这道题的答案是什么---**Page Number:** 25
**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 of Question Stem (for context, not part of the requested output but useful for understanding):**
6. A simplified model of a synchrotron is shown in the figure, where only the straight channel PQ has an accelerating electric field, and the three arc segments all have adjustable uniform deflecting magnetic fields B. A charged particle with charge -q and mass m enters the accelerating field from point P with an initial velocity v₀, and then circulates and accelerates in the accelerator in a clockwise direction. It is known that the accelerating voltage is U, and the deflection radius of the particle in the magnetic field region is R. Neglecting the gravitational force on the particle and relativistic effects, which of the following statements is correct?
**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 $\frac{\sqrt{m^2v_0^2 - 2kqUm}}{qR}$。
**Chart/Diagram Description:**
* **Type:** Simplified schematic diagram of a particle accelerator (resembling a synchrotron or cyclotron).
* **Main Elements:**
* **Overall Shape:** The accelerator path forms a closed loop, roughly triangular with rounded corners. It consists of three straight segments and three curved (arc) segments.
* **Particle Path:** Represented by two concentric lines, indicating a channel for particles.
* **Straight Accelerating Segment:** The bottom straight segment is labeled "PQ". A label "U" is placed below this segment, indicating an accelerating voltage. The text specifies this is where the accelerating electric field is located.
* **Curved Deflecting Segments:** There are three curved segments connecting the straight parts. Each curved segment has "B" labels at its ends, indicating regions with a uniform magnetic field. These fields are for deflecting the particle.
* **Radius of Curvature (R):** An arrow labeled "R" extends from an implied center within the loop to the inner edge of one of the curved path segments, representing the radius of curvature of the particle's path in the magnetic field.
* **Points:** "P" and "Q" are specific points on the accelerating segment. "P" is the entry point for the ion.
* **Dashed Lines:** Dashed lines form an inner triangle, connecting the inner vertices of the path, likely indicating the boundaries of the magnetic field regions or the overall structure.
* **Labels and Annotations:**
* "B": Denotes the magnetic field regions in the curved segments.
* "R": Denotes the radius of curvature.
* "P", "Q": Denotes specific points on the path, with PQ being the accelerating channel.
* "U": Denotes the accelerating voltage across the PQ segment.
* **Relative Position and Direction:**
* The particle enters at point P with initial velocity $v_0$.
* The particle circulates in a clockwise direction within the accelerator.
* Acceleration occurs only in the straight segment PQ.
* Deflection occurs in the three curved segments due to magnetic fields.