In most tokamaks, additional heating or extra power input is used to achieve the necessary plasma parameters such as temperature, confinement time, etc. This makes it possible to address current scientific challenges and conduct advanced research. The KTM tokamak will implement additional power input into the plasma using ion-cyclotron heating, as specified in the design. The additional plasma heating system on the KTM consists of four identical high-frequency generators, each with a capacity of 2 MW. No other systems for additional power input and plasma heating are provided on the KTM tokamak. Before operating such systems in normal mode, debugging and testing are conducted using load equivalents. This article presents the calculation of an active load equivalent. Based on the calculation results, the shape and geometric dimensions that ensure the absorption of up to 300 kW of high-frequency power are determined. The dimensions and main parameters of the load equivalent design for the additional high-frequency plasma heating system of the KTM tokamak have been determined. The calculations were carried out based on the assumption that the most preferable option is to create the load equivalent in the form of a resonator with an absorber made of saline aqueous solution. Experimental results from debugging using the developed active load equivalent are also presented. It has been demonstrated that with the developed load equivalent, it is possible to successfully carry out the necessary tests and adjustments of a high-power generator, and to prepare the additional power input system on the KTM tokamak for further debugging and switching to operation under plasma load.

The article presents the results of measuring the parameters of the amplitude-frequency characteristics (AFC) of the antenna module circuit of the system for additional high frequency (HF) heating of the KTM tokamak plasma in laboratory conditions. A description of the antenna-feeder device and the HF system of the KTM tokamak is presented. At this stage of time, commissioning works for launching of the HF system of additional heating are performed at the KTM tokamak. The design and launch of such system requires conducting of separate research. Since the HF system consists of four modules, which includes various subsystems and components, before testing the entire HF system as an assembly, it is necessary to check and determine the parameters of individual components of the HF system. The antenna module is a part of the antenna-feeder device and is a very important component in the HF system, because it transfers energy from the generator to the tokamak plasma, thus heating the plasma. In case if the transmitting system does not match the declared operating frequency, HF system will be mismatched, which will affect the efficiency of plasma heating and operation of the entire HF system. It is impossible to bring the KTM tokamak to the nominal declared power without putting into operation of the system for additional HF heating of the plasma. Additional components are attached to the antenna module, the influence of which must also be studied for the correct operation of the entire HF system in the future. This paper presents a method for measuring the frequency response of the antenna module and the results of determining the operating parameters of the antenna module such as: wave impedance, inductance, capacitance, resonant frequency and quality factor of the antenna module circuit, depending on various additional inductance adjustment elements. В статье представлены результаты измерения параметров амплитудно-частотных характеристик (АЧХ) контура модуля антенного системы дополнительного высокочастотного (ВЧ) нагрева плазмы токамака КТМ в лабораторных условиях. Представлено описание антенно-фидерного устройства и ВЧ системы токамака КТМ. На данном этапе времени на токамаке КТМ проводятся пуско-наладочные работы по введению в строй ВЧ системы дополнительного нагрева. Проектировка и запуск подобной системы требуют проведения отдельных научно-исследовательских работ. Так как ВЧ система состоит из четырех модулей в состав которого входят разнообразные подсистемы и узлы, то перед испытанием всей ВЧ системы в сборе, необходимо проведение работ по проверке и определению параметров отдельных узлов ВЧ системы. Антенный модуль входит в состав антенно-фидерного устройства и является очень важным элементом в ВЧ системе так как именно он осуществляет передачу энергии от генератора в плазму токамака, таким образом осуществляя нагрев плазмы. В случае если передающая система не будет согласована на заявленную рабочую частоту, то ВЧ система будет рассогласованной, что повлияет на эффективность нагрева плазмы и работу всей ВЧ системы в целом. Без ввода в эксплуатацию системы дополнительного ВЧ нагрева плазмы невозможен вывод токамака КТМ на номинальные заявленные мощности. К антенному модулю прилагаются дополнительные элементы влияние которых также необходимо изучить для корректной работы всей ВЧ системы в будущем. В данной работе приведены методика измерения АЧХ модуля антенного и результаты определения рабочих параметров модуля антенного таких как: волновое сопротивление, индуктивность, ёмкость, резонансная частота и добротность контура модуля антенного в зависимости от различных дополнительных элементов подстройки индуктивности. Мақалада КТМ токамагы плазмасының қосымша жоғары жиілікті (ЖЖ) қыздыру жүйесінің антенналық модулі контурының амплитудалық-жиіліктік сипаттамаларының (АЖС) параметрлерін зертхана жағдайларында өлшеу нәтижелері ұсынылған. КТМ токамагының антенналық-фидерлік құрылғысы мен ЖЖ жүйесінің сипаттамасы ұсынылған. Уақыттың осы кезеңінде КТМ токамагында қосымша қыздырудың ЖЖ жүйесін қатарға қосу бойынша іске...

In the Kazakhstan Material Testing Tokamak (KTM), additional plasma heating will be achieved by injecting power in the ion cyclotron resonance frequency range using four identical generators, each delivering 2 MW of output power. Prior to transitioning the KTM into regular operation, it is necessary to tune these generators using a load equivalent that simulates plasma-like operating conditions. This article presents the electrodynamic design and analysis of a load equivalent capable of absorbing up to 2 MW of high-frequency power. The geometry and key parameters of the load equivalent for the additional high-frequency (HF) plasma heating system of the KTM tokamak are defined. The calculations are based on the assumption that the optimal solution is to construct the load equivalent as a resonator containing a saline aqueous solution absorber housed in a tank with a dielectric window. A dielectric material with high permittivity is proposed for use in the resonator structure. The results demonstrate that the developed load equivalent enables effective testing and tuning of the high-power generators, thus ensuring the readiness of the additional power injection system for scheduled activation on the KTM tokamak. Two plasma load equivalent (PLE) configurations were investigated for different bench-testing purposes. The large PLE was optimized for high RF power absorption in the standing-wave regime, whereas the small PLE was designed to provide a low-impedance loading condition for antenna-matching tests in preparation for plasma operation.

This paper presents the results of the first experimental tests of the ion cyclotron radio-frequency (RF) plasma heating system of the KTM tokamak with an equivalent plasma load. Measurements of the operating parameters of the RF generator and the antenna-feeder system were carried out under conditions approximating plasma operation. The generator circuits were tuned and matched to the load, and the generation characteristics as well as the conditions for stable RF power transmission to the load were investigated. Stable operating regimes of the system and the conditions ensuring stable RF power generation were determined. The test results confirm the functionality of the main components of the RF heating system and demonstrate the possibility of further testing with plasma in the KTM tokamak.

At present, one of the key challenges in the development of controlled thermonuclear fusion (CTF) facilities is to ensure stable auxiliary plasma heating to the parameters required to sustain long-duration, high-power discharges. To achieve such operating regimes in tokamaks, reliable operation of ion-cyclotron resonance heating (ICRH) systems is required. These systems must be capable of efficiently transferring megawatt-level radio-frequency (RF) power to the plasma under substantially varying load conditions. Of particular importance is the commissioning of high-power RF generators, since tuning and impedance-matching errors can result in damage to expensive equipment and significantly increase the time required to prepare for experimental campaigns. Despite considerable experience in the application of ion-cyclotron resonance heating (ICRH) systems at tokamak facilities worldwide, the testing and commissioning of high-power triode-based generators using load equivalents remain relevant for each specific system. This is due, among other factors, to the individual characteristics of the antenna–feeder path, matching devices, and generator specifications. For the KTM tokamak, this task is of particular importance because commissioning of the ICRH system is a prerequisite for achieving the plasma parameters required to investigate the behaviour of promising candidate materials for the first wall and divertor under conditions as close as possible to those expected in future fusion reactors. In this work, an active load equivalent based on an aqueous saline solution was developed and used to experimentally test a high-frequency generator based on GU-98AM triodes operating in push–pull mode. The generator was tested at a reduced anode voltage of up to 5 kV, with stable RF generation at 13.1 MHz and RF power transfer of up to approximately 20 kW to the active load equivalent. These results demonstrate the applicability of the developed active load equivalent for preliminary tuning and testing of the RF generator and antenna–feeder system. The obtained results are limited to the reduced-voltage and reduced-power conditions investigated in this study and do not represent validation at the nominal anode voltage of 18 kV and rated RF power of 2 MW.