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EicC对撞模式光学参数如表1所列。
参数 pRing eRing 能量/GeV 20 3.5 磁刚度/(T·m) 69.8 11.7 周长/m 1347.7 819.4 对撞点数 2 对撞频率/MHz 30 交叉角/mrad 50 束团粒子数/$\times 10^{10}$ 10.4 62.5 发射度/$\epsilon _{x,y}$/
(nm·rad,rms)300/180 60/60 工作点 18.315/18.300 16.58/16.55 自然色品$\xi _{x}/\xi _{y}$ –120.5/–95.5 –37.3/–70.4 对撞点$\beta _{x,y}^{\ast}$函数/m 0.08/0.04 0.40/0.12 对撞区最大$\beta _{x,y}^{\rm max}$函数/m 889.0/640.7 191.8/497.3 亮度/(cm–2s–1) $2\times 10^{33}$ EicC的pRing与eRing全环磁铁排布如图3所示。EicC对撞区磁铁采用超导四极磁铁。质子环pRing全环共有156块四极磁铁,76块二极磁铁,其中弧区四极铁82块,二极铁64块,偏转半径为21.5 m;电子环eRing全环共有195块四极磁铁,88块二极磁铁,其中弧区四极铁80块,二极铁80块,偏转半径为28 m。
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pRing全环
$ \beta $ 函数及色散函数如图4所示。为了与BRing安装于同一隧道,pRing八字环弧区采用与BRing同样的布局。每个弧区由8组相移为
$ \mu _{x,y} = (\frac{\pi }{2},\frac{\pi }{2}) $ 的FODO节结构组成,其中有2组FODO节用于$ \beta $ 函数匹配,6组FODO节包含非线性六极磁铁用以进行色品补偿,每台六极铁间隔2组FODO节组成一个相移为$ \pi $ 的超周期结构,满足相互抵消六极磁铁非线性效应的要求。为了增强y方向色品补偿能力,EicC充分利用连接两弧区处的短直线节,采用中心对称非消色散光学设计,包含一组y方向色品补偿六极磁铁(
$ \bigtriangleup \mu _{y} = \pi $ ),以进一步提高y方向色品补偿能力,如图5所示。EicC pRing对撞区光学挑战之一是在满足对撞点
$ \beta $ 函数尽量低地同时保证中心探测器有足够的安装空间,$ \beta_{\max} $ 尽可能低以减小色品补偿压力使得动力学孔径大于束团尺寸6$ \sigma $ 。图6表示$ \beta_{x,y}^{*} $ =(0.08 m,0.04 m)时pRing对撞区光学,对撞区最大β函数为$ \beta_{x,y}^{\max} $ =(889 m,641 m),满足对撞点处完全消色散要求。对撞区采用超导四极磁铁,磁场梯度最大为80 T/m,对撞点之后二极磁铁磁场强度为2.1 T,偏转角度30 mrad,以满足对撞点之后Triplet所需10
$ \sigma $ 束流清晰区要求,为后置前向探测器提供0.1 m色散,主要目的是提高探测器分辨率。 -
eRing全环光学如图7所示,eRing弧区由20组相移为
$ \mu _{x,y} = (\frac{\pi }{3},\frac{\pi }{3}) $ 的FODO节结构组成,弧区两端共有4组FODO节用以满足消色散及$ \beta $ 函数匹配需求,中间16组FODO节包含非线性六极磁铁用以进行色品补偿,每6组FODO节组成一个相移为$ \pi $ 的超周期结构,以抵消该结构内六极磁铁非线性效应。图8表示
$ \beta_{x,y}^{*} $ =(0.4 m,0.12 m)时eRing对撞区光学,满足对撞点处完全消色散要求,对撞区最大$ \beta $ 函数为$ \beta_{x,y}^{\max} $ =(192 m,497 m)。对撞区采用超导四极磁铁,磁场梯度为17.6 T/m,对撞点之后有一段由二极铁组成的电子对撞产物前向探测器安装区域,为探测器提供最大0.4 m色散以提高探测器分辨率,第一块二极磁铁可以将电子束与其附近的其他带电粒子分离开来,以便位于其后的探测器探测中心探测器探测不到的对撞产物。
EicC Collider Lattice Design
doi: 10.11804/NuclPhysRev.37.2019048
- Received Date: 2019-09-23
- Rev Recd Date: 2019-10-20
- Publish Date: 2020-03-01
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Key words:
- EicC /
- collider /
- lattice design /
- chromaticity compensation /
- dynamic aperture
Abstract: Electron Ion Collider in China (EicC), a new plan proposed by Institute of Modern Physics, Chinese Academy of Science to upgrade the HIAF facility, is mainly designed for studying sea quark, gluon and valence quark. The Center Mass Energy of the EicC is near 20 GeV. In order to maintain polarizability of proton bunched beams, the pRing (proton Ring) is designed to have the octave shape layout, while the racetrack layout is adopted by the eRing (electron Ring) to make full use of the tunnel space. For pRing, the proton center energy is 20 GeV, the horizontal and vertical rms emittance is 300 and 180 nm·rad respectively, and the β function at collider point is 0.08 and 0.04 m in the horizontal and vertical plane. For eRing, the electron beam center energy is 3.5 GeV, the rms emittance in transversal plane is 60 nm·rad, and the β function at collider point is optimized to be 0.4 and 0.12 m in horizontal and vertical direction respectively. As a result, the designed luminosity can achieve 2×1033 cm–2s–1. Furthermore, the influence of chromaticity compensation scheme on the Dynamic Aperture (DA), including the compensation patterns, the beta function and the phase advance in the collision points, is also studied. Accordingly, chromaticity compensation scheme is finalized as compensating by arc and short straight sextupoles, the DA of the pRing (>8σ) and the eRing (>20σ) can meet the design requirement of the beam size larger than 6σ.
Citation: | Ruiru WANG, Jiancheng YANG, Guodong SHEN, Geng WANG. EicC Collider Lattice Design[J]. Nuclear Physics Review, 2020, 37(1): 40-45. doi: 10.11804/NuclPhysRev.37.2019048 |