tuesday, june 25, 2002 marc ross –isg8 · 2002. 6. 27. · june 26, 2002 marc ross isg 8– slac....
TRANSCRIPT
NLC - The Next Linear Collider Project
Tuesday, June 25, 2002 Marc Ross – ISG8
Author NameDate
Slide #2
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
Why measure tilt?• Most emittance dilution effects introduce a first order
y – z or x – z correlation(also E – z is very interesting)
• Profile monitors are ineffective at measuring small correlations– Measures projection – and that with at best 5% (SLC ~10%)– Very sparsely located
• A ‘tilt’ (y – z) monitor with 1 mrad resolution allows rapid tuning of linac
• Important for IP • Two methods proposed:
– Transverse deflecting structure (RF streak)– Cavity BPM
NLC linac should not be tuned as SLC was!
Author NameDate
Slide #3
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
Transverse deflection Old idea – 1965 ‘LOLA IV’Testing in linac sector 29
Brute forceCalibratedExpensiveExcellent resolution
SLAC LCLS – Krejcik/Emma (EPAC 02)SLAC/DESY TTF2
Krejcik / Emma EPAC 2002
Krejcik / Emma EPAC 2002
Krejcik / Emma EPAC 2002
Author NameDate
Slide #8
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
Response of Cavity BPMto Point Charge
S. Smith – Snowmass 2001
Q
�
)sin()( taqtV ���
Response of BPM to Tilted BunchCentered in Cavity
q
2sincos
2)
2(sin
22)
2(sin
22)( ttt tqatqatqatV ��
���
���
��
�����
Treat as pair of macroparticles:
���
�tq/2
���
q/2
Tilted bunch
)sin()( taqtVy ���• Point charge offset by �
• Centered, extended bunch tilted at slope ���t
• Tilt signal is in quadratureto displacement
• The amplitude due to a tilt of ��� is down by a factor of:with respect to that of a displacement of �(~bunch length / Cavity Period )
2sincos
2)( t
t tqatV ���
��
TVV tt
y
t
24����
��
Example
• Bunch length �t = 200 �m/c = 0.67 ps • Tilt tolerance d = 200 nm• Cavity Frequency F = 11.424 GHz• Ratio of tilt to position sensitivity ½�f�t = 0.012• A bunch tilt of 200 nm / 200 �m (1 mrad) yields as much signal
as a beam offset of 0.012 * 200 nm = 2.4nm• Need BPM resolution of ~ 2 nm to measure this tilt
• Challenging!– Getting resolution– Separating tilt from position
• Use higher cavity frequency?
Need 1 mrad tilt sensitivity for linac tuning
Angled trajectories
��y res/�y ~ 5%��y’ res/�y’ ~ 10x
Relative normalized precisionBeam position/beam traj angle
• A trajectory that is not parallel to the cavity axis also introduces a quadrature signal (in phase with ‘tilt’ signal)
• Projected ‘dipole’ sensitivity is increased by �z/cavity length– ~ 50
Cavity BPMFFTB (Shintake) ATF ext line (Vogel) X-band (Naito)
f 5.712 6.426 11.424 (GHz)position resolution 20 200 200 (nm)Vt/Vy (200um sig_z) 0.6% 0.7% 1.2% (.5 pi sig_t f)achieved 'projected dipole resolution' (200um sig_z) 3.3 29.7 16.7 umachieved 'tilt' angle resolution 17 149 84 mradachieved 'trajectory angle resolution' 3 26 30 uradcavity 'length' 15 15 8 mm
�
ATF �z ~ 8mm gives expected tilt resolution ~ 0.1mrad
�Wave cavity BPM X-band
12 mm bore
Naito/Li
Very good resolution possible – 25 nm achieved in FFTB few nm possible by limiting spatial dynamic range
ATF Cavity BPM – V. Vogel / H. Hayano ATF extraction lineC-band cavityL = 12mm, Radius = 26mm, f = 6426MHz, �=46.6mmMovers – x, y, pitch (y-z)
Author NameDate
Slide #15
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
ReferenceCavity
BPMcavity C-band
Amplifiers15dB gain
X
X
X
Splitter
6410MHzsource
StriplineBPM
4:1 combinerX4
Scope, 250Ms/s4 channel, external trigger500 samples/ch
20MHz BW limit
Ch1
Ch2
Ch3 (Y)
Ch4 (X)
Tilt monitor electronicsJ. Frisch
Author NameDate
Slide #16
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
Raw ‘mixed –down’ scope data from cavity BPM
Phase and amplitude wrt ref are extracted
(I and Q)
Author NameDate
Slide #17
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
If there is a large offset in one plane, and little in the other, we see beating between modes
(nominally cylindrically symmetric cavity)
Author NameDate
Slide #18
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
I Q response as the cavity is moved vertically using mover
The angle is arbitrary (phase offset between ref and BPM cavity)
A ‘monopole’ beam with an axial trajectory should give a (0,0) response at some point
Author NameDate
Slide #19
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
Use the cavity ‘tilter’ to observe response to tilted trajectories
(Beam ‘tilter’ was not ready during this test – May 2002)
Compare 35 urad with 26 in table estimate
Author NameDate
Slide #20
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
SLD at SLC – the innermost vacuum chamber is a crude cavity BPM
Author NameDate
Slide #21
Beam Tilt MonitorMarc Ross ISG 8– SLACJune 26, 2002
CLIC J/NLC TESLA
Plans• Collaboration with LBNL for cavity BPM ‘tiltmeter’
– AFRD and UCB Physics Department– Possible use at LBL ‘Femtosecond Light Source’– LDRD application submitted for 2003 funding
• Tests at ATF in November 2002• Couple with tests of deflecting structure – TTF2
• Cavity BPM is a ubiquitous device and can serve many functions –• calibration and modeling (PT)• beam ‘angle’ monitor• structure manifold BPM’s