The Modeling of Time-Structured Multiturn Injection into Fermilab Main Injector (Microbunch Injection with Parasitic Longitudinal Painting)

📝 Abstract

This paper presents the modeling of time-structured multiturn injection for an upgraded Main Injector with the 8-GeV Superconducting RF proton driver, or an ILC-style linac, or a Project-X linac. The Radio-Frequency mismatch between a linac and the upgraded Main Injector will induce parasitic longitudinal painting in RF-phase direction. Several different scenarios with a choice of different RF parameters for single RF system and double RF system in the presence of longitudinal space charge have been investigated. From the studies of microbunch injection with the aid of ESME (2003) numerical simulations, it is found that the dual RF system with a choice of appropriate RF parameters allows us to overcome the space-charge limitation set by beam intensity during the multiturn-injection process. A double RF system with a harmonic ratio (R_H = H_2/H_1) of 2.0 and a voltage ratio (R_V = V_2/V_1) of 0.5 are most favored to reduce both longitudinal and transverse effects of space charge in the Main Injector.

💡 Analysis

This paper presents the modeling of time-structured multiturn injection for an upgraded Main Injector with the 8-GeV Superconducting RF proton driver, or an ILC-style linac, or a Project-X linac. The Radio-Frequency mismatch between a linac and the upgraded Main Injector will induce parasitic longitudinal painting in RF-phase direction. Several different scenarios with a choice of different RF parameters for single RF system and double RF system in the presence of longitudinal space charge have been investigated. From the studies of microbunch injection with the aid of ESME (2003) numerical simulations, it is found that the dual RF system with a choice of appropriate RF parameters allows us to overcome the space-charge limitation set by beam intensity during the multiturn-injection process. A double RF system with a harmonic ratio (R_H = H_2/H_1) of 2.0 and a voltage ratio (R_V = V_2/V_1) of 0.5 are most favored to reduce both longitudinal and transverse effects of space charge in the Main Injector.

📄 Content

Modeling of Time-Structured Multi-Turn Injection into Fermilab’s Main Injector (Micro-Bunch Injection with Uncontrolled Longitudinal Painting) Phil S. Yoon∗, David E. Johnson, and Weiren Chou Fermi National Accelerator Laboratory, Batavia, IL 60510, USA † Februrary 2008 Abstract This article presents the modeling of time-structured multi-turn injection for an upgraded version of Fermilab’s Main Injector with the 8-GeV Superconducting RF proton driver, or the International Linear Collider (ILC)-style linac, or the Project-X linac. The Radio-Frequency (RF) mismatch between a linac and the Main Injector will induce uncontrolled longitudinal painting in RF-phase direction. Four scenarios have been explored with different choices of RF parameters of a single RF system and a double RF system in the presence of longitudinal space charge. It is found from the studies of micro-bunch injection with the aid of ESME (2003) simulations that a dual RF system with an optimized choice of RF parameters enables overcoming the space-charge limits set by beam intensity during the multi-turn injection pro- cess. A double RF system with a harmonic ratio (RH = H2/H1) of 2.0 and a voltage ratio (RV = V2/V1) of 0.5 are most favored to reduce both longitudinal and transverse effects of space charge residing in the Main Injector. ∗E-mail: phil.s.yoon@hotmail.com † Work supported by Fermilab Research Alliance (FRA), LLC under contract No. DE-AC02-07-CH11359 with the United States Department of Energy 1 arXiv:0802.2430v2 [physics.acc-ph] 5 Aug 2012 1 Micro-Bunch Injection into the Main Injector from a Superconducting RF Linac Following the method of time-structured multi-turn injection from the 400-MeV linac to Fer- milab’s Booster [1], we have further explored the scheme of micro-bunch injection for applications to Fermilab’s Main Injector, (from a future Superconducting RF (SCRF) linac to an upgraded Main Injector (MI-2)) 1 considering parasitic longitudinal painting. The future SCRF linac referred here can be either the 8-GeV SCRF linac Proton Driver [2, 3, 4], or the Project-X linac [5]. 1.1 Overview of the Main Injector The Main Injector (MI) is a ring with a circumference of about 3.3 (km). The central role of the MI is to connect to the Tevatron, the Booster, the Anti-Proton source, switchyard, and the Recycler Ring via a number of beam transport lines within the Fermilab accelerator complex. The MI accelerates and decelerates particle beams with energy ranging from 8 (GeV) and 150 (GeV), depending on the operation mode. The harmonic number of the MI is 588 and the harmonic RF at injection is 52.8114 (MHz)2. 1.2 Overview of the 8-GeV Superconducting RF Linac An 8-GeV SCRF linac has been proposed as a single-stage H−injector into the Main Injector as a replacement for the aging 400-MeV Linac and the 8-GeV Booster. This new 8-GeV SCRF linac would be the highest-energy H−multi-turn injection system in the world. Fermilab has been carrying out design studies [4, 6] of the SCRF linac and injection systems[7] over the last several years. The linac design[8] utilizes a warm-temperature 325-MHz RFQ and rebunching cavities to bunch the beam at 325 (MHz). At β = 0.89 (about Ekin = 1.1 (GeV)), the RF of the Supercon- ducting (SC) cavities is 1.3 (GHz). The ultimate bunch structure required for injection into the MI will be formed by a 325-MHz fast chopper system[9]. The fast chopper system will be required to remove individual 325-MHz bunches or bunch trains for matching to the MI RF structure and providing a beam-abort notch: two out of every six micro-bunches3 are to be removed. 1 We will use the Main Injector (MI) and an upgraded version of the Main Injector (MI-2) interchangeably through- out this article. 2 For the sake of brevity and convenience, 53 MHz is referred to as MI RF hereafter. 3 The micro-bunch is referred to as a 325-MHz bunch hereafter. 2 1.3 Time Structure of the Main Injector In the injection model the fast chopper system located at the front end of the 8-GeV SCRF linac produces a train of four micro-bunches for being injected into the MI. Illustrated in Figure 1 is a schematic for one MI RF bucket populated with an initial train of four micro-bunches. The two chopped micro-bunches are represented by two consecutive empty 325-MHz RF buckets. A train of four 325-MHz micro-bunches are synchronously injected into a standing 53-MHz bucket. The length of the two chopped micro-bunches is equivalent to 6 ns. More details of the time structure of each MI RF bucket after the first synchronous injection from a SCRF linac are illustrated in Figure 2. A total beam notch per MI RF bucket is about 6 ns, which corresponds to two 325- MHz RF buckets, whereas the principal RF harmonic of 52.8 (MHz) and the sub-harmonic of 325 (MHz). Illustrated in Figure 3 is a phase-space (∆E,θ) plot containing the very first train of four micro-bunches with an RF-voltage waveform drawn in the background. The following is a list of Figure 1: Three con

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