A gamma ray spectrometer with Compton suppression on the HL-2A tokamak.

A new broad-energy, high-resolution gamma ray spectrometer (GRS) with Compton suppression function has been developed recently in the HL-2A tokamak to obtain the gamma ray information in the energy range of 0.1-10 MeV. This is the first time to develop an anti-Compton GRS for a magnetic confinement fusion device. The anticoincidence detector consists of a large-volume high purity germanium (HPGe) crystal (Φ63 × 63 mm2) as the primary detector and eight trapezoidal bismuth germinate (BGO) scintillators (trapezoid crystal with 30 mm thickness) as the secondary detector. The anti-coincidence data processing is implemented by a digital-based data acquisition system with fast digitization and software signal processing technology. Using radioisotope gamma ray sources and Monte Carlo N-Particle code, the energy and efficiency of the spectrometer have been calibrated and quantitatively tested. The Compton continuum suppression factor reaches 4.2, and the energy resolution (Full Width at Half Maximum) of the 1.332 MeV full energy peak for 60Co is 2.1 keV. Measurements of gamma ray spectra with Compton suppression using the spectrometer have been successfully performed during HL-2A discharges with different conditions. The performance of the spectrometer and the first experimental results are presented in this paper.

Development of the radial neutron camera system for the HL-2A tokamak.

A new radial neutron camera system has been developed and operated recently in the HL-2A tokamak to measure the spatial and time resolved 2.5 MeV D-D fusion neutron, enhancing the understanding of the energetic-ion physics. The camera mainly consists of a multichannel collimator, liquid-scintillation detectors, shielding systems, and a data acquisition system. Measurements of the D-D fusion neutrons using the camera have been successfully performed during the 2015 HL-2A experiment campaign. The measurements show that the distribution of the fusion neutrons in the HL-2A plasma has a peaked profile, suggesting that the neutral beam injection beam ions in the plasma have a peaked distribution. It also suggests that the neutrons are primarily produced from beam-target reactions in the plasma core region. The measurement results from the neutron camera are well consistent with the results of both a standard (235)U fission chamber and NUBEAM neutron calculations. In this paper, the new radial neutron camera system on HL-2A and the first experimental results are described.

Diagnostics for energetic particle studies on the HL-2A tokamak.

About 13 kinds of diagnostics for energetic particle physics studied on the HuanLiuqi-2A (commonly referred to as HL-2A) tokamak are described in this paper. Their measurement ranges, resolutions, and arrangement are presented. Three under-construction diagnostics including imaging fast ion D-alpha, scintillator matrix (for hard X-ray detection), and bundle fission chamber are described in detail.

Development of the scintillator-based probe for fast-ion losses in the HL-2A tokamak.

A new scintillator-based lost fast-ion probe (SLIP) has been developed and operated in the HL-2A tokamak [L. W. Yan, X. R. Duan, X. T. Ding, J. Q. Dong, Q. W. Yang, Yi Liu, X. L. Zou, D. Q. Liu, W. M. Xuan, L. Y. Chen, J. Rao, X. M. Song, Y. Huang, W. C. Mao, Q. M. Wang, Q. Li, Z. Cao, B. Li, J. Y. Cao, G. J. Lei, J. H. Zhang, X. D. Li, W. Chen, J. Chen, C. H. Cui, Z. Y. Cui, Z. C. Deng, Y. B. Dong, B. B. Feng, Q. D. Gao, X. Y. Han, W. Y. Hong, M. Huang, X. Q. Ji, Z. H. Kang, D. F. Kong, T. Lan, G. S. Li, H. J. Li, Qing Li, W. Li, Y. G. Li, A. D. Liu, Z. T. Liu, C. W. Luo, X. H. Mao, Y. D. Pan, J. F. Peng, Z. B. Shi, S. D. Song, X. Y. Song, H. J. Sun, A. K. Wang, M. X. Wang, Y. Q. Wang, W. W. Xiao, Y. F. Xie, L. H. Yao, D. L. Yu, B. S. Yuan, K. J. Zhao, G. W. Zhong, J. Zhou, J. C. Yan, C. X. Yu, C. H. Pan, Y. Liu, and the HL-2A Team, Nucl. Fusion 51, 094016 (2011)] to measure the losses of neutral beam ions. The design of the probe is based on the concept of the α-particle detectors on Tokamak Fusion Test Reactor (TFTR) using scintillator plates. The probe is capable of traveling across an equatorial plane port and sweeping the aperture angle rotationally with respect to the axis of the probe shaft by two step motors, in order to optimize the radial position and the collimator angle. The energy and the pitch angle of the lost fast ions can be simultaneously measured if the two-dimensional image of scintillation light intensity due to the impact of the lost fast ions is detected. Measurements of the fast-ion losses using the probe have been performed during HL-2A neutral beam injection discharges. The clear experimental evidence of enhanced losses of beam ions during disruptions has been obtained by means of the SLIP system. A detailed description of the probe system and the first experimental results are reported.

CT and MRI features of patients with diastematomyelia.

OBJECTIVE: To evaluate computed tomography (CT) and magnetic resonance imaging (MRI) features in patients with diastematomyelia and to investigate clinical characteristics of this lesion. STUDY DESIGN: A retrospectively study. SETTING: The Second Affiliated Hospital, School of Medicine, Xi'an Jiaotong University. METHODS: A total of 82 diastematomyelia cases were retrospectively studied. All the patients underwent neurological examinations as well as MRI and CT of the spine. A self-established neurological functional grading system was used, and posterior tibial nerve somatosensory cortical-evoked potential (PTNSCEP) was measured to assess the neurological status of the patients. Imaging features of symmetry of splitting, presence of septum, location of lesion and number of split segments were studied. The neurological functional grading, PTNSCEP, and imaging findings were then analyzed and compared, and the difference was considered to be significant if P-value was lower than 0.05. RESULTS: Neurological functional grading and latency of PTNSCEP were significantly different but related in terms of symmetry of splitting, presence of septum and location of lesion. Although no significant differences were present in the number of split segments, the severity of the neurological functional grading and PTNSCEP impairment were not related to the number of split segments. CONCLUSION: The imaging features in diastematomyelia are characteristic and relate well with the clinical manifestations according to neurological functional grading and PTNSCEP measurement, except the number of split segments.

Measurements of the fast electron bremsstrahlung emission during electron cyclotron resonance heating in the HL-2A tokamak.

A fast electron bremsstrahlung (FEB) diagnostic technique based on cadmium telluride (CdTe) detector has been developed recently in the HL-2A tokamak for measurements of the temporal evolution of FEB emission in the energy range of 10-200 keV. With a perpendicular viewing into the plasma on the equatorial plane, the hard x-ray spectra with eight different energy channels are measured. The discrimination of the spectra is implemented by an accurate spectrometry. The system also makes use of fast digitization and software signal processing technology. An ambient environment of neutrons, gammas, and magnetic disturbance requires careful shielding. During electron cyclotron resonance heating, the generation of fast electrons and the oscillations of electron fishbone (e-fishbone) have been found. Using the FEB measurement system, it has been experimentally identified that the mode strongly correlates with the electron cyclotron resonance heating produced fast electrons with 30-70 keV.

ß-induced Alfvén eigenmodes destabilized by energetic electrons in a Tokamak plasma.

The ß-induced Alfvén eigenmode (BAE) excited by energetic electrons has been identified for the first time both in the Ohmic and electron cyclotron resonance heating plasma in HL-2A. The features of the instability, including its frequency, mode number, and propagation direction, can be observed by magnetic pickup probes. The mode frequency is comparable to that of the continuum accumulation point of the lowest frequency gap induced by the shear Alfvén continuous spectrum due to finite ß effect, and it is proportional to Alfvén velocity at thermal ion ß held constant. The experimental results show that the BAE is related not only with the population of the energetic electrons, but also their energy and pitch angles. The results indicate that the barely circulating and deeply trapped electrons play an important role in the mode excitation.

A new soft x-ray pulse height analysis array in the HL-2A tokamak.

A new soft x-ray pulse height analysis (PHA) array including nine independent subsystems, on basis of a nonconventional software multichannel analysis system and a silicon drift detector (SDD) linear array consisting of nine high performance SDD detectors, has been developed in the HL-2A tokamak. The use of SDD has greatly improved the measurement accuracy and the spatiotemporal resolutions of the soft x-ray PHA system. Since the ratio of peak to background counts obtained from the SDD PHA system is very high, p/b > or = 3000, the soft x-ray spectra measured by the SDD PHA system can approximatively be regarded as electron velocity distribution. The electron velocity distribution can be well derived in the pure ohmic and auxiliary heating discharges. The performance of the new soft x-ray PHA array and the first experimental results with some discussions are presented.

[Trend and prediction of cancer mortality in Beijing, China, during 1980-2001].

Mortality data gathered through registration system were analyzed systematically to predict the trend of cancer mortality. A grey-system model was established to forecast the epidemic trend for cancer mortality of Beijing in 2001. In result, the mortality of cancer in Beijing will increase annually upto 2001. The composition of various malignant tumer will charge notably. Rapid increase will occure in lung cancer. Liver cancer and colon-rectal cancer will aslo increase. Cancers of esophagus and cervix uteri will steadly decline. Stomach cancer begin to decrease. These information on the change of cancer mortality will provide scientific reference for the study of cancer prevention and control in Beijing.