Thrust measurement and thrust balance development at DLR’s electric propulsion test facility

Electric space propulsion thrusters only produce low thrust forces. For the fulfillment of a space mission this implies long thruster runtimes, and this entails long qualification times on ground. For such long testing times, a ground facility requires a vacuum chamber and a powerful pumping system which can guarantee high vacuum over extended times and under thruster gas load. DLR’s STG-ET is such a ground test facility. It has a high pumping capability for the noble gases typically used as propellants. One basic diagnostic tool is a thrust measurement device, among various other diagnostic systems required for electric propulsion testing, e.g. beam diagnostics. At DLR we operate a thrust balance developed by the company AST with a thrust measurement range of 250 mN and capable of thruster weights up to 40 kg. Adversely, it is a bulky and heavy device and all upgrades and qualification work needs to be done in a large vacuum chamber. In order to have a smaller device at hand a second thrust stand is under development at DLR. The idea is to have a light and compact balance that could also be placed in one of the smaller DLR vacuum chambers. Furthermore, the calibration is more robust and the whole device is equipped with a watercooled housing. First tests are promising and showed a resolution well below 1 mN. In this paper we give background information about the chamber, describe the basics of thrust measurement and the development of a new balance.

Controlling the process of muon formation for muon-catalyzed fusion: method of non-destructive average muon sign detection

The recent development of intense muon sources (Holmlid, Swedish Patent SE 539,684 C 2 (2017)) is crucial for the use of muon-catalyzed fusion reactors (L. Holmlid, Fusion Science and Technology 75, 208 (2019)) which are likely to be the first generation of practical fusion reactors. For this purpose, only negative muons are useful. For existing sources where negative muons can be ejected (if not formed) preferentially, it is necessary to know the amount of negative muons to determine and optimize the fusion reactor efficiency on-line. Here, a method is developed to measure the absolute muon flux and its average sign without collecting or deflecting the muons. The muons from the patented muon generator have an energy of 100 MeV and above and an intensity of 1013 muons per laser pulse. Here, the detection of the relativistic laser-induced muons from H(0) is reported with a standard particle beam method, using a wire coil on a ferrite toroid as detector for the relativistic particles. The coil detection method shows that these relativistic particles are charged, thus not photons, neutrinos or neutral kaons. This makes the coil method superior to scintillator methods and it is the only possible method due to the large muon intensity. If an equal number of positive and negative mouns passed the coil, no signal would be observed. The signal at the coil in the case shown here is due to relativistic positive muons as concluded from a signal charge sign verification in the coil.

The cryogenic control system of SHINE

The Shanghai High repetition rate XFEL and Extreme Light Facility (SHINE), an advanced XFEL project, is now being built at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences. It includes a hard X-ray free electron laser and a 100 pW intense laser facilities with overall length of 3.1 km. The XFEL part including an 8 GeV LINAC and 3 undulator lines is cooled with forced superfluid and supercritical helium at 2 K/4 K. The cryogenic system of SHINE consists of test facility cryogenic system (TFCS), accelerator cryogenic system (ACCS), and undulator cryogenic system (UNCS). A dedicated control system based on Experimental Physics and Industrial Control System (EPICS) will be built to automate the cryogenic system with process control, PID control loops, real-time data acquisition and storage, alarm handler and human machine interface. It is capable of automatic recovery as well. This paper describes details of control system structure, interfaces, controllers and the integration under EPICS framework.

Dependence of charge-exchange efficiency on cooling water temperature of a beam transport line

The 3-GeV Rapid Cycling Synchrotron at the Japan Proton Accelerator Research Complex supplies a high-intensity proton beam for neutron experiments and to the Main Ring synchrotron. Various parameters are monitored to achieve a stable operation, and it was found that the oscillations of the charge-exchange efficiency and cooling water temperature were synchronized. We evaluated the orbit fluctuations at the injection point using a beam current of the injection dump, which is proportional to the number of particles that miss the foil and fail in the charge exchange, and profile of the injection beam. The total width of the fluctuations was approximately 0.072 mm. This value is negligible from the user operation viewpoint as our existing beam position monitors cannot detect such a small signal deviation. This displacement corresponds to a 1.63 × 10− 5 variation in the dipole magnetic field. Conversely, the magnetic field variation in the L3BT dipole magnet, which was estimated by the temperature change directly, is 4.08 × 10− 5. This result suggested that the change in the cooling water temperature is one of the major causes of the efficiency fluctuation.

Global models for radio-frequency ion thrusters

The emerging “new space” age strengthens the importance of rapid development and qualification procedures of electric engines and their peripheral devices. A key element is the reliable simulation of the thrusters and their supply units on short time scales. Global models seem to be well suited for this purpose. In this article, three variants of global models are presented and validated by comparison with experimental results. All models show excellent agreement with experiment, illustrating the strength of this modeling approach. Future developments of radio-frequency ion thrusters can be significantly accelerated with the help of these global models.

ESS Cryogenic Controls Design

The European Spallation Source (ESS) is a neutron-scattering facility funded and supported in collaboration with 13 European countries in Lund, Sweden. Cryogenic cooling at ESS is vital particularly for the linear accelerator, the hydrogen target moderators, a test stand for cryomodules, the neutron instruments and their sample environments. The paper will focus on the control system design for the different cryogenic subsystems, hardware and software selected, industry and in-house development, advantages and disadvantages of the chosen setup and operational experience. There is also a lessons learned, feedback from providers and stakeholders and an outlook for further development described.