possible interpretation of fermilab crystal collimation experiment dick carrigan fermilab care...

Possible interpretation of Fermilab crystal collimation experiment

Dick Carrigan

Fermilab

CARE Crystal channeling workshop

CERN

March 9, 2006

Interpretation of TeV results CARE channeling collimation workshop

D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 20062

Channeling collimation related issues

• E853 geometry and collimation

• Tevatron crystal collimation

• Fliller-Still shoulder

• Does Tevatron crystal deflect, collimate?

• Channeling information needed

• Radiation damage

• Self-monitoring crystals?



C0 at the time of E853

At crystal

Lambertson, crystal

U counters

“Murphy geometry”

Beam halo effects and collimation

Extraction rate depended on shadowing of crystal by collimator

5 mm retraction to behind collimators precipitously cut rate

Characteristically the D0 proton loss rate rose by 5% to 20% as the collimators were opened.

Xc (mm)

Rel

ativ

e ra

teSeries of ~100 m step

collimator retraction

Moving crystals or collimators gives information on halo

retracting crystal 200 microns cut signal by 4. In 2 minutes recovered somewhat.

moving in-initial spurt for several minutes followed by 1/e decays of 0.5 to 5 hours



FNAL PROPOSAL FOR CRYSTAL COLLIMATION

Current collimation system in Tevatron is somewhat different comparedto the one planned before Run-II. Based on detailed modeling, Carrigan,Drozhdin, Mokhov and Still, proposed to implement a bent crystal in theEØ straight section. Done in 2004-2005.

Blm

Detector

T:LE033

LE03 pinE0

L shaped

tungsten Pin diode

?

6

CRYSTAL COLLIMATOR SYSTEM

E03 SecondaryCollimatorE0 Crystal Collimator Assembly

E0 Scintillator Paddles

PIN DiodeBLM

Laser – angularmeasurement

crystal

E03H 2nd Collimator

14 mm

channeled beam

31.542 m

Pin Diode

BLM

23.8 m



Fliller-Still Effect: 980-GEV BEAM at E0 (5.5 σ fit)

Oct. 6, 2005

Jan. 31, 2006

With E03H out,LE033C BLM isproportional tonuclear interact.rate in crystal

Peak width is22±4 rad (rms)440 microrad

Channeling Full arc

coherent



Possible explanations for whole bend effect

•Volume capture

•Volume reflection

•Miscut angle for crystal

•Something else

What to call effect?•Whole arc channeling (gets at characteristic of process)

•Volume reflection (probably correct)

•Volume capture (probably wrong)

•Vorobiev-Taratin effect (sort of predicted but does not include accelerator)

•Fliller shoulder (yes, but Tevatron confirmation helped)

•Fliller-Still shoulder (includes Tevatron confirmation)

•L5 effect (silly but 42% of Fliller-Still is ls)

Potential picture for volume reflection, volume capture (Ivanov)

Volume reflection

(Taratin-Vorobiev)Particle bounces off plane at some place in passage through a curved crystal. Deflection order of ψc

Volume capture

(Sumbaev/PNPI)Particle scatters into channel with lower transverse energy and remains there. Continues to end of bend.



Volume capture

“Volume capture” is the putative process whereby particles outside a channel in a bent crystal diffuse into the channel. It was first investigated at Gatchina by Samsonov, Sumbaev and their colleagues at 1 GeV. Volume capture should deflect in the direction of the bend. This diffusion process is an analog of dechanneling where the particles diffuse in to the channel. Process occurs over the whole arc of the bend. Deflections can range up to the whole arc of the bend.

In their book BCK (Crystal channeling …) give a formula (BCK 5.27) for the transition probability to diffuse into the channel as:

2/3

)(~

2~

p

Rconst

L

Rw

D

cs

where p is the momentum and R is the radius of curvature

Thus as the energy goes up, volume channeling goes down. As R gets smaller (tighter bend) it also decreases. Biryukov, et al., have shown that this relation holds true for 70 GeV protons and is characteristically small compared to ordinary bent crystal channeling (Fig. 3.30 in BCK)



Volume reflection

Volume reflection was discovered in simulations by Taratin and Vorobiev in the eighties [Phys. Lett A, 119, 425 (1987 for English language version]. In essence particles reflect off of planes when they are nearly parallel and are deflected on the order of a critical angle away from the bend. The process will occur over the whole arc of the bend. It can be cumulative for many passes.

Since the expected deflection is O(θc) the deflection will go as 1/(pβ)½. R does not appear but θc for a bent crystal will be a function of R. As a result the effect will diminish more slowly than volume capture as the energy increases.

This is why many expect the whole arc effect seen at RHIC and the Tevatron is due to volume reflection.

Useful to understand p, R scaling since we are extrapolating to LHC



Possible volume reflections in E853 at the Tevatron

E853 Run 22 Theta V for U2 vs goniometersmoothed

0

4000

8000

12000

16000

-1800 -1600 -1400 -1200 -1000 -800 -600

Theta V (~microrad) [more negative is convex]

U2

(co

un

ts)

U2

AG1*CAL (/10)

< -910

Gaussian

> -831

left line

Linear (> -831)

865 microrad

-856 microrad

640 microrad bend

Normal extraction did not see whole arc effects. Needed kick almost whole bend for extraction.

Interaction (U counter) often drifted, was disregarded.

Figure is selected (bad science but also wide variety of running conditions).

Note that more negative angle is convex side, the volume reflection side.



Summary of coherent bend effects

Effect Angle dist Deflection Magnitude Comment Volume reflection

2/1)/(1~~ pcd Away from bend

Strength same as channeling

Cumulative with beam passes

Volume capture

Up to full bend Toward bend

2/3)(~

pR

constws Small at high energy

Miscut Lowers deflection

Toward bend

0 to full deflection

Something else

Keep an open mind

Relaxed bend

Smaller bend

Ruled out by whole arc distribution

14

Crystal Angle vs displacement at E03H

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-10 -8 -6 -4 -2 0

E03H collimator position (mm)

Lo

ss o

n L

E03

3 (v

olt

s)

118 urad

343 urad

520 urad

806 urad

238 urad

out

Crystal Angle vs displacement at E03H

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-10 -8 -6 -4 -2 0

E03H collimator position (mm)

Lo

ss o

n L

E03

3 (v

olt

s)

118 urad

343 urad

520 urad

806 urad

238 urad

out

E03 COLLIMATOR SCAN FOR DIFFERENT CRYSTAL ANGLES (Mokhov)

ChannelChannel

ReflectionsReflections

ScatterScatter•Channeled beam produces a shoulder 7 mm from the coreChanneled beam produces a shoulder 7 mm from the core•The channeled beam should have been ~10.5 mm from the core.The channeled beam should have been ~10.5 mm from the core.•First data set suggested the channeled beam was hitting an aperture.First data set suggested the channeled beam was hitting an aperture.•But on 1/10/2006, after moving the crystal 10mm, new data proved there But on 1/10/2006, after moving the crystal 10mm, new data proved there was no aperture limit.was no aperture limit.

Beam probe w/out crystal

E03 data fitted and differentiated

0

0.5

1

1.5

2

2.5

3

-10 -8 -6 -4 -2 0

EO3H (mm)

LE

033

yie

ld

chan peak is exponentialmax = 0.9center = -7.05 mm, 440 micro radsig = 0.3 mm or 12.6 micro rad, psi c = 5

tail

500 400 300 200

angle (micro rad)

"118 micro rad"

"343 microrad"

PuzzleApparent deflected angle is 296 micro radians. Should be 440. But maybe appropriate beam center is not E03H = 0.

Channeling peak is 50% of deflected beam. Remainder dechanneling? Sigma is twice critical angle, some due to beam divergence.

Negative hadron and e+/e- channeling?

Could one collimate antiprotons at the Tevatron?Could one collimate e+/e- at ILC?In TOTEM, etc. at LHC could one deflect negative

particles including leptons?

e+/e- channeling• channeling radiation impact must be considered

• crystal lengths must be short

• not so much dependence on charge

• little of no experimental information at high energy,

particularly for bending

Negative hadron bendingBak et al. did studies of negative particle axial deflection at 10 - 12 Gev with pions [S. Anderson et al., Nucl. Phys. B167, 1 (81), J. Bak, et al., Nucl Phys. A389, 533(82)] Schiott simulated their data in Carrigan and Ellison (Relativistic Channeling, NATO 165, Plenum (87)). Saw only small effects on order of critical angle. Taratin & Vorobiev, Phys. Lett. A119, 425 (1987) also discuss negative bending simulation.

Negative hadron and e+/e- channeling -continued

More recently Greenenko and Shul’ga [NIM B90, 179 (94)] studied negative deflection with a simulation program. For axial channeling at 400 GeV they saw deflection at the same scale as the Schiott simulation. Their distributions for 100 GeV hadrons bent in a 3 cm crystal are shown below.

+ - Note that the negative deflection is of the same order as the positive case but very diffuse.

In thinking about the possibility of negative particle deflection in the early eighties I discounted it because I thought in terms of discrete angular deflections in the spirit of an external beam. The situation is different for collimation where the important thing is to give the particles a kick, any kick, provided it is more than the multiple scattering. Multi-pass channeling also helps. High energy may also help.

We need more information on negative channeling, negative bending!

Some radiation damage experienceE853: 70 hours of halo on crystal, no effect Baker et al NIMB90, 119 (1994) – 3*10^19 protons @ 28 GeV (BNL) or fluence of

4*10^20/cm^2. Channeling minimum yield went from 2.3% to 4.1%. Related to crystal disorder. From Dynamitron study with energy there was a suggestion it may have been dislocationsThis article also considers relative impacts of dislocations, point defects

CERN saw 25% degradation of bending efficiency for 2*10^20p/cm^2IHEP bent crystal with temperature to 150 degree, 1 W beam power

Issues

• temperature effects (see later slides)

• controlling damages

• material?

• types of defects

• extrapolation to 7 TeV

Scale

1/16 in/div

Self monitoring crystal?

Bad things happen to crystals break

radiation damage

bend relaxes…

Bad things happen to collimators melt ground

plane

fuse

strip

xtal

diode

electrode

diode

electrode

Self monitoring? radiation damage via depletion voltage,

leakage current ala Si strip detectors

bend via capacitance?

continuity via plated on fuse surface?



Summary

Tevatron crystal collimation has been a big successpuzzle concerning apparent deflection angleimprovements ahead!

ChannelingFliller-Still shoulder is probably volume reflectionunderstand scaling with p, Θb?

Negative particles, leptons?Radiation damage

extrapolation to 7 GeV, very intense beams

Are self monitoring crystals useful?

possible interpretation of fermilab crystal collimation experiment dick carrigan fermilab care...

Documents

bent crystal

shadowing of crystal

haloretracting crystal

curved crystal

shoulderdoes tevatron

book bck crystal channeling

volume channeling

arc channeling