STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
to maintaining adequate control over two co-propagating beams of different energy traveling through a common transport channel while preserving beam quality. An illustrative plot showing the current state of ERLs and trends towards the future is shown in Fig. 2.1. Each point on the plot marks the maximum energy and maximum average current for energy recovery. Only same-cell energy recovery in SRF cavities is considered. The black markers represent machines where energy recovery has already been demonstrated while the red markers represent proposed ERL based accelerators. Making the leap from the current state of the art to the next generation of ERLs will require roughly an order of magnitude increase in the energy and an order of magnitude in average beam current. To date, the CEBAF with energy recovery (CEBAF-ER) experiment has energy recovered the highest beam energy while the highest average beam current was energy recovered in the Jefferson Laboratory 10 kW FEL Upgrade Driver. 2.1.1 CEBAF Overview The CEBAF machine at Jefferson Laboratory is a five-pass recirculating linac based on SRF technology. The machine is a dedicated user facility for nuclear physics experiments and is capable of delivering cw beam to three experimental halls simultaneously [29]. Construction of CEBAF commenced in 1987 and by 1995 successful five-pass operation with a 4 GeV beam had been demonstrated. The two innovations which made CEBAF unique at the time were the choice of superconducting RF technol- ogy and the use of multipass beam recirculation. The motivation for using multiple beam recirculations was twofold. The first was to reduce the costs associated with implementing a long linac and the second was to reduce the real estate required. Recirculating the beam n times through a linac with an energy gain 1/n trades 21
FIG. 2.1: Energy versus average current for machines which have demonstrated energy recovery (black) and for proposed machines (red). expensive SRF accelerating structures for less expensive magnets required for recir- culation. CEBAF is in a racetrack configuration, comprised of two antiparallel linacs with 180 ◦ recirculation arcs connecting them. Because of the difference in energy, each recirculation pass needs to be handled by an independent beam transport system [29]. At the exit of each linac, a spreader region is used to separate the beam via differential vertical bending according to energy into several transport lines. At the end of the arc a recombiner section is used to merge the individual beams and match them for acceleration through the next linac. The arcs themselves consist of a total of nine transport lines (five in the east arc and four in west arc) making it possible for a total of five passes. The arcs were designed to image the beam phase space 22
- Page 1 and 2: STUDIES OF ENERGY RECOVERY LINACS A
- Page 3 and 4: DEDICATION To my wife Danielle and
- Page 5 and 6: 2 CEBAF with Energy Recovery . . .
- Page 7 and 8: 5.2 HOM Power . . . . . . . . . . .
- Page 9 and 10: ACKNOWLEDGMENTS First and foremost
- Page 11 and 12: 6.1 Summary of the measured effects
- Page 13 and 14: 2.10 Illustration of quadrupole sca
- Page 15 and 16: 5.1 Successive frames in time (prog
- Page 17 and 18: 6.8 A plot of 1/Qeff versus average
- Page 19 and 20: ABSTRACT An energy recovering linac
- Page 21 and 22: CHAPTER 1 Introduction An increasin
- Page 23 and 24: FIG. 1.1: Schematic of a generic li
- Page 25 and 26: FIG. 1.2: A CEBAF 5-cell cavity wit
- Page 27 and 28: The solution to Eq. (1.3) is U(t) =
- Page 29 and 30: y reducing the impedance of HOMs, a
- Page 31 and 32: Despite its success, this method of
- Page 33 and 34: design parameters, most notably ach
- Page 35 and 36: 1.4.2 Machine Optics The second cat
- Page 37 and 38: analytic model elucidates many impo
- Page 39: CHAPTER 2 CEBAF with Energy Recover
- Page 43 and 44: FIG. 2.3: Additional hardware insta
- Page 45 and 46: FIG. 2.4: A picture of the energy r
- Page 47 and 48: dipoles and beam diagnostics such a
- Page 49 and 50: FIG. 2.7: Horizontal (red) and vert
- Page 51 and 52: FIG. 2.8: Illustration of the cryom
- Page 53 and 54: linac and θNL is the RF phase. The
- Page 55 and 56: 2.4 Transverse Emittance One of the
- Page 57 and 58: where σ2 is the rms beam size meas
- Page 59 and 60: eams. The effects of varying the qu
- Page 61 and 62: FIG. 2.12: A typical wire scan near
- Page 63 and 64: quadratic fit and a multiple regres
- Page 65 and 66: ting the data is difficult. Without
- Page 67 and 68: primary source of error is measurin
- Page 69 and 70: identified, although the phase dela
- Page 71 and 72: TABLE 2.3: Comparison of Twiss para
- Page 73 and 74: the results of the fits. The vertic
- Page 75 and 76: FIG. 2.18: Schematic illustrating t
- Page 77 and 78: FIG. 2.19: The GASK signal measured
- Page 79 and 80: FIG. 2.20: The measured normalized
- Page 81 and 82: CHAPTER 3 The Jefferson Laboratory
- Page 83 and 84: FIG. 3.1: Schematic of the 10 kW FE
- Page 85 and 86: FIG. 3.2: Layout of the DC photocat
- Page 87 and 88: accelerating gradient at the front
- Page 89 and 90: eason for making the endloops achro
to maintaining adequate control over two co-propagating beams of different energy<br />
traveling through a common transport channel while preserving beam quality.<br />
An illustrative plot showing the current state of ERLs and trends towards the<br />
future is shown in Fig. 2.1. Each point on the plot marks the maximum energy<br />
and maximum average current for energy recovery. Only same-cell energy recovery<br />
in SRF cavities is considered. The black markers represent machines where energy<br />
recovery has already been demonstrated while the red markers represent proposed<br />
ERL based accelerators. Making the leap from the current state of the art to the<br />
next generation of ERLs will require roughly an order of magnitude increase in the<br />
energy and an order of magnitude in average beam current. To date, the CEBAF<br />
with energy recovery (CEBAF-ER) experiment has energy recovered the highest<br />
beam energy while the highest average beam current was energy recovered in the<br />
Jefferson Laboratory 10 kW FEL Upgrade Driver.<br />
2.1.1 CEBAF Overview<br />
The CEBAF machine at Jefferson Laboratory is a five-pass recirculating linac<br />
based on SRF technology. The machine is a dedicated user facility for nuclear<br />
physics experiments and is capable of delivering cw beam to three experimental<br />
halls simultaneously [29].<br />
Construction of CEBAF commenced in 1987 and by 1995 successful five-pass<br />
operation with a 4 GeV beam had been demonstrated. The two innovations which<br />
made CEBAF unique at the time were the choice of superconducting RF technol-<br />
ogy and the use of multipass beam recirculation. The motivation for using multiple<br />
beam recirculations was twofold. The first was to reduce the costs associated with<br />
implementing a long linac and the second was to reduce the real estate required.<br />
Recirculating the beam n times through a linac with an energy gain 1/n trades<br />
21
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