Laboratory tests of the Pulse Height Analysis system for Wendelstein 7-X

Abstract

A pulse height analysis (PHA) system has been designed and manufactured for the Wendelstein 7-X stellarator, in such a way as to be already compatible with later quasi-continuous operation requirements. The diagnostic will provide X-ray spectra with energy resolution better than 180 eV. The system has three energy channels: 0.25-20 keV, 0.95-20 keV and 1.5-20 keV. For each channel a separate Silicon Drift Detector (SDD) equipped with a suitably selected beryllium foil is used. The range of the 3 energy channels can be further adapted to particular experiments by moving via a pneumatic actuator additional beryllium filters in front of the fixed ones. The PHA system is intended for measuring impurity species (e.g. C, Fe, Ni), electron temperature and for investigating possible suprathermal tails in the spectra. The system will be installed on the horizontal port AEK50 on W7-X. The SDD detectors, the replaceable filters and the adjustable piezo driven slits which allow to suitably adapt the X-ray signal intensity are mounted inside a vacuum chamber which is connected to the plasma vessel via a gate valve. The on-air diagnostic components are the preamplifiers, the Digital X-Ray Processor (XIA, U.S.A.), a computer, and an X-ray calibration source. For controlling the operation of the entire diagnostic system, as well as, for the data acquisition of the electrical pulses coming a special code was developed. The paper presents the construction of the PHA system for W7-X and the laboratory tests of its mechanical parts together with the information on the code developed to operate the diagnostic. The diagnostic was also tested and characterised by measuring Fe55 spectrum and fluorescence spectra of Ni, Fe, Cr and Cu induced by an X-ray mini-tube.

Study of impurity behaviour for first magnetic configuration changes in W7-X plasmas by means of PHA spectra

“…Impurity data analysis were performed using the measurements from the Pulse Height Analysis (PHA) system installed at W7-X [16][17][18][19][20]. The PHA diagnostic is designed to measure soft X-ray radiation in the energy range of 0.25 -20 keV.…”

“…The PHA diagnostic is designed to measure soft X-ray radiation in the energy range of 0.25 -20 keV. This diagnostic is dedicated for delivering information about the impurities content in the plasma, Te and estimation of Zeff [16,21]. As presented in [19], the PHA diagnostic was commissioned during OP1.1 but only one energy channel of the PHA system has been optimized to deliver well-resolved spectra.…”

Conceptual design of the multi-foil system for the stellarator W7-X

“…The resulting spectrum does not have an energy resolution high enough to reveal the line structure (as it is e.g. in the case of a PHA system [10]), but it gives the possibility of determining the slope of spectrum, which is directly related to the electron temperature of the plasma. Reconstruction of the energy spectra based on the experimental data can be realized by the deconvolution using e.g.…”

Overview of diagnostic performance and results for the first operation phase in Wendelstein 7-X (invited)

“…The Pulse Height Analysis (PHA) system 40,41 is used for investigation of soft X-ray emission in the energy range from 250 eV to 20 keV. It consists of 3 energy channels equipped with Silicon Drift Detectors (SDDs).…”