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論文

J-PARC MR遅い取り出しにおける運動量ロスとその対策

田村 文彦; 山本 昌亘; 大森 千広*; 吉井 正人*; Schnase, A.*; 野村 昌弘; 冨澤 正人*

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.125 - 129, 2014/06

J-PARC MRでの遅い取り出しにおいては、陽子ビームをデバンチさせるためにRF電圧をオフにする必要がある。ビームが十分にデバンチするまでの間、空胴のインピーダンスにより、加速ギャップにウェーク電圧が発生し、ビームは運動量を失う。J-PARC MRでは比較的低いビームパワーでも 有意な運動量ロスを観測している。運動量のロスが大きくなると、クロマティシティの効果によりチューンの広がりが大きくなり、取り出し効率を下げる原因となることが判明している。高い取り出し効率を保ちつつビームパワーを上げるためには、デバンチ過程での運動量ロスの低減が必須である。本発表では、運動量ロスの実際について報告するとともに、その対策について報告する。RFフィードフォワード法を用いたビームローディング補償により、20kWのビームパワーにおいても運動量ロスを大幅に低減させることに成功し、99.5%の高い取り出し効率を達成した。

論文

J-PARC MR horizontal exciter test for transversal noise application

Schnase, A.; 佐藤 健一郎*; 冨澤 正人*; 外山 毅*; 魚田 雅彦*; 吉井 正人*

Proceedings of 8th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.338 - 342, 2011/08

To improve the duty factor of the proton beam, extracted by slow extraction to the Hadron hall, we applied transversal noise using the existing horizontal exciter in J-PARC Main-Ring (MR). For noise center frequencies of 5 and 7.5 MHz, operation was possible; however in a band above 6 MHz, we noticed that the pressure in the vacuum chamber increased near the exciter structure. Higher noise center frequencies seem to improve the duty factor seen by the Hadron experiment, therefore we tried frequencies near 30, 25, and 20 MHz. Problems with vacuum pressure rise prevented longer time operation. Therefore, we mapped safe and unsafe operation points as function of frequency and amplifier output power. We found a safe operation area for the extraction beam time planned for the April 2011 run, however due to the big Tohoku earthquake the beam time was postponed. Improved noise signals, where the amplitude distribution is independent of noise bandwidth have been created and we drove the exciter with them to confirm the feasibility. We confirmed that a solenoid around the exciter improves the multi-pactor issues. With a solenoid current of 2 A, the frequency range from 1 to 35 MHz is free from vacuum problem for the whole output power range of the used 1 kW RF transistor-amplifiers.

論文

Simulation of narrow-band longitudinal noise applied to J-PARC Main Ring

Schnase, A.; 田村 文彦; 小関 忠*; 冨澤 正人*; 外山 毅*; 吉井 正人*; 大森 千広*; 野村 昌弘; 山本 昌亘; 戸田 信*; et al.

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.1079 - 1081, 2010/08

In MR extraction studies in the beginning of 2010, the application of narrow band longitudinal noise to the MR-beam at 30 GeV in flat-top to increase the duty factor of the extracted spill was tested. The longitudinal spectrum with noise became wider than expected from the bandwidth of the band-limited noise. Here we show longitudinal beam simulations, using the same digital noise that was applied to the beam, to understand the measured spectra. This also allows to estimate, which would be good combinations of harmonic number, bandwidth and amplitude of the noise to obtain a desired beam shaping.

論文

Application of digital narrow band noise to J-PARC Main Ring

Schnase, A.; 田村 文彦; 小関 忠*; 冨澤 正人*; 外山 毅*; 吉井 正人*; 大森 千広*; 野村 昌弘; 山本 昌亘; 戸田 信*; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.1446 - 1448, 2010/05

Applying narrow band noise to the beam in J-PARC Main Ring in flattop, while the acceleration voltage is off helps to counteract the effect of ripple on the slow extraction. For this purpose, a complex noise sequence output by DSP modulates a custom made DDS synthesizer to create single side spectra without carrier. The noise is calculated starting from a description in frequency domain. An algorithm creates narrow band spectra with optimized behavior in time domain. Frequency domain data is transformed to time domain, and the amplitude is smoothed. The smoothed data is transformed back to frequency domain, and the spectral shape is restored. This process repeats until the amplitude in time domain has converged, while the desired spectrum shape is preserved. Noise generated in this way can be tailored for different requirements. We show the signal properties, the hardware, and preliminary beam test results, when the noise is applied (a) to the MR RF system, and (b) to the horizontal exciter system.

論文

Beam injection tuning of the J-PARC main ring

Wei, G.; 小関 忠*; 五十嵐 進*; 冨澤 正人*; 高野 淳平*; 石井 恒次*; 白形 政司*; Fan, K.*; 畠山 衆一郎; 魚田 雅彦*; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.3915 - 3917, 2010/05

The beam commissioning of J-PARC (Japan Proton Accelerator Research Complex) MR (Main Ring) was started from May 2008 and is in progress. As usual, injection tuning is in the first stage and strongly related to other tuning items. Starting with design schemes, making adjustment due to leakage field influence from injection septum, doing envelope matching considering dilution of beam profile in Main Ring are reported in this papers.

論文

Beam fast extraction tuning of the J-PARC main ring

Wei, G.; 小関 忠*; 冨澤 正人*; 五十嵐 進*; 石井 恒次*; 安東 愛之輔; 高野 淳平*; 魚田 雅彦*; Fan, K.*; 畠山 衆一郎; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.3918 - 3920, 2010/05

The beam commissioning of J-PARC/MR has been started from May 2008 and is in good progress. One key purpose of MR commissioning is the 30 GeV beam fast extraction to neutrino beam line, which reflect the overall commissioning result. In the MR, fast extraction system comprises 5 kickers and 8 septa which give a bipolar kick to neutrino beam line or abort dump. However before commissioning, the measured magnetic field distribution of each fast extraction septa shows non-linear profile along the horizontal direction. In order to find the influence, a beam simulation with the measured field distributions of septa has been performed. Depends on this study and some OPI (Operation Interface) made by code SAD for orbit modification online, fast extraction of 30 GeV beam to neutrino beam line has been achieved on April 23rd 2009. And so far, 100 kW continual operation to neutrino line have been achieved, too.

口頭

Physics design and commissioning experience of J-PARC main ring injection and extraction

Wei, G.; 小関 忠; 五十嵐 進*; 高野 淳平*; 冨澤 正人*

no journal, , 

The beam commissioning of J-PARC MR was started from May 2008. As usual, injection tuning is in the first stage and strongly related to other tuning items including the fast extraction to neutrino beam line, where extracted beams finally reflect the overall commissioning result. Starting with design schemes, making adjustment due to leakage field influence from injection septum, doing injection envelope matching considering dilution of beam profile in Main Ring, simulations with measured magnetic field distribution for fast extraction and orbit tuning for 30 GeV extraction are reported in this papers.

口頭

Refining narrow-band noise signals for transversal beam excitation to improve J-PARC MR slow extraction

Schnase, A.; 田村 文彦; 冨澤 正人*; 外山 毅*; 吉井 正人*

no journal, , 

At the 2009 LLRF workshop, we showed procedures to create complex modulation sequences for well-defined narrow-band signals. A DSP controlled the modulation data for a DDS-synthesizer. In 2010 such noise signals fed to the MR-transversal exciter were used to study the duty factor improvement of the extracted proton beam from J-PARC Main-Ring (MR). According to the experiment group higher noise frequencies are preferred, where the DDS is at its limits. A commercial vector signal generator with built-in digital IQ modulation was examined. It stores several million sample long IQ-modulation sequences and can generate higher frequency signals. Signal preparation is similar to the DDS board. We present properties of the narrow-band noise signals generated by the vector generator, and Nov. 2010 extraction beam study results where we used such signals. The duty-factor improved by transverse noise near 20 MHz, but there was pressure rise due to multi-pactor in the horizontal exciter. The multi-pactor problems are solved, giving more freedom for the operating frequency. This helps future beam tests with transversal noise aiming at higher frequency. The IQ-modulation sequence creating process is refined to make sure that the peak power is only 3 dB higher than the average power. A verified signal level prevents power amplifier problems. We describe synthesis details, output signal measurement methodology, and results.

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