High power impulse magnetron sputtering (HiPIMS) discharges have become an important tool for the deposition of thin, hard coatings. Such discharges are operated at a very low working gas pressure in the order of 1 Pa. Therefore, elastic collisions between ions and other heavy particles are often calculated to occur with low frequency, using the hard sphere approximation. However, inside the magnetic trap region of the discharge, a very dense plasma is created and Coulomb collisions become the dominant collision process for ions. In this article, we show that Coulomb collisions are a necessary part of a complete description of ion movement in the magnetic trap region of HiPIMS. To this end, the velocity distribution function (VDF) of chromium and titanium ions is measured using high-resolution optical emission spectroscopy. The VDF of those ions is then described using a simple simulation which employs a direct simulation Monte Carlo scheme. The simulation describes the self-relaxation of the VDF that is initially a Thompson distribution as being created during the sputtering process. Measurement positions inside the discharge are matched to the simulation results choosing an appropriate relaxation time. In this fashion, excellent agreement between simulation and measurement is obtained. We find, that the distribution quickly becomes mostly Maxwellian with a temperature of 9 eV for titanium ions and 4.5 eV in the case of chromium ions. Only the high energy tail of the VDF retains the shape of the initial Thompson distribution. The observed high temperature is explained with an energy redistribution from the highly energetic Thompson distribution into an partly-thermalized Maxwell-like distribution. Finally, the temperature resulting from this energy redistribution is calculated using a simple analytical model which shows good agreement with the measurements.

高功率脉冲磁控溅射（HiPIMS）放电已成为沉积薄而硬涂层的重要工具。这种放电是在大约1 Pa的非常低的工作气体压力下进行的。因此，使用硬球近似法，经常会计算出离子与其他重粒子之间的弹性碰撞以低频发生。但是，在放电的磁阱区域内，会产生非常密集的等离子体，并且库仑碰撞成为离子的主要碰撞过程。在本文中，我们证明库仑碰撞是完整描述HiPIMS磁阱区域中离子运动的必要部分。为此，使用高分辨率光学发射光谱法测量铬和钛离子的速度分布函数（VDF）。然后使用简单的模拟描述这些离子的VDF，该模拟采用直接模拟的蒙特卡洛方案。仿真描述了VDF的自松弛，它最初是在溅射过程中产生的汤普森分布。选择合适的弛豫时间，使放电内部的测量位置与模拟结果相匹配。以这种方式，在仿真和测量之间获得了极好的一致性。我们发现，钛离子的分布迅速变为麦克斯韦分布，温度为9 eV，铬离子为4.5 eV。仅VDF的高能量尾部保留了初始汤普森分布的形状。通过将能量从高能的汤普森分布重新分配为部分热的麦克斯韦状分布来解释观测到的高温。最后，使用简单的分析模型计算出由能量重新分布产生的温度，该模型显示出与测量值良好的一致性。