这道题的答案是什么---**Question 6** **Question Stem:** 6. 某同步加速器简化模型如图所示，其中仅直通道 PQ 内有加速电场，三段圆弧内均有可调的匀强偏转磁场 B。带电荷量为 -q、质量为 m 的离子以初速度 v₀ 从 P 处进入加速电场后，沿顺时针方向在加速器内循环加速。已知加速电压为 U，磁场区域中离子的偏转半径均为 R。忽略离子重力和相对论效应，下列说法正确的是 (□□)。 **Translation (for context, not part of extracted content):** (A simplified model of a synchronous accelerator is shown in the figure. Only the straight channel PQ has an accelerating electric field, and the three circular arcs all have adjustable uniform deflecting magnetic fields B. An ion with charge -q and mass m enters the accelerating electric field from P with an initial velocity v₀, then circulates and accelerates clockwise within the accelerator. It is known that the accelerating voltage is U, and the deflection radius of the ion in the magnetic field region is R. Neglecting ion gravity and relativistic effects, which of the following statements is correct (□□)?) **Chart/Diagram Description:** * **Type:** Schematic diagram of a particle accelerator/synchrotron. * **Overall Shape:** The accelerator track is shaped like a rounded triangle, consisting of three straight sections and three curved (circular arc) sections. * **Path/Track:** Represented by a double-lined closed loop. * **Main Elements & Labels:** * **P and Q:** Two points on one of the straight sections at the bottom. An arrow points from P to Q along the track, indicating the initial direction of ion movement into the accelerating field. * **U:** Labeled below the PQ straight section, with a small arrow pointing from P towards Q, indicating the accelerating voltage. * **B:** Labeled on each of the three curved sections, indicating regions with a uniform deflecting magnetic field. * **R:** A radial line with an arrow and label 'R' is shown in one of the curved sections, indicating the radius of curvature of the ion's path in the magnetic field. * **Inner Boundary:** Dashed lines form an inner triangular shape, connecting the ends of the straight sections, defining the inner boundary of the curved magnetic field regions. * **Relative Position and Direction:** The ion enters at P and moves towards Q, then circulates clockwise around the track, passing through straight accelerating sections (like PQ) and curved magnetic field sections (labeled B). **Options:** A. 偏转磁场的方向垂直纸面向里。 B. 第 1 次加速后，离子的动能增加了 2qU。 C. 第 k 次加速后，离子的速度大小变为 $\frac{\sqrt{m^2v_0^2 + kqUm}}{m}$。 D. 第 k 次加速后，偏转磁场的磁感应强度大小应为 $\frac{\sqrt{m^2v_0^2 + 2kqUm}}{qR}$。