HT-7装置软X射线诊断系统及锯齿行为研究

利用HT-7装置上建立的多阵列软X射线诊断系统对等离子体放电中的锯齿不稳定性进行研究,发现锯齿的出现及其行为特点与等离子体电子密度N_e、电子温度T_e、边界安全因子q_α、壁条件等放电参数有密切关系。在低杂波电流驱动等离子体放电条件下,观察到m/n=1/1的中间模振荡出现在锯齿的上升阶段,并迅速发展、饱和、衰减,在锯齿塌陷或先兆振荡出现以前消失。分析和讨论了欧姆加热条件下和低杂波加热条件下的锯齿行为。     

Nd：LiTaO3背散射组态下的喇曼光谱异常

本文研究了掺钕钽酸锂组体背射几何组态下的喇曼光谱，与纯钽酸锂晶体的喇曼光谱相比，发现喇曼谱中不仅有Ｅ（ＬＯ＋ＴＯ）模向Ａ１（ＴＯ）模的转变，而且还有新振动模的出现和部分振动模强度的变化，本文用光折变理论结合掺杂后晶体微观结构的改变对实验结果作了分析和探讨。     

Nd∶LiTaO_3背散射组态下的喇曼光谱异常

本文研究了掺钕钽酸锂晶体背散射几何组态下的喇曼光谱，与纯钽酸锂晶体的喇曼光谱相比，发现喇曼谱中不仅有Ｅ（ＬＯ＋ＴＯ）模向Ａ１（ＴＯ）模的转变，而且还有新振动模的出现和部分振动模强度的变化，本文用光折变理论结合掺杂后晶体微观结构的改变对实验结果作了分析和探讨．     

烧蚀RT不稳定性非线性过程模拟

重点研究了不同预热对烧蚀RT弱非线性模耦合的影响。首先不同预热情况烧蚀RT不稳定性的线性增长率曲线明显不同。不同预热情况的模拟结果都表明：烧蚀RT的模耦合系数是k／kc的函数，二次和三次谐波的产生系数C（k）和D（k）遵从定标关系C（k）：c1（1-c2k/kc），D（k）=d1-d2k/kc＋d3（k/kc）^2。弱预热和中等预热情况，二次谐波的产生系数约只有经典RT的50％，三次谐波的产生系数约只有经典RT的20％。两体模耦合起主要作用，n次高次谐波可近似看作是由（”一1）次两体模耦合产生的。由于烧蚀RT不稳定性两体模耦合系数小于1，所以高次谐波的产生系数很快衰减。由于非线性作用变弱，单模扰动的非线性饱和阈值明显增大，意味着基模有较长时间的线性增长，另外，向长波长方向的模耦合系数明显大于经典尺丁不稳定性数值，因此，烧蚀RT非线性模耦合容易形成长的尖顶，从而对点火构成严重威胁。     

分段式电子回旋波驱动电流对早期新经典撕裂模的抑制

新经典撕裂模的产生会严重影响托卡马克装置的约束性能，而且在高参数运行状态下的所有装置中该不稳定性不可避免。新经典撕裂模的抑制工作对于聚变装置至关重要，电子回旋波驱动电流(ECCD)是目前抑制新经典撕裂模的主要手段之一。用数值模拟的方法研究了在新经典撕裂模发展的早期加入ECCD后，对新经典撕裂模发展的影响。通过数值模拟发现较小份额的连续ECCD可以减小新经典撕裂模早期的增长速度，同时可以提高再次加入电子回旋波驱动电流抑制处于增长期的新经典撕裂模的效率。     

HL-lM装置杂质粒子输运与约束特性

在HL-lM装置上利用激光吹气技术,在等离子体边缘瞬态注入少量Al杂质粒子,通过对真空紫外光谱和软X射线区的杂质辐射测量,分别研究了欧姆等离子体和低杂波电流驱动等离子体两种情况下,Al杂质粒子输运与约束特性。结果表明：在欧姆等离子体和低杂波电流驱动等离子体两种情况下,等离子体中心区,在没有MHD锯齿震荡和有MHD锯齿震荡非锯齿破裂期间,杂质粒子输运基本上受新经典规律支配;在有MHD锯齿震荡锯齿破裂期间,杂质粒子输运受MHD不稳定性支配,但其时间很短(通常小于300μs),所以在这种情况下,杂质粒子输运的平均效应比新经典值稍大。而约束区杂质粒子输运则比新经典的值大很多,是反常的。在一定条件下低混杂波电流驱动可以改善等离子体粒子约束。     

HL—1装置等离子体输运与锯齿特性的数值研究

本文利用一维圆柱等离子体输运编码（ＴＲＡＮＰＹ），编制了模拟锯齿振荡的大型编码（ＳＡＷＭＯＤ）。对锯齿振荡的研究，我们选用了两种具有代表性的理论模型：重联模型和湍流模型，后者特别适用于低ｑａ放电的锯齿特性研究。重联模型的锯齿振荡是由于磁力线的完全重联引起的，而湍流模型的锯齿振荡是因为微观湍流或磁力线的随机化而产生的。最后，我们将ＨＬ－１装置的一次典型高密放电的参数代入（ＳＡＷＭＯＤ）编码，运算结果     

托卡马克理想磁流体不稳定性的统一描述 (I)

在与平衡磁面相联系的坐标系下，用剪切阿尔芬波近似给出了统一描述托卡马克等离子体理想磁流体线性运动的本征模方程。利用此方程，可以进一步给出大尺度扰动（扭曲模、低模数气球模、阿尔芬模）和小尺度扰动（高模数气球模、Mercier模）的本征模方程。本文详细讨论了小尺度扰动的本征模方程。     

HL─1装置等离子体输运与锯齿特性的数值研究

本文利用一维圆柱等离子体输运编码（ＴＲＡＮＰＹ），编制了模拟锯齿振荡的大型编码（ＳＡＷＭＯＤ）。对锯齿振荡的研究，我们选用了两种具有代表性的理论模型：重联模型和湍流模型，后者特别适用于低ｑａ放电的锯齿特性研究。重联模型的锯齿振荡是由于磁力线的完全重联引起的，而湍流模型的锯齿振荡是因为微观湍流或磁力线的随机化而产生的。最后，我们将ＨＬ─１装置的一次典型高密放电的参数代入（ＳＡＷＭＯＤ）编码，运算结果表明，重联模型和湍流模型均能解释实验观测的锯齿现象，理论模拟与实验结果符合较好。     

反磁剪切等离子体中的电阻交换模不稳定性

具有内部输运垒（ITB）的反磁剪切（RS）等离子体位形是在托卡马克中获得高参数的最具前景的途径之一。这种位形不仅改善等离子体约束,而且可以改进象气球模和新经典撕裂模等这类宏观模的稳定性。然而,反磁剪切区域的高压强可以驱动电阻交换模不稳定性,从而破坏中心区的等离子体高参数。为了研究电阻交换模不稳定性的性质,并确定其在RS等离子体中发展的区域,我们利用在HL－2A中使用中性束注入建立的RS位形来分析电阻交换模不稳定性。     

低场脉冲NMR中静磁场不均匀性的射频场补偿

在低场脉冲核磁共振实验中为了增大射频激励的带宽,通常采用的方法是提高射频激励磁场的场强. 针对共振区域中静磁场的不均匀性,本文提出了根据共振区域中的静磁场分布设计射频线圈以提高射频激励带宽,并用目标场方法实现了这一构想.      

热阴极微波电子枪模拟计算

用模拟计算方法,研究了热阴极微波电子枪的束流动力学行为,采用笛卡尔坐标,编制了准三维模拟计算程序──HOTGUN.计算中除考虑了射频场外,还充分考虑了空间电荷效应(空间电荷场为轴对称场)、肖特基效应及稳态负载效应等.文中给出了HOTGUN程序与PARMELA部分模拟结果及中科院高能所自由电子激光室微波电子枪热测实验台部分实验结果的比较,最后以用于北京自由电子激光器的多腔热阴极微波电子枪为例,给出了详细的HOTGUN程序模拟计算结果.     

Adiabatic Mixing in the Liquid State

Adiabatic spin inversion has been used in the liquid state very efficiently for decoupling purposes. Here we show that it can also be adapted for spin mixing experiments, such as the TOCSY and clean TOCSY experiment, and is superior to previously employed mixing sequences. The main advantage of adiabatic mixing sequences over the conventional mixing schemes used in liquid state experiments is an extremely low sensitivity to RF field inhomogeneity and miscalibration of theB₁field strength. The method is evaluated experimentally by comparing results obtained with different mixing schemes in the basic 2D TOCSY experiment. In addition to higher reliability, adiabatic mixing provides a sensitivity improvement of ca. 20% as compared to conventional mixing schemes. This is explained by higher signal losses due to RF inhomogeneity in the experiments employing traditional mixing schemes. More significant sensitivity improvements can be expected in situations where RF homogeneity is traditionally poor, for example, in large volume probes and magnetic resonance imaging experiments.     

“Unusual” lines observed in low-frequency cw ENDOR of photoexcited triplet state molecules: the primary donor triplet in photosynthetic reaction centers as an example

The origin of frequently observed “negative” (opposite phase) ENDOR lines in the low-frequency region of triplet state ENDOR spectra is explained in terms of microwave hole burning and RF modulation phenomena. From this, a new method of detecting burnt side holes in EPR spectra is derived which is based on cw ENDOR instrumentation. The method uses the modulation satellites that are induced by a longitudinal RF field component and appear around any EPR line, including burnt holes (“negative” lines). The longitudinal RF field was generated by a coil oriented parallel to the external field, but a longitudinal component of the RF field also exists in most conventional ENDOR spectrometers because of slight misalignments of the ENDOR coil generating the transversal RF field. The lines it induces in the low-frequency part of ENDOR spectra are generally considered as artifacts. It is shown, however, that RF induced modulation satellites provide valuable information concerning the lines distant from the spectral position in the EPR spectrum chosen for ENDOR observation. This allows one to record the pattern of side holes burnt by microwave saturation through forbidden transitions that carries information about ENDOR frequencies comparable to what can be extracted from ESEEM experiments. Such comparability is demonstrated for examples of nitrogen ENDOR of photoexcited triplet states of the primary donor in photosynthetic reaction centers and related compounds.     

Analysis of RF heating and sample stability in aligned static solid-state NMR spectroscopy

Sample instability during solid-state NMR experiments frequently arises due to RF heating in aligned samples of hydrated lipid bilayers. A new, simple approach for estimating sample temperature is used to show that, at 9.4 T, sample heating depends mostly on (1)H decoupling power rather than on (15)N irradiation in PISEMA experiments. Such heating for different sample preparations, including lipid composition, salt concentration and hydration level was assessed and the hydration level was found to be the primary parameter correlated with sample heating. The contribution to RF heating from the dielectric loss appears to be dominant under our experimental conditions. The heat generated by a single scan was approximately calculated from the Q values of the probe, to be a 1.7 degrees C elevation per single pulse sequence iteration under typical sample conditions. The steady-state sample temperature during PISEMA experiments can be estimated based on the method presented here, which correlates the loss factor with the temperature rise induced by the RF heating of the sample.     

Analysis of homonuclear RF gradient NMR spectroscopy

A formalism for describing the spin dynamics of radio frequency (RF) gradient experiments is introduced. It has the advantage over the most straight-forward applications of product operator methods of cleanly separating the steps of coherence transformation and gradient evolution which become confused in many RF gradient methods. The analysis is used to explore the dynamics of RF gradient homonuclear multiple quantum filtering experiments. Experimental results of these new sequences are included.     

射频溅射沉积硅薄膜实验

本文描述采用射频溅射法在GH39不锈钢基体上沉积硅薄膜的实验。对直接溅射沉积硅薄膜的工艺进行了实验研究,并对硅膜进行了SIMS分析。用称重法测出无定形硅膜的最大厚度可达400—500nm,为HL-1装置等离子体边界层物理实验制作了所需的无定形硅膜收集探针。     

Tailored slice selection in solid-state MRI by DANTE under magic-echo line narrowing

We propose a method of slice selection in solid-state MRI by combining DANTE selective excitation with magic-echo (ME) line narrowing. The DANTE RF pulses applied at the ME peaks practically do not interfere with the ME line narrowing in the combined ME DANTE sequence. This allows straightforward tailoring of the slice profile simply by introducing an appropriate modulation, such as a sinc modulation, into the flip angles of the applied DANTE RF pulses. The utility of the method has been demonstrated by preliminary experiments performed on a test sample of adamantane.     

Low temperature probe for dynamic nuclear polarization and multiple-pulse solid-state NMR

Here, we describe the design and performance characteristics of a low temperature probe for dynamic nuclear polarization (DNP) experiments, which is compatible with demanding multiple-pulse experiments. The competing goals of a high-Q microwave cavity to achieve large DNP enhancements and a high efficiency NMR circuit for multiple-pulse control lead to inevitable engineering tradeoffs. We have designed two probes-one with a single-resonance RF circuit and a horn-mirror cavity configuration for the microwaves and a second with a double-resonance RF circuit and a double-horn cavity configuration. The advantage of the design is that the sample is in vacuum, the RF circuits are locally tuned, and the microwave resonator has a large internal volume that is compatible with the use of RF and gradient coils.