Download Introduction to particle accelerators

Introduction to particle accelerators
presenter: 陳家祥
material edited by 周炳榮
2017.01.19
Important Notes to Students: The sole purpose of this lecture notes is meant for educational use only. Some photographs and graphic illustrations are adapted from various reference literatures, which are NOT to be distributed beyond the classroom.
[Further Readings]
1. My lecture notes can be downloaded from Google Drive:
https://docs.google.com/folder/d/0B9aE0DAUR8VBUmN2dUlmUEJEMms/edit
2. H. Wiedemann, Particle Accelerator Physics , 3rd ed. (Springer, 2007)
3. A. W. Chao et al. (eds), Handbook of Accelerator Physics and Engineering, 2nd ed.
(World Scientific, 2012)
4. A. Sessler and E. Wilson, Engines of Discovery, (World Scientific, 2007)
Milestones of NSRRC Development
1983
July
Approval of the SRRC project
1986
August
Ground breaking of civil construction in Hsinchu
1993
April
First beam stored
1993
October
SRRC dedication ceremony
1994
April
Three photon beamlines open to users
1995
January
W200 wiggler installed
1995
October
U100 undulator installed
1996
September
Ring energy raised from 1.3 GeV to 1.5 GeV
1997
March
U50 undulator installed
1998
December
SRRC & Spring‐8 signed cooperation agreement
2004
December
Doris cavities replaced by Cornell‐type SRF cavity in ring
2005
October
Top‐up injection implemented
2006
June
TPS proposal submitted to NSC
2007
December
TPS project & budget approved by Legislative Yuan
2010
February
Ground breaking of TPS civil construction
Technologies for Particle Acceleration
DC voltage acceleration:
(DC electric field)
+V
‐V
Battery (DC power supply)
Magnetic induction acceleration:
(Faraday’s Law of Induction)
Resonance acceleration:
(AC electric field)


B
 E  
t
 
 
 E  d    B  dS
W  eV
V  V0 sin(rf t   )
e.g. the oscillating electromagnetic fields in a pillbox cavity (Maxwell Eqs. + boundary conditions)
E z ( r , t )  E0 J 0 (
B (r , t ) 

c
r )e jt
E0

J1 ( r )e jt
c
c
DC voltage acceleration (developed in 1930s)
• Voltage multiplier cascade (Cascade accelerators, Cockcroft and Walton)
• Electrostatic generator (Van de Graaff accelerators)
 Electron microscope, ion implanter
Resonance acceleration (Gustaf Ising, Sweden, first proposed it in 1924)
• Radio‐frequency (RF) Linear accelerators (Rolf Wideröe, Norway, built the first linac using an RF accelerating field)
• Radio‐frequency quadrupole (RFQ) (first proposed by I.M. Kapchinski and V.A. Teplyakov in 1970)
• Cyclic accelerators
Cyclotron (first one built in 1931)
Microtron (first proposed in 1944 by V. Veksler and J. Schwinger)
Synchrocyclotron (first proposed in 1945 by E. McMillan and V. Veksler)
Synchrotron (used by most high energy accelerators)
Magnetic induction acceleration
• Betatron (reinvented & built in 1940 by Donald Kerst, but the concept was formulated by R. Wideröe in 1928)
• Induction linac (invented by N.C. Christofilos in 1950s)
Synchrotron (higher energy electron)
when e‐ travels at 0.98c the beam energy is only at 2 MeV
e‐ travels at a constant speed above few MeV
The operation principles of e‐ synchrotron combine:
• cyclotron method of acceleration: use of rf cavities
• Strength of magnetic guiding field increases as the e‐ energy increases
Synchrotron must be pulsed.
國家同步輻射研究中心增能環（新竹科學園區）
The 300 MeV electron synchrotron built at General Electric Co. in 1940s. The photograph shows the synchrotron radiation emitted from the accelerator.
The first dedicated synchrotron light source, became operational for users on August 7, 1968. The circulating beam current was 1.4 mA.
240 MeV e‐ storage ring (Tantalus), U. of Wisconsin‐ Madison.
50 MHz rf cavity
Ednor M. Rowe
[Ref.] http://www.src.wisc.edu/about/erowe.htm
[Ref.] G. Margaritondo, “The evolution of a dedicated synchrotron light source”, Physics Today (May 2008), p.37.
Cockcroft‐Walton Voltage Multiplier
(cascade accelerator)
The 750 keV Cockcroft‐Walton accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, USA
The original Cockcroft‐Walton generator developed by J. Cockcroft and E. Walton at Cavendish Laboratory in Cambridge, U.K.
Ernest T.S. Walton
Ernest Rutherford
John D. Cockcroft
(founding father of nuclear physics)
•The Cockcroft‐Walton generator can convert AC or raise a low DC voltage to a much
higher DC voltage level. It is used to provide higher DC electric fields for particle
acceleration.
•It is based on the principles of voltage multiplying circuit. A voltage multiplier can step up
a relatively low voltage to an extremely high value. This technique is different from the
transformer. It does not require the heavy core and use only capacitors and rectifiers
(diodes).
•The voltage potential achieved by the first Cockcroft‐Walton voltage multiplier is 700 kV
with a voltage variation within few percent. Positive ions of hydrogen with a beam current
of the order of 10 A being obtained (protons of 710 keV).
•This is the first accelerator to demonstrate disintegration of atomic nuclei by artificially
accelerated particles! They induced the nucear reaction:
Li+ p  2He
Early History of Accelerator Development in Taiwan
The development of first particle accelerator was led by Prof. B. Arakatsu （荒勝文策）in the physics department of Taipei Imperial University （台北帝國大學）, now the National Taiwan University （國立台灣大學）. It was an electrostatic accelerator, a modified design of Cockcroft‐Walton accelerator. Prof. Arakatsu’s team had successfully achieved the nuclear fission experiment in 1934. That is the first nuclear fission experiment carried out in Asia. After World War II Prof. 戴運軌、許雲基 in National Taiwan University rebuilt and continued the previous research efforts before WW II.
A detailed collection of the early history of accelerator and nuclear physics programs in Taiwan can be found in the references given below：
1. 物理雙月刊（二十九卷四期）2007年8月，竹腰秀邦（鄭伯昆譯）
“在台北帝國大學的加速器開發及原子核物理學的研究＂
2. 物理雙月刊（三十卷五期）2008年10月，鄭伯昆
“台大核子物理實驗室（四）有關的日本科學家＂
B. Arakatsu
[Ref.] 台大物理文物廳（原子核物理）
http://museum.phys.ntu.edu.tw/
戴運軌
[Ref.] http://sec.ncu.edu.tw/ncuhis/history/president.php
PJ18
Belt‐charged Electrostatic Generator (invented by Robert J. Van de Graaff)
High‐voltage terminal
+
+
+
+
+
Charge is sprayed from a sharp tip at A on
a moving belt (insulating material). The
belt carries the charge to the high‐voltage
terminal, where it is removed from the
belt at B (a sharp tip connected to the
outer conductor of terminal) and transfers
to the outer conductor of terminal.
+
+
beam
Ion source
+
+
+
+
B
+
+
insulating belt
driving motor
+
+
+
+
+
A
The limiting factors: leakage of charge through the insulating supports, breakdown of air due to the moisture (corona discharge: near sharp points or edges)
Mechanical energy (motor)  Electrical potential energy
Phys. Rev., 38: 1919 (1931), R.J. Van de Graaff
Phys. Rev., 48: 315 (1935), M.A. Tuve, L.R. Hafstad, and O. Dahl
投影片 12
PJ18
D. Halliday, R. Resnick, K. Krane, PHYSICS, 4th ed., vol.2, Chap.30
Ping J. Chou, 2007/7/13
Diameter of the aluminum sphere: 15 ft.
Diameter of the supporting column: 6 ft.
The machine was used as a research accelerator at MIT
operating at potentials up to 2.75 MV. The effect of
pigeons’ droppings on the sphere is very dramatic as
shown by those sparks.
[Ref.] Museum of Science, Boston; http://www.mos.org/sln/toe/construction.html
Tandem Van de Graaff accelerator
Negative ion sources were developed in 1950s
High‐voltage terminal
Pressure tank
+ + + + + + + + + + +
Ion source for negative ions
Stripper foil (e.g. carbon foil)
Charging belt
Advantage over the cascade accelerator: the terminal voltage is extremely stable and lacks the AC ripple of the cascade accelerator (very low energy spread of ions); relative voltage stability~ 10‐4
Disadvantage: low current output compared with the cascade accelerator
[Ref.] J. Takacs, Energy Stabilization of Electrostatic Accelerators (Wiley, 1997)
A 25URC NEC Pelletron at Oak Ridge Nat’l Lab built by National Electrostatic Corp. (NEC). It holds the record of the highest achieved DC voltage about 30 MV.
[Ref.] A. Sessler (LBNL), private communication.
Ray Herb at the control console
[Ref.] J. Adney, “Notes on the Oak Ridge Pelletron”, Physics Today, (Dec. 2010), p. 10.
國立清華大學加速器實驗室
http://acc.web.nthu.edu.tw/bin/home.php
Electron Linac (disk loaded structure)
[Ref.] http://www.slac.stanford.edu
Drift tube linac (a proton linac developed by Luis. W. Alvarez)
[Ref.] Visual Media Service, Fermilab
[Ref.]: http://bancroft.berkeley.edu/Exhibits/physics/additional06.html
[ref.] http://www‐bd.fnal.gov/ops/images/main/DCP08667.JPG
/2 mode, Side‐coupled Linac
Linac gallery at Fermilab
Source: Visual Media Service, Fermilab
Betatron
Donald Kerst and the first betatron (2.3 MeV electrons) he built in Univ. of Illinois in 1940. The betatron had been used by the Manhattan Project to determine basic properties of thorium, uranium, and plutonium. [Ref.] http://www.physics.uiuc.edu/history/Timeline/1940s.html
A modern compact betatron, commercially available. The compact betatron is used as a portable x‐ray source for the detection of flaws in metal, such as steel beams, ship hulls, pressure vessels, bridges, etc.
[Ref.] http://www.globalxray.com/betatron_photo.html
Basic Configuration of a High Energy Accelerator Facility
injector
Electron source: electron gun
Electron linear accelerator (linac)
Booster synchrotron
Transport line
Storage ring
Insertion devices
Beamlines & end stations
•Particle source
•Beam guiding & focusing
•Beam acceleration
•Beam transfer & delivery
•Beam storage
•Beam quality
•System control
•Beam diagnostics
•Particle source
Field emission in high electric field
Limited by DC breakdown 2~3 MV/m thermionic DC gun
DC breakdown limit could be increased using high pressure insulating gas, e.g. SF6
RF accelerating field has a much higher breakdown limit RF gun
Photoelectric emission (laser beam)+ RF gun low beam emittance
Thermionic DC gun+ single crystal cathode CeB6 (Japan X‐FEL) low beam emittance
Superconducting photocathode RF gun low emittance, high beam current
What’s the advantage of using RF superconducting technology? low wall loss
•Beam guiding & focusing
Accelerator lattice design
(transfer matrix)
Beam dynamics (emittance)

Ray optics (matrix) Gaussian beam optics (diffraction limited)
Prisms Dipole magnets
Focusing lens Quadrupole magnets
Aberration Sextupole magnets
Lorentz force:
 
  
dp
 F  q( E    B)
dt
•Beam acceleration

2
1
1
‐
drift tubes made of good conductors
3
A chain of drift tube been folded over
2
+
3
‐
beam
‐V(t)
+V(t)
+
e‐
RF generator
Example: the 500 MHz normal conducting Doris cavities used at NSRRC (Taiwan). e‐
Cut‐away view of a Doris cavity
Low‐temperature Superconducting RF Cavity
SRF cavity at Taiwan Light Source
2  10 4
BCS theory R Nb 
T
2
 f   17T.67
 R0
  e
 1.5 
where T is in unit of Kelvin, f is in unit of [GHz], and R0 is the residual resistance which depends on the impurity of superconductor only.
CESR‐III type niobium cavity (SRF lab at NSRRC)
•Beam quality
Photon beam stability
•Intensity constancy
•Position & pointing accuracy
on small samples
•Timing & pump‐probe
synchronization
•Energy resolution
<0.1%
<5% x,y
<5% x’,y’
<10% t
<0.01%
insertion device
LLRF
klystron
magnets
Power supply
RF cavity
y
ee-
x
sample
Beamline (vacuum < 10-8 Torr)
Photon beam fluctuation caused by:
•Orbit instability (transverse)
•Beam size instability (transverse)
•Timing instability (longitudinal)
leading bunch
trailing bunch
Longitudinal collective instability
s
longitudinal

2
1
1
0
2
3
s
0
0
3
time
Transverse collective instability
•Coupled bunch instability
snapshot
of coherent
•Head‐tail instability
oscillation
m=0, =0
1
m=0, 0
0.5
0
m=1
m=2
-0.5
-1
-1
-0.5
0
0.5
1
[References]: Frontiers of Particle Beams: Intensity Limitation, M. Dienes et al (eds.), Springer‐Verlag LNP 400 (1992)
Impacts due to Fluctuations of Utility Systems (water, electricity)
[Ref.] Phys. Rev. ST Accel. Beams, 6, 052803 (2003), P.J. Chou et al.
•System control
console/computer
(real‐time OS)
Application layer
Database layer
high speed network
Network layer
Device layer (Intelligent Local Controller, ILC)
VME crate (ILC)
Front end hardware
CERN Control Center
[Ref.] http://www.cern.ch
Fermilab, Main Control Room
[Ref.] Visual Media Service, Fermilab
SLAC Main Control Center (MCC)
Courtesy of SLAC National Accelerator Laboratory
[Ref.] http://slac.stanford.edu
Appendix.1: 電子束團的轉彎與聚焦
勞倫茲力 Lorentz force:

  
F  q( E    B)
y
磁場所造成的受力方向
速度 v
電場 E
z
x
電場所造成的受力方向
33
二極磁鐵（轉彎用的）
e‐
B
34
四極磁鐵（聚焦用的）
y
北
南
N
S
By
Bx
x
S
南
N
北
磁極的橫剖面必須是雙曲線, xy＝ 常數
35
超導磁鐵 (美國費米國家加速器實驗室，Fermilab)
cos2
cos
二極磁鐵
return
四極磁鐵
36