"SYSTEM AND METHOD FOR REDUCING VIBRATIONS IN PRESSURE OSCILLATION SYSTEMS"

Technical field The present invention relates to the field of systems that produce vibrations, such as, for example, cryogenic systems, i.e. cryocoolers or cryorefrigerators , which comprises means for producing pressure oscillations (e.g., rotary valves, pistons, or displacers), and in particular it relates to closed-cycle cryocoolers not using cryogenic liquids, also referred to as "cryogen-free cryocoolers" or "dry cryocoolers". More specifically, the present invention relates to a device and to a method for stabilizing and suppressing the vibration noise induced by the simultaneous operation of at least two of said means producing pressure oscillations, such as, for example, rotary valves present in pulse tube cryocoolers (PTC) of the Gifford-McMahon type, for applications that must operate in high cooling power and low-vibration cryogenic environments. Background

As known, technologies using rotary valve, piston or displacer systems are widely used in various fields of industry and of scientific research. An example thereof includes cryogenic systems based on the use of closed-cycle cryocooling machines, which exploit the expansion of a fluid, typically gaseous helium, to generate cooling power. These cryocooling machines find a particular application in those fields, both scientific and industrial, where there is a need for reaching a temperature below 100-120 °K, in that they have a high refrigerating power and/or a low vibration level. For example, low temperature, high cooling power, and low vibration environments are to be set up in the field of quantum computers, i.e. computers that exploit the laws of quantum physics and mechanics, whose operation requires very low temperatures, close to absolute zero (approximately - 273 °C). For this purpose, quantum computers often use a series of pulse tube cryocoolers (PTC) as pre-cooling devices integrated in multistage cryogenic systems, typically in so- called dilution cryostats, i.e. cryogenic apparatuses that reach temperatures below fractions of one Kelvin degree in a continuous manner.

As compared to other closed-cycle cryocoolers, an advantage of PTCs is in that they provide a lower vibration level, thanks to the absence of low temperature moving parts, to the detriment of a poorer refrigerating power. For this reason, it is a common practice to equip one and the same cryogenic system with more than one PTC whenever a high refrigerating power is required without renouncing a low vibration level.

In addition to quantum computers, there are numerous other industrial applications where PTCs, and more in general closed-cycle cryocoolers, are widely used, such as, for example:

• precoolers for dilution cryostats; · refrigerators for gas or gas compound (nitrogen, helium, air, etc.) liquefaction plants;

• cryogenic pumps, i.e. gas capture cryopumps wherein the gaseous substances bind to the cold surfaces inside the pump and are used to produce a high vacuum degree in the chambers used, for example, for manufacturing semiconductor products;

• military applications, such as infrared sensor cooling, whose thermal chambers are cooled down in order to reduce thermal noise; · SQUID (Superconducting Quantum Interference Device) magnetometers, which are extremely sensitive instruments used for measuring very feeble magnetic fields, in sanitary and medical applications.

Closed-cycle cryocoolers are also particularly useful in space telescopes, such as the James Webb Space Telescope, which will reach the Hubble space observatory in the space and where it will not be possible to replenish cryogens as they exhaust, or in space explorations, such as, for example, in futures missions to Mars, where they could be used for liquefying oxygen on that planet's surface. Finally, it is possible to list numerous other uses of closed-cycle cryocoolers, and in particular PTCs, in a scientific environment, including:

• scanning tunnelling microscopy; · cold optical systems;

• low energy and rare event physical experiments, such as, for example, the CUORE (Cryogenic Underground Observatory for Rare Events) experiment presently in function at the underground seat of the Italian Gran Sasso national laboratories;

• particle accelerators and structures for high energy physics (CERN, etc.);

• interferometry for researching gravitational waves (for example, KAGRA, Einstein Telescope); · astronomy detectors (for example, the cosmologic telescope of Atacama, the Qubic experiment).

In all these applications a high refrigerating power and a low vibration level are required.

Just as an example, in the present invention reference is made to cryogenic systems containing at least two pulse tube cryocoolers (PTC) of the Gifford-McMahon type (GM- type). However, the present invention is not limited to GM- type PTC only, but it is also applicable to PTCs of different types (for example Stirling-type PTCs), Stirling machines, and Gifford McMahon type coolers. More in general, the here below described invention is not limited to cryogenic systems only, but it relates to all those systems which produce vibrations in general and comprise means for producing pressure oscillations, such as, for example, rotary valves, pistons, and displacers that are operated simultaneously.

The component parts that are mostly responsible for producing vibrations internally to cryogenic systems that use, for example, GM-type PTCs, and, in general, internally to all systems that use several means for producing pressure oscillations simultaneously, are the motors used to drive said means. For example, in a cryogenic system equipped with more than one GM-type PTC, every rotary valve belonging to every PTC is driven individually and independently of the others. Consequently, every PTC operates at an operating frequency of its own, which is defined around a characteristic value (typically in the order of few Hz), apart from the accuracy defined by the driving device used. Whenever a number of PTCs is driven simultaneously and in a not-synchronized manner, forced vibrations of different and close frequencies are produced in the cryogenic system, due to the effect of the phase shift existing between the alternating forces which, by superposing to each other, originate beats internally to the system. Because of this, the power spectrum of the system noise will contain components whose amplitude varies over time, which render the signal filtering and extraction operations unavoidably little effective. Also, amongst all possible phase-shift configurations between the different PTCs installed in the system, there will be at least one that optimizes given system variables/parameters, such as vibration level and cooling power.

In general, different approaches exist for mitigating the problem of vibrations in low temperature systems. They can basically be grouped into two categories, both at ambient temperature and at cryogenic temperature:

• passive countermeasures, including shock absorbers, decouplers, bellows, spring systems, remote PTC rotary valve drives, PTC remote commands;

• active countermeasures, including electronic shock absorbers or actuators.

For example, American patent US 10,162,023 B2, owned by Oxford Instruments, discloses an apparatus for reducing noise in a pulse tube cooler, which finds a particular application in imaging magnetic resonance systems. This apparatus comprises a dispersion chamber wherein the pressure oscillations coming from a PTC are directed and scattered. The apparatus operates onto the pressure oscillations caused by one single PTC and scatters them thanks to its specific architecture, but it is not usable in the case that vibrations are generated by the motion of several conflicting mechanical parts, such as, for example, a system comprising more than one PTC.

For example, American patent application

US2 007/107448A1 (Dresens et al.) discloses a system for controlling helium feeding to a plurality of cryocoolers, which uses a plurality of compressors connected to a common manifold, so as to provide an appropriate supply of refrigerating fluid. The proposed solution makes it possible to control helium consumption in each of the cryocoolers through the use of a controller or vacuum network master (VNC), capable of modifying the speed of operation of displacers, thus affecting consumption of refrigerant and properly re-distributing helium amongst the individual cryocoolers. In this system, every cryocooler is mounted internally to a cryopump, not all cryopumps shall necessarily operate simultaneously in the same conditions, but they might be in different operating statuses (for example, running during a cooling step, running at a basic temperature, or switched off in a re-cycling step, etc.). Conversely, a system designed for minimizing mechanical vibration level in a cryogenic apparatus, like that discussed below, has a need for and allows to operate all cryocoolers simultaneously under the same operating conditions (for example, all switched on in the same instant in time and all operated at the same operating frequency). Another patent, WO 2018/136415 A2 (Sonotherm LCC), discloses a solution for a cooling system that adopts the high frequency thermoacoustic technology with the aim of rendering it competitive with respect to other cooling technologies based on mechanical compression. The solution adopted for the high frequency thermoacoustic cryocooler includes an acoustic driver or "speaker", a resonator block, and a heat exchanger unit. A control unit is provided to send a signal to the "speakers", which drive into vibration a membrane responsible for producing an acoustic wave, typically via a diaphragm. In one particular embodiment, an electronic circuit is configured for driving the acoustic drivers in order to produce pressure waves featuring the same intensity and frequency, this way generating combined high intensity sound waves. The control unit effectively manage the operation of the drivers in order to provide a desired cooling level. Thus, according to the proposed solution, sound waves produced by different acoustic drivers installed in the same cryocooler are made constructively interfere internally to one and the same cryocooler in order to increase cooling power. Vice versa, the purpose of a system aiming at minimizing the mechanical vibration level in a cryogenic apparatus comprising more than one cryocooler is that of making the mechanical vibrations introduced by the individual cryocoolers inside the apparatus to destructively interfere with each other in order to reduce the mechanical noise generated by them as a side effect of their operation.

For example, patent US 8,639,388 B2 owned by Raytheon Company, discloses a system for an "adaptive phase control for active cancellation of cryocooler vibrations", which applies a force for cancelling (via an actuator) a cryocooler (PTC) vibrations and comprises a sensor for regulating the oscillations in such a way as to render them out-of-phase and make them interfere with each other destructively. In this system, the vibrations generated by the pressure oscillations coming from one individual PTC are used to make them destructively interfere with those produced by a mechanical actuator. The proposed invention is thus applied to the case of a cryogenic system that comprises one cryocooler, whereas it does not represent a useful solution in the case that a cryogenic system comprises a higher number of PTCs.

In summary, the solutions adopted so far to deal with the problem of vibrations in cryogen-free cryocoolers are essentially based on modifying the hardware of the PTC architecture or cryogenic infrastructure, but they have a disadvantage in that they reduce the produced cooling power and/or increase system complexity. Besides being rather invasive, most existing solutions also operate as mere passive countermeasures. Finally, none of the known countermeasures acts onto systems wherein two or more cryocoolers operate simultaneously.

It is therefore necessary to develop a device and a method that allow for a substantial vibration level decrease in systems comprising several means for producing simultaneously operatable pressure oscillations, such as, for example, cryogenic systems comprising at least two PTC cryocoolers, without being obliged to introduce substantial modifications in the cryocooler infrastructure, or to introduce further thermodynamical and/or mechanical components inside the cryogenic system itself.

Summary A scope of the present invention is a method and a device for reducing the vibration level in systems that produce vibrations, based on synchronizing the motors that drive pressure oscillations production means (for example, rotary valves, pistons, or displacers) inside a system that comprises at least two of said identical means or a combination thereof.

According to one embodiment of the claimed method, one device is used, configured for synchronizing the operation of the motors that drive said pressure oscillation production means, accommodated inside said system, all said motors being operated exactly at the same frequency.

According to one specific embodiment, the claimed method uses a motor drive comprising one power converter, specifically designed and optimized for controlling, in a synchronized and coordinated manner, the operation of the motors driving said pressure oscillation production means, in a system comprising at least two of said means.

According to one specific embodiment, said system that produces vibrations is a cryogenic system formed of at least two Stirling type cryocoolers and said pressure oscillations production means are at least two piston/displacer pairs, each pair being associated with its own Stirling cryocooler.

According to a different embodiment, said system that produces vibrations is a cryogenic system formed of at least two Gifford-McMahon (GM) type cryocoolers, and said pressure oscillations production means are at least two rotary valve/displacer pairs, each pair being associated with a compressor included in its own GM cryocooler.

According to another embodiment, said system that produces vibrations is a cryogenic system formed of at least two Stirling-type pulse tube cryocoolers and said pressure oscillations production means are at least two pistons, each piston being associated with its own Stirling-type PTC cryocooler .

According to a further embodiment, said system that produces vibrations is a cryogenic system formed of at least two Gifford-McMahon pulse tube cryocoolers (GM-type PTCs), and said pressure oscillation production means are at least two rotary valves, each pair being associated with a compressor included in its own GM-type PTC.

According to one preferred embodiment, the claimed method allows to reduce the vibration noise level produced inside a cryogenic system comprising at least two GM-type PTC cryocoolers, by the superposition of the operating frequencies of each of said at least two GM-type PTC cryocoolers, through the synchronization of the operation of the motors that drive the rotary valves of said at least two PTC cryocoolers. The movement of every rotary valve in every PTC originates pressure oscillations that are at the base of the cooling power of the PTC and of the generation of its characteristic noise.

According to one embodiment, the proposed method uses one motor drive, said drive being a power converter used for driving all rotary valves - each accommodated inside each PTC - simultaneously and on the basis of a common synchronization signal. The proposed device is also capable of reducing the vibration noise level, by managing the relative movement of every rotary valve and making it simultaneously rotate at the same frequency.

According to a further embodiment, the claimed method uses the characteristic noise produced by each of the individual at least two GM-type PTCs to create destructive interferences, by taking advantage of the coherent superposition of the mechanical vibrations generated by pressure oscillations in order to obtain noise cancellation.

According to a further embodiment, the claimed method uses the operating frequency characteristic of each of the individual at least two GM-type PTCs to exploit the coherent superposition of the oscillations in order to maximize the cooling power of the system.

A previous applicant's project, called "Active Pulse Tube Noise Cancellation" (APTNC), provided a first validation of effectiveness of this noise cancellation technique, both in experimental physics (D'Addabbo et al., "An active noise cancellation technique for the CUORE Pulse Tube Cryocoolers", Cryogenics, 93:56-65, May 2018; V. Dompe et al.; "The CUORE Pulse Tube Noise Cancellation Technique J. Low Temp. Phys ., https://doi.org/10.1007/sl0909-020-

02435-0, March 2020) and in pertinent industrial environments, through the development of a software that guides two or more linear motor drives commercially available on the market. The two mentioned articles describe the results obtained by applying an active noise cancellation technique in the CUORE experiment, which uses a cryostat that simultaneously operates up to five GM-type PTCs. The methodology that is the scope of the present invention features three elements of innovation with respect to the previous APTNC project, even though it uses the same technique as a means: 1. use of one motor drive for one complete cryogenic system, instead of one drive for each PTC cryocooler or similar;

2. development of a device, specifically designed and optimized for the operations of means responsible for pressure oscillations (such as, rotary valves, pistons, and displacers) of PTC cryocoolers or the like, instead of using commercial linear drives manufactured for different purposes;

3. implementation of a method based on synchronizing the operations of the means responsible for pressure oscillations (such as, rotary valves, pistons, and displacers) by way of one common synchronization signal, instead of using methods based on a continuous regulation of the speeds of said means (as implemented in the APTNC project and in the CUORE experiment). The technology according to the present invention represents a further step forward as compared to the previous technology. As a matter of fact, the use of commercial low- noise linear drives for driving said means (such as, for example, the rotary valves of the GM-type PTCs) is already known in the industrial field, but this use is limited down to a ratio 1:1 (i.e., one linear drive for driving one single pressure oscillation production mean), and with the only purpose of passively reducing the electromagnetic noise and the radiofrequency interferences generated by the operation thereof and by the operating environment. Just as an example, the use of said low-noise linear drives has been adopted for driving the rotary valves installed on the five GM-type PTCs manufactured by the company Cryomech and installed in the CUORE experiment. As a further advantage, said device is compatible with

GM-type PTCs manufactured by a number of companies, such as, for example, the previously mentioned Cryomech or the company Sumitomo, which manufacture GM-type PTCs equipped with rotary valves with different motor drive types. In addition, the device provided by the present invention is compatible and can be integrated with all types of closed-cycle cryogen- free cryocoolers present on the market, and it is finally backwards-compatible with cryogen-free cryocoolers already in operation, and can be added, and made operational, after a system has already been commissioned.

The device according to the present invention is provided with a management software that interfaces to the system user. According to one preferred embodiment, said software is provided with a graphical interface and with a set of algorithms, whose implementation makes it possible to obtain an active noise cancellation in a system comprising a number of GM-type PCTs equal to at least two units.

According to a different embodiment, said software makes it possible to use a set of algorithms for obtaining the maximization of the cooling power of a system comprising a number of GM-type PCTs equal to at least two units.

According to a further embodiment, said software can also be implemented in systems comprising a number of GM- type PTCs ranging from two to four units.

According to a further embodiment, said software can be implemented in systems comprising a number of closed-cycle cryogen-free cryocoolers (including PTCs) greater than or equal to two units.

Brief description of the figures

- Fig. 1. Block diagrams showing the principle of operation of a closed-cycle cryocooler according to the present status of the art.

- Fig. 2. A schematic representation of a device used for controlling motors driving N>2 rotary valves in a cryogenic system formed of N>2 pulse tube cryocoolers (PTC) according to one embodiment of the present invention.

Fig. 3. A block diagram of a device designed for controlling motors that drive N>2 rotary valves in a cryogenic system according to the present invention. Detailed description

Here follows a description of a method and a device for reducing vibration level in vibration producing systems, based on controlling the motors used to drive the pressure oscillation production means (such as, for example: rotary valves, pistons, displacers) in a system comprising at least two of said means.

In particular, the proposed method is particularly effective for reducing the mechanical vibration noise and/or for maximizing the cooling power generated in a cryogenic system formed of at least two closed-cycle cryocoolers, each of said cryocoolers being equipped with at least one of said pressure oscillation production means, and applicable in all those environments in which high vacuum degree and/or cooling power and low vibration level are required.

Combinations of compressors and/or pistons/displacers operating at a high frequency (typically 25-400 Hz), or combinations of compressors and rotary valves/displacers operating at a lower frequency (typically 0.5-5 Hz) can be alternatively used for producing pressure oscillations.

For example, in Stirling cryocoolers (Fig. 1A), pressure oscillations are generated by the movement of one or several pistons (10A) directly connected to a chamber (11A), coordinated with the movement of a displacer (12A) arranged internally thereto, and controlled by a motor (not shown in figure).

In another example, in cryocoolers of the Gifford- McMahon type (Fig. IB), pressure oscillations are generated by a compressor (13B) associated with a rotary valve (14B) directly connected to a chamber (11B), coordinated with the movement of a displacer (12B) arranged internally thereto, and controlled by a motor (not shown in the figure).

The pulse tube cryocoolers (PTC) operate in a manner fully similar to the previous ones, the only difference being in that the role of the displacer (12A, 12B) is played by the gas itself, which moves forwards and backwards in a so- called "pulse-tube".

So, for example, in Stirling-type pulse tube cryocoolers (Stirling-type PTC), Fig. 1C, pressure oscillations are generated by the movement of one or several pistons (IOC) directly connected to the pulse tube (15C) and controlled by a motor.

Conversely, for example, in pulse tube cryocoolers of the Gifford-McMahon type (GM-type PTCs), Fig. ID, pressure oscillations are generated by a compressor (13D) associated with a rotary valve (14D) directly connected to the pulse tube (15D) and controlled by a motor.

As already said, the proposed method can be applied to one whatsoever of the types of closed-cycle cryocoolers out of those listed above, aiming at reducing vibration noise and/or maximizing cooling power.

The proposed method is particularly effective in reducing the mechanical vibration noise created in a cryogenic system formed of at least two close-cycle pulse tube cryocoolers (PTC) of the GM type (GM-type PTCs).

A pulse tube cryocooler (PTC) is a fluid machine used for producing cold, in particular cryogenic temperatures below ~120 °K, whose cooling power is provided by way of expansion/compression cycles acting on a fluid flowing therethrough, usually helium pressurized to few tens of bars, obtained by using a high frequency pressure oscillation generator (such as, for instance, in a Stirling cooler (Fig.1C), for example by using an expansion/compression piston) or by using a low frequency compressor associated with a rotary valve (such as, for example, in a "Gifford- McMahon cooler, Fig.ID). For this reason, the PTCs of the former type are also called Stirling-type PTCs, whereas those of the second type are also called GM-type PTCs.

The cooling effect is based on a periodical variation of pressure inside one or several thin wall tubes (15C, 15D) equipped with heat exchangers (17C, 17D, 18C, 18D) at both ends and connected to a regenerator (16C, 16D) featuring a high thermal capacity.

As shown in Fig.1C and Fig.ID, a thin hollow cylindrical tube (15C, 15D), or pulse tube, is interposed between a "hot exchanger" (17C, 17D), which releases the heat accumulated during a cycle to the external world, and a "cold" exchanger (18C, 18D), put in contact with the body to be cooled, and is connected to a regenerator material (16C, 16D), in the form of metal (e.g. stainless steel, bronze, brass, copper, lead, or rare earth metal) grains or meshes. For instance, in GM-type PTCs (Fig.ID), the pressure cycles are generated by a rotary valve (14D) placed inside the motor head at the ambient temperature of the PTC. Said rotary valve typically performs 0.5 to 5 revolutions per second and connects the PTC to the high- and low-pressure sides of a compressor (13D) alternately. This results in pressure oscillations at a frequency that depends on the PTC model used.

The variations of the thermodynamical parameters of the gas provide the cooling power (or frigorific power), but they are also a source of mechanical noise at the rotary valve frequency and its harmonics.

The rotary valves in use in the modern PTCs are driven by motors, which might require different types of power supply, depending on the selected model.

According to one embodiment of the invention, as shown in Fig.2, the claimed method provides a device (20) which allows to synchronize the rotary movement of two or more rotary valves (21), each serving a different GM-type PTC, so that they operate at an exactly identical frequency.

The device (20) provided according to the invention, or motor drive, acts onto the complete system and is designed to fit different systems comprising at least two pressure oscillation generation means, arranged in two different machines independent of each other (such as, for example, two rotary valves or two pistons or two valve/displacer pairs or two valve/piston pairs, in one system formed of two closed-cycle cryocoolers); for example, it can be used in a cryogenic system (200) formed of two or more GM-type PTC cryocoolers for simultaneously controlling the motors that drive the rotary valves (21) contained in each of the PTCs (one rotary valve for every PTC). The device is customized in accordance with the system wherein it shall operate and can be tailored, for example, on the basis of the model of PTC cryocoolers to be driven. For exemplary purposes only, in the case of GM-type PTC cryocoolers marketed by one of the companies that are leaders in this sector, the motors used to drive the rotary valves are stepping motors driven by a pair of square waves, in phase quadrature with each other, featuring a fixed amplitude and a frequency proportional to the frequency of rotation of the valve.

Still for exemplary purposes only, in the case of GM- type PTC cryocoolers marketed by another company, the motors used to drive the rotary valves are synchronous or asynchronous motors driven by a triplet of sine waves, phased shifted by an angle of 120° from each other, featuring a fixed amplitude and a frequency that is proportional to the frequency of rotation of the valve. Usually, in a cryogenic system every rotary valve is driven by its own motor. In a cryogenic system formed of two or more PTCs, every rotary valve is driven by a motor receiving a set of waveforms, the number, form, amplitude, and frequency of which are typical of the model of PTC in use. The difference in the operating frequency of the different sets of waveforms, each driving an independent rotary valve belonging to an independent PTC, generates a progressive phase shift between the operating frequencies of the individual PTCs. This phase shift originates forced vibrations of different and close frequencies which are at the base of the generation of beats and consequently of the variable noise of the system.

According to one embodiment of the claimed method, each of the motors involved in the cryogenic apparatus receives a set (for instance, a pair or a triplet) of waveforms from the same source and featuring the same frequency, which maintain their reciprocal difference of phase unchanged over time. The frequency of each of the pairs or triplets of waveforms can be modified independently of the others, in order to find that reciprocal phase configuration between the pressure oscillations generated by the different cryocoolers involved in the system, which minimizes the noise of the system and/or maximizes the cooling power of the system. According to one preferred embodiment, as shown in Fig. 2, the device (20) provided according to the claimed method is configured for managing a plurality of rotary valves (21) and comprises a plurality of electronic boards, each electronic board being associated with one or more different rotary valves (21); a first electronic board of said plurality of boards operates as a "master", whereas the remaining electronic boards operate as "slaves", each having its own drive. Said first electronic board operating as a "master" manages the operations of said "slave" boards via a microcontroller, whose sequence of instructions is programmed with an integrated software, or low-level "firmware", which operates at a higher frequency than the movement of the valves. Said first electronic board, operating as a "master" also outputs a synchronization signal for said "slave" boards.

According to one embodiment of the device in accordance with the present invention (Fig.3), the hardware architecture (300) of said device (20) comprises a power converter (30), whose diagnostics and control are also managed by that firmware. Said power converter (30) comprises one or several power boards (32), which are responsible for the electrical transformation of the waveform coming from the mains (33), and one or more control boards (34), which control a conditioning network formed of switches (35) which are part of the power board (32) and is slaved thereto. According to one embodiment, said "master" board (34A) is also responsible for managing the peripherals and the communication protocols and the interface to the external world via a microcontroller (35A). According to a further embodiment, a second microcontroller (35B) deals with the peripherals and the communication protocols and the interface to the external world via a second higher-level firmware. In particular, said interface is configured for receiving commands from a software (36) for controlling and managing the user interface and sending readouts to said software (36), all rights of which are owned by this applicant, according to a communication protocol, which is defined in accordance with the performance requirements and speed of the device.

According to one embodiment of said software (36), the interface is configured for communicating with a number of pressure sensors (37) equal to the number of cryocoolers involved in the system, each being installed in communication with the chamber where pressure oscillations are produced, in accordance with cooling power generation and characteristic noise. According to one embodiment of said software (36), the interface is configured for communicating with a number of vibration sensors (37) (for example, accelerometers, geophones, etc.) equal to the number of (cartesian) geometric axes involved in the system, each installed in direct mechanical contact with the chamber wherein characteristic noise is to be minimized.

According to one embodiment of said software (36), the interface is configured for communicating with a number whatsoever of temperature sensors (37), installed in direct thermal contact with the chamber wherein cooling power is to be maximized.

According to one embodiment of said software, the interface is configured for communicating with the firmware (s) of the device in order to modify the relative phase between the means (38) responsible for generating pressure oscillations belonging to cryocoolers that are different but installed on the same system. The phase configuration selected is identified by an indexer integrated in the device and can be associated with a real phase configuration of the system thanks to the readouts provided by the pressure sensors. Thanks to an algorithm of this software, it is possible to map the whole space of the possible phase configurations and to preset noise and/or temperature readouts to be associated with every specific configuration. In this way, it is possible to locate, identify, select, and maintain over time that specific phase configuration which minimizes noise or maximizes refrigerating power. According to the preferred embodiment of the invention, the software (36) used for controlling and managing the user interface, as well as all operations necessary for minimizing noise and/or maximizing cooling power, is configured for a cryogenic system formed of at least two PTCs. According to another embodiment, said software (36) is configured for operating with a cryogenic system formed of a number of PTCs ranging from two to four units. According to a further embodiment, said software (36) is configured for operating with a cryogenic system formed of a number of cryocoolers greater than or equal to two units.

It is finally clear that modifications and variants can be brought to what here described and illustrated without departing from the scope of protection of the present invention, as set forth in the attached claims. In particular, it is here pointed out that the means

(38) used for producing pressure oscillations (38) can be not only rotary valves, but also pistons, displacers, or any other means driven by a motor controllable by the device here proposed, according to the here proposed method. It is also pointed out once again that the number of rotary valves (or any other types of means used for producing pressure oscillations) that can be managed by means of the proposed method can vary with respect to what illustrated above, and said method can be applied for controlling motors that drive said means in a system that might also have purposes different from those illustrated in the previous description, but is formed of a number of said means equal to at least two.