal to 1 cm, or by the transit of the center of the 40th tube. The results of the simulation are
shown in Figure 6. The experimental results are in good agreement with the calculated data, the error
of calculation does not exceed 3.5%.
7000
Vout, м/с
6000
5000
4000
3000
2000
1000
0
Q/M ,[C/кg]
0,5 5 50
Figure 6. Comparison of experimental and model data on the velocity of the particle at the exit from
the dynamic path, the absolute error bars have a scale of 10 to 1.
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To test the performance of the acceleration system for other combinations of particle parameters, a
set of 16384 particles with different initial characteristics and different specific charges was formed.
Simulation of particle motion in the tract of the dynamic part of the accelerator was carried out using
the implementation of the software for a personal computer and for a supercomputer Sergey Korolev.
The simulation results are shown in Figures 7 and 8.
Figure 7. Difference between the calculated
voltage switching times on the drift tubes of
the electrodynamic accelerator, embedded in
the FLASH memory of the control system and
the time of particles occurrence in the centers
of the drift tubes. Results are obtained by
simulating the particle trajectories on the
supercomputer Sergey Korolev.
Figure 8. The difference between the calculated
speeds of particles during the voltage switching
on the drift tubes of the electrodynamic
accelerator embedded in the FLASH memory of
the control system and the particle velocities
during their occurrence in the centers of the drift
tubes. Results are obtained by simulating particle
trajectories on the supercomputer Sergey
Korolev.
Figures 7 and 8 show that the first half of the path particles are slightly ahead of the calculated
switching times and, as a consequence, at the initial stage they accelerated more than the calculated
data suggests, but in the second half of the tract they are slowed down, and the difference between the
calculated and real data is leveled.
5. Conclusion
Based on the results of simulation the of particles trajectories in the path of a linear electrodynamic
accelerator, it can be concluded that the control system with adjustable pulse frequency of the master
DDS generator from 10MHz to 12.403MHz ensures the operability of the accelerator when the real
accelerating voltage of the electrostatic section deviates from the calculated one by 20%. The obtained
simulation results for real particles are in good agreement with experimental values, and the
simulation of the system operation for a large range of input values will allow to choose the optimal
switching frequency without conducting a full-scale experiment.
The implementation of software for a personal computer and supercomputer showed the same
accuracy of calculations, which is explained by the choice of the same parameters of the
computational grid and the time step. The version for the personal computer showed a longer
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execution time of 56 minutes 16 seconds compared to 5 minutes 46 seconds for the supercomputer,
but in terms of one processor performance the first one provides a count of 1.2 million iterations per
second, and the second one 740 thousand iterations per second. The loss of performance can be
explained by the fact that the version for the personal computer retains all results in RAM, the same
version for the supercomputer requires transferring the results of calculations between the nodes.
This problem contains a lot of mutually independent processes, so it is easy to implement the
algorithm in parallel programming languages. Performance can be improved by increasing the number
of computational nodes. Independence of calculating threads provides a proportional increase in
performance with an increase in the number of nodes. The application of caching and preliminary
processing of results on computing nodes can minimize the amount of data transferred and also
increase the speed of execution.
6. References
[1] Semkin N D, Voronov K E and Novikov L S 2005 Registration of dust and gas particles in
laboratory and space conditions (Samara: Samara State Aerospace University) p 470
[2] Raikunov G G 2014 Space debris. In 2 books. Book 1. Methods of observation and models of
space debris (Moscow: FIZMATLIT) p 248
[3] Semkin N D, Kalaev M P, Telegin A M, Pijakov A V and Rodin D V 2012 Multilayer film
structures under the influence of micrometeoroids and space debris Applied Physics 2 104-115
[4] Slattery J C, Becker D G, Hamermesh B and Roy N L 1973 A linear accelerator for simulated
micrometeors Review of Scientific Instruments 44 755-762
[5] Thomas E, Simolka J, DeLuca M, Horányi M, Janches D, Marshall R A, Munsat T, Plane J M C,
and Sternovsky Z 2017 Review of Scientific Instruments 1-12
[6] Piyakov A V, Rodin D V, Rodina M A and Telegin A M 2017 Numerical simulation of motion of
dust particles in an accelerator path CEUR Workshop Proceedings 1902 55-61
[7] Semkin, N D and Piyakov A V 2015 Measurements of particle distributions over the cross
section of the accelerator channel for simulating micrometeorites Instruments and Experimental
Techniques 58(5) 703-707
[8] Semkin, N D, Voronov K E, Piyakov A V and Piyakov I V 2009 Simulation of micrometeorites
using an electrodynamical accelerator Instruments and Experimental Techniques 52(4) 595-601
[9] Semkin N D, Piyakov A V, Voronov K E, Bogoyavlenskii N L and Goryunov D V 2007 A
linear accelerator for simulating micrometeorites Instruments and Experimental Techniques
50(2) 275-281
[10] Telegin A M and Piyakov A V 2017 A study of the performance of an induction sensor for an
accelerator of charged microparticles Instruments and Experimental Techniques 60(6) 875-879
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