A. D. Khilchenko

Dispersion interferometer based on a CO2 laser for TEXTOR and burning plasma experiments

A dispersion interferometer based on a continuous-wave CO2 laser source (λ=9.57 μm) with double plasma passage for measurements of the line-integrated electron density in the TEXTOR tokamak and the GDT linear system has been developed and tested in experiments. A sensitivity of 〈nel〉min=2×1017 m−2 and a temporal resolution of 1 ms have been achieved. The interferometer does not need any rigid frame for vibration insulation. Its basic components are installed compactly on an optical bench placed on a stable support outside of the torus. The possibility for the development of a multichannel dispersion interferometer for the next generation of fusion devices (e.g., W7-X, ITER) is discussed.

Development of a multichannel dispersion interferometer at TEXTOR

The design and main characteristics of 14-channel dispersion interferometer for plasma profile measurement and control in TEXTOR tokamak are presented. The diagnostic is engineered on the basis of modular concept, the 10.6 microm CO(2) laser source and all optical and mechanical elements of each module are arranged in a compact housing. A set of mirrors and retroreflectors inside the TEXTOR vacuum vessel provides full coverage of the torus cross section with 12 vertical and two diagonal lines of sight, no rigid frame for vibration isolation is required. Results of testing of the single-channel prototype diagnostic and the pilot module of the multichannel dispersion interferometer are presented.

New fast beam profile monitor for electron-positron colliders

A new fast beam profile monitor has been developed at the Budker Institute of Nuclear Physics. This monitor is based on the Hamamatsu multianode photomultiplier with 16 anode strips and provides turn-by-turn measurement of the transverse beam profile. The device is equipped with an internal memory, which has enough capacity to store 131,072 samples of the beam profile. The dynamic range of the beam profile monitor allows us to study turn-by-turn beam dynamics within the bunch charge range from 1 pC up to 10 nC. Using this instrument, we have investigated at the VEPP-4M electron-positron collider a number of beam dynamics effects which cannot be observed by other beam diagnostics tools.

First experimental results from 2 MeV proton tandem accelerator for neutron production.

A 2 MeV proton tandem accelerator with vacuum insulation was developed and first experiments are carried out in the Budker Institute of Nuclear Physics (Novosibirsk). The accelerator is designed for neutron production via reaction (7)Li(p,n)(7)Be for the boron neutron-capture therapy of the brain tumors, and for explosive detection based on 9.1724 MeV resonance gamma, which are produced via reaction (13)C(p,gamma)(14)N, absorption in nitrogen.

Advanced direct current negative-ion source for accelerator use

Status of direct current hydrogen negative-ion source development for tandem accelerator is described. The electrodes enforcing its water cooling and introducing of the electrons’ interception permitted to increase the source discharge power and to obtain regularly the H−-ion beam with energy >25kV and current up to 15mA.

Direct current H− source for boron neutron capture therapy tandem acceleratora)

One year experience of dc H(-) source operation at 2 MeV tandem accelerator is described. The source delivers H(-) ion beams with controlled current in the range of 1-8 mA and energy up to 25 keV. Normalized 1 rms emittance for 8 mA beam is less than 0.2 pi mm mrad. Negative ions are produced on the cesiated anode of the Penning discharge, driven by plasma injection from the hollow cathode inserts.

Computer System for Unattended Control of Negative Ion Source

The computer system for control of cw surface‐plasma source of negative ions is described. The system provides an automatic handling of source parameters by the specified scenario. It includes the automatic source start and long‐term operation with switching and control of the power supplies blocks, setting and reading of source parameters like hydrogen feed, cesium seed, electrodes’ temperature, checking of the protection and blockings elements like vacuum degradation, absence of cooling water, etc. The semi‐automatic mode of control is also available, where the order of steps and magnitude of parameters, included to scenario, is corrected in situ by the operator. Control system includes the main controller and a set of peripheral local controllers. Commands execution is carried out by the main controller. Each peripheral controller is driven by the stand‐alone program, stored in its ROM. Control system is handled from PC via Ethernet. The PC and controllers are connected by fiber optic lines, which prov...

Application of precise phase detector for density profile and fluctuation measurements using CO2 imaging heterodyne interferometer on LHD

The two-color CO2∕YAG laser imaging heterodyne interferometer was recently equipped with a precise digital phase counter (eight channels, 0.5mrad resolution, 1MHz carrier frequency and sampling rate, 500kHz bandwidth, ±250rad recording range, and a maximum data record of 8.4×106 samples/channel). This modification enables detailed measurements of plasma density dynamics during pellet ablation and, in addition, observations of density fluctuations. Examples of fast rising density peaks in pellet discharges as well as spatial and spectral characteristics of plasma density fluctuations obtained with the heterodyne interferometer are presented.

Dispersion interferometer based on CO2 laser

A dispersion interferometer based on CO2 laser for measurements of plasma line density in the gas dynamic trap (GDT) experiment has been developed with sensitivity min ~ 1·1013 cm-2, temporal resolution ~50 ns. The main advantages of the interferometer are compactness and low sensitivity to vibrations. The interferometer does not require specific vibration isolation structure and can be mounted directly on the working chamber of the plasma device. The above mentioned advantages have been successfully demonstrated in the Gas Dynamic Trap experiments.

Measurement of Plasma Density in Modern Fusion Devices by Dispersion Interferometer

Abstract We propose to use dispersion interferometer for measurement of plasma density and control of plasma position on present and future fusion devices. Distinguishing feature of this scheme is probing of plasma on two wavelengths. Short-wave radiation is formed by method of frequency fundamental radiation doubling. Probing first and second harmonics rays are combined spatially at the same time. It allows to create interferometer which is sensitive only to dispersion of studied medium and weakly sensitive to vibration of optical elements. Designs of the optical system dispersion interferometer and results of plasma density measurements on GDT mirror and TEXTOR tokamak are presented.