Advanced ion beam calorimetry for the test facility ELISE

Abstract

Abstract. The negative ion source test facility ELISE (Extraction from a Large Ion Source Experiment) is in operation since beginning of 2013 at the Max-Planck-Institut für Plasmaphysik (IPP) in Garching bei München. The large radio frequency driven ion source of ELISE is about 1x1 m 2 in size (1/2 the ITER source) and can produce a plasma for up to 1 h. Negative ions can be extracted and accelerated by an ITER-like extraction system made of 3 grids with an area of 0.1 m 2 , for 10 s every 3 minutes. A total accelerating voltage of up to 60 kV is available, i.e. a maximum ion beam power of about 1.2 MW can be produced. ELISE is equipped with several beam diagnostic tools for the evaluation of the beam characteristics. In order to evaluate the beam properties with a high level of detail, a sophisticated diagnostic calorimeter has been installed in the test facility at the end of 2013, starting operation in January 2014. The diagnostic calorimeter is split into 4 copper plates with separate water calorimetry for each of the plates. Each calorimeter plate is made of 15x15 copper blocks, which act as many separate inertial calorimeters and are attached to a copper plate with an embedded cooling circuit. The block geometry and the connection with the cooling plate are optimized to accurately measure the time-averaged power of the 10 s ion beam. The surface of the blocks is covered with a black coating that allows infrared (IR) thermography which provides a 2D profile of the beam power density. In order to calibrate the IR thermography, 48 thermocouples are installed in as many blocks, arranged in two vertical and two horizontal rows. The paper describes the beam calorimetry in ELISE, including the methods used for the IR thermography, the water calorimetry and the analytical methods for beam profile evaluation. It is shown how the maximum beam inhomogeneity amounts to 13% in average. The beam divergence derived by IR thermography ranges between 1° and 4° and correlates relatively well with the values measured by beam emission spectroscopy with up to 30% difference. It has also been observed that the beam inhomogeneity decreases with lower beam divergence.

Towards powerful negative ion beams at the test facility ELISE for the ITER and DEMO NBI systems

“…ELISE is equipped with several diagnostic techniques, mainly optical emission spectroscopy and pin probes using ports close to the extraction system [16]. A set of beam diagnostic tools provides information about the large ion beam: a tungsten wire calorimeter for qualitative online monitoring of the beam during operation and the beam emission spectroscopy with 20 lines of sight with a dedicated diagnostic calorimeter for quantitative measurement of parameters such as divergence and uniformity [13]. Due to the available extraction and acceleration voltages, ELISE operates mostly in the underperveant range resulting typically in divergences of about 3°.…”

“…Figure 2 shows a vertical cross section through the ELISE test facility and gives the characteristic parameters and target values. The ELISE source and extraction system was designed to be as close as possible to the ITER design with some modifications aimed at improving the experimental flexibility and to provide better access for source and beam diagnostics (see [11][12][13] for details). Unlike at ITER, the source vessel is in air allowing easy source access and modifications, but the four drivers are enclosed in a vacuum containment, called dome, such that the RF drivers are operated in vacuum like at ITER.…”

Beam calorimetry at the large negative ion source test facility ELISE: Experimental setup and latest results

“…5. Average emissivity coefficient of diagnostic calorimeter coating against the pulse number [16]. The average emissivity coefficient shows a decreasing trend with increasing beam operation time.…”

Progress on development of SPIDER diagnostics

“…To this purpose the front surface of the dump, with expected temperature up to 350 °C, will be coated with a suitable black molybdenum disulphide coating, i.e. Molykote D-321R, made by Dow Corning, to overcome the problem of the low copper emissivity, as effectively achieved at IPP [33], and in this case also to reduce the reflection from the opposite panel. …”