Low Startup Voltage Research Articles

Monolithically Integrated Boost Converter Based on 0.5-<tex>$mu$</tex>m CMOS Process

Today and in the future, a huge market arises for mobile power . Efficient performance, functionality, small profile and low cost are the most desired features for mobile power management integrated circuits. Compared with the discrete-switching dc-dc converter, monolithic integration offers many benefits and new design challenges. In this paper, a monolithically integrated high-efficiency boost dc-dc converter for nickel metal hydride or alkaline battery-powered applications is designed based on the low-voltage CMOS process. Several novel concepts are proposed for compensator design, low-voltage startup, light-load efficiency and power device optimization.

Tokamak Start-up under Assistance of RF Waves

To improve the start-up behavior of tokamak discharges and realize the low loop voltage start-up is required by performance of large scale, full superconductor tokamaks. In recent years, some kinds of RF wave have been used to assist the start-up and some exciting results have been gained. This paper introduce the investigation on both in physical principle and experimental research of the start-up process, in which high frequency RF waves were used to assist it.

The Realization of Low Loop Voltage Start-up of HT-7 Tokamak Discharge with the Assistance of Lower Hybrid Wave

Low voltage start-up was realized in HT-7 discharges under the assistance of lower hybrid (LH) waves. The use of a strong LH wave, which can change its N// spectrum in a large range of several milliseconds, made the loop voltage for start-up reduce from around 20 V to less than 5 V. It means that the electric field for HT-7 start-up decreases from 2.5-3 V/m to 0.6 V/m. Some physical phenomena such as the consumption of magnetic flux in start-up phase and the radiation from the initial plasma were observed in this kind of low voltage start-up discharges.

Inharmonic Overtone Spurious Mode Suppression by Partial Mass-Loading onto the Electrode for Energy-Trapped-Type Thickness-Extensional-Mode Piezoelectric Ceramic Resonators

Experimental studies have been performed on the suppression of the inharmonic overtone responses for realizing piezoelectric ceramic resonators with low resonance impedance compatible with a wide-area electrode(>φ15λ). The circumferential mass-loading onto the electrode is effective for the fabrication of an oscillator with a low oscillation startup voltage, without any jump to spurious frequencies. In addition, this technique results in a wide rejection bandwidth for TV/VCR adjacent-channel sound-carrier-signal traps. This effect (stepped energy-trapping) is observed to arise from the spatial vibration energy distribution dispersion by the additive weighting electrode using optical laser interferometry and finite- element-method analysis.

Low Loop Voltage Startup and Equilibrium Control Using Multivariable Poloidal Field Coils in the Hitachi Tokamak HT-2

Tokamak operation techniques to control the poloidal magnetic field using multivariable poloidal field coils (MPFCs) were applied to the Hitachi tokamak HT-2. Two problems encountered in operating a tokamak with MPFCs were identified: low-voltage startup and equilibrium control without interference. The key to their solution was accurate control of the poloidal magnetic field. To obtain multipole fields, a singular value decomposition was applied to a response matrix from the coil current to the magnetic flux value at the plasma surface region. The multipole fields are orthogonal bases of the poloidal field, and the interference was cleared using these modes. A control technique using the multipole fields was applied to control the null point position of the poloidal magnetic field during breakdown, which made it possible to get breakdown with a low loop voltage. During the flattop phase, good controllability without interference was obtained using the concept of a multipole magnetic field.

The electron cyclotron resonance heating experiments on HL-1 tokamak

The electron cyclotron resonance heating (ECRH) experiments on HL-1 tokamak with 300 kW of power generated by a gyrotron are described. With ECE diagnostics, a 30% increase of electron temperature has been obtained. The following phenomena have been observed with various diagnostics during ECRH: increase of radiation intensity of soft x-ray; amplitude change and period elongation of sawtooth oscillation; MHD instability suppression; increase of Hα spectral line intensity and ionized impurity radiation from edge plasma; increase of the temperature and density of edge plasma. Although the total plasma energy content increases, the energy confinement time is decreased. Initial results of low voltage start-up experiments have also been obtained.

Low voltage Ohmic and electron cyclotron heating assisted startup in DIII-D

There is considerable interest in the development of low voltage startup scenarios for large tokamaks since it is proposed that in ITER the electric field which will be applied for ionization and plasma current ramp-up will be limited to values of E ≤ 0.3 V/m. Studies of low voltage startup have been carried out in DIII-D with and without electron cyclotron preionization and preheating. Successful Ohmic startup has been achieved with E ∼ 0.25 V/m by paying careful attention to error fields and prefill pressure, while electron cyclotron heating (ECH) assisted startup with E ∼ 0.15 V/m has been demonstrated. ECH assisted startup gives improved reliability at such low electric fields and permits operation over an extended range of prefill pressures and error magnetic fields. Using ECH, startup at E = 0.3 V/m with |B⊥| > 50 G over most of the vessel cross-section has been demonstrated. Such an error field represents an increase by more than a factor of two over the highest value for which Ohmic startup was achieved at the same electric field. During low voltage Ohmic startup with extreme values of prefill pressure and/or error magnetic fields, excessive breakdown delays are observed. The experimental data agree well with theoretical predictions based on the Townsend avalanche theory. ECH assisted startup is always prompt. The primary effect of ECH during the plasma current ramp-up is a decrease of the resistive component of the loop voltage Vrcs. A significant reduction (∼30%) in Vres is achieved for low ECH powers (PRF ∼ 300-400 kW), but a further large increase in PRF results in only a modest additional decrease in Vres. ECH was not applied over the whole ramp-up phase in these experiments and produced a reduction in volt-second consumption up to the current flat-top (Ip ∼ 1 MA) of ⪅ 10%. These experiments confirm that the low electric fields specified in the ITER design are acceptable and demonstrate the substantial benefits which accrue from the use of ECH assisted startup.

Low voltage start-up in the CLEO Tokamak using ECRH

Studies of ECRH-assisted start-up in the CLEO Tokamak have resulted in the production of well-controlled discharges with Ip approximately 13 kA, ne approximately 5*1018 m-3 in the presence of a loop voltage Vl<2 V throughout. The average loop voltage during the start-up phase is approximately 1.1 V, corresponding to an electric field E approximately 0.19 V m-1, and results in an average rate of current rise of dIp/dt approximately 0.44 MA s-1. Calculated over the whole of the current rise there is a approximately 50% reduction in volt-second consumption when compared with the best case in the absence of RF power. It is estimated that during the plasma current rise approximately 30-50% of the electromagnetic energy input from the poloidal field system is converted to stored magnetic energy.