Разработка инструментов для измерения бетатронной частоты в реальном времени на Нуклотроне
Е.В. Горбачев, А.Е. Кириченко, Д.В. Монахов, С.В. Романов, В.И. Волков, ОИЯИ, Дубна
Ключевые слова: бетатронная частота, БПФ на базе FPGA, FlexRIO дигитайзер.
Аннотация
Разработана и протестирована на пучке Нуклотрона система измерения бетатронной частоты. Для возбуждения поперечных колебаний пучка использовались два вида сигналов — белый шум и сканирование частоты. Для реализации непрерывного измерения бетатронной частоты в реальном времени разработан модуль FlexRIO для преобразования аналогового сигнала в цифровой код и генерации сигналов возбуждения пучка. Алгоритм получения БПФ с высоким разрешением реализован на базе FPGA модуля, к которому подключен модуль FlexRIO. Система измерения интегрирована в систему управления NICA на базе TANGO Controls. В статье приведены результаты тестов и измерений, проведенных на пучках Нуклотрона.
Development of tools for real-time betatron tune measurements at the Nuclotron
E.V. Gorbachev, A.E. Kirichenko, D.V. Monakhov, S.V. Romanov, V.I. Volkov, JINR, Dubna
Keywords: betatron tune, FPGA-based FFT, FlexRIO digitizer.
Abstract
A betatron tune measurement system has been developed and tested at the Nuclotron. A white noise and chirp signals are used for transverse beam motion excitation. A custom FlexRIO digitizer module has been developed for a continuous signal acquisition in a real-time and generation of excitation signals. A high resolution FFT algorithm has been implemented inside a FPGA module, connected to digitizer. The measurement system is integrated with the NICA control system based on the TANGO Controls. Results and tests performed with the Nuclotron beam are presented.
1. Introduction
One of the key parameters of the synchrotron accelerator is the betatron tune. It is defined by the arrangement and strength of the focusing and defocusing quadrupoles (FODO lattice) around the ring. The ideal particle will follow a particular trajectory, which closes on itself after one revolution – the closed orbit. The real particles perform oscillations around the ideal closed orbit. These transverse oscillations are called betatron oscillations, and they exist in both horizontal (x) and vertical (z) planes. The number of such oscillations per one beam turn is called betatron tunes – Qx and Qz. If the integer part of the tune agrees with the accelerator model predictions, large optics errors can be ruled out, such as dipole errors, which lead to the integer resonances. The fractional part of the tune have a strong effect on a beam lifetime and emittance, since quadrupole errors lead to resonances at half-integer Q values, sextupole fields excite resonances at third-integer Q values and so on [1]. That is why the accelerator working point (Qx, Qz) has to be chosen in a reasonable distance from the resonance lines (Figure 1). Measuring and controlling the betatron tunes can improve the beam lifetime and reduce the beam loss during acceleration. The betatron tune measurement system can be used to investigate a coupling between horizontal and vertical betatron oscillations due to sextupoles, misalignment of magnets and skew of quadrupole fields. In the following, the fractional part of the tune will also be denoted by Q.
F
igure
1. Diagram of resonances up to 7-th order (calculated for NICA) [2].
Working points (Qx, Qz) are denoted by red squares.