The research progress of an E//B neutral particle analyzer

An E//B neutral particle analyzer(NPA)has been designed and is under development at Sichuan University and Southwestern Institute of Physics.The main purpose of the E//B NPA is to measure the distribution function of fast ions in the HL-2A/3 tokamak.The E//B NPA contains three main units,i.e.the stripping unit,the analyzing unit and the detection unit.A gas stripping chamber was adopted as the stripping unit.The results of the simulations and beam tests for the stripping chamber are presented.Parallel electric and magnetic fields provided by a NdFeB permanent magnet and two parallel electric plates were designed and constructed for the analyzing unit.The calibration of the magnetic and electric fields was performed using a 50 kV electron cyclotron resonance ion source(ECRIS)platform.The detection unit consists of 32lutetium-yttrium oxyorthosilicate(LYSO)detector modules arranged in two rows.The response functions ofα,hydrogen ions(H^(+),H_(2)^(+)and H_(3)^(+))andγfor a detector module were measured with^(241)Am,^(137)Cs and^(152)Eu sources together with the 50 kV ECRIS platform.The overall results indicate that the designed E//B NPA device is capable of measuring the intensity of neutral hydrogen and deuteron atoms with energy higher than 20 keV.

Proton pitch angle distributions in the Martian induced magnetosphere: A survey of Tianwen-1 Mars Ion and Neutral Particle Analyzer observations

The pitch angle distributions of ions and electrons can be affected by various processes;thus,they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas.From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter,we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field,and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions.Even though no symmetrical features were seen in the dataset,we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV.Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region.Although our results are more or less restricted by the adopted magnetic field,they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere.

A simulation study of a windowless gas-stripping room in an E//B neutral particle analyzer

The neutral particle analyzer(NPA)is one of the crucial diagnostic devices in a Tokamak facility.The stripping unit is one of the main parts of the NPA.A windowless gas-stripping room with two differential pipes has been constructed in a parallel electric and magnetic fields(E//B)NPA.The pressure distributions in the stripping chamber are simulated by ANSYS Fluent together with MolFlow+.Based on the pressure distributions obtained from the simulation,the stripping efficiency of the E//B NPA is studied using GEANT4.Hadron reaction physics is modified to track the charge state of each particle in a cross-section-based method in GEANT4.The transmission rates(R)and stripping efficiencies f_(+1)are examined for particle energies ranging from 20 to 200 keV with the input pressure(P_(0)),ranging from 20 to 400 Pa.According to the combined global efficiency,R×f_(+1),P_(0)=240 Pa is obtained as the optimum pressure for the maximum global efficiency in the incident energy range investigated.

Neutral Particle Transport in Cylindrical Plasma Simulated by a Monte Carlo Code

A Monte Carlo code （MCHGAS） has been developed to investigate the neutral particle transport. The code can calculate the radial profile and energy spectrum of neutral particles in cylindrical plasmas. The calculation time of the code is dramatically reduced when the Splitting and Roulette schemes are applied. The plasma model of an infinite cylinder is assumed in the code, which is very convenient in simulating neutral particle transports in small and middle-sized tokamaks. The design of the multi-channel neutral particle analyser （NPA） on HL-2A can be optimized by using this code.

Calculation of Neutral Particle Energy Spectra in Tokamak by Using the Monte Carlo Method

Neutral particle energy spectra in the HT-7 tokamak are calculated by using the Monte Carlo method. It can reproduce the spectra measured in experiment. Differences of neutral particle energy spectra in higher and lower electron density plasma are discussed. Results show that the ion temperature given by neutral particle energy spectra is lower than the real ion temperature, but the deviation is within 10% if the ion temperature is less than 800 eV and thecentral chord-averaged electron density does not exceed 3 ×1013 cm-3. But for ion temperature higher than 1000 eV at the central chord-averaged density limit up to 5 ×1013 cm-3, the neutral particle energy spectra can still give the ion temperature within 10% deviation.

Design of the stripping unit and the electromagnetic analysis unit for the E//B NPA on HL-2A/2M tokamak

An E//B neutral particle analyzer is under development for fast ion diagnosis on HL-2A/2 M tokamak.The stripping unit is composed of a stripping room(equipped with two differential tubes and a gas supply bellows),a vacuum chamber and a vacuum pumping system.The stripping efficiency of the stripping room is calculated in the form of global efficiency R×f_(+1),where R is the non-scattered-away rate and f_(+1)is the fraction of charge state+1.The magnetic field of the E//B analyzer is produced with a permanent magnet.The yoke and the poles of the magnet are made of mild steel and the magnet plates are made of Nd Fe B.The magnetic poles are specially designed to focus the ion trajectories and to increase the use rate of the magnet.The shape of the magnet and the electric plates are carefully designed so that the ions are dispersed into two lines of H^(+) and D^(+) on the detector plane.For each line,the energy increases from 10 to 200 ke V from one side to another.

Field study of a soft X-ray aerosol neutralizer combined with electrostatic classifiers for nanoparticle size distribution measurements

Most conventional aerosol neutralizers are based on radioactive sources, which are controlled by strict regulations restricting their handling, transport, and storage. The TSI 3087 soft X-ray （SXR） neutralizer circumvents these legal restrictions. The aim of the present work is to compare the performance of a standalone SXR aerosol neutralizer with that of conventional radioactive aerosol neutralizers based on 85Kr （TSI 3077） and 241Am （Grimm 5522） by performing field tests in a real environmental scenario. The results obtained when the SXR neutralizer was connected to a mobility particle sizer spectrometer （MPS）, different from the device suggested by the manufacturer, were comparable with those obtained with the use of radioactive aerosol neutralizers. In changing the neutralizer, the particle number concentrations, measured with the MPS connected to the SXR neutralizer, almost remained within the 10% uncertainty bounds for the particle size interval 10-300 nm, when diffusion losses inside the SXR tube were considered. Based on our comparisons, the SXR neutralizer can be regarded as a standalone instrument that could solve the problems associated with legal restrictions on radioactive neutralizers and fulfil the need for a portable instrument for different field test purposes.